HTML 4.01 Specification - Université des Antilles et de la Guyane

HTML 4.01 Specification
HTML 4.01 Specification
W3C Recommendation 24 December 1999
This version:
http://www.w3.org/TR/1999/REC-html401-19991224
(plain text [794Kb], gzip’ed tar archive of HTML files [371Kb], a .zip archive of
HTML files [405Kb], gzip’ed Postscript file [746Kb, 389 pages], gzip’ed PDF file
[963Kb])
Latest version of HTML 4.01:
http://www.w3.org/TR/html401
Latest version of HTML 4:
http://www.w3.org/TR/html4
Latest version of HTML:
http://www.w3.org/TR/html
Previous version of HTML 4.01:
http://www.w3.org/TR/1999/PR-html40-19990824
Previous HTML 4 Recommendation:
http://www.w3.org/TR/1998/REC-html40-19980424
Editors:
Dave Raggett <dsr@w3.org>
Arnaud Le Hors, W3C
Ian Jacobs, W3C
Copyright ©1997-1999 W3C ® (MIT, INRIA, Keio), All Rights Reserved. W3C
liability, trademark, document use and software licensing rules apply.
Abstract
This specification defines the HyperText Markup Language (HTML), the publishing
language of the World Wide Web. This specification defines HTML 4.01, which is a
subversion of HTML 4. In addition to the text, multimedia, and hyperlink features of
the previous versions of HTML (HTML 3.2 [HTML32] [p.356] and HTML 2.0
[RFC1866] [p.356] ), HTML 4 supports more multimedia options, scripting
languages, style sheets, better printing facilities, and documents that are more
accessible to users with disabilities. HTML 4 also takes great strides towards the
internationalization of documents, with the goal of making the Web truly World Wide.
HTML 4 is an SGML application conforming to International Standard ISO 8879 -Standard Generalized Markup Language [ISO8879] [p.353] .
1
24 Dec 1999 18:26
HTML 4.01 Specification
Status of this document
This section describes the status of this document at the time of its publication.
Other documents may supersede this document. The latest status of this document
series is maintained at the W3C.
This document specifies HTML 4.01, which is part of the HTML 4 line of
specifications. The first version of HTML 4 was HTML 4.0 [HTML40] [p.353] ,
published on 18 December 1997 and revised 24 April 1998. This specification is the
first HTML 4.01 Recommendation. It includes non-editorial changes since the 24
April version of HTML 4.0 [p.312] . There have been some changes to the DTDs, for
example. This document obsoletes previous versions of HTML 4.0, although W3C
will continue to make those specifications and their DTDs available at the W3C Web
site.
This document has been reviewed by W3C Members and other interested parties
and has been endorsed by the Director as a W3C Recommendation. It is a stable
document and may be used as reference material or cited as a normative reference
from another document. W3C’s role in making the Recommendation is to draw
attention to the specification and to promote its widespread deployment. This
enhances the functionality and interoperability of the Web.
W3C recommends that user agents and authors (and in particular, authoring tools)
produce HTML 4.01 documents rather than HTML 4.0 documents. W3C
recommends that authors produce HTML 4 documents instead of HTML 3.2
documents. For reasons of backward compatibility, W3C also recommends that tools
interpreting HTML 4 continue to support HTML 3.2 and HTML 2.0 as well.
For information about the next generation of HTML, "The Extensible HyperText
Markup Language" [XHTML] [p.357] , please refer to the W3C HTML Activity and the
list of W3C Technical Reports.
This document has been produced as part of the W3C HTML Activity. The goals of
the HTML Working Group (Members only) are discussed in the HTML Working
Group charter (Members only).
A list of current W3C Recommendations and other technical documents can be
found at http://www.w3.org/TR.
Public discussion on HTML features takes place on www-html@w3.org (archives
of www-html@w3.org).
Available languages
The English version of this specification is the only normative version. However, for
translations of this document, see
http://www.w3.org/MarkUp/html4-updates/translations.
24 Dec 1999 18:26
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HTML 4.01 Specification
Errata
The list of known errors in this specification is available at:
http://www.w3.org/MarkUp/html4-updates/errata
Please report errors in this document to www-html-editor@w3.org.
3
24 Dec 1999 18:26
HTML 4.01 Specification
Quick Table of Contents
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About the HTML 4 Specification .
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Introduction to HTML 4 .
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On SGML and HTML
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Conformance: requirements and recommendations .
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HTML Document Representation - Character sets, character encodings, and
entities .
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Basic HTML data types - Character data, colors, lengths, URIs, content types,
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The global structure of an HTML document - The HEAD and BODY of a
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Language information and text direction - International considerations for text 79
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Text - Paragraphs, Lines, and Phrases .
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Lists - Unordered, Ordered, and Definition Lists .
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Tables .
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Links - Hypertext and Media-Independent Links .
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Objects, Images, and Applets
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Style Sheets - Adding style to HTML documents .
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Alignment, font styles, and horizontal rules
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Frames - Multi-view presentation of documents .
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Forms - User-input Forms: Text Fields, Buttons, Menus, and more
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Scripts - Animated Documents and Smart Forms .
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SGML reference information for HTML - Formal definition of HTML and
validation
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SGML Declaration of HTML 4
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Document Type Definition
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Transitional Document Type Definition
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Frameset Document Type Definition .
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Character entity references in HTML 4
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A. Changes
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B. Performance, Implementation, and Design Notes .
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References .
Index of Elements
Index of Attributes
Index
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4
HTML 4.01 Specification
Full Table of Contents
1. About the HTML 4 Specification .
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1. How the specification is organized .
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2. Document conventions .
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1. Elements and attributes
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2. Notes and examples
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3. Acknowledgments .
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1. Acknowledgments for the current revision
4. Copyright Notice
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2. Introduction to HTML 4 .
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1. What is the World Wide Web? .
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1. Introduction to URIs
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2. Fragment identifiers
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3. Relative URIs .
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2. What is HTML? .
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1. A brief history of HTML .
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3. HTML 4
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1. Internationalization .
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2. Accessibility
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3. Tables .
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4. Compound documents .
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5. Style sheets
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6. Scripting
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7. Printing .
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4. Authoring documents with HTML 4 .
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1. Separate structure and presentation
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2. Consider universal accessibility to the Web
3. Help user agents with incremental rendering
3. On SGML and HTML
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1. Introduction to SGML
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2. SGML constructs used in HTML .
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1. Elements .
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2. Attributes .
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3. Character references
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4. Comments .
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3. How to read the HTML DTD .
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1. DTD Comments
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2. Parameter entity definitions .
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3. Element declarations
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Content model definitions .
4. Attribute declarations
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DTD entities in attribute definitions .
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24 Dec 1999 18:26
HTML 4.01 Specification
4.
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Boolean attributes .
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. 36
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Conformance: requirements and recommendations .
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. 37
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1. Definitions .
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. 37
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2. SGML .
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. 39
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3. The text/html content type .
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. 39
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HTML Document Representation - Character sets, character encodings, and
entities .
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. 41
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1. The Document Character Set
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. 41
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2. Character encodings
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. 42
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1. Choosing an encoding .
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Notes on specific encodings
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. 43
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2. Specifying the character encoding .
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3. Character references
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. 45
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1. Numeric character references .
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. 45
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2. Character entity references .
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4. Undisplayable characters
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. 47
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Basic HTML data types - Character data, colors, lengths, URIs, content types,
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1. Case information
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. 49
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2. SGML basic types .
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3. Text strings .
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4. URIs
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5. Colors .
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1. Notes on using colors .
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6. Lengths
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7. Content types (MIME types) .
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8. Language codes
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9. Character encodings
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10. Single characters
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11. Dates and times
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. 54
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12. Link types .
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13. Media descriptors .
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14. Script data .
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15. Style sheet data
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. 57
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16. Frame target names .
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The global structure of an HTML document - The HEAD and BODY of a
document
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. 59
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1. Introduction to the structure of an HTML document .
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2. HTML version information .
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. 60
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3. The HTML element .
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4. The document head
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1. The HEAD element .
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2. The TITLE element
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24 Dec 1999 18:26
6
HTML 4.01 Specification
3. The title attribute
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. 63
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4. Meta data .
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. 64
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Specifying meta data .
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The META element .
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. 65
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Meta data profiles .
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. 68
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5. The document body .
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1. The BODY element .
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2. Element identifiers: the id and class attributes .
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3. Block-level and inline elements .
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. 73
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4. Grouping elements: the DIV and SPAN elements
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5. Headings: The H1, H2, H3, H4, H5, H6 elements .
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6. The ADDRESS element .
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8. Language information and text direction - International considerations for text 79
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1. Specifying the language of content: the lang attribute
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1. Language codes
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2. Inheritance of language codes .
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3. Interpretation of language codes .
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2. Specifying the direction of text and tables: the dir attribute .
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1. Introduction to the bidirectional algorithm
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2. Inheritance of text direction information .
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3. Setting the direction of embedded text .
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4. Overriding the bidirectional algorithm: the BDO element .
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5. Character references for directionality and joining control
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6. The effect of style sheets on bidirectionality .
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9. Text - Paragraphs, Lines, and Phrases .
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1. White space
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2. Structured text .
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1. Phrase elements: EM, STRONG, DFN, CODE, SAMP, KBD, VAR, CITE,
ABBR, and ACRONYM
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. 90
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2. Quotations: The BLOCKQUOTE and Q elements .
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. 92
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Rendering quotations .
3. Subscripts and superscripts: the SUB and SUP elements .
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3. Lines and Paragraphs .
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1. Paragraphs: the P element .
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2. Controlling line breaks .
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. 95
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Forcing a line break: the BR element
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. 96
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Prohibiting a line break .
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. 96
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3. Hyphenation
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. 96
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4. Preformatted text: The PRE element .
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. 97
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5. Visual rendering of paragraphs .
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3. Definition lists: the DL, DT, and DD elements .
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4. Column groups: the COLGROUP and COL elements .
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4. Unavailable and unidentifiable resources
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HTML 4.01 Specification
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13. Objects, Images, and Applets
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4. Including an applet: the APPLET element
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1. Client-side image maps: the MAP and AREA elements
Client-side image map examples
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2. Server-side image maps
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14. Style Sheets - Adding style to HTML documents .
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3. Header style information: the STYLE element
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4. Media types
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1. Preferred and alternate style sheets .
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4. Cascading style sheets .
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1. Media-dependent cascades
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2. Inheritance and cascading .
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5. Hiding style data from user agents .
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6. Linking to style sheets with HTTP headers .
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15. Alignment, font styles, and horizontal rules
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1. Formatting .
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Float an object .
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Float text around an object .
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2. Fonts .
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2. Font modifier elements: FONT and BASEFONT
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16. Frames - Multi-view presentation of documents .
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1. Introduction to frames .
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2. Layout of frames
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1. The FRAMESET element
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Rows and columns .
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Nested frame sets .
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Sharing data among frames .
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2. The FRAME element
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Setting the initial contents of a frame
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Visual rendering of a frame .
3. Specifying target frame information .
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1. Setting the default target for links
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2. Target semantics .
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4. Alternate content
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1. The NOFRAMES element
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2. Long descriptions of frames .
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5. Inline frames: the IFRAME element .
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17. Forms - User-input Forms: Text Fields, Buttons, Menus, and more
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1. Introduction to forms
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2. Controls
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1. Control types .
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3. The FORM element .
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4. The INPUT element .
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1. Control types created with INPUT .
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2. Examples of forms containing INPUT controls
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5. The BUTTON element
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6. The SELECT, OPTGROUP, and OPTION elements .
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1. Pre-selected options
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7. The TEXTAREA element .
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8. The ISINDEX element .
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9. Labels .
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1. The LABEL element .
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10. Adding structure to forms: the FIELDSET and LEGEND elements .
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11. Giving focus to an element .
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1. Tabbing navigation .
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HTML 4.01 Specification
18.
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24.
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2. Access keys
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. 242
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12. Disabled and read-only controls .
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. 243
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1. Disabled controls .
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. 244
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2. Read-only controls .
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. 244
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13. Form submission
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. 245
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1. Form submission method
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. 245
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2. Successful controls .
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. 245
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3. Processing form data .
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. 246
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Step one: Identify the successful controls
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. 246
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Step two: Build a form data set .
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. 246
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Step three: Encode the form data set
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. 246
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Step four: Submit the encoded form data set
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. 247
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4. Form content types .
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. 247
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. 247
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application/x-www-form-urlencoded
multipart/form-data .
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. 248
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Scripts - Animated Documents and Smart Forms .
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. 251
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1. Introduction to scripts
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. 251
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2. Designing documents for user agents that support scripting .
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. 252
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1. The SCRIPT element .
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. 252
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2. Specifying the scripting language
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. 253
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The default scripting language .
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. 253
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Local declaration of a scripting language
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. 254
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. 254
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References to HTML elements from a script .
3. Intrinsic events .
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. 254
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4. Dynamic modification of documents .
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. 258
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3. Designing documents for user agents that don’t support scripting .
. 258
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1. The NOSCRIPT element
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. 258
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2. Hiding script data from user agents .
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. 259
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SGML reference information for HTML - Formal definition of HTML and
validation
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. 261
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1. Document Validation
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. 261
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2. Sample SGML catalog .
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. 262
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SGML Declaration of HTML 4
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. 263
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1. SGML Declaration .
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. 263
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Document Type Definition
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. 265
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Transitional Document Type Definition
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. 279
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Frameset Document Type Definition .
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. 297
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Character entity references in HTML 4
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. 299
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1. Introduction to character entity references
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. 299
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2. Character entity references for ISO 8859-1 characters
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. 299
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1. The list of characters
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. 300
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3. Character entity references for symbols, mathematical symbols, and Greek
letters .
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HTML 4.01 Specification
1. The list of characters
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. 304
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4. Character entity references for markup-significant and internationalization
characters .
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. 308
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1. The list of characters
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. 308
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A. Changes
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. 311
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1. Changes between 24 April 1998 HTML 4.0 and 24 December 1999 HTML
4.01 versions
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. 312
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1. Changes to the specification
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. 312
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General changes .
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. 312
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On SGML and HTML .
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. 312
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HTML Document Representation
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. 312
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Basic HTML data types
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. 312
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Global structure of an HTML document .
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. 313
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Language information and text direction
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. 313
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Tables .
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.
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. 313
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Links .
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. 313
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Objects, Images, and Applets .
.
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. 314
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. 314
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Style Sheets in HTML Documents .
Frames
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. 314
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Forms .
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12
HTML 4.01 Specification
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HTML 4.01 Specification
1. Security issues for forms
References .
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2. Informative references
Index of Elements
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14
About the HTML 4 Specification
1 About the HTML 4 Specification
Contents
1. How the specification is organized
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1. Acknowledgments for the current revision
4. Copyright Notice .
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1.1 How the specification is organized
This specification is divided into the following sections:
Sections 2 and 3: Introduction to HTML 4
The introduction describes HTML’s place in the scheme of the World Wide Web,
provides a brief history of the development of HTML, highlights what can be
done with HTML 4, and provides some HTML authoring tips.
The brief SGML tutorial gives readers some understanding of HTML’s
relationship to SGML and gives summary information on how to read the HTML
Document Type Definition (DTD).
Sections 4 - 24: HTML 4 reference manual
The bulk of the reference manual consists of the HTML language reference,
which defines all elements and attributes of the language.
This document has been organized by topic rather than by the grammar of
HTML. Topics are grouped into three categories: structure, presentation, and
interactivity. Although it is not easy to divide HTML constructs perfectly into
these three categories, the model reflects the HTML Working Group’s
experience that separating a document’s structure from its presentation
produces more effective and maintainable documents.
The language reference consists of the following information:
What characters [p.41] may appear in an HTML document.
Basic data types [p.49] of an HTML document.
Elements that govern the structure of an HTML document, including text
[p.89] , lists [p.103] , tables [p.111] , links [p.145] , and included objects,
images, and applets [p.159] .
Elements that govern the presentation of an HTML document, including
style sheets [p.183] , fonts, colors, rules, and other visual presentation
[p.195] , and frames for multi-windowed presentations [p.205] .
15
24 Dec 1999 18:26
About the HTML 4 Specification
Elements that govern interactivity with an HTML document, including forms
for user input [p.219] and scripts for active documents [p.251] .
The SGML formal definition of HTML:
The SGML declaration of HTML [p.263] .
Three DTDs: strict [p.265] , transitional [p.279] , and frameset [p.297] .
The list of character references [p.299] .
Appendixes
The first appendix contains information about changes from HTML 3.2 [p.311] to
help authors and implementors with the transition to HTML 4, and changes from
the 18 December 1997 specification [p.322] . The second appendix contains
performance and implementation notes [p.333] , and is primarily intended to
help implementors create user agents for HTML 4.
References
A list of normative and informative references.
Indexes
Three indexes give readers rapid access to the definition of key concepts
[p.375] , elements [p.359] and attributes [p.363] .
1.2 Document conventions
This document has been written with two types of readers in mind: authors and
implementors. We hope the specification will provide authors with the tools they
need to write efficient, attractive, and accessible documents, without over-exposing
them to HTML’s implementation details. Implementors, however, should find all they
need to build conforming user agents.
The specification may be approached in several ways:
Read from beginning to end. The specification begins with a general
presentation of HTML and becomes more and more technical and specific
towards the end.
Quick access to information. In order to get information about syntax and
semantics as quickly as possible, the online version of the specification includes
the following features:
1. Every reference to an element or attribute is linked to its definition in the
specification. Each element or attribute is defined in only one location.
2. Every page includes links to the indexes, so you never are more than two
links away from finding the definition of an element [p.359] or attribute
[p.363] .
3. The front pages of each section of the language reference manual extend
the initial table of contents with more detail about that section.
24 Dec 1999 18:26
16
About the HTML 4 Specification
1.2.1 Elements and attributes
Element names are written in uppercase letters (e.g., BODY). Attribute names are
written in lowercase letters (e.g., lang, onsubmit). Recall that in HTML, element and
attribute names are case-insensitive; the convention is meant to encourage
readability.
Element and attribute names in this document have been marked up and may be
rendered specially by some user agents.
Each attribute definition specifies the type of its value. If the type allows a small
set of possible values, the definition lists the set of values, separated by a bar (|).
After the type information, each attribute definition indicates the case-sensitivity of
its values, between square brackets ("[]"). See the section on case information [p.49]
for details.
1.2.2 Notes and examples
Informative notes are emphasized to stand out from surrounding text and may be
rendered specially by some user agents.
All examples illustrating deprecated [p.38] usage are marked as "DEPRECATED
EXAMPLE". Deprecated examples also include recommended alternate solutions.
All examples that illustrates illegal usage are clearly marked "ILLEGAL EXAMPLE".
Examples and notes have been marked up and may be rendered specially by
some user agents.
1.3 Acknowledgments
Thanks to everyone who has helped to author the working drafts that went into the
HTML 4 specification, and to all those who have sent suggestions and corrections.
Many thanks to the Web Accessibility Initiative task force (WAI HC group) for their
work on improving the accessibility of HTML and to T.V. Raman (Adobe) for his early
work on developing accessible forms.
The authors of this specification, the members of the W3C HTML Working Group,
deserve much applause for their diligent review of this document, their constructive
comments, and their hard work: John D. Burger (MITRE), Steve Byrne (JavaSoft),
Martin J. Dürst (University of Zurich), Daniel Glazman (Electricité de France), Scott
Isaacs (Microsoft), Murray Maloney (GRIF), Steven Pemberton (CWI), Robert
Pernett (Lotus), Jared Sorensen (Novell), Powell Smith (IBM), Robert Stevahn (HP),
Ed Tecot (Microsoft), Jeffrey Veen (HotWired), Mike Wexler (Adobe), Misha Wolf
(Reuters), and Lauren Wood (SoftQuad).
Thank you Dan Connolly (W3C) for rigorous and bountiful input as part-time editor
and thoughtful guidance as chairman of the HTML Working Group. Thank you Sally
Khudairi (W3C) for your indispensable work on press releases.
17
24 Dec 1999 18:26
About the HTML 4 Specification
Thanks to David M. Abrahamson and Roger Price for their careful reading of the
specification and constructive comments.
Thanks to Jan Kärrman, author of html2ps for helping so much in creating the
Postscript version of the specification.
Of particular help from the W3C at Sophia-Antipolis were Janet Bertot, Bert Bos,
Stephane Boyera, Daniel Dardailler, Yves Lafon, Håkon Lie, Chris Lilley, and Colas
Nahaboo (Bull).
Lastly, thanks to Tim Berners-Lee without whom none of this would have been
possible.
1.3.1 Acknowledgments for the current revision
Many thanks to Shane McCarron for tracking errata for this revision of the
specification.
1.4 Copyright Notice
For information about copyrights, please refer to the W3C Intellectual Property
Notice, the W3C Document Notice, and the W3C IPR Software Notice.
24 Dec 1999 18:26
18
Introduction to HTML 4
2 Introduction to HTML 4
Contents
1. What is the World Wide Web?
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1. A brief history of HTML .
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2. Consider universal accessibility to the Web
3. Help user agents with incremental rendering
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2.1 What is the World Wide Web?
The World Wide Web (Web) is a network of information resources. The Web relies
on three mechanisms to make these resources readily available to the widest
possible audience:
1. A uniform naming scheme for locating resources on the Web (e.g., URIs).
2. Protocols, for access to named resources over the Web (e.g., HTTP).
3. Hypertext, for easy navigation among resources (e.g., HTML).
The ties between the three mechanisms are apparent throughout this
specification.
2.1.1 Introduction to URIs
Every resource available on the Web -- HTML document, image, video clip, program,
etc. -- has an address that may be encoded by a Universal Resource Identifier, or
"URI".
URIs typically consist of three pieces:
19
24 Dec 1999 18:26
Introduction to HTML 4
1. The naming scheme of the mechanism used to access the resource.
2. The name of the machine hosting the resource.
3. The name of the resource itself, given as a path.
Consider the URI that designates the W3C Technical Reports page:
http://www.w3.org/TR
This URI may be read as follows: There is a document available via the HTTP
protocol (see [RFC2616] [p.354] ), residing on the machine www.w3.org, accessible
via the path "/TR". Other schemes you may see in HTML documents include "mailto"
for email and "ftp" for FTP.
Here is another example of a URI. This one refers to a user’s mailbox:
...this is text...
For all comments, please send email to
<A href="mailto:joe@someplace.com">Joe Cool</A>.
Note. Most readers may be familiar with the term "URL" and not the term "URI".
URLs form a subset of the more general URI naming scheme.
2.1.2 Fragment identifiers
Some URIs refer to a location within a resource. This kind of URI ends with "#"
followed by an anchor identifier (called the fragment identifier). For instance, here is
a URI pointing to an anchor named section_2:
http://somesite.com/html/top.html#section_2
2.1.3 Relative URIs
A relative URI doesn’t contain any naming scheme information. Its path generally
refers to a resource on the same machine as the current document. Relative URIs
may contain relative path components (e.g., ".." means one level up in the hierarchy
defined by the path), and may contain fragment identifiers [p.20] .
Relative URIs are resolved to full URIs [p.158] using a base URI. As an example
of relative URI resolution, assume we have the base URI
"http://www.acme.com/support/intro.html". The relative URI in the following markup
for a hypertext link:
<A href="suppliers.html">Suppliers</A>
would expand to the full URI "http://www.acme.com/support/suppliers.html", while
the relative URI in the following markup for an image
<IMG src="../icons/logo.gif" alt="logo">
would expand to the full URI "http://www.acme.com/icons/logo.gif".
24 Dec 1999 18:26
20
Introduction to HTML 4
In HTML, URIs are used to:
Link to another document or resource, (see the A and LINK elements).
Link to an external style sheet or script (see the LINK and SCRIPT elements).
Include an image, object, or applet in a page, (see the IMG, OBJECT, APPLET
and INPUT elements).
Create an image map (see the MAP and AREA elements).
Submit a form (see FORM).
Create a frame document (see the FRAME and IFRAME elements).
Cite an external reference (see the Q, BLOCKQUOTE, INS and DEL elements).
Refer to metadata conventions describing a document (see the HEAD element).
Please consult the section on the URI [p.51] type for more information about URIs.
2.2 What is HTML?
To publish information for global distribution, one needs a universally understood
language, a kind of publishing mother tongue that all computers may potentially
understand. The publishing language used by the World Wide Web is HTML (from
HyperText Markup Language).
HTML gives authors the means to:
Publish online documents with headings, text, tables, lists, photos, etc.
Retrieve online information via hypertext links, at the click of a button.
Design forms for conducting transactions with remote services, for use in
searching for information, making reservations, ordering products, etc.
Include spread-sheets, video clips, sound clips, and other applications directly in
their documents.
2.2.1 A brief history of HTML
HTML was originally developed by Tim Berners-Lee while at CERN, and popularized
by the Mosaic browser developed at NCSA. During the course of the 1990s it has
blossomed with the explosive growth of the Web. During this time, HTML has been
extended in a number of ways. The Web depends on Web page authors and
vendors sharing the same conventions for HTML. This has motivated joint work on
specifications for HTML.
HTML 2.0 (November 1995, see [RFC1866] [p.356] ) was developed under the
aegis of the Internet Engineering Task Force (IETF) to codify common practice in
late 1994. HTML+ (1993) and HTML 3.0 (1995, see [HTML30] [p.355] ) proposed
much richer versions of HTML. Despite never receiving consensus in standards
discussions, these drafts led to the adoption of a range of new features. The efforts
of the World Wide Web Consortium’s HTML Working Group to codify common
practice in 1996 resulted in HTML 3.2 (January 1997, see [HTML32] [p.356] ).
Changes from HTML 3.2 are summarized in Appendix A [p.311]
21
24 Dec 1999 18:26
Introduction to HTML 4
Most people agree that HTML documents should work well across different
browsers and platforms. Achieving interoperability lowers costs to content providers
since they must develop only one version of a document. If the effort is not made,
there is much greater risk that the Web will devolve into a proprietary world of
incompatible formats, ultimately reducing the Web’s commercial potential for all
participants.
Each version of HTML has attempted to reflect greater consensus among industry
players so that the investment made by content providers will not be wasted and that
their documents will not become unreadable in a short period of time.
HTML has been developed with the vision that all manner of devices should be
able to use information on the Web: PCs with graphics displays of varying resolution
and color depths, cellular telephones, hand held devices, devices for speech for
output and input, computers with high or low bandwidth, and so on.
2.3 HTML 4
HTML 4 extends HTML with mechanisms for style sheets, scripting, frames,
embedding objects, improved support for right to left and mixed direction text, richer
tables, and enhancements to forms, offering improved accessibility for people with
disabilities.
HTML 4.01 is a revision of HTML 4.0 that corrects errors and makes some
changes since the previous revision. [p.311]
2.3.1 Internationalization
This version of HTML has been designed with the help of experts in the field of
internationalization, so that documents may be written in every language and be
transported easily around the world. This has been accomplished by incorporating
[RFC2070] [p.356] , which deals with the internationalization of HTML.
One important step has been the adoption of the ISO/IEC:10646 standard (see
[ISO10646] [p.353] ) as the document character set for HTML. This is the world’s
most inclusive standard dealing with issues of the representation of international
characters, text direction, punctuation, and other world language issues.
HTML now offers greater support for diverse human languages within a document.
This allows for more effective indexing of documents for search engines,
higher-quality typography, better text-to-speech conversion, better hyphenation, etc.
2.3.2 Accessibility
As the Web community grows and its members diversify in their abilities and skills, it
is crucial that the underlying technologies be appropriate to their specific needs.
HTML has been designed to make Web pages more accessible to those with
physical limitations. HTML 4 developments inspired by concerns for accessibility
include:
24 Dec 1999 18:26
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Introduction to HTML 4
Better distinction between document structure and presentation, thus
encouraging the use of style sheets instead of HTML presentation elements and
attributes.
Better forms, including the addition of access keys, the ability to group form
controls semantically, the ability to group SELECT options semantically, and
active labels.
The ability to markup a text description of an included object (with the OBJECT
element).
A new client-side image map mechanism (the MAP element) that allows authors
to integrate image and text links.
The requirement that alternate text accompany images included with the IMG
element and image maps included with the AREA element.
Support for the title and lang attributes on all elements.
Support for the ABBR and ACRONYM elements.
A wider range of target media (tty, braille, etc.) for use with style sheets.
Better tables, including captions, column groups, and mechanisms to facilitate
non-visual rendering.
Long descriptions of tables, images, frames, etc.
Authors who design pages with accessibility issues in mind will not only receive
the blessings of the accessibility community, but will benefit in other ways as well:
well-designed HTML documents that distinguish structure and presentation will
adapt more easily to new technologies.
Note. For more information about designing accessible HTML documents, please
consult [WAI] [p.357] .
2.3.3 Tables
The new table model in HTML is based on [RFC1942] [p.356] . Authors now have
greater control over structure and layout (e.g., column groups). The ability of
designers to recommend column widths allows user agents to display table data
incrementally (as it arrives) rather than waiting for the entire table before rendering.
Note. At the time of writing, some HTML authoring tools rely extensively on tables
for formatting, which may easily cause accessibility problems.
2.3.4 Compound documents
HTML now offers a standard mechanism for embedding generic media objects and
applications in HTML documents. The OBJECT element (together with its more
specific ancestor elements IMG and APPLET) provides a mechanism for including
images, video, sound, mathematics, specialized applications, and other objects in a
document. It also allows authors to specify a hierarchy of alternate renderings for
user agents that don’t support a specific rendering.
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Introduction to HTML 4
2.3.5 Style sheets
Style sheets simplify HTML markup and largely relieve HTML of the responsibilities
of presentation. They give both authors and users control over the presentation of
documents -- font information, alignment, colors, etc.
Style information can be specified for individual elements or groups of elements.
Style information may be specified in an HTML document or in external style sheets.
The mechanisms for associating a style sheet with a document is independent of
the style sheet language.
Before the advent of style sheets, authors had limited control over rendering.
HTML 3.2 included a number of attributes and elements offering control over
alignment, font size, and text color. Authors also exploited tables and images as a
means for laying out pages. The relatively long time it takes for users to upgrade
their browsers means that these features will continue to be used for some time.
However, since style sheets offer more powerful presentation mechanisms, the
World Wide Web Consortium will eventually phase out many of HTML’s presentation
elements and attributes. Throughout the specification elements and attributes at risk
are marked as "deprecated [p.38] ". They are accompanied by examples of how to
achieve the same effects with other elements or style sheets.
2.3.6 Scripting
Through scripts, authors may create dynamic Web pages (e.g., "smart forms" that
react as users fill them out) and use HTML as a means to build networked
applications.
The mechanisms provided to include scripts in an HTML document are
independent of the scripting language.
2.3.7 Printing
Sometimes, authors will want to make it easy for users to print more than just the
current document. When documents form part of a larger work, the relationships
between them can be described using the HTML LINK element or using W3C’s
Resource Description Framework (RDF) (see [RDF10] [p.356] ).
2.4 Authoring documents with HTML 4
We recommend that authors and implementors observe the following general
principles when working with HTML 4.
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Introduction to HTML 4
2.4.1 Separate structure and presentation
HTML has its roots in SGML which has always been a language for the specification
of structural markup. As HTML matures, more and more of its presentational
elements and attributes are being replaced by other mechanisms, in particular style
sheets. Experience has shown that separating the structure of a document from its
presentational aspects reduces the cost of serving a wide range of platforms, media,
etc., and facilitates document revisions.
2.4.2 Consider universal accessibility to the Web
To make the Web more accessible to everyone, notably those with disabilities,
authors should consider how their documents may be rendered on a variety of
platforms: speech-based browsers, braille-readers, etc. We do not recommend that
authors limit their creativity, only that they consider alternate renderings in their
design. HTML offers a number of mechanisms to this end (e.g., the alt attribute, the
accesskey attribute, etc.)
Furthermore, authors should keep in mind that their documents may be reaching a
far-off audience with different computer configurations. In order for documents to be
interpreted correctly, authors should include in their documents information about the
natural language and direction of the text, how the document is encoded, and other
issues related to internationalization.
2.4.3 Help user agents with incremental rendering
By carefully designing their tables and making use of new table features in HTML 4,
authors can help user agents render documents more quickly. Authors can learn
how to design tables for incremental rendering (see the TABLE element).
Implementors should consult the notes on tables [p.342] in the appendix for
information on incremental algorithms.
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Introduction to HTML 4
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On SGML and HTML
3 On SGML and HTML
Contents
1. Introduction to SGML
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3. Character references
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3. How to read the HTML DTD .
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1. DTD Comments
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2. Parameter entity definitions .
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3. Element declarations
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Content model definitions .
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4. Attribute declarations
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DTD entities in attribute definitions
Boolean attributes .
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This section of the document introduces SGML and discusses its relationship to
HTML. A complete discussion of SGML is left to the standard (see [ISO8879] [p.353]
).
3.1 Introduction to SGML
SGML is a system for defining markup languages. Authors mark up their documents
by representing structural, presentational, and semantic information alongside
content. HTML is one example of a markup language. Here is an example of an
HTML document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>My first HTML document</TITLE>
</HEAD>
<BODY>
<P>Hello world!
</BODY>
</HTML>
An HTML document is divided into a head section (here, between <HEAD> and
</HEAD>) and a body (here, between <BODY> and </BODY>). The title of the
document appears in the head (along with other information about the document),
and the content of the document appears in the body. The body in this example
contains just one paragraph, marked up with <P>.
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On SGML and HTML
Each markup language defined in SGML is called an SGML application. An SGML
application is generally characterized by:
1. An SGML declaration [p.263] . The SGML declaration specifies which
characters and delimiters may appear in the application.
2. A document type definition (DTD) [p.265] . The DTD defines the syntax of
markup constructs. The DTD may include additional definitions such as
character entity references [p.30] .
3. A specification that describes the semantics to be ascribed to the markup. This
specification also imposes syntax restrictions that cannot be expressed within
the DTD.
4. Document instances containing data (content) and markup. Each instance
contains a reference to the DTD to be used to interpret it.
This specification includes an SGML declaration [p.263] , three document type
definitions (see the section on HTML version information [p.59] for a description of
the three), and a list of character references [p.30] .
3.2 SGML constructs used in HTML
The following sections introduce SGML constructs that are used in HTML.
The appendix lists some SGML features [p.337] that are not widely supported by
HTML tools and user agents and should be avoided.
3.2.1 Elements
An SGML document type definition [p.265] declares element types that represent
structures or desired behavior. HTML includes element types that represent
paragraphs, hypertext links, lists, tables, images, etc.
Each element type declaration generally describes three parts: a start tag, content,
and an end tag.
The element’s name appears in the start tag (written <element-name>) and the
end tag (written </element-name>); note the slash before the element name in the
end tag. For example, the start and end tags of the UL element type delimit the items
in a list:
<UL>
<LI><P>...list item 1...
<LI><P>...list item 2...
</UL>
Some HTML element types allow authors to omit end tags (e.g., the P and LI
element types). A few element types also allow the start tags to be omitted; for
example, HEAD and BODY. The HTML DTD indicates for each element type whether
the start tag and end tag are required.
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On SGML and HTML
Some HTML element types have no content. For example, the line break element
BR has no content; its only role is to terminate a line of text. Such empty elements
never have end tags. The document type definition [p.265] and the text of the
specification indicate whether an element type is empty (has no content) or, if it can
have content, what is considered legal content.
Element names are always case-insensitive.
Please consult the SGML standard for information about rules governing elements
(e.g., they must be properly nested, an end tag closes, back to the matching start
tag, all unclosed intervening start tags with omitted end tags (section 7.5.1), etc.).
For example, the following paragraph:
<P>This is the first paragraph.</P>
...a block element...
may be rewritten without its end tag:
<P>This is the first paragraph.
...a block element...
since the <P> start tag is closed by the following block element. Similarly, if a
paragraph is enclosed by a block element, as in:
<DIV>
<P>This is the paragraph.
</DIV>
the end tag of the enclosing block element (here, </DIV>) implies the end tag of
the open <P> start tag.
Elements are not tags. Some people refer to elements as tags (e.g., "the P tag").
Remember that the element is one thing, and the tag (be it start or end tag) is
another. For instance, the HEAD element is always present, even though both start
and end HEAD tags may be missing in the markup.
All the element types declared in this specification are listed in the element index
[p.359] .
3.2.2 Attributes
Elements may have associated properties, called attributes, which may have values
(by default, or set by authors or scripts). Attribute/value pairs appear before the final
">" of an element’s start tag. Any number of (legal) attribute value pairs, separated
by spaces, may appear in an element’s start tag. They may appear in any order.
In this example, the id attribute is set for an H1 element:
<H1 id="section1">
This is an identified heading thanks to the id attribute
</H1>
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On SGML and HTML
By default, SGML requires that all attribute values be delimited using either double
quotation marks (ASCII decimal 34) or single quotation marks (ASCII decimal 39).
Single quote marks can be included within the attribute value when the value is
delimited by double quote marks, and vice versa. Authors may also use numeric
character references [p.30] to represent double quotes (&#34;) and single quotes
(&#39;). For double quotes authors can also use the character entity reference [p.30]
&quot;.
In certain cases, authors may specify the value of an attribute without any
quotation marks. The attribute value may only contain letters (a-z and A-Z), digits
(0-9), hyphens (ASCII decimal 45), periods (ASCII decimal 46), underscores (ASCII
decimal 95), and colons (ASCII decimal 58). We recommend using quotation marks
even when it is possible to eliminate them.
Attribute names are always case-insensitive.
Attribute values are generally case-insensitive. The definition of each attribute in
the reference manual indicates whether its value is case-insensitive.
All the attributes defined by this specification are listed in the attribute index
[p.363] .
3.2.3 Character references
Character references are numeric or symbolic names for characters that may be
included in an HTML document. They are useful for referring to rarely used
characters, or those that authoring tools make it difficult or impossible to enter. You
will see character references throughout this document; they begin with a "&" sign
and end with a semi-colon (;). Some common examples include:
"&lt;" represents the < sign.
"&gt;" represents the > sign.
"&quot;" represents the " mark.
"&#229;" (in decimal) represents the letter "a" with a small circle above it.
"&#1048;" (in decimal) represents the Cyrillic capital letter "I".
"&#x6C34;" (in hexadecimal) represents the Chinese character for water.
We discuss HTML character references [p.45] in detail later in the section on the
HTML document character set [p.41] . The specification also contains a list of
character references [p.299] that may appear in HTML 4 documents.
3.2.4 Comments
HTML comments have the following syntax:
<!-- this is a comment -->
<!-- and so is this one,
which occupies more than one line -->
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On SGML and HTML
White space is not permitted between the markup declaration open delimiter("<!")
and the comment open delimiter ("--"), but is permitted between the comment close
delimiter ("--") and the markup declaration close delimiter (">"). A common error is to
include a string of hyphens ("---") within a comment. Authors should avoid putting
two or more adjacent hyphens inside comments.
Information that appears between comments has no special meaning (e.g.,
character references [p.30] are not interpreted as such).
Note that comments are markup.
3.3 How to read the HTML DTD
Each element and attribute declaration in this specification is accompanied by its
document type definition [p.265] fragment. We have chosen to include the DTD
fragments in the specification rather than seek a more approachable, but longer and
less precise means of describing an element’s properties. The following tutorial
should allow readers unfamiliar with SGML to read the DTD and understand the
technical details of the HTML specification.
3.3.1 DTD Comments
In DTDs, comments may spread over one or more lines. In the DTD, comments are
delimited by a pair of "--" marks, e.g.
<!ELEMENT PARAM - O EMPTY
-- named property value -->
Here, the comment "named property value" explains the use of the PARAM element
type. Comments in the DTD are informative only.
3.3.2 Parameter entity definitions
The HTML DTD [p.265] begins with a series of parameter entity definitions. A
parameter entity definition defines a kind of macro that may be referenced and
expanded elsewhere in the DTD. These macros may not appear in HTML
documents, only in the DTD. Other types of macros, called character references
[p.30] , may be used in the text of an HTML document or within attribute values.
When the parameter entity is referred to by name in the DTD, it is expanded into a
string.
A parameter entity definition begins with the keyword <!ENTITY % followed by
the entity name, the quoted string the entity expands to, and finally a closing >.
Instances of parameter entities in a DTD begin with "%", then the parameter entity
name, and terminated by an optional ";".
The following example defines the string that the "%fontstyle;" entity will expand
to.
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On SGML and HTML
<!ENTITY % fontstyle "TT | I | B | BIG | SMALL">
The string the parameter entity expands to may contain other parameter entity
names. These names are expanded recursively. In the following example, the
"%inline;" parameter entity is defined to include the "%fontstyle;", "%phrase;",
"%special;" and "%formctrl;" parameter entities.
<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">
You will encounter two DTD entities frequently in the HTML DTD [p.265] :
"%block;" "%inline;". They are used when the content model includes block-level and
inline elements [p.73] , respectively (defined in the section on the global structure of
an HTML document [p.59] ).
3.3.3 Element declarations
The bulk of the HTML DTD consists of the declarations of element types and their
attributes. The <!ELEMENT keyword begins a declaration and the > character ends
it. Between these are specified:
1. The element’s name.
2. Whether the element’s tags are optional. Two hyphens that appear after the
element name mean that the start and end tags are mandatory. One hyphen
followed by the letter "O" indicates that the end tag can be omitted. A pair of
letter "O"s indicate that both the start and end tags can be omitted.
3. The element’s content, if any. The allowed content for an element is called its
content model. Element types that are designed to have no content are called
empty elements. The content model for such element types is declared using
the keyword "EMPTY".
In this example:
<!ELEMENT UL - - (LI)+>
The element type being declared is UL.
The two hyphens indicate that both the start tag <UL> and the end tag </UL> for
this element type are required.
The content model for this element type is declared to be "at least one LI
element". Below, we explain how to specify content models.
This example illustrates the declaration of an empty element type:
<!ELEMENT IMG - O EMPTY>
The element type being declared is IMG.
The hyphen and the following "O" indicate that the end tag can be omitted, but
together with the content model "EMPTY", this is strengthened to the rule that
the end tag must be omitted.
The "EMPTY" keyword means that instances of this type must not have content.
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On SGML and HTML
Content model definitions
The content model describes what may be contained by an instance of an element
type. Content model definitions may include:
The names of allowed or forbidden element types (e.g., the UL element contains
instances of the LI element type, and the P element type may not contain other
P elements).
DTD entities (e.g., the LABEL element contains instances of the "%inline;"
parameter entity).
Document text (indicated by the SGML construct "#PCDATA"). Text may
contain character references [p.45] . Recall that these begin with & and end with
a semicolon (e.g., "Herg&eacute;’s adventures of Tintin" contains the character
entity reference for the "e acute" character).
The content model of an element is specified with the following syntax. Please
note that the list below is a simplification of the full SGML syntax rules and does not
address, e.g., precedences.
( ... )
Delimits a group.
A
A must occur, one time only.
A+
A must occur one or more times.
A?
A must occur zero or one time.
A*
A may occur zero or more times.
+(A)
A may occur.
-(A)
A must not occur.
A|B
Either A or B must occur, but not both.
A,B
Both A and B must occur, in that order.
A&B
Both A and B must occur, in any order.
Here are some examples from the HTML DTD:
<!ELEMENT UL - - (LI)+>
The UL element must contain one or more LI elements.
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On SGML and HTML
<!ELEMENT DL
- - (DT|DD)+>
The DL element must contain one or more DT or DD elements in any order.
<!ELEMENT OPTION - O (#PCDATA)>
The OPTION element may only contain text and entities, such as &amp; -- this is
indicated by the SGML data type #PCDATA.
A few HTML element types use an additional SGML feature to exclude elements
from their content model. Excluded elements are preceded by a hyphen. Explicit
exclusions override permitted elements.
In this example, the -(A) signifies that the element A cannot appear in another A
element (i.e., anchors may not be nested).
<!ELEMENT A - - (%inline;)* -(A)>
Note that the A element type is part of the DTD parameter entity "%inline;", but is
excluded explicitly because of -(A).
Similarly, the following element type declaration for FORM prohibits nested forms:
<!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM)>
3.3.4 Attribute declarations
The <!ATTLIST keyword begins the declaration of attributes that an element may
take. It is followed by the name of the element in question, a list of attribute
definitions, and a closing >. Each attribute definition is a triplet that defines:
The name of an attribute.
The type of the attribute’s value or an explicit set of possible values. Values
defined explicitly by the DTD are case-insensitive. Please consult the section on
basic HTML data types [p.49] for more information about attribute value types.
Whether the default value of the attribute is implicit (keyword "#IMPLIED"), in
which case the default value must be supplied by the user agent (in some cases
via inheritance from parent elements); always required (keyword
"#REQUIRED"); or fixed to the given value (keyword "#FIXED"). Some attribute
definitions explicitly specify a default value for the attribute.
In this example, the name attribute is defined for the MAP element. The attribute is
optional for this element.
<!ATTLIST MAP
name
CDATA
>
#IMPLIED
The type of values permitted for the attribute is given as CDATA, an SGML data
type. CDATA is text that may contain character references [p.45] .
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On SGML and HTML
For more information about "CDATA", "NAME", "ID", and other data types, please
consult the section on HTML data types [p.49] .
The following examples illustrate several attribute definitions:
rowspan
http-equiv
id
valign
NUMBER
1
-- number of rows spanned by cell -NAME
#IMPLIED -- HTTP response header name -ID
#IMPLIED -- document-wide unique id -(top|middle|bottom|baseline) #IMPLIED
The rowspan attribute requires values of type NUMBER. The default value is
given explicitly as "1". The optional http-equiv attribute requires values of type
NAME. The optional id attribute requires values of type ID. The optional valign
attribute is constrained to take values from the set {top, middle, bottom, baseline}.
DTD entities in attribute definitions
Attribute definitions may also contain parameter entity references.
In this example, we see that the attribute definition list for the LINK element
begins with the "%attrs;" parameter entity.
<!ELEMENT LINK - O EMPTY
<!ATTLIST LINK
%attrs;
charset
%Charset;
href
%URI;
hreflang
%LanguageCode;
type
%ContentType;
rel
%LinkTypes;
rev
%LinkTypes;
media
%MediaDesc;
>
-- a media-independent link -->
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
---------
%coreattrs, %i18n, %events -char encoding of linked resource -URI for linked resource -language code -advisory content type -forward link types -reverse link types -for rendering on these media --
Start tag: required, End tag: forbidden
The "%attrs;" parameter entity is defined as follows:
<!ENTITY % attrs "%coreattrs; %i18n; %events;">
The "%coreattrs;" parameter entity in the "%attrs;" definition expands as follows:
<!ENTITY % coreattrs
"id
ID
class
CDATA
style
%StyleSheet;
title
%Text;
>
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
-----
document-wide unique id -space-separated list of classes -associated style info -advisory title --"
The "%attrs;" parameter entity has been defined for convenience since these
attributes are defined for most HTML element types.
Similarly, the DTD defines the "%URI;" parameter entity as expanding into the
string "CDATA".
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On SGML and HTML
<!ENTITY % URI "CDATA"
-- a Uniform Resource Identifier,
see [URI]
-->
As this example illustrates, the parameter entity "%URI;" provides readers of the
DTD with more information as to the type of data expected for an attribute. Similar
entities have been defined for "%Color;", "%Charset;", "%Length;", "%Pixels;", etc.
Boolean attributes
Some attributes play the role of boolean variables (e.g., the selected attribute for
the OPTION element). Their appearance in the start tag of an element implies that
the value of the attribute is "true". Their absence implies a value of "false".
Boolean attributes may legally take a single value: the name of the attribute itself
(e.g., selected="selected").
This example defines the selected attribute to be a boolean attribute.
selected
(selected)
#IMPLIED
-- option is pre-selected --
The attribute is set to "true" by appearing in the element’s start tag:
<OPTION selected="selected">
...contents...
</OPTION>
In HTML, boolean attributes may appear in minimized form -- the attribute’s value
appears alone in the element’s start tag. Thus, selected may be set by writing:
<OPTION selected>
instead of:
<OPTION selected="selected">
Authors should be aware that many user agents only recognize the minimized
form of boolean attributes and not the full form.
24 Dec 1999 18:26
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Conformance: requirements and recommendations
4 Conformance: requirements and
recommendations
Contents
1. Definitions .
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2. SGML .
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3. The text/html content type
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In this section, we begin the specification of HTML 4, starting with the contract
between authors, documents, users, and user agents.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] [p.354] . However, for
readability, these words do not appear in all uppercase letters in this specification.
At times, the authors of this specification recommend good practice for authors
and user agents. These recommendations are not normative and conformance with
this specification does not depend on their realization. These recommendations
contain the expression "We recommend ...", "This specification recommends ...", or
some similar wording.
4.1 Definitions
HTML document
An HTML document is an SGML document that meets the constraints of this
specification.
Author
An author is a person or program that writes or generates HTML documents. An
authoring tool is a special case of an author, namely, it’s a program that
generates HTML.
We recommend that authors write documents that conform to the strict DTD
[p.265] rather than the other DTDs defined by this specification. Please see the
section on version information [p.60] for details about the DTDs defined in
HTML 4.
User
A user is a person who interacts with a user agent to view, hear, or otherwise
use a rendered HTML document.
HTML user agent
An HTML user agent is any device that interprets HTML documents. User
agents include visual browsers (text-only and graphical), non-visual browsers
(audio, Braille), search robots, proxies, etc.
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Conformance: requirements and recommendations
A conforming user agent for HTML 4 is one that observes the mandatory
conditions ("must") set forth in this specification, including the following points:
A user agent should avoid imposing arbitrary length limits on attribute value
literals (see the section on capacities in the SGML Declaration [p.263] ). For
introductory information on SGML attributes, please consult the section on
attribute definitions [p.34] .
A user agent must ensure that rendering is unchanged by the presence or
absence of start tags and end tags when the HTML DTD indicates that
these are optional. See the section on element definitions [p.32] for
introductory information on SGML elements.
For reasons of backwards compatibility, we recommend that tools
interpreting HTML 4 continue to support HTML 3.2 (see [HTML32] [p.356] )
and HTML 2.0 (see [RFC1866] [p.356] ).
Error conditions
This specification does not define how conforming user agents handle general
error conditions, including how user agents behave when they encounter
elements, attributes, attribute values, or entities not specified in this document.
However, for recommended error handling behavior, please consult the notes
on invalid documents [p.334] .
Deprecated
A deprecated element or attribute is one that has been outdated by newer
constructs. Deprecated elements are defined in the reference manual in
appropriate locations, but are clearly marked as deprecated. Deprecated
elements may become obsolete in future versions of HTML.
User agents should continue to support deprecated elements for reasons of
backward compatibility.
Definitions of elements and attributes clearly indicate which are deprecated.
This specification includes examples that illustrate how to avoid using
deprecated elements. In most cases these depend on user agent support for
style sheets. In general, authors should use style sheets to achieve stylistic and
formatting effects rather than HTML presentational attributes. HTML
presentational attributes have been deprecated when style sheet alternatives
exist (see, for example, [CSS1] [p.353] ).
Obsolete
An obsolete element or attribute is one for which there is no guarantee of
support by a user agent. Obsolete elements are no longer defined in the
specification, but are listed for historical purposes in the changes section [p.311]
of the reference manual.
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Conformance: requirements and recommendations
4.2 SGML
HTML 4 is an SGML application conforming to International Standard ISO 8879 -Standard Generalized Markup Language SGML (defined in [ISO8879] [p.353] ).
Examples in the text conform to the strict document type definition [p.265] unless
the example in question refers to elements or attributes only defined by the
transitional document type definition [p.279] or frameset document type definition
[p.297] . For the sake of brevity, most of the examples in this specification do not
begin with the document type declaration [p.60] that is mandatory at the beginning of
each HTML document.
DTD fragments in element definitions come from the strict document type
definition [p.265] except for the elements related to frames.
Please consult the section on HTML version information [p.60] for details about
when to use the strict, transitional, or frameset DTD.
Comments appearing in the HTML 4 DTD [p.265] have no normative value; they
are informative only.
User agents must not render SGML processing instructions (e.g., <?full volume>)
or comments. For more information about this and other SGML features that may be
legal in HTML but aren’t widely supported by HTML user agents, please consult the
section on SGML features with limited support. [p.337]
4.3 The text/html content type
HTML documents are sent over the Internet as a sequence of bytes accompanied by
encoding information (described in the section on character encodings [p.42] ). The
structure of the transmission, termed a message entity, is defined by [RFC2045]
[p.354] and [RFC2616] [p.354] . A message entity with a content type [p.53] of
"text/html" represents an HTML document.
The content type for HTML documents is defined as follows:
Content type name:
text
Content subtype name:
html
Required parameters:
none
Optional parameters:
charset
Encoding considerations:
any encoding is allowed
Security considerations:
See the notes on security [p.350]
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The optional parameter "charset" refers to the character encoding [p.42] used to
represent the HTML document as a sequence of bytes. Legal values for this
parameter are defined in the section on character encodings [p.42] . Although this
parameter is optional, we recommend that it always be present.
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HTML Document Representation
5 HTML Document Representation
Contents
1. The Document Character Set
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2. Character encodings
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1. Choosing an encoding .
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Notes on specific encodings .
2. Specifying the character encoding
3. Character references
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1. Numeric character references
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2. Character entity references .
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4. Undisplayable characters
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41
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47
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In this chapter, we discuss how HTML documents are represented on a computer
and over the Internet.
The section on the document character set [p.41] addresses the issue of what
abstract characters may be part of an HTML document. Characters include the Latin
letter "A", the Cyrillic letter "I", the Chinese character meaning "water", etc.
The section on character encodings [p.42] addresses the issue of how those
characters may be represented in a file or when transferred over the Internet. As
some character encodings cannot directly represent all characters an author may
want to include in a document, HTML offers other mechanisms, called character
references [p.45] , for referring to any character.
Since there are a great number of characters throughout human languages, and a
great variety of ways to represent those characters, proper care must be taken so
that documents may be understood by user agents around the world.
5.1 The Document Character Set
To promote interoperability, SGML requires that each application (including HTML)
specify its document character set. A document character set consists of:
A Repertoire: A set of abstract characters,, such as the Latin letter "A", the
Cyrillic letter "I", the Chinese character meaning "water", etc.
Code positions: A set of integer references to characters in the repertoire.
Each SGML document (including each HTML document) is a sequence of
characters from the repertoire. Computer systems identify each character by its code
position; for example, in the ASCII character set, code positions 65, 66, and 67 refer
to the characters ’A’, ’B’, and ’C’, respectively.
The ASCII character set is not sufficient for a global information system such as
the Web, so HTML uses the much more complete character set called the Universal
Character Set (UCS), defined in [ISO10646]. [p.353] This standard defines a
41
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HTML Document Representation
repertoire of thousands of characters used by communities all over the world.
The character set defined in [ISO10646] [p.353] is character-by-character
equivalent to Unicode ([UNICODE] [p.355] ). Both of these standards are updated
from time to time with new characters, and the amendments should be consulted at
the respective Web sites. In the current specification, "[ISO10646]" is used to refer to
the document character set while "[UNICODE]" is reserved for references to the
Unicode bidirectional text algorithm. [p.82]
The document character set, however, does not suffice to allow user agents to
correctly interpret HTML documents as they are typically exchanged -- encoded as a
sequence of bytes in a file or during a network transmission. User agents must also
know the specific character encoding [p.42] that was used to transform the
document character stream into a byte stream.
5.2 Character encodings
What this specification calls a character encoding is known by different names in
other specifications (which may cause some confusion). However, the concept is
largely the same across the Internet. Also, protocol headers, attributes, and
parameters referring to character encodings share the same name -- "charset" -- and
use the same values from the [IANA] [p.353] registry (see [CHARSETS] [p.355] for a
complete list).
The "charset" parameter identifies a character encoding, which is a method of
converting a sequence of bytes into a sequence of characters. This conversion fits
naturally with the scheme of Web activity: servers send HTML documents to user
agents as a stream of bytes; user agents interpret them as a sequence of
characters. The conversion method can range from simple one-to-one
correspondence to complex switching schemes or algorithms.
A simple one-byte-per-character encoding technique is not sufficient for text
strings over a character repertoire as large as [ISO10646] [p.353] . There are several
different encodings of parts of [ISO10646] [p.353] in addition to encodings of the
entire character set (such as UCS-4).
5.2.1 Choosing an encoding
Authoring tools (e.g., text editors) may encode HTML documents in the character
encoding of their choice, and the choice largely depends on the conventions used by
the system software. These tools may employ any convenient encoding that covers
most of the characters contained in the document, provided the encoding is correctly
labeled. [p.43] Occasional characters that fall outside this encoding may still be
represented by character references [p.45] . These always refer to the document
character set, not the character encoding.
Servers and proxies may change a character encoding (called transcoding) on the
fly to meet the requests of user agents (see section 14.2 of [RFC2616] [p.354] , the
"Accept-Charset" HTTP request header). Servers and proxies do not have to serve a
24 Dec 1999 18:26
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HTML Document Representation
document in a character encoding that covers the entire document character set.
Commonly used character encodings on the Web include ISO-8859-1 (also
referred to as "Latin-1"; usable for most Western European languages), ISO-8859-5
(which supports Cyrillic), SHIFT_JIS (a Japanese encoding), EUC-JP (another
Japanese encoding), and UTF-8 (an encoding of ISO 10646 using a different
number of bytes for different characters). Names for character encodings are
case-insensitive, so that for example "SHIFT_JIS", "Shift_JIS", and "shift_jis" are
equivalent.
This specification does not mandate which character encodings a user agent must
support.
Conforming user agents [p.38] must correctly map to ISO 10646 all characters in
any character encodings that they recognize (or they must behave as if they did).
Notes on specific encodings
When HTML text is transmitted in UTF-16 (charset=UTF-16), text data should be
transmitted in network byte order ("big-endian", high-order byte first) in accordance
with [ISO10646] [p.353] , Section 6.3 and [UNICODE] [p.355] , clause C3, page 3-1.
Furthermore, to maximize chances of proper interpretation, it is recommended that
documents transmitted as UTF-16 always begin with a ZERO-WIDTH
NON-BREAKING SPACE character (hexadecimal FEFF, also called Byte Order
Mark (BOM)) which, when byte-reversed, becomes hexadecimal FFFE, a character
guaranteed never to be assigned. Thus, a user-agent receiving a hexadecimal FFFE
as the first bytes of a text would know that bytes have to be reversed for the
remainder of the text.
The UTF-1 transformation format of [ISO10646] [p.353] (registered by IANA as
ISO-10646-UTF-1), should not be used. For information about ISO 8859-8 and the
bidirectional algorithm, please consult the section on bidirectionality and character
encoding [p.86] .
5.2.2 Specifying the character encoding
How does a server determine which character encoding applies for a document it
serves? Some servers examine the first few bytes of the document, or check against
a database of known files and encodings. Many modern servers give Web masters
more control over charset configuration than old servers do. Web masters should
use these mechanisms to send out a "charset" parameter whenever possible, but
should take care not to identify a document with the wrong "charset" parameter
value.
How does a user agent know which character encoding has been used? The
server should provide this information. The most straightforward way for a server to
inform the user agent about the character encoding of the document is to use the
"charset" parameter of the "Content-Type" header field of the HTTP protocol
([RFC2616] [p.354] , sections 3.4 and 14.17) For example, the following HTTP
header announces that the character encoding is EUC-JP:
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Content-Type: text/html; charset=EUC-JP
Please consult the section on conformance [p.37] for the definition of text/html
[p.39] .
The HTTP protocol ([RFC2616] [p.354] , section 3.7.1) mentions ISO-8859-1 as a
default character encoding when the "charset" parameter is absent from the
"Content-Type" header field. In practice, this recommendation has proved useless
because some servers don’t allow a "charset" parameter to be sent, and others may
not be configured to send the parameter. Therefore, user agents must not assume
any default value for the "charset" parameter.
To address server or configuration limitations, HTML documents may include
explicit information about the document’s character encoding; the META element can
be used to provide user agents with this information.
For example, to specify that the character encoding of the current document is
"EUC-JP", a document should include the following META declaration:
<META http-equiv="Content-Type" content="text/html; charset=EUC-JP">
The META declaration must only be used when the character encoding is
organized such that ASCII-valued bytes stand for ASCII characters (at least until the
META element is parsed). META declarations should appear as early as possible in
the HEAD element.
For cases where neither the HTTP protocol nor the META element provides
information about the character encoding of a document, HTML also provides the
charset attribute on several elements. By combining these mechanisms, an author
can greatly improve the chances that, when the user retrieves a resource, the user
agent will recognize the character encoding.
To sum up, conforming user agents must observe the following priorities when
determining a document’s character encoding (from highest priority to lowest):
1. An HTTP "charset" parameter in a "Content-Type" field.
2. A META declaration with "http-equiv" set to "Content-Type" and a value set for
"charset".
3. The charset attribute set on an element that designates an external resource.
In addition to this list of priorities, the user agent may use heuristics and user
settings. For example, many user agents use a heuristic to distinguish the various
encodings used for Japanese text. Also, user agents typically have a user-definable,
local default character encoding which they apply in the absence of other indicators.
User agents may provide a mechanism that allows users to override incorrect
"charset" information. However, if a user agent offers such a mechanism, it should
only offer it for browsing and not for editing, to avoid the creation of Web pages
marked with an incorrect "charset" parameter.
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HTML Document Representation
Note. If, for a specific application, it becomes necessary to refer to characters
outside [ISO10646] [p.353] , characters should be assigned to a private zone to
avoid conflicts with present or future versions of the standard. This is highly
discouraged, however, for reasons of portability.
5.3 Character references
A given character encoding may not be able to express all characters of the
document character set. For such encodings, or when hardware or software
configurations do not allow users to input some document characters directly,
authors may use SGML character references. Character references are a character
encoding-independent mechanism for entering any character from the document
character set.
Character references in HTML may appear in two forms:
Numeric character references (either decimal or hexadecimal).
Character entity references.
Character references within comments have no special meaning; they are
comment data only.
Note. HTML provides other ways to present character data, in particular inline
images [p.159] .
Note. In SGML, it is possible to eliminate the final ";" after a character reference in
some cases (e.g., at a line break or immediately before a tag). In other
circumstances it may not be eliminated (e.g., in the middle of a word). We strongly
suggest using the ";" in all cases to avoid problems with user agents that require this
character to be present.
5.3.1 Numeric character references
Numeric character references specify the code position [p.41] of a character in the
document character set. Numeric character references may take two forms:
The syntax "&#D;", where D is a decimal number, refers to the ISO 10646
decimal character number D.
The syntax "&#xH;" or "&#XH;", where H is a hexadecimal number, refers to the
ISO 10646 hexadecimal character number H. Hexadecimal numbers in numeric
character references are case-insensitive.
Here are some examples of numeric character references:
&#229; (in decimal) represents the letter "a" with a small circle above it (used,
for example, in Norwegian).
&#xE5; (in hexadecimal) represents the same character.
&#Xe5; (in hexadecimal) represents the same character as well.
&#1048; (in decimal) represents the Cyrillic capital letter "I".
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HTML Document Representation
&#x6C34; (in hexadecimal) represents the Chinese character for water.
Note. Although the hexadecimal representation is not defined in [ISO8879] [p.353]
, it is expected to be in the revision, as described in [WEBSGML] [p.355] . This
convention is particularly useful since character standards generally use
hexadecimal representations.
5.3.2 Character entity references
In order to give authors a more intuitive way of referring to characters in the
document character set, HTML offers a set of character entity references. Character
entity references use symbolic names so that authors need not remember code
positions. [p.41] For example, the character entity reference &aring; refers to the
lowercase "a" character topped with a ring; "&aring;" is easier to remember than
&#229;.
HTML 4 does not define a character entity reference for every character in the
document character set. For instance, there is no character entity reference for the
Cyrillic capital letter "I". Please consult the full list of character references [p.299]
defined in HTML 4.
Character entity references are case-sensitive. Thus, &Aring; refers to a different
character (uppercase A, ring) than &aring; (lowercase a, ring).
Four character entity references deserve special mention since they are frequently
used to escape special characters:
"&lt;" represents the < sign.
"&gt;" represents the > sign.
"&amp;" represents the & sign.
"&quot; represents the " mark.
Authors wishing to put the "<" character in text should use "&lt;" (ASCII decimal
60) to avoid possible confusion with the beginning of a tag (start tag open delimiter).
Similarly, authors should use "&gt;" (ASCII decimal 62) in text instead of ">" to avoid
problems with older user agents that incorrectly perceive this as the end of a tag (tag
close delimiter) when it appears in quoted attribute values.
Authors should use "&amp;" (ASCII decimal 38) instead of "&" to avoid confusion
with the beginning of a character reference (entity reference open delimiter). Authors
should also use "&amp;" in attribute values since character references are allowed
within CDATA [p.50] attribute values.
Some authors use the character entity reference "&quot;" to encode instances of
the double quote mark (") since that character may be used to delimit attribute
values.
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5.4 Undisplayable characters
A user agent may not be able to render all characters in a document meaningfully,
for instance, because the user agent lacks a suitable font, a character has a value
that may not be expressed in the user agent’s internal character encoding, etc.
Because there are many different things that may be done in such cases, this
document does not prescribe any specific behavior. Depending on the
implementation, undisplayable characters may also be handled by the underlying
display system and not the application itself. In the absence of more sophisticated
behavior, for example tailored to the needs of a particular script or language, we
recommend the following behavior for user agents:
1. Adopt a clearly visible, but unobtrusive mechanism to alert the user of missing
resources.
2. If missing characters are presented using their numeric representation, use the
hexadecimal (not decimal) form since this is the form used in character set
standards.
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48
Basic HTML data types
6 Basic HTML data types
Contents
1.
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Case information
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SGML basic types .
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Text strings .
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URIs
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Colors .
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1. Notes on using colors
Lengths .
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Content types (MIME types)
Language codes
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Character encodings
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Single characters
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Dates and times .
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Link types .
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Media descriptors
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Script data .
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Style sheet data .
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Frame target names .
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This section of the specification describes the basic data types that may appear as
an element’s content or an attribute’s value.
For introductory information about reading the HTML DTD, please consult the
SGML tutorial [p.27] .
6.1 Case information
Each attribute definition includes information about the case-sensitivity of its values.
The case information is presented with the following keys:
CS
The value is case-sensitive (i.e., user agents interpret "a" and "A" differently).
CI
The value is case-insensitive (i.e., user agents interpret "a" and "A" as the
same).
CN
The value is not subject to case changes, e.g., because it is a number or a
character from the document character set.
CA
The element or attribute definition itself gives case information.
CT
Consult the type definition for details about case-sensitivity.
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If an attribute value is a list, the keys apply to every value in the list, unless
otherwise indicated.
6.2 SGML basic types
The document type definition [p.265] specifies the syntax of HTML element content
and attribute values using SGML tokens (e.g., PCDATA, CDATA, NAME, ID, etc.).
See [ISO8879] [p.353] for their full definitions. The following is a summary of key
information:
CDATA is a sequence of characters from the document character set and may
include character entities. User agents should interpret attribute values as
follows:
Replace character entities with characters,
Ignore line feeds,
Replace each carriage return or tab with a single space.
User agents may ignore leading and trailing white space in CDATA attribute
values (e.g., " myval " may be interpreted as "myval"). Authors should not
declare attribute values with leading or trailing white space.
For some HTML 4 attributes with CDATA attribute values, the specification
imposes further constraints on the set of legal values for the attribute that may
not be expressed by the DTD.
Although the STYLE and SCRIPT elements use CDATA for their data model,
for these elements, CDATA must be handled differently by user agents. Markup
and entities must be treated as raw text and passed to the application as is. The
first occurrence of the character sequence "</" (end-tag open delimiter) is
treated as terminating the end of the element’s content. In valid documents, this
would be the end tag for the element.
ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by
any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"),
and periods (".").
IDREF and IDREFS are references to ID tokens defined by other attributes.
IDREF is a single token and IDREFS is a space-separated list of tokens.
NUMBER tokens must contain at least one digit ([0-9]).
6.3 Text strings
A number of attributes ( %Text; [p.266] in the DTD) take text that is meant to be
"human readable". For introductory information about attributes, please consult the
tutorial discussion of attributes [p.29] .
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6.4 URIs
This specification uses the term URI as defined in [URI] [p.355] (see also [RFC1630]
[p.356] ).
Note that URIs include URLs (as defined in [RFC1738] [p.354] and [RFC1808]
[p.354] ).
Relative URIs are resolved to full URIs using a base URI. [RFC1808] [p.354] ,
section 3, defines the normative algorithm for this process. For more information
about base URIs, please consult the section on base URIs [p.157] in the chapter on
links [p.145] .
URIs are represented in the DTD by the parameter entity %URI; [p.266] .
URIs in general are case-sensitive. [p.49] There may be URIs, or parts of URIs,
where case doesn’t matter (e.g., machine names), but identifying these may not be
easy. Users should always consider that URIs are case-sensitive (to be on the safe
side).
Please consult the appendix for information about non-ASCII characters in URI
attribute values [p.334] .
6.5 Colors
The attribute value type "color" (%Color; [p.281] ) refers to color definitions as
specified in [SRGB] [p.354] . A color value may either be a hexadecimal number
(prefixed by a hash mark) or one of the following sixteen color names. The color
names are case-insensitive. [p.49]
Color names and sRGB values
51
Black = "#000000"
Green = "#008000"
Silver = "#C0C0C0"
Lime = "#00FF00"
Gray = "#808080"
Olive = "#808000"
White = "#FFFFFF"
Yellow = "#FFFF00"
Maroon = "#800000"
Navy = "#000080"
Red = "#FF0000"
Blue = "#0000FF"
Purple = "#800080"
Teal = "#008080"
Fuchsia = "#FF00FF"
Aqua = "#00FFFF"
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Basic HTML data types
Thus, the color values "#800080" and "Purple" both refer to the color purple.
6.5.1 Notes on using colors
Although colors can add significant amounts of information to documents and make
them more readable, please consider the following guidelines when including color in
your documents:
The use of HTML elements and attributes for specifying color is deprecated
[p.38] . You are encouraged to use style sheets [p.183] instead.
Don’t use color combinations that cause problems for people with color
blindness in its various forms.
If you use a background image or set the background color, then be sure to set
the various text colors as well.
Colors specified with the BODY and FONT elements and bgcolor on tables look
different on different platforms (e.g., workstations, Macs, Windows, and LCD
panels vs. CRTs), so you shouldn’t rely entirely on a specific effect. In the
future, support for the [SRGB] [p.354] color model together with ICC color
profiles should mitigate this problem.
When practical, adopt common conventions to minimize user confusion.
6.6 Lengths
HTML specifies three types of length values for attributes:
1. Pixels: The value (%Pixels; [p.270] in the DTD) is an integer that represents the
number of pixels of the canvas (screen, paper). Thus, the value "50" means fifty
pixels. For normative information about the definition of a pixel, please consult
[CSS1] [p.353] .
2. Length: The value (%Length; [p.270] in the DTD) may be either a %Pixel; or a
percentage of the available horizontal or vertical space. Thus, the value "50%"
means half of the available space.
3. MultiLength: The value ( %MultiLength; [p.270] in the DTD) may be a %Length;
or a relative length. A relative length has the form "i*", where "i" is an integer.
When allotting space among elements competing for that space, user agents
allot pixel and percentage lengths first, then divide up remaining available space
among relative lengths. Each relative length receives a portion of the available
space that is proportional to the integer preceding the "*". The value "*" is
equivalent to "1*". Thus, if 60 pixels of space are available after the user agent
allots pixel and percentage space, and the competing relative lengths are 1*, 2*,
and 3*, the 1* will be alloted 10 pixels, the 2* will be alloted 20 pixels, and the 3*
will be alloted 30 pixels.
Length values are case-neutral. [p.49]
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6.7 Content types (MIME types)
Note. A "media type" (defined in [RFC2045] [p.354] and [RFC2046] [p.354] )
specifies the nature of a linked resource. This specification employs the term
"content type" rather than "media type" in accordance with current usage.
Furthermore, in this specification, "media type" may refer to the media [p.56] where a
user agent renders a document.
This type is represented in the DTD by %ContentType;. [p.266]
Content types are case-insensitive. [p.49]
Examples of content types include "text/html", "image/png", "image/gif",
"video/mpeg", "text/css", and "audio/basic". For the current list of registered MIME
types, please consult [MIMETYPES]. [p.354]
6.8 Language codes
The value of attributes whose type is a language code ( %LanguageCode [p.266] in
the DTD) refers to a language code as specified by [RFC1766] [p.354] , section 2.
For information on specifying language codes in HTML, please consult the section
on language codes [p.80] . Whitespace is not allowed within the language-code.
Language codes are case-insensitive. [p.49]
6.9 Character encodings
The "charset" attributes (%Charset [p.266] in the DTD) refer to a character encoding
as described in the section on character encodings [p.42] . Values must be strings
(e.g., "euc-jp") from the IANA registry (see [CHARSETS] [p.355] for a complete list).
Names of character encodings are case-insensitive. [p.49]
User agents must follow the steps set out in the section on specifying character
encodings [p.43] in order to determine the character encoding of an external
resource.
6.10 Single characters
Certain attributes call for a single character from the document character set [p.41] .
These attributes take the %Character [p.266] type in the DTD.
Single characters may be specified with character references [p.45] (e.g.,
"&amp;").
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6.11 Dates and times
[ISO8601] [p.353] allows many options and variations in the representation of dates
and times. The current specification uses one of the formats described in the profile
[DATETIME] [p.353] for its definition of legal date/time strings ( %Datetime [p.266] in
the DTD).
The format is:
YYYY-MM-DDThh:mm:ssTZD
where:
YYYY
MM
DD
hh
mm
ss
TZD
=
=
=
=
=
=
=
four-digit year
two-digit month (01=January, etc.)
two-digit day of month (01 through 31)
two digits of hour (00 through 23) (am/pm NOT allowed)
two digits of minute (00 through 59)
two digits of second (00 through 59)
time zone designator
The time zone designator is one of:
Z
indicates UTC (Coordinated Universal Time). The "Z" must be uppercase.
+hh:mm
indicates that the time is a local time which is hh hours and mm minutes ahead of
UTC.
-hh:mm
indicates that the time is a local time which is hh hours and mm minutes behind
UTC.
Exactly the components shown here must be present, with exactly this
punctuation. Note that the "T" appears literally in the string (it must be uppercase),
to indicate the beginning of the time element, as specified in [ISO8601] [p.353]
If a generating application does not know the time to the second, it may use the
value "00" for the seconds (and minutes and hours if necessary).
Note. [DATETIME] [p.353] does not address the issue of leap seconds.
6.12 Link types
Authors may use the following recognized link types, listed here with their
conventional interpretations. In the DTD, %LinkTypes [p.266] refers to a
space-separated list of link types. White space characters are not permitted within
link types.
These link types are case-insensitive, [p.49] i.e., "Alternate" has the same
meaning as "alternate".
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Basic HTML data types
User agents, search engines, etc. may interpret these link types in a variety of
ways. For example, user agents may provide access to linked documents through a
navigation bar.
Alternate
Designates substitute versions for the document in which the link occurs. When
used together with the lang attribute, it implies a translated version of the
document. When used together with the media attribute, it implies a version
designed for a different medium (or media).
Stylesheet
Refers to an external style sheet. See the section on external style sheets
[p.190] for details. This is used together with the link type "Alternate" for
user-selectable alternate style sheets.
Start
Refers to the first document in a collection of documents. This link type tells
search engines which document is considered by the author to be the starting
point of the collection.
Next
Refers to the next document in a linear sequence of documents. User agents
may choose to preload the "next" document, to reduce the perceived load time.
Prev
Refers to the previous document in an ordered series of documents. Some user
agents also support the synonym "Previous".
Contents
Refers to a document serving as a table of contents. Some user agents also
support the synonym ToC (from "Table of Contents").
Index
Refers to a document providing an index for the current document.
Glossary
Refers to a document providing a glossary of terms that pertain to the current
document.
Copyright
Refers to a copyright statement for the current document.
Chapter
Refers to a document serving as a chapter in a collection of documents.
Section
Refers to a document serving as a section in a collection of documents.
Subsection
Refers to a document serving as a subsection in a collection of documents.
Appendix
Refers to a document serving as an appendix in a collection of documents.
Help
Refers to a document offering help (more information, links to other sources
information, etc.)
Bookmark
Refers to a bookmark. A bookmark is a link to a key entry point within an
extended document. The title attribute may be used, for example, to label the
55
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bookmark. Note that several bookmarks may be defined in each document.
Authors may wish to define additional link types not described in this specification.
If they do so, they should use a profile [p.68] to cite the conventions used to define
the link types. Please see the profile attribute of the HEAD element for more
details.
For further discussions about link types, please consult the section on links in
HTML documents [p.145] .
6.13 Media descriptors
The following is a list of recognized media descriptors ( %MediaDesc [p.266] in the
DTD).
screen
Intended for non-paged computer screens.
tty
Intended for media using a fixed-pitch character grid, such as teletypes,
terminals, or portable devices with limited display capabilities.
tv
Intended for television-type devices (low resolution, color, limited scrollability).
projection
Intended for projectors.
handheld
Intended for handheld devices (small screen, monochrome, bitmapped
graphics, limited bandwidth).
print
Intended for paged, opaque material and for documents viewed on screen in
print preview mode.
braille
Intended for braille tactile feedback devices.
aural
Intended for speech synthesizers.
all
Suitable for all devices.
Future versions of HTML may introduce new values and may allow parameterized
values. To facilitate the introduction of these extensions, conforming user agents
must be able to parse the media attribute value as follows:
1. The value is a comma-separated list of entries. For example,
media="screen, 3d-glasses, print and resolution > 90dpi"
is mapped to:
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Basic HTML data types
"screen"
"3d-glasses"
"print and resolution > 90dpi"
2. Each entry is truncated just before the first character that isn’t a US ASCII letter
[a-zA-Z] (ISO 10646 hex 41-5a, 61-7a), digit [0-9] (hex 30-39), or hyphen (hex
2d). In the example, this gives:
"screen"
"3d-glasses"
"print"
3. A case-sensitive [p.49] match is then made with the set of media types defined
above. User agents may ignore entries that don’t match. In the example we are
left with screen and print.
Note. Style sheets may include media-dependent variations within them (e.g., the
CSS @media construct). In such cases it may be appropriate to use "media=all".
6.14 Script data
Script data ( %Script; [p.266] in the DTD [p.265] ) can be the content of the SCRIPT
element and the value of intrinsic event attributes [p.251] . User agents must not
evaluate script data as HTML markup but instead must pass it on as data to a script
engine.
The case-sensitivity of script data depends on the scripting language.
Please note that script data that is element content may not contain character
references [p.45] , but script data that is the value of an attribute may contain them.
The appendix provides further information about specifying non-HTML data [p.336] .
6.15 Style sheet data
Style sheet data (%StyleSheet; [p.266] in the DTD [p.265] ) can be the content of the
STYLE element and the value of the style attribute. User agents must not evaluate
style data as HTML markup.
The case-sensitivity of style data depends on the style sheet language.
Please note that style sheet data that is element content may not contain
character references [p.45] , but style sheet data that is the value of an attribute may
contain them. The appendix provides further information about specifying non-HTML
data [p.336] .
6.16 Frame target names
Except for the reserved names listed below, frame target names (%FrameTarget;
[p.281] in the DTD) must begin with an alphabetic character (a-zA-Z). User agents
should ignore all other target names.
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The following target names are reserved and have special meanings.
_blank
The user agent should load the designated document in a new, unnamed
window.
_self
The user agent should load the document in the same frame as the element that
refers to this target.
_parent
The user agent should load the document into the immediate FRAMESET parent
of the current frame. This value is equivalent to _self if the current frame has
no parent.
_top
The user agent should load the document into the full, original window (thus
canceling all other frames). This value is equivalent to _self if the current
frame has no parent.
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The global structure of an HTML document
7 The global structure of an HTML document
Contents
1.
2.
3.
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Introduction to the structure of an HTML document
HTML version information
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The HTML element .
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Specifying meta data
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Meta data profiles .
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1. The BODY element .
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2. Element identifiers: the id and class attributes
3. Block-level and inline elements .
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4. Grouping elements: the DIV and SPAN elements
5. Headings: The H1, H2, H3, H4, H5, H6 elements
6. The ADDRESS element .
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7.1 Introduction to the structure of an HTML document
An HTML 4 document is composed of three parts:
1. a line containing HTML version information [p.60] ,
2. a declarative header section (delimited by the HEAD element),
3. a body, which contains the document’s actual content. The body may be
implemented by the BODY element or the FRAMESET element.
White space (spaces, newlines, tabs, and comments) may appear before or after
each section. Sections 2 and 3 should be delimited by the HTML element.
Here’s an example of a simple HTML document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>My first HTML document</TITLE>
</HEAD>
<BODY>
<P>Hello world!
</BODY>
</HTML>
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7.2 HTML version information
A valid HTML document declares what version of HTML is used in the document.
The document type declaration names the document type definition (DTD) in use for
the document (see [ISO8879] [p.353] ).
HTML 4.01 specifies three DTDs, so authors must include one of the following
document type declarations in their documents. The DTDs vary in the elements they
support.
The HTML 4.01 Strict DTD [p.265] includes all elements and attributes that have
not been deprecated [p.38] or do not appear in frameset documents. For
documents that use this DTD, use this document type declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
The HTML 4.01 Transitional DTD [p.279] includes everything in the strict DTD
plus deprecated elements and attributes (most of which concern visual
presentation). For documents that use this DTD, use this document type
declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
The HTML 4.01 Frameset DTD [p.297] includes everything in the transitional
DTD plus frames as well. For documents that use this DTD, use this document
type declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
The URI in each document type declaration allows user agents to download the
DTD and any entity sets [p.299] that are needed. The following (relative) URIs refer
to DTDs and entity sets for HTML 4:
"strict.dtd" -- default strict DTD
"loose.dtd" -- loose DTD
"frameset.dtd" -- DTD for frameset documents
"HTMLlat1.ent" -- Latin-1 entities
"HTMLsymbol.ent" -- Symbol entities
"HTMLspecial.ent" -- Special entities
The binding between public identifiers and files can be specified using a catalog
file following the format recommended by the Oasis Open Consortium (see
[OASISOPEN] [p.356] ). A sample catalog file for HTML 4.01 [p.262] is included at
the beginning of the section on SGML reference information for HTML. The last two
letters of the declaration indicate the language of the DTD. For HTML, this is always
English ("EN").
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The global structure of an HTML document
Note. As of the 24 December version of HTML 4.01, the HTML Working Group
commits to the following policy:
Any changes to future HTML 4 DTDs will not invalidate documents that conform
to the DTDs of the present specification. The HTML Working Group reserves
the right to correct known bugs.
Software conforming to the DTDs of the present specification may ignore
features of future HTML 4 DTDs that it does not recognize.
This means that in a document type declaration, authors may safely use a system
identifier that refers to the latest version of an HTML 4 DTD. Authors may also
choose to use a system identifier that refers to a specific (dated) version of an HTML
4 DTD when validation to that particular DTD is required. W3C will make every effort
to make archival documents indefinitely available at their original address in their
original form.
7.3 The HTML element
<!ENTITY % html.content "HEAD, BODY">
<!ELEMENT HTML O O (%html.content;)
<!ATTLIST HTML
%i18n;
>
-- document root element -->
-- lang, dir --
Start tag: optional, End tag: optional
Attribute definitions
version = cdata [p.50] [CN] [p.49]
Deprecated. [p.38] The value of this attribute specifies which HTML DTD
version governs the current document. This attribute has been deprecated
because it is redundant with version information [p.60] provided by the
document type declaration.
Attributes defined elsewhere
lang (language information [p.79] ), dir (text direction [p.82] )
After document type declaration, the remainder of an HTML document is
contained by the HTML element. Thus, a typical HTML document has this structure:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
...The head, body, etc. goes here...
</HTML>
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7.4 The document head
7.4.1 The HEAD element
<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & BASE?">
<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
%i18n;
-- lang, dir -profile
%URI;
#IMPLIED -- named dictionary of meta info ->
Start tag: optional, End tag: optional
Attribute definitions
profile = uri [p.51] [CT] [p.49]
This attribute specifies the location of one or more meta data profiles, separated
by white space. For future extensions, user agents should consider the value to
be a list even though this specification only considers the first URI to be
significant. Profiles [p.68] are discussed below in the section on meta data [p.64]
.
Attributes defined elsewhere
lang (language information [p.79] ), dir (text direction [p.82] )
The HEAD element contains information about the current document, such as its
title, keywords that may be useful to search engines, and other data that is not
considered document content. User agents do not generally render elements that
appear in the HEAD as content. They may, however, make information in the HEAD
available to users through other mechanisms.
7.4.2 The TITLE element
<!-- The TITLE element is not considered part of the flow of text.
It should be displayed, for example as the page header or
window title. Exactly one title is required per document.
-->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>
Start tag: required, End tag: required
Attributes defined elsewhere
lang (language information [p.79] ), dir (text direction [p.82] )
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Every HTML document must have a TITLE element in the HEAD section.
Authors should use the TITLE element to identify the contents of a document.
Since users often consult documents out of context, authors should provide
context-rich titles. Thus, instead of a title such as "Introduction", which doesn’t
provide much contextual background, authors should supply a title such as
"Introduction to Medieval Bee-Keeping" instead.
For reasons of accessibility, user agents must always make the content of the
TITLE element available to users (including TITLE elements that occur in frames).
The mechanism for doing so depends on the user agent (e.g., as a caption, spoken).
Titles may contain character entities [p.299] (for accented characters, special
characters, etc.), but may not contain other markup (including comments). Here is a
sample document title:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
... other head elements...
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>
7.4.3 The title attribute
Attribute definitions
title = text [p.50] [CS] [p.49]
This attribute offers advisory information about the element for which it is set.
Unlike the TITLE element, which provides information about an entire document
and may only appear once, the title attribute may annotate any number of
elements. Please consult an element’s definition to verify that it supports this
attribute.
Values of the title attribute may be rendered by user agents in a variety of
ways. For instance, visual browsers frequently display the title as a "tool tip" (a short
message that appears when the pointing device pauses over an object). Audio user
agents may speak the title information in a similar context. For example, setting the
attribute on a link allows user agents (visual and non-visual) to tell users about the
nature of the linked resource:
...some text...
Here’s a photo of
<A href="http://someplace.com/neatstuff.gif" title="Me scuba diving">
me scuba diving last summer
</A>
...some more text...
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The title attribute has an additional role when used with the LINK element to
designate an external style sheet. [p.190] Please consult the section on links and
style sheets [p.155] for details.
Note. To improve the quality of speech synthesis for cases handled poorly by
standard techniques, future versions of HTML may include an attribute for encoding
phonemic and prosodic information.
7.4.4 Meta data
Note. The W3C Resource Description Framework (see [RDF10] [p.356] ) became a
W3C Recommendation in February 1999. RDF allows authors to specify
machine-readable metadata about HTML documents and other network-accessible
resources.
HTML lets authors specify meta data -- information about a document rather than
document content -- in a variety of ways.
For example, to specify the author of a document, one may use the META element
as follows:
<META name="Author" content="Dave Raggett">
The META element specifies a property (here "Author") and assigns a value to it
(here "Dave Raggett").
This specification does not define a set of legal meta data properties. The
meaning of a property and the set of legal values for that property should be defined
in a reference lexicon called a profile [p.68] . For example, a profile designed to help
search engines index documents might define properties such as "author",
"copyright", "keywords", etc.
Specifying meta data
In general, specifying meta data involves two steps:
1. Declaring a property and a value for that property. This may be done in two
ways:
1. From within a document, via the META element.
2. From outside a document, by linking to meta data via the LINK element
(see the section on link types [p.54] ).
2. Referring to a profile [p.68] where the property and its legal values are defined.
To designate a profile, use the profile attribute of the HEAD element.
Note that since a profile is defined for the HEAD element, the same profile applies
to all META and LINK elements in the document head.
User agents are not required to support meta data mechanisms. For those that
choose to support meta data, this specification does not define how meta data
should be interpreted.
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The global structure of an HTML document
The META element
<!ELEMENT META - O EMPTY
<!ATTLIST META
%i18n;
http-equiv NAME
name
NAME
content
CDATA
scheme
CDATA
>
-- generic metainformation -->
#IMPLIED
#IMPLIED
#REQUIRED
#IMPLIED
------
lang, dir, for use with content -HTTP response header name -metainformation name -associated information -select form of content --
Start tag: required, End tag: forbidden
Attribute definitions
For the following attributes, the permitted values and their interpretation are
profile dependent:
name = name [p.50] [CS] [p.49]
This attribute identifies a property name. This specification does not list legal
values for this attribute.
content = cdata [p.50] [CS] [p.49]
This attribute specifies a property’s value. This specification does not list legal
values for this attribute.
scheme = cdata [p.50] [CS] [p.49]
This attribute names a scheme to be used to interpret the property’s value (see
the section on profiles [p.68] for details).
http-equiv = name [p.50] [CI] [p.49]
This attribute may be used in place of the name attribute. HTTP servers use this
attribute to gather information for HTTP response message headers.
Attributes defined elsewhere
lang (language information [p.79] ), dir (text direction [p.82] )
The META element can be used to identify properties of a document (e.g., author,
expiration date, a list of key words, etc.) and assign values to those properties. This
specification does not define a normative set of properties.
Each META element specifies a property/value pair. The name attribute identifies
the property and the content attribute specifies the property’s value.
For example, the following declaration sets a value for the Author property:
<META name="Author" content="Dave Raggett">
The lang attribute can be used with META to specify the language for the value of
the content attribute. This enables speech synthesizers to apply language
dependent pronunciation rules.
In this example, the author’s name is declared to be French:
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24 Dec 1999 18:26
The global structure of an HTML document
<META name="Author" lang="fr" content="Arnaud Le Hors">
Note. The META element is a generic mechanism for specifying meta data.
However, some HTML elements and attributes already handle certain pieces of meta
data and may be used by authors instead of META to specify those pieces: the
TITLE element, the ADDRESS element, the INS and DEL elements, the title
attribute, and the cite attribute.
Note. When a property specified by a META element takes a value that is a URI
[p.51] , some authors prefer to specify the meta data via the LINK element. Thus,
the following meta data declaration:
<META name="DC.identifier"
content="http://www.ietf.org/rfc/rfc1866.txt">
might also be written:
<LINK rel="DC.identifier"
type="text/plain"
href="http://www.ietf.org/rfc/rfc1866.txt">
META and HTTP headers
The http-equiv attribute can be used in place of the name attribute and has a
special significance when documents are retrieved via the Hypertext Transfer
Protocol (HTTP). HTTP servers may use the property name specified by the
http-equiv attribute to create an [RFC822] [p.356] -style header in the HTTP
response. Please see the HTTP specification ([RFC2616] [p.354] ) for details on
valid HTTP headers.
The following sample META declaration:
<META http-equiv="Expires" content="Tue, 20 Aug 1996 14:25:27 GMT">
will result in the HTTP header:
Expires: Tue, 20 Aug 1996 14:25:27 GMT
This can be used by caches to determine when to fetch a fresh copy of the
associated document.
Note. Some user agents support the use of META to refresh the current page after
a specified number of seconds, with the option of replacing it by a different URI.
Authors should not use this technique to forward users to different pages, as this
makes the page inaccessible to some users. Instead, automatic page forwarding
should be done using server-side redirects.
META and search engines
A common use for META is to specify keywords that a search engine may use to
improve the quality of search results. When several META elements provide
language-dependent information about a document, search engines may filter on the
lang attribute to display search results using the language preferences of the user.
For example,
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The global structure of an HTML document
<-- For speakers of US English -->
<META name="keywords" lang="en-us"
content="vacation, Greece, sunshine">
<-- For speakers of British English -->
<META name="keywords" lang="en"
content="holiday, Greece, sunshine">
<-- For speakers of French -->
<META name="keywords" lang="fr"
content="vacances, Gr&egrave;ce, soleil">
The effectiveness of search engines can also be increased by using the LINK
element to specify links to translations of the document in other languages, links to
versions of the document in other media (e.g., PDF), and, when the document is part
of a collection, links to an appropriate starting point for browsing the collection.
Further help is provided in the section on helping search engines index your Web
site [p.339] .
META and PICS
The Platform for Internet Content Selection (PICS, specified in [PICS] [p.356] ) is an
infrastructure for associating labels (meta data) with Internet content. Originally
designed to help parents and teachers control what children can access on the
Internet, it also facilitates other uses for labels, including code signing, privacy, and
intellectual property rights management.
This example illustrates how one can use a META declaration to include a PICS
1.1 label:
<HEAD>
<META http-equiv="PICS-Label" content=’
(PICS-1.1 "http://www.gcf.org/v2.5"
labels on "1994.11.05T08:15-0500"
until "1995.12.31T23:59-0000"
for "http://w3.org/PICS/Overview.html"
ratings (suds 0.5 density 0 color/hue 1))
’>
<TITLE>... document title ...</TITLE>
</HEAD>
META and default information
The META element may be used to specify the default information for a document in
the following instances:
The default scripting language [p.253] .
The default style sheet language [p.186] .
The document character encoding [p.41] .
The following example specifies the character encoding [p.41] for a document as
being ISO-8859-5
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<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-5">
Meta data profiles
The profile attribute of the HEAD specifies the location of a meta data profile. The
value of the profile attribute is a URI. User agents may use this URI in two ways:
As a globally unique name. User agents may be able to recognize the name
(without actually retrieving the profile) and perform some activity based on
known conventions for that profile. For instance, search engines could provide
an interface for searching through catalogs of HTML documents, where these
documents all use the same profile for representing catalog entries.
As a link. User agents may dereference the URI and perform some activity
based on the actual definitions within the profile (e.g., authorize the usage of the
profile within the current HTML document). This specification does not define
formats for profiles.
This example refers to a hypothetical profile that defines useful properties for
document indexing. The properties defined by this profile -- including "author",
"copyright", "keywords", and "date" -- have their values set by subsequent META
declarations.
<HEAD profile="http://www.acme.com/profiles/core">
<TITLE>How to complete Memorandum cover sheets</TITLE>
<META name="author" content="John Doe">
<META name="copyright" content="&copy; 1997 Acme Corp.">
<META name="keywords" content="corporate,guidelines,cataloging">
<META name="date" content="1994-11-06T08:49:37+00:00">
</HEAD>
As this specification is being written, it is common practice to use the date formats
described in [RFC2616] [p.354] , section 3.3. As these formats are relatively hard to
process, we recommend that authors use the [ISO8601] [p.353] date format. For
more information, see the sections on the INS and DEL elements.
The scheme attribute allows authors to provide user agents more context for the
correct interpretation of meta data. At times, such additional information may be
critical, as when meta data may be specified in different formats. For example, an
author might specify a date in the (ambiguous) format "10-9-97"; does this mean 9
October 1997 or 10 September 1997? The scheme attribute value
"Month-Day-Year" would disambiguate this date value.
At other times, the scheme attribute may provide helpful but non-critical
information to user agents.
For example, the following scheme declaration may help a user agent determine
that the value of the "identifier" property is an ISBN code number:
<META scheme="ISBN"
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The global structure of an HTML document
Values for the scheme attribute depend on the property name and the associated
profile.
Note. One sample profile is the Dublin Core (see [DCORE] [p.355] ). This profile
defines a set of recommended properties for electronic bibliographic descriptions,
and is intended to promote interoperability among disparate description models.
7.5 The document body
7.5.1 The BODY element
<!ELEMENT BODY O O (%block;|SCRIPT)+ +(INS|DEL) -- document body -->
<!ATTLIST BODY
%attrs;
-- %coreattrs, %i18n, %events -onload
%Script;
#IMPLIED -- the document has been loaded -onunload
%Script;
#IMPLIED -- the document has been removed ->
Start tag: optional, End tag: optional
Attribute definitions
background = uri [p.51] [CT] [p.49]
Deprecated. [p.38] The value of this attribute is a URI that designates an image
resource. The image generally tiles the background (for visual browsers).
text = color [p.51] [CI] [p.49]
Deprecated. [p.38] This attribute sets the foreground color for text (for visual
browsers).
link = color [p.51] [CI] [p.49]
Deprecated. [p.38] This attribute sets the color of text marking unvisited
hypertext links (for visual browsers).
vlink = color [p.51] [CI] [p.49]
Deprecated. [p.38] This attribute sets the color of text marking visited hypertext
links (for visual browsers).
alink = color [p.51] [CI] [p.49]
Deprecated. [p.38] This attribute sets the color of text marking hypertext links
when selected by the user (for visual browsers).
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
bgcolor (background color [p.195] )
onload, onunload (intrinsic events [p.254] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
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The body of a document contains the document’s content. The content may be
presented by a user agent in a variety of ways. For example, for visual browsers,
you can think of the body as a canvas where the content appears: text, images,
colors, graphics, etc. For audio user agents, the same content may be spoken. Since
style sheets [p.183] are now the preferred way to specify a document’s presentation,
the presentational attributes of BODY have been deprecated [p.38] .
DEPRECATED EXAMPLE:
The following HTML fragment illustrates the use of the deprecated [p.38] attributes. It
sets the background color of the canvas to white, the text foreground color to black,
and the color of hyperlinks to red initially, fuchsia when activated, and maroon once
visited.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
</HEAD>
<BODY bgcolor="white" text="black"
link="red" alink="fuchsia" vlink="maroon">
... document body...
</BODY>
</HTML>
Using style sheets [p.183] , the same effect could be accomplished as follows:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
<STYLE type="text/css">
BODY { background: white; color: black}
A:link { color: red }
A:visited { color: maroon }
A:active { color: fuchsia }
</STYLE>
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>
Using external (linked) style sheets gives you the flexibility to change the
presentation without revising the source HTML document:
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A study of population dynamics</TITLE>
<LINK rel="stylesheet" type="text/css" href="smartstyle.css">
</HEAD>
<BODY>
... document body...
</BODY>
</HTML>
Framesets and HTML bodies. Documents that contain framesets replace the
BODY element by the FRAMESET element. Please consult the section on frames
[p.205] for more information.
7.5.2 Element identifiers: the id and class attributes
Attribute definitions
id = name [p.50] [CS] [p.49]
This attribute assigns a name to an element. This name must be unique in a
document.
class = cdata-list [p.50] [CS] [p.49]
This attribute assigns a class name or set of class names to an element. Any
number of elements may be assigned the same class name or names. Multiple
class names must be separated by white space characters.
The id attribute assigns a unique identifier to an element (which may be verified by
an SGML parser). For example, the following paragraphs are distinguished by their
id values:
<P id="myparagraph"> This is a uniquely named paragraph.</P>
<P id="yourparagraph"> This is also a uniquely named paragraph.</P>
The id attribute has several roles in HTML:
As a style sheet [p.183] selector.
As a target anchor [p.145] for hypertext links.
As a means to reference a particular element from a script [p.254] .
As the name of a declared OBJECT element.
For general purpose processing by user agents (e.g. for identifying fields when
extracting data from HTML pages into a database, translating HTML documents
into other formats, etc.).
The class attribute, on the other hand, assigns one or more class names to an
element; the element may be said to belong to these classes. A class name may be
shared by several element instances. The class attribute has several roles in
HTML:
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The global structure of an HTML document
As a style sheet [p.183] selector (when an author wishes to assign style
information to a set of elements).
For general purpose processing by user agents.
In the following example, the SPAN element is used in conjunction with the id and
class attributes to markup document messages. Messages appear in both English
and French versions.
<!-- English messages -->
<P><SPAN id="msg1" class="info" lang="en">Variable declared twice</SPAN>
<P><SPAN id="msg2" class="warning" lang="en">Undeclared variable</SPAN>
<P><SPAN id="msg3" class="error" lang="en">Bad syntax for variable name</SPAN>
<!-- French messages -->
<P><SPAN id="msg1" class="info" lang="fr">Variable d&eacute;clar&eacute;e deux fois</SPAN>
<P><SPAN id="msg2" class="warning" lang="fr">Variable ind&eacute;finie</SPAN>
<P><SPAN id="msg3" class="error" lang="fr">Erreur de syntaxe pour variable</SPAN>
The following CSS style rules would tell visual user agents to display informational
messages in green, warning messages in yellow, and error messages in red:
SPAN.info
{ color: green }
SPAN.warning { color: yellow }
SPAN.error
{ color: red }
Note that the French "msg1" and the English "msg1" may not appear in the same
document since they share the same id value. Authors may make further use of the
id attribute to refine the presentation of individual messages, make them target
anchors, etc.
Almost every HTML element may be assigned identifier and class information.
Suppose, for example, that we are writing a document about a programming
language. The document is to include a number of preformatted examples. We use
the PRE element to format the examples. We also assign a background color (green)
to all instances of the PRE element belonging to the class "example".
<HEAD>
<TITLE>... document title ...</TITLE>
<STYLE type="text/css">
PRE.example { background : green }
</STYLE>
</HEAD>
<BODY>
<PRE class="example" id="example-1">
...example code here...
</PRE>
</BODY>
By setting the id attribute for this example, we can (1) create a hyperlink to it and
(2) override class style information with instance style information.
Note. The id attribute shares the same name space as the name attribute when
used for anchor names. Please consult the section on anchors with id [p.152] for
more information.
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7.5.3 Block-level and inline elements
Certain HTML elements that may appear in BODY are said to be "block-level" while
others are "inline" (also known as "text level"). The distinction is founded on several
notions:
Content model
Generally, block-level elements may contain inline elements and other
block-level elements. Generally, inline elements may contain only data and
other inline elements. Inherent in this structural distinction is the idea that block
elements create "larger" structures than inline elements.
Formatting
By default, block-level elements are formatted differently than inline elements.
Generally, block-level elements begin on new lines, inline elements do not. For
information about white space, line breaks, and block formatting, please consult
the section on text [p.89] .
Directionality
For technical reasons involving the [UNICODE] [p.355] bidirectional text
algorithm, block-level and inline elements differ in how they inherit directionality
information. For details, see the section on inheritance of text direction [p.83] .
Style sheets [p.183] provide the means to specify the rendering of arbitrary
elements, including whether an element is rendered as block or inline. In some
cases, such as an inline style for list elements, this may be appropriate, but generally
speaking, authors are discouraged from overriding the conventional interpretation of
HTML elements in this way.
The alteration of the traditional presentation idioms for block level and inline
elements also has an impact on the bidirectional text algorithm. See the section on
the effect of style sheets on bidirectionality [p.88] for more information.
7.5.4 Grouping elements: the DIV and SPAN elements
<!ELEMENT
<!ATTLIST
%attrs;
>
<!ELEMENT
<!ATTLIST
%attrs;
>
DIV - - (%flow;)*
DIV
-- generic language/style container -->
-- %coreattrs, %i18n, %events --
SPAN - - (%inline;)*
SPAN
-- generic language/style container -->
-- %coreattrs, %i18n, %events --
Start tag: required, End tag: required
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
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align (alignment [p.195] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
The DIV and SPAN elements, in conjunction with the id and class attributes,
offer a generic mechanism for adding structure to documents. These elements
define content to be inline (SPAN) or block-level (DIV) but impose no other
presentational idioms on the content. Thus, authors may use these elements in
conjunction with style sheets [p.183] , the lang attribute, etc., to tailor HTML to their
own needs and tastes.
Suppose, for example, that we wanted to generate an HTML document based on
a database of client information. Since HTML does not include elements that identify
objects such as "client", "telephone number", "email address", etc., we use DIV and
SPAN to achieve the desired structural and presentational effects. We might use the
TABLE element as follows to structure the information:
<!-- Example of data from the client database: -->
<!-- Name: Stephane Boyera, Tel: (212) 555-1212, Email: sb@foo.org -->
<DIV id="client-boyera" class="client">
<P><SPAN class="client-title">Client information:</SPAN>
<TABLE class="client-data">
<TR><TH>Last name:<TD>Boyera</TR>
<TR><TH>First name:<TD>Stephane</TR>
<TR><TH>Tel:<TD>(212) 555-1212</TR>
<TR><TH>Email:<TD>sb@foo.org</TR>
</TABLE>
</DIV>
<DIV id="client-lafon" class="client">
<P><SPAN class="client-title">Client information:</SPAN>
<TABLE class="client-data">
<TR><TH>Last name:<TD>Lafon</TR>
<TR><TH>First name:<TD>Yves</TR>
<TR><TH>Tel:<TD>(617) 555-1212</TR>
<TR><TH>Email:<TD>yves@coucou.com</TR>
</TABLE>
</DIV>
Later, we may easily add style sheet declarations to fine tune the presentation of
these database entries.
For another example of usage, please consult the example in the section on the
class and id attributes [p.72] .
Visual user agents generally place a line break before and after DIV elements, for
instance:
<P>aaaaaaaaa<DIV>bbbbbbbbb</DIV><DIV>ccccc<P>ccccc</DIV>
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The global structure of an HTML document
which is typically rendered as:
aaaaaaaaa
bbbbbbbbb
ccccc
ccccc
7.5.5 Headings: The H1, H2, H3, H4, H5, H6 elements
<!ENTITY % heading "H1|H2|H3|H4|H5|H6">
<!-There are six levels of headings from H1 (the most important)
to H6 (the least important).
-->
<!ELEMENT (%heading;)
<!ATTLIST (%heading;)
%attrs;
>
- - (%inline;)* -- heading -->
-- %coreattrs, %i18n, %events --
Start tag: required, End tag: required
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
align (alignment [p.195] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
A heading element briefly describes the topic of the section it introduces. Heading
information may be used by user agents, for example, to construct a table of
contents for a document automatically.
There are six levels of headings in HTML with H1 as the most important and H6 as
the least. Visual browsers usually render more important headings in larger fonts
than less important ones.
The following example shows how to use the DIV element to associate a heading
with the document section that follows it. Doing so allows you to define a style for the
section (color the background, set the font, etc.) with style sheets.
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<DIV class="section" id="forest-elephants" >
<H1>Forest elephants</H1>
<P>In this section, we discuss the lesser known forest elephants.
...this section continues...
<DIV class="subsection" id="forest-habitat" >
<H2>Habitat</H2>
<P>Forest elephants do not live in trees but among them.
...this subsection continues...
</DIV>
</DIV>
This structure may be decorated with style information such as:
<HEAD>
<TITLE>... document title ...</TITLE>
<STYLE type="text/css">
DIV.section { text-align: justify; font-size: 12pt}
DIV.subsection { text-indent: 2em }
H1 { font-style: italic; color: green }
H2 { color: green }
</STYLE>
</HEAD>
Numbered sections and references
HTML does not itself cause section numbers to be generated from headings. This
facility may be offered by user agents, however. Soon, style sheet languages such
as CSS will allow authors to control the generation of section numbers (handy for
forward references in printed documents, as in "See section 7.2").
Some people consider skipping heading levels to be bad practice. They accept H1
H2 H1 while they do not accept H1 H3 H1 since the heading level H2 is skipped.
7.5.6 The ADDRESS element
<!ELEMENT ADDRESS - - (%inline;)* -- information on author -->
<!ATTLIST ADDRESS
%attrs;
-- %coreattrs, %i18n, %events ->
Start tag: required, End tag: required
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
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The ADDRESS element may be used by authors to supply contact information for a
document or a major part of a document such as a form. This element often appears
at the beginning or end of a document.
For example, a page at the W3C Web site related to HTML might include the
following contact information:
<ADDRESS>
<A href="../People/Raggett/">Dave Raggett</A>,
<A href="../People/Arnaud/">Arnaud Le Hors</A>,
contact persons for the <A href="Activity">W3C HTML Activity</A><BR>
$Date: 1999/12/24 23:07:14 $
</ADDRESS>
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Language information and text direction
8 Language information and text direction
Contents
1. Specifying the language of content: the lang attribute
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1. Language codes
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2. Inheritance of language codes .
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3. Interpretation of language codes .
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2. Specifying the direction of text and tables: the dir attribute
1. Introduction to the bidirectional algorithm
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2. Inheritance of text direction information .
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3. Setting the direction of embedded text .
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4. Overriding the bidirectional algorithm: the BDO element
5. Character references for directionality and joining control
6. The effect of style sheets on bidirectionality .
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This section of the document discusses two important issues that affect the
internationalization of HTML: specifying the language (the lang attribute) and
direction (the dir attribute) of text in a document.
8.1 Specifying the language of content: the lang
attribute
Attribute definitions
lang = language-code [p.53] [CI] [p.49]
This attribute specifies the base language of an element’s attribute values and
text content. The default value of this attribute is unknown.
Language information specified via the lang attribute may be used by a user
agent to control rendering in a variety of ways. Some situations where
author-supplied language information may be helpful include:
Assisting search engines
Assisting speech synthesizers
Helping a user agent select glyph variants for high quality typography
Helping a user agent choose a set of quotation marks
Helping a user agent make decisions about hyphenation [p.96] , ligatures, and
spacing
Assisting spell checkers and grammar checkers
The lang attribute specifies the language of element content and attribute values;
whether it is relevant for a given attribute depends on the syntax and semantics of
the attribute and the operation involved.
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The intent of the lang attribute is to allow user agents to render content more
meaningfully based on accepted cultural practice for a given language. This does not
imply that user agents should render characters that are atypical for a particular
language in less meaningful ways; user agents must make a best attempt to render
all characters, regardless of the value specified by lang.
For instance, if characters from the Greek alphabet appear in the midst of English
text:
<P><Q lang="en">Her super-powers were the result of
&gamma;-radiation,</Q> he explained.</P>
a user agent (1) should try to render the English content in an appropriate manner
(e.g., in its handling the quotation marks) and (2) must make a best attempt to
render γ even though it is not an English character.
Please consult the section on undisplayable characters [p.47] for related
information.
8.1.1 Language codes
The lang attribute’s value is a language code that identifies a natural language
spoken, written, or otherwise used for the communication of information among
people. Computer languages are explicitly excluded from language codes.
[RFC1766] [p.354] defines and explains the language codes that must be used in
HTML documents.
Briefly, language codes consist of a primary code and a possibly empty series of
subcodes:
language-code = primary-code ( "-" subcode )*
Here are some sample language codes:
"en": English
"en-US": the U.S. version of English.
"en-cockney": the Cockney version of English.
"i-navajo": the Navajo language spoken by some Native Americans.
"x-klingon": The primary tag "x" indicates an experimental language tag
Two-letter primary codes are reserved for [ISO639] [p.353] language
abbreviations. Two-letter codes include fr (French), de (German), it (Italian), nl
(Dutch), el (Greek), es (Spanish), pt (Portuguese), ar (Arabic), he (Hebrew), ru
(Russian), zh (Chinese), ja (Japanese), hi (Hindi), ur (Urdu), and sa (Sanskrit).
Any two-letter subcode is understood to be a [ISO3166] [p.353] country code.
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8.1.2 Inheritance of language codes
An element inherits language code information according to the following order of
precedence (highest to lowest):
The lang attribute set for the element itself.
The closest parent element that has the lang attribute set (i.e., the lang
attribute is inherited).
The HTTP "Content-Language" header (which may be configured in a server).
For example:
Content-Language: en-cockney
User agent default values and user preferences.
In this example, the primary language of the document is French ("fr"). One
paragraph is declared to be in Spanish ("es"), after which the primary language
returns to French. The following paragraph includes an embedded Japanese ("ja")
phrase, after which the primary language returns to French.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML lang="fr">
<HEAD>
<TITLE>Un document multilingue</TITLE>
</HEAD>
<BODY>
...Interpreted as French...
<P lang="es">...Interpreted as Spanish...
<P>...Interpreted as French again...
<P>...French text interrupted by<EM lang="ja">some
Japanese</EM>French begins here again...
</BODY>
</HTML>
Note. Table cells may inherit lang values not from its parent but from the first cell in
a span. Please consult the section on alignment inheritance [p.133] for details.
8.1.3 Interpretation of language codes
In the context of HTML, a language code should be interpreted by user agents as a
hierarchy of tokens rather than a single token. When a user agent adjusts rendering
according to language information (say, by comparing style sheet language codes
and lang values), it should always favor an exact match, but should also consider
matching primary codes to be sufficient. Thus, if the lang attribute value of "en-US"
is set for the HTML element, a user agent should prefer style information that
matches "en-US" first, then the more general value "en".
Note. Language code hierarchies do not guarantee that all languages with a
common prefix will be understood by those fluent in one or more of those languages.
They do allow a user to request this commonality when it is true for that user.
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8.2 Specifying the direction of text and tables: the dir
attribute
Attribute definitions
dir = LTR | RTL [CI] [p.49]
This attribute specifies the base direction of directionally neutral text (i.e., text
that doesn’t have inherent directionality as defined in [UNICODE] [p.355] ) in an
element’s content and attribute values. It also specifies the directionality of
tables [p.115] . Possible values:
LTR: Left-to-right text or table.
RTL: Right-to-left text or table.
In addition to specifying the language of a document with the lang attribute,
authors may need to specify the base directionality (left-to-right or right-to-left) of
portions of a document’s text, of table structure, etc. This is done with the dir
attribute.
The [UNICODE] [p.355] specification assigns directionality to characters and
defines a (complex) algorithm for determining the proper directionality of text. If a
document does not contain a displayable right-to-left character, a conforming user
agent is not required to apply the [UNICODE] [p.355] bidirectional algorithm. If a
document contains right-to-left characters, and if the user agent displays these
characters, the user agent must use the bidirectional algorithm.
Although Unicode specifies special characters that deal with text direction, HTML
offers higher-level markup constructs that do the same thing: the dir attribute (do
not confuse with the DIR element) and the BDO element. Thus, to express a Hebrew
quotation, it is more intuitive to write
<Q lang="he" dir="rtl">...a Hebrew quotation...</Q>
than the equivalent with Unicode references:
&#x202B;&#x05F4;...a Hebrew quotation...&#x05F4;&#x202C;
User agents must not use the lang attribute to determine text directionality.
The dir attribute is inherited and may be overridden. Please consult the section
on the inheritance of text direction information [p.83] for details.
8.2.1 Introduction to the bidirectional algorithm
The following example illustrates the expected behavior of the bidirectional
algorithm. It involves English, a left-to-right script, and Hebrew, a right-to-left script.
Consider the following example text:
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english1 HEBREW2 english3 HEBREW4 english5 HEBREW6
The characters in this example (and in all related examples) are stored in the
computer the way they are displayed here: the first character in the file is "e", the
second is "n", and the last is "6".
Suppose the predominant language of the document containing this paragraph is
English. This means that the base direction is left-to-right. The correct presentation
of this line would be:
english1 2WERBEH english3 4WERBEH english5 6WERBEH
<-----<-----<-----H
H
H
------------------------------------------------->
E
The dotted lines indicate the structure of the sentence: English predominates and
some Hebrew text is embedded. Achieving the correct presentation requires no
additional markup since the Hebrew fragments are reversed correctly by user agents
applying the bidirectional algorithm.
If, on the other hand, the predominant language of the document is Hebrew, the
base direction is right-to-left. The correct presentation is therefore:
6WERBEH english5 4WERBEH english3 2WERBEH english1
------->
------->
------->
E
E
E
<------------------------------------------------H
In this case, the whole sentence has been presented as right-to-left and the
embedded English sequences have been properly reversed by the bidirectional
algorithm.
8.2.2 Inheritance of text direction information
The Unicode bidirectional algorithm requires a base text direction for text blocks. To
specify the base direction of a block-level element, set the element’s dir attribute.
The default value of the dir attribute is "ltr" (left-to-right text).
When the dir attribute is set for a block-level element, it remains in effect for the
duration of the element and any nested block-level elements. Setting the dir
attribute on a nested element overrides the inherited value.
To set the base text direction for an entire document, set the dir attribute on the
HTML element.
For example:
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML dir="RTL">
<HEAD>
<TITLE>...a right-to-left title...</TITLE>
</HEAD>
...right-to-left text...
<P dir="ltr">...left-to-right text...</P>
<P>...right-to-left text again...</P>
</HTML>
Inline elements, on the other hand, do not inherit the dir attribute. This means
that an inline element without a dir attribute does not open an additional level of
embedding with respect to the bidirectional algorithm. (Here, an element is
considered to be block-level or inline based on its default presentation. Note that the
INS and DEL elements can be block-level or inline depending on their context.)
8.2.3 Setting the direction of embedded text
The [UNICODE] [p.355] bidirectional algorithm automatically reverses embedded
character sequences according to their inherent directionality (as illustrated by the
previous examples). However, in general only one level of embedding can be
accounted for. To achieve additional levels of embedded direction changes, you
must make use of the dir attribute on an inline element.
Consider the same example text as before:
english1 HEBREW2 english3 HEBREW4 english5 HEBREW6
Suppose the predominant language of the document containing this paragraph is
English. Furthermore, the above English sentence contains a Hebrew section
extending from HEBREW2 through HEBREW4 and the Hebrew section contains an
English quotation (english3). The desired presentation of the text is thus:
english1 4WERBEH english3 2WERBEH english5 6WERBEH
------->
E
<----------------------H
------------------------------------------------->
E
To achieve two embedded direction changes, we must supply additional
information, which we do by delimiting the second embedding explicitly. In this
example, we use the SPAN element and the dir attribute to mark up the text:
english1 <SPAN dir="RTL">HEBREW2 english3 HEBREW4</SPAN> english5 HEBREW6
Authors may also use special Unicode characters to achieve multiple embedded
direction changes. To achieve left-to-right embedding, surround embedded text with
the characters LEFT-TO-RIGHT EMBEDDING ("LRE", hexadecimal 202A) and POP
DIRECTIONAL FORMATTING ("PDF", hexadecimal 202C). To achieve right-to-left
embedding, surround embedded text with the characters RIGHT-TO-LEFT
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EMBEDDING ("RTE", hexadecimal 202B) and PDF.
Using HTML directionality markup with Unicode characters. Authors and
designers of authoring software should be aware that conflicts can arise if the dir
attribute is used on inline elements (including BDO) concurrently with the
corresponding [UNICODE] [p.355] formatting characters. Preferably one or the other
should be used exclusively. The markup method offers a better guarantee of
document structural integrity and alleviates some problems when editing
bidirectional HTML text with a simple text editor, but some software may be more apt
at using the [UNICODE] [p.355] characters. If both methods are used, great care
should be exercised to insure proper nesting of markup and directional embedding
or override, otherwise, rendering results are undefined.
8.2.4 Overriding the bidirectional algorithm: the BDO element
<!ELEMENT BDO - - (%inline;)*
<!ATTLIST BDO
%coreattrs;
lang
%LanguageCode; #IMPLIED
dir
(ltr|rtl)
#REQUIRED
>
-- I18N BiDi over-ride -->
-- id, class, style, title --- language code --- directionality --
Start tag: required, End tag: required
Attribute definitions
dir = LTR | RTL [CI] [p.49]
This mandatory attribute specifies the base direction of the element’s text
content. This direction overrides the inherent directionality of characters as
defined in [UNICODE] [p.355] . Possible values:
LTR: Left-to-right text.
RTL: Right-to-left text.
Attributes defined elsewhere
lang (language information [p.79] )
The bidirectional algorithm and the dir attribute generally suffice to manage
embedded direction changes. However, some situations may arise when the
bidirectional algorithm results in incorrect presentation. The BDO element allows
authors to turn off the bidirectional algorithm for selected fragments of text.
Consider a document containing the same text as before:
english1 HEBREW2 english3 HEBREW4 english5 HEBREW6
but assume that this text has already been put in visual order. One reason for this
may be that the MIME standard ([RFC2045] [p.354] , [RFC1556] [p.354] ) favors
visual order, i.e., that right-to-left character sequences are inserted right-to-left in the
byte stream. In an email, the above might be formatted, including line breaks, as:
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english1 2WERBEH english3
4WERBEH english5 6WERBEH
This conflicts with the [UNICODE] [p.355] bidirectional algorithm, because that
algorithm would invert 2WERBEH, 4WERBEH, and 6WERBEH a second time, displaying
the Hebrew words left-to-right instead of right-to-left.
The solution in this case is to override the bidirectional algorithm by putting the
Email excerpt in a PRE element (to conserve line breaks) and each line in a BDO
element, whose dir attribute is set to LTR:
<PRE>
<BDO dir="LTR">english1 2WERBEH english3</BDO>
<BDO dir="LTR">4WERBEH english5 6WERBEH</BDO>
</PRE>
This tells the bidirectional algorithm "Leave me left-to-right!" and would produce
the desired presentation:
english1 2WERBEH english3
4WERBEH english5 6WERBEH
The BDO element should be used in scenarios where absolute control over
sequence order is required (e.g., multi-language part numbers). The dir attribute is
mandatory for this element.
Authors may also use special Unicode characters to override the bidirectional
algorithm -- LEFT-TO-RIGHT OVERRIDE (202D) or RIGHT-TO-LEFT OVERRIDE
(hexadecimal 202E). The POP DIRECTIONAL FORMATTING (hexadecimal 202C)
character ends either bidirectional override.
Note. Recall that conflicts can arise if the dir attribute is used on inline elements
(including BDO) concurrently with the corresponding [UNICODE] [p.355] formatting
characters.
Bidirectionality and character encoding According to [RFC1555] [p.354] and
[RFC1556] [p.354] , there are special conventions for the use of "charset" parameter
values to indicate bidirectional treatment in MIME mail, in particular to distinguish
between visual, implicit, and explicit directionality. The parameter value
"ISO-8859-8" (for Hebrew) denotes visual encoding, "ISO-8859-8-i" denotes implicit
bidirectionality, and "ISO-8859-8-e" denotes explicit directionality.
Because HTML uses the Unicode bidirectionality algorithm, conforming
documents encoded using ISO 8859-8 must be labeled as "ISO-8859-8-i". Explicit
directional control is also possible with HTML, but cannot be expressed with ISO
8859-8, so "ISO-8859-8-e" should not be used.
The value "ISO-8859-8" implies that the document is formatted visually, misusing
some markup (such as TABLE with right alignment and no line wrapping) to ensure
reasonable display on older user agents that do not handle bidirectionality. Such
documents do not conform to the present specification. If necessary, they can be
made to conform to the current specification (and at the same time will be displayed
correctly on older user agents) by adding BDO markup where necessary. Contrary to
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what is said in [RFC1555] [p.354] and [RFC1556] [p.354] , ISO-8859-6 (Arabic) is
not visual ordering.
8.2.5 Character references for directionality and joining
control
Since ambiguities sometimes arise as to the directionality of certain characters (e.g.,
punctuation), the [UNICODE] [p.355] specification includes characters to enable their
proper resolution. Also, Unicode includes some characters to control joining behavior
where this is necessary (e.g., some situations with Arabic letters). HTML 4 includes
character references [p.299] for these characters.
The following DTD excerpt presents some of the directional entities:
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
zwnj
zwj
lrm
rlm
CDATA
CDATA
CDATA
CDATA
"&#8204;"--=zero width non-joiner-->
"&#8205;"--=zero width joiner-->
"&#8206;"--=left-to-right mark-->
"&#8207;"--=right-to-left mark-->
The zwnj entity is used to block joining behavior in contexts where joining will
occur but shouldn’t. The zwj entity does the opposite; it forces joining when it
wouldn’t occur but should. For example, the Arabic letter "HEH" is used to
abbreviate "Hijri", the name of the Islamic calendar system. Since the isolated form
of "HEH" looks like the digit five as employed in Arabic script (based on Indic digits),
in order to prevent confusing "HEH" as a final digit five in a year, the initial form of
"HEH" is used. However, there is no following context (i.e., a joining letter) to which
the "HEH" can join. The zwj character provides that context.
Similarly, in Persian texts, there are cases where a letter that normally would join a
subsequent letter in a cursive connection should not. The character zwnj is used to
block joining in such cases.
The other characters, lrm and rlm, are used to force directionality of directionally
neutral characters. For example, if a double quotation mark comes between an
Arabic (right-to-left) and a Latin (left-to-right) letter, the direction of the quotation
mark is not clear (is it quoting the Arabic text or the Latin text?). The lrm and rlm
characters have a directional property but no width and no word/line break property.
Please consult [UNICODE] [p.355] for more details.
Mirrored character glyphs. In general, the bidirectional algorithm does not mirror
character glyphs but leaves them unaffected. An exception are characters such as
parentheses (see [UNICODE] [p.355] , table 4-7). In cases where mirroring is
desired, for example for Egyptian Hieroglyphs, Greek Bustrophedon, or special
design effects, this should be controlled with styles.
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8.2.6 The effect of style sheets on bidirectionality
In general, using style sheets to change an element’s visual rendering from
block-level to inline or vice-versa is straightforward. However, because the
bidirectional algorithm relies on the inline/block-level distinction [p.83] , special care
must be taken during the transformation.
When an inline element that does not have a dir attribute is transformed to the
style of a block-level element by a style sheet, it inherits the dir attribute from its
closest parent block element to define the base direction of the block.
When a block element that does not have a dir attribute is transformed to the
style of an inline element by a style sheet, the resulting presentation should be
equivalent, in terms of bidirectional formatting, to the formatting obtained by explicitly
adding a dir attribute (assigned the inherited value) to the transformed element.
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9 Text
Contents
1. White space
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2. Structured text .
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1. Phrase elements: EM, STRONG, DFN, CODE, SAMP, KBD, VAR, CITE, ABBR,
and ACRONYM .
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2. Quotations: The BLOCKQUOTE and Q elements .
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Rendering quotations .
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3. Subscripts and superscripts: the SUB and SUP elements .
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3. Lines and Paragraphs
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1. Paragraphs: the P element .
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2. Controlling line breaks .
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Forcing a line break: the BR element
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Prohibiting a line break .
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3. Hyphenation
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4. Preformatted text: The PRE element .
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5. Visual rendering of paragraphs .
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4. Marking document changes: The INS and DEL elements .
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The following sections discuss issues surrounding the structuring of text. Elements
that present text [p.195] (alignment elements, font elements, style sheets, etc.) are
discussed elsewhere in the specification. For information about characters, please
consult the section on the document character set. [p.41]
9.1 White space
The document character set [p.41] includes a wide variety of white space characters.
Many of these are typographic elements used in some applications to produce
particular visual spacing effects. In HTML, only the following characters are defined
as white space characters:
ASCII space (&#x0020;)
ASCII tab (&#x0009;)
ASCII form feed (&#x000C;)
Zero-width space (&#x200B;)
Line breaks [p.95] are also white space characters. Note that although &#x2028;
and &#x2029; are defined in [ISO10646] [p.353] to unambiguously separate lines
and paragraphs, respectively, these do not constitute line breaks in HTML, nor does
this specification include them in the more general category of white space
characters.
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This specification does not indicate the behavior, rendering or otherwise, of space
characters other than those explicitly identified here as white space characters. For
this reason, authors should use appropriate elements and styles to achieve visual
formatting effects that involve white space, rather than space characters.
For all HTML elements except PRE, sequences of white space separate "words"
(we use the term "word" here to mean "sequences of non-white space characters").
When formatting text, user agents should identify these words and lay them out
according to the conventions of the particular written language (script) and target
medium.
This layout may involve putting space between words (called inter-word space),
but conventions for inter-word space vary from script to script. For example, in Latin
scripts, inter-word space is typically rendered as an ASCII space (&#x0020;), while
in Thai it is a zero-width word separator (&#x200B;). In Japanese and Chinese,
inter-word space is not typically rendered at all.
Note that a sequence of white spaces between words in the source document may
result in an entirely different rendered inter-word spacing (except in the case of the
PRE element). In particular, user agents should collapse input white space
sequences when producing output inter-word space. This can and should be done
even in the absence of language information (from the lang attribute, the HTTP
"Content-Language" header field (see [RFC2616] [p.354] , section 14.12), user
agent settings, etc.).
The PRE element is used for preformatted text [p.97] , where white space is
significant.
In order to avoid problems with SGML line break rules [p.335] and inconsistencies
among extant implementations, authors should not rely on user agents to render
white space immediately after a start tag or immediately before an end tag. Thus,
authors, and in particular authoring tools, should write:
<P>We offer free <A>technical support</A> for subscribers.</P>
and not:
<P>We offer free<A> technical support </A>for subscribers.</P>
9.2 Structured text
9.2.1 Phrase elements: EM, STRONG, DFN, CODE, SAMP, KBD,
VAR, CITE, ABBR, and ACRONYM
<!ENTITY % phrase "EM | STRONG | DFN | CODE |
SAMP | KBD | VAR | CITE | ABBR | ACRONYM" >
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
%attrs;
-- %coreattrs, %i18n, %events ->
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Start tag: required, End tag: required
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
Phrase elements add structural information to text fragments. The usual meanings
of phrase elements are following:
EM:
Indicates emphasis.
STRONG:
Indicates stronger emphasis.
CITE:
Contains a citation or a reference to other sources.
DFN:
Indicates that this is the defining instance of the enclosed term.
CODE:
Designates a fragment of computer code.
SAMP:
Designates sample output from programs, scripts, etc.
KBD:
Indicates text to be entered by the user.
VAR:
Indicates an instance of a variable or program argument.
ABBR:
Indicates an abbreviated form (e.g., WWW, HTTP, URI, Mass., etc.).
ACRONYM:
Indicates an acronym (e.g., WAC, radar, etc.).
EM and STRONG are used to indicate emphasis. The other phrase elements have
particular significance in technical documents. These examples illustrate some of the
phrase elements:
As <CITE>Harry S. Truman</CITE> said,
<Q lang="en-us">The buck stops here.</Q>
More information can be found in <CITE>[ISO-0000]</CITE>.
Please refer to the following reference number in future
correspondence: <STRONG>1-234-55</STRONG>
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The presentation of phrase elements depends on the user agent. Generally, visual
user agents present EM text in italics and STRONG text in bold font. Speech
synthesizer user agents may change the synthesis parameters, such as volume,
pitch and rate accordingly.
The ABBR and ACRONYM elements allow authors to clearly indicate occurrences of
abbreviations and acronyms. Western languages make extensive use of acronyms
such as "GmbH", "NATO", and "F.B.I.", as well as abbreviations like "M.", "Inc.", "et
al.", "etc.". Both Chinese and Japanese use analogous abbreviation mechanisms,
wherein a long name is referred to subsequently with a subset of the Han characters
from the original occurrence. Marking up these constructs provides useful
information to user agents and tools such as spell checkers, speech synthesizers,
translation systems and search-engine indexers.
The content of the ABBR and ACRONYM elements specifies the abbreviated
expression itself, as it would normally appear in running text. The title attribute of
these elements may be used to provide the full or expanded form of the expression.
Here are some sample uses of ABBR:
<P>
<ABBR title="World Wide Web">WWW</ABBR>
<ABBR lang="fr"
title="Soci&eacute;t&eacute; Nationale des Chemins de Fer">
SNCF
</ABBR>
<ABBR lang="es" title="Do&ntilde;a">Do&ntilde;a</ABBR>
<ABBR title="Abbreviation">abbr.</ABBR>
Note that abbreviations and acronyms often have idiosyncratic pronunciations. For
example, while "IRS" and "BBC" are typically pronounced letter by letter, "NATO"
and "UNESCO" are pronounced phonetically. Still other abbreviated forms (e.g.,
"URI" and "SQL") are spelled out by some people and pronounced as words by
other people. When necessary, authors should use style sheets to specify the
pronunciation of an abbreviated form.
9.2.2 Quotations: The BLOCKQUOTE and Q elements
<!ELEMENT
<!ATTLIST
%attrs;
cite
>
<!ELEMENT
<!ATTLIST
%attrs;
cite
>
BLOCKQUOTE - - (%block;|SCRIPT)+ -- long quotation -->
BLOCKQUOTE
-- %coreattrs, %i18n, %events -%URI;
#IMPLIED -- URI for source document or msg -Q - - (%inline;)*
Q
%URI;
-- short inline quotation -->
#IMPLIED
-- %coreattrs, %i18n, %events --- URI for source document or msg --
Start tag: required, End tag: required
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Attribute definitions
cite = uri [p.51] [CT] [p.49]
The value of this attribute is a URI that designates a source document or
message. This attribute is intended to give information about the source from
which the quotation was borrowed.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
These two elements designate quoted text. BLOCKQUOTE is for long quotations
(block-level content) and Q is intended for short quotations (inline content) that don’t
require paragraph breaks.
This example formats an excerpt from "The Two Towers", by J.R.R. Tolkien, as a
blockquote.
<BLOCKQUOTE cite="http://www.mycom.com/tolkien/twotowers.html">
<P>They went in single file, running like hounds on a strong scent,
and an eager light was in their eyes. Nearly due west the broad
swath of the marching Orcs tramped its ugly slot; the sweet grass
of Rohan had been bruised and blackened as they passed.</P>
</BLOCKQUOTE>
Rendering quotations
Visual user agents generally render BLOCKQUOTE as an indented block.
Visual user agents must ensure that the content of the Q element is rendered with
delimiting quotation marks. Authors should not put quotation marks at the beginning
and end of the content of a Q element.
User agents should render quotation marks in a language-sensitive manner (see
the lang attribute). Many languages adopt different quotation styles for outer and
inner (nested) quotations, which should be respected by user-agents.
The following example illustrates nested quotations with the Q element.
John said, <Q lang="en-us">I saw Lucy at lunch, she told me
<Q lang="en-us">Mary wants you
to get some ice cream on your way home.</Q> I think I will get
some at Ben and Jerry’s, on Gloucester Road.</Q>
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Since the language of both quotations is American English, user agents should
render them appropriately, for example with single quote marks around the inner
quotation and double quote marks around the outer quotation:
John said, "I saw Lucy at lunch, she told me ’Mary wants you
to get some ice cream on your way home.’ I think I will get some
at Ben and Jerry’s, on Gloucester Road."
Note. We recommend that style sheet implementations provide a mechanism for
inserting quotation marks before and after a quotation delimited by BLOCKQUOTE in a
manner appropriate to the current language context and the degree of nesting of
quotations.
However, as some authors have used BLOCKQUOTE merely as a mechanism to
indent text, in order to preserve the intention of the authors, user agents should not
insert quotation marks in the default style.
The usage of BLOCKQUOTE to indent text is deprecated [p.38] in favor of style
sheets.
9.2.3 Subscripts and superscripts: the SUB and SUP elements
<!ELEMENT (SUB|SUP) - - (%inline;)*
<!ATTLIST (SUB|SUP)
%attrs;
>
-- subscript, superscript -->
-- %coreattrs, %i18n, %events --
Start tag: required, End tag: required
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
Many scripts (e.g., French) require superscripts or subscripts for proper rendering.
The SUB and SUP elements should be used to markup text in these cases.
H<sub>2</sub>O
E = mc<sup>2</sup>
<SPAN lang="fr">M<sup>lle</sup> Dupont</SPAN>
9.3 Lines and Paragraphs
Authors traditionally divide their thoughts and arguments into sequences of
paragraphs. The organization of information into paragraphs is not affected by how
the paragraphs are presented: paragraphs that are double-justified contain the same
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Paragraphs, Lines, and Phrases
thoughts as those that are left-justified.
The HTML markup for defining a paragraph is straightforward: the P element
defines a paragraph.
The visual presentation of paragraphs is not so simple. A number of issues, both
stylistic and technical, must be addressed:
Treatment of white space
Line breaking and word wrapping
Justification
Hyphenation
Written language conventions and text directionality
Formatting of paragraphs with respect to surrounding content
We address these questions below. Paragraph alignment and floating objects
[p.195] are discussed later in this document.
9.3.1 Paragraphs: the P element
<!ELEMENT P - O (%inline;)*
<!ATTLIST P
%attrs;
>
-- paragraph -->
-- %coreattrs, %i18n, %events --
Start tag: required, End tag: optional
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
align (alignment [p.195] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
The P element represents a paragraph. It cannot contain block-level elements
[p.73] (including P itself).
We discourage authors from using empty P elements. User agents should ignore
empty P elements.
9.3.2 Controlling line breaks
A line break is defined to be a carriage return (&#x000D;), a line feed (&#x000A;), or
a carriage return/line feed pair. All line breaks constitute white space. [p.89]
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For more information about SGML’s specification of line breaks, please consult the
notes on line breaks [p.335] in the appendix.
Forcing a line break: the BR element
<!ELEMENT BR - O EMPTY
<!ATTLIST BR
%coreattrs;
>
-- forced line break -->
-- id, class, style, title --
Start tag: required, End tag: forbidden
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
title (element title [p.63] )
style (inline style information [p.186] )
clear (alignment and floating objects [p.195] )
The BR element forcibly breaks (ends) the current line of text.
For visual user agents, the clear attribute can be used to determine whether
markup following the BR element flows around images and other objects floated to
the left or right margin, or whether it starts after the bottom of such objects. Further
details are given in the section on alignment and floating objects [p.195] . Authors
are advised to use style sheets to control text flow around floating images and other
objects.
With respect to bidirectional formatting, the BR element should behave the same
way the [ISO10646] [p.353] LINE SEPARATOR character behaves in the
bidirectional algorithm.
Prohibiting a line break
Sometimes authors may want to prevent a line break from occurring between two
words. The &nbsp; entity (&#160; or &#xA0;) acts as a space where user agents
should not cause a line break.
9.3.3 Hyphenation
In HTML, there are two types of hyphens: the plain hyphen and the soft hyphen. The
plain hyphen should be interpreted by a user agent as just another character. The
soft hyphen tells the user agent where a line break can occur.
Those browsers that interpret soft hyphens must observe the following semantics:
If a line is broken at a soft hyphen, a hyphen character must be displayed at the end
of the first line. If a line is not broken at a soft hyphen, the user agent must not
display a hyphen character. For operations such as searching and sorting, the soft
hyphen should always be ignored.
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In HTML, the plain hyphen is represented by the "-" character (&#45; or &#x2D;).
The soft hyphen is represented by the character entity reference &shy; (&#173; or
&#xAD;)
9.3.4 Preformatted text: The PRE element
<!ENTITY % pre.exclusion "IMG|OBJECT|BIG|SMALL|SUB|SUP">
<!ELEMENT PRE - - (%inline;)* -(%pre.exclusion;) -- preformatted text -->
<!ATTLIST PRE
%attrs;
-- %coreattrs, %i18n, %events ->
Start tag: required, End tag: required
Attribute definitions
width = number [p.50] [CN] [p.49]
Deprecated. [p.38] This attribute provides a hint to visual user agents about the
desired width of the formatted block. The user agent can use this information to
select an appropriate font size or to indent the content appropriately. The
desired width is expressed in number of characters. This attribute is not widely
supported currently.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
The PRE element tells visual user agents that the enclosed text is "preformatted".
When handling preformatted text, visual user agents:
May leave white space [p.89] intact.
May render text with a fixed-pitch font.
May disable automatic word wrap.
Must not disable bidirectional processing.
Non-visual user agents are not required to respect extra white space [p.89] in the
content of a PRE element.
For more information about SGML’s specification of line breaks, please consult the
notes on line breaks [p.335] in the appendix.
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The DTD fragment above indicates which elements may not appear within a PRE
declaration. This is the same as in HTML 3.2, and is intended to preserve constant
line spacing and column alignment for text rendered in a fixed pitch font. Authors are
discouraged from altering this behavior through style sheets.
The following example shows a preformatted verse from Shelly’s poem To a
Skylark:
<PRE>
Higher still and higher
From the earth thou springest
Like a cloud of fire;
The blue deep thou wingest,
And singing still dost soar, and soaring ever singest.
</PRE>
Here is how this is typically rendered:
Higher still and higher
From the earth thou springest
Like a cloud of fire;
The blue deep thou wingest,
And singing still dost soar, and soaring ever singest.
The horizontal tab character
The horizontal tab character (decimal 9 in [ISO10646] [p.353] and [ISO88591]
[p.354] ) is usually interpreted by visual user agents as the smallest non-zero
number of spaces necessary to line characters up along tab stops that are every 8
characters. We strongly discourage using horizontal tabs in preformatted text since it
is common practice, when editing, to set the tab-spacing to other values, leading to
misaligned documents.
9.3.5 Visual rendering of paragraphs
Note. The following section is an informative description of the behavior of some
current visual user agents when formatting paragraphs. Style sheets allow better
control of paragraph formatting.
How paragraphs are rendered visually depends on the user agent. Paragraphs are
usually rendered flush left with a ragged right margin. Other defaults are appropriate
for right-to-left scripts.
HTML user agents have traditionally rendered paragraphs with white space before
and after, e.g.,
At the same time, there began to take form a system of numbering,
the calendar, hieroglyphic writing, and a technically advanced
art, all of which later influenced other peoples.
Within the framework of this gradual evolution or cultural
progress the Preclassic horizon has been divided into Lower,
Middle and Upper periods, to which can be added a transitional
or Protoclassic period with several features that would later
distinguish the emerging civilizations of Mesoamerica.
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This contrasts with the style used in novels which indents the first line of the
paragraph and uses the regular line spacing between the final line of the current
paragraph and the first line of the next, e.g.,
At the same time, there began to take form a system of
numbering, the calendar, hieroglyphic writing, and a technically
advanced art, all of which later influenced other peoples.
Within the framework of this gradual evolution or cultural
progress the Preclassic horizon has been divided into Lower,
Middle and Upper periods, to which can be added a transitional
or Protoclassic period with several features that would later
distinguish the emerging civilizations of Mesoamerica.
Following the precedent set by the NCSA Mosaic browser in 1993, user agents
generally don’t justify both margins, in part because it’s hard to do this effectively
without sophisticated hyphenation routines. The advent of style sheets, and
anti-aliased fonts with subpixel positioning promises to offer richer choices to HTML
authors than previously possible.
Style sheets provide rich control over the size and style of a font, the margins,
space before and after a paragraph, the first line indent, justification and many other
details. The user agent’s default style sheet renders P elements in a familiar form, as
illustrated above. One could, in principle, override this to render paragraphs without
the breaks that conventionally distinguish successive paragraphs. In general, since
this may confuse readers, we discourage this practice.
By convention, visual HTML user agents wrap text lines to fit within the available
margins. Wrapping algorithms depend on the script being formatted.
In Western scripts, for example, text should only be wrapped at white space. Early
user agents incorrectly wrapped lines just after the start tag or just before the end
tag of an element, which resulted in dangling punctuation. For example, consider this
sentence:
A statue of the <A href="cih78">Cihuateteus</A>, who are patron ...
Wrapping the line just before the end tag of the A element causes the comma to
be stranded at the beginning of the next line:
A statue of the Cihuateteus
, who are patron ...
This is an error since there was no white space at that point in the markup.
9.4 Marking document changes: The INS and DEL
elements
<!-- INS/DEL are handled by inclusion on BODY -->
<!ELEMENT (INS|DEL) - - (%flow;)*
-- inserted text, deleted text -->
<!ATTLIST (INS|DEL)
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%attrs;
cite
datetime
>
%URI;
%Datetime;
#IMPLIED
#IMPLIED
-- %coreattrs, %i18n, %events --- info on reason for change --- date and time of change --
Start tag: required, End tag: required
Attribute definitions
cite = uri [p.51] [CT] [p.49]
The value of this attribute is a URI that designates a source document or
message. This attribute is intended to point to information explaining why a
document was changed.
datetime = datetime [p.54] [CS] [p.49]
The value of this attribute specifies the date and time when the change was
made.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
INS and DEL are used to markup sections of the document that have been
inserted or deleted with respect to a different version of a document (e.g., in draft
legislation where lawmakers need to view the changes).
These two elements are unusual for HTML in that they may serve as either
block-level or inline elements (but not both). They may contain one or more words
within a paragraph or contain one or more block-level elements such as paragraphs,
lists and tables.
This example could be from a bill to change the legislation for how many deputies
a County Sheriff can employ from 3 to 5.
<P>
A Sheriff can employ <DEL>3</DEL><INS>5</INS> deputies.
</P>
The INS and DEL elements must not contain block-level content when these
elements behave as inline elements.
ILLEGAL EXAMPLE:
The following is not legal HTML.
<P>
<INS><DIV>...block-level content...</DIV></INS>
</P>
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User agents should render inserted and deleted text in ways that make the change
obvious. For instance, inserted text may appear in a special font, deleted text may
not be shown at all or be shown as struck-through or with special markings, etc.
Both of the following examples correspond to November 5, 1994, 8:15:30 am, US
Eastern Standard Time.
1994-11-05T13:15:30Z
1994-11-05T08:15:30-05:00
Used with INS, this gives:
<INS datetime="1994-11-05T08:15:30-05:00"
cite="http://www.foo.org/mydoc/comments.html">
Furthermore, the latest figures from the marketing department
suggest that such practice is on the rise.
</INS>
The document "http://www.foo.org/mydoc/comments.html" would contain
comments about why information was inserted into the document.
Authors may also make comments about inserted or deleted text by means of the
title attribute for the INS and DEL elements. User agents may present this
information to the user (e.g., as a popup note). For example:
<INS datetime="1994-11-05T08:15:30-05:00"
title="Changed as a result of Steve B’s comments in meeting.">
Furthermore, the latest figures from the marketing department
suggest that such practice is on the rise.
</INS>
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102
Lists in HTML documents
10 Lists
Contents
1. Introduction to lists .
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2. Unordered lists (UL), ordered lists (OL), and list items (LI)
3. Definition lists: the DL, DT, and DD elements .
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1. Visual rendering of lists .
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4. The DIR and MENU elements .
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103
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104
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106
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108
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109
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10.1 Introduction to lists
HTML offers authors several mechanisms for specifying lists of information. All lists
must contain one or more list elements. Lists may contain:
Unordered information.
Ordered information.
Definitions.
The previous list, for example, is an unordered list, created with the UL element:
<UL>
<LI>Unordered information.
<LI>Ordered information.
<LI>Definitions.
</UL>
An ordered list, created using the OL element, should contain information where
order should be emphasized, as in a recipe:
1.
2.
3.
4.
Mix dry ingredients thoroughly.
Pour in wet ingredients.
Mix for 10 minutes.
Bake for one hour at 300 degrees.
Definition lists, created using the DL element, generally consist of a series of
term/definition pairs (although definition lists may have other applications). Thus,
when advertising a product, one might use a definition list:
Lower cost
The new version of this product costs significantly less than the previous one!
Easier to use
We’ve changed the product so that it’s much easier to use!
Safe for kids
You can leave your kids alone in a room with this product and they won’t get
hurt (not a guarantee).
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defined in HTML as:
<DL>
<DT><STRONG>Lower cost</STRONG>
<DD>The new version of this product costs significantly less than the
previous one!
<DT><STRONG>Easier to use</STRONG>
<DD>We’ve changed the product so that it’s much easier to use!
<DT><STRONG>Safe for kids</STRONG>
<DD>You can leave your kids alone in a room with this product and
they won’t get hurt (not a guarantee).
</DL>
Lists may also be nested and different list types may be used together, as in the
following example, which is a definition list that contains an unordered list (the
ingredients) and an ordered list (the procedure):
The ingredients:
100 g. flour
10 g. sugar
1 cup water
2 eggs
salt, pepper
The procedure:
1. Mix dry ingredients thoroughly.
2. Pour in wet ingredients.
3. Mix for 10 minutes.
4. Bake for one hour at 300 degrees.
Notes:
The recipe may be improved by adding raisins.
The exact presentation of the three list types depends on the user agent. We
discourage authors from using lists purely as a means of indenting text. This is a
stylistic issue and is properly handled by style sheets.
10.2 Unordered lists (UL), ordered lists (OL), and list
items (LI)
<!ELEMENT
<!ATTLIST
%attrs;
>
<!ELEMENT
<!ATTLIST
%attrs;
>
UL - - (LI)+
UL
-- unordered list -->
-- %coreattrs, %i18n, %events --
OL - - (LI)+
OL
24 Dec 1999 18:26
-- ordered list -->
-- %coreattrs, %i18n, %events --
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Lists in HTML documents
Start tag: required, End tag: required
<!ELEMENT LI - O (%flow;)*
<!ATTLIST LI
%attrs;
>
-- list item -->
-- %coreattrs, %i18n, %events --
Start tag: required, End tag: optional
Attribute definitions
type = style-information [CI] [p.49]
Deprecated. [p.38] This attribute sets the style of a list item. Currently available
values are intended for visual user agents. Possible values [p.108] are
described below (along with case information).
start = number [p.50] [CN] [p.49]
Deprecated. [p.38] For OL only. This attribute specifies the starting number of
the first item in an ordered list. The default starting number is "1". Note that
while the value of this attribute is an integer, the corresponding label may be
non-numeric. Thus, when the list item style is uppercase latin letters (A, B, C,
...), start=3 means "C". When the style is lowercase roman numerals,
start=3 means "iii", etc.
value = number [p.50] [CN] [p.49]
Deprecated. [p.38] For LI only. This attribute sets the number of the current list
item. Note that while the value of this attribute is an integer, the corresponding
label may be non-numeric (see the start attribute).
compact [CI] [p.49]
Deprecated. [p.38] When set, this boolean attribute gives a hint to visual user
agents to render the list in a more compact way. The interpretation of this
attribute depends on the user agent.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
Ordered and unordered lists are rendered in an identical manner except that visual
user agents number ordered list items. User agents may present those numbers in a
variety of ways. Unordered list items are not numbered.
Both types of lists are made up of sequences of list items defined by the LI
element (whose end tag may be omitted).
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This example illustrates the basic structure of a list.
<UL>
<LI> ... first list item...
<LI> ... second list item...
...
</UL>
Lists may also be nested:
DEPRECATED EXAMPLE:
<UL>
<LI> ... Level one, number one...
<OL>
<LI> ... Level two, number one...
<LI> ... Level two, number two...
<OL start="10">
<LI> ... Level three, number one...
</OL>
<LI> ... Level two, number three...
</OL>
<LI> ... Level one, number two...
</UL>
Details about number order. In ordered lists, it is not possible to continue list
numbering automatically from a previous list or to hide numbering of some list items.
However, authors can reset the number of a list item by setting its value attribute.
Numbering continues from the new value for subsequent list items. For example:
<ol>
<li value="30"> makes this list item number 30.
<li value="40"> makes this list item number 40.
<li> makes this list item number 41.
</ol>
10.3 Definition lists: the DL, DT, and DD elements
<!-- definition lists - DT for term, DD for its definition -->
<!ELEMENT DL - - (DT|DD)+
<!ATTLIST DL
%attrs;
>
-- definition list -->
-- %coreattrs, %i18n, %events --
Start tag: required, End tag: required
<!ELEMENT DT - O (%inline;)*
<!ELEMENT DD - O (%flow;)*
<!ATTLIST (DT|DD)
%attrs;
>
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-- definition term -->
-- definition description -->
-- %coreattrs, %i18n, %events --
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Lists in HTML documents
Start tag: required, End tag: optional
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
Definition lists vary only slightly from other types of lists in that list items consist of
two parts: a term and a description. The term is given by the DT element and is
restricted to inline content. The description is given with a DD element that contains
block-level content.
Here is an example:
<DL>
<DT>Dweeb
<DD>young excitable person who may mature
into a <EM>Nerd</EM> or <EM>Geek</EM>
<DT>Hacker
<DD>a clever programmer
<DT>Nerd
<DD>technically bright but socially inept person
</DL>
Here is an example with multiple terms and descriptions:
<DL>
<DT>Center
<DT>Centre
<DD> A point equidistant from all points
on the surface of a sphere.
<DD> In some field sports, the player who
holds the middle position on the field, court,
or forward line.
</DL>
Another application of DL, for example, is for marking up dialogues, with each DT
naming a speaker, and each DD containing his or her words.
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10.3.1 Visual rendering of lists
Note. The following is an informative description of the behavior of some current
visual user agents when formatting lists. Style sheets allow better control of list
formatting (e.g., for numbering, language-dependent conventions, indenting, etc.).
Visual user agents generally indent nested lists with respect to the current level of
nesting.
For both OL and UL, the type attribute specifies rendering options for visual user
agents.
For the UL element, possible values for the type attribute are disc, square, and
circle. The default value depends on the level of nesting of the current list. These
values are case-insensitive.
How each value is presented depends on the user agent. User agents should
attempt to present a "disc" as a small filled-in circle, a "circle" as a small circle
outline, and a "square" as a small square outline.
A graphical user agent might render this as:
for the value "disc"
for the value "circle"
for the value "square"
For the OL element, possible values for the type attribute are summarized in the
table below (they are case-sensitive):
Type
Numbering style
1
arabic numbers
1, 2, 3, ...
a
lower alpha
a, b, c, ...
A
upper alpha
A, B, C, ...
i
lower roman
i, ii, iii, ...
I
upper roman
I, II, III, ...
Note that the type attribute is deprecated [p.38] and list styles should be handled
through style sheets.
For example, using CSS, one may specify that the style of numbers for list
elements in a numbered list should be lowercase roman numerals. In the excerpt
below, every OL element belonging to the class "withroman" will have roman
numerals in front of its list items.
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Lists in HTML documents
<STYLE type="text/css">
OL.withroman { list-style-type: lower-roman }
</STYLE>
<BODY>
<OL class="withroman">
<LI> Step one ...
<LI> Step two ...
</OL>
</BODY>
The rendering of a definition list also depends on the user agent. The example:
<DL>
<DT>Dweeb
<DD>young excitable person who may mature
into a <EM>Nerd</EM> or <EM>Geek</EM>
<DT>Hacker
<DD>a clever programmer
<DT>Nerd
<DD>technically bright but socially inept person
</DL>
might be rendered as follows:
Dweeb
young excitable person who may mature into a Nerd or Geek
Hacker
a clever programmer
Nerd
technically bright but socially inept person
10.4 The DIR and MENU elements
DIR and MENU are deprecated [p.38] .
See the Transitional DTD [p.288] for the formal definition.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
The DIR element was designed to be used for creating multicolumn directory lists.
The MENU element was designed to be used for single column menu lists. Both
elements have the same structure as UL, just different rendering. In practice, a user
agent will render a DIR or MENU list exactly as a UL list.
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We strongly recommend using UL instead of these elements.
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110
Tables in HTML documents
11 Tables
Contents
1. Introduction to tables
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2. Elements for constructing tables .
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1. The TABLE element .
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Table directionality .
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2. Table Captions: The CAPTION element .
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3. Row groups: the THEAD, TFOOT, and TBODY elements
4. Column groups: the COLGROUP and COL elements
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The COLGROUP element
The COL element .
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Calculating the number of columns in a table
Calculating the width of columns .
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5. Table rows: The TR element
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6. Table cells: The TH and TD elements
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Cells that span several rows or columns .
3. Table formatting by visual user agents
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1. Borders and rules .
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2. Horizontal and vertical alignment
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Inheritance of alignment specifications .
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3. Cell margins
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4. Table rendering by non-visual user agents
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1. Associating header information with data cells
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2. Categorizing cells .
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3. Algorithm to find heading information .
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5. Sample table
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11.1 Introduction to tables
The HTML table model allows authors to arrange data -- text, preformatted text,
images, links, forms, form fields, other tables, etc. -- into rows and columns of cells.
Each table may have an associated caption (see the CAPTION element) that
provides a short description of the table’s purpose. A longer description may also be
provided (via the summary attribute) for the benefit of people using speech or
Braille-based user agents.
Table rows [p.116] may be grouped into a head, foot, and body sections, (via the
THEAD, TFOOT and TBODY elements, respectively). Row groups convey additional
structural information and may be rendered by user agents in ways that emphasize
this structure. User agents may exploit the head/body/foot division to support
scrolling of body sections independently of the head and foot sections. When long
tables are printed, the head and foot information may be repeated on each page that
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contains table data.
Authors may also group columns [p.118] to provide additional structural
information that may be exploited by user agents. Furthermore, authors may declare
column properties at the start of a table definition (via the COLGROUP and COL
elements) in a way that enables user agents to render the table incrementally rather
than having to wait for all the table data to arrive before rendering.
Table cells [p.125] may either contain "header" information (see the TH element)
or "data" (see the TD element). Cells may span multiple rows and columns. The
HTML 4 table model allows authors to label each cell so that non-visual user agents
[p.136] may more easily communicate heading information about the cell to the user.
Not only do these mechanisms greatly assist users with visual disabilities, they make
it possible for multi-modal wireless browsers with limited display capabilities (e.g.,
Web-enabled pagers and phones) to handle tables.
Tables should not be used purely as a means to layout document content as this
may present problems when rendering to non-visual media. Additionally, when used
with graphics, these tables may force users to scroll horizontally to view a table
designed on a system with a larger display. To minimize these problems, authors
should use style sheets [p.183] to control layout rather than tables.
Note. This specification includes more detailed information about tables in
sections on table design rationale and implementation issues [p.342] .
Here’s a simple table that illustrates some of the features of the HTML table
model. The following table definition:
<TABLE border="1"
summary="This table gives some statistics about fruit
flies: average height and weight, and percentage
with red eyes (for both males and females).">
<CAPTION><EM>A test table with merged cells</EM></CAPTION>
<TR><TH rowspan="2"><TH colspan="2">Average
<TH rowspan="2">Red<BR>eyes
<TR><TH>height<TH>weight
<TR><TH>Males<TD>1.9<TD>0.003<TD>40%
<TR><TH>Females<TD>1.7<TD>0.002<TD>43%
</TABLE>
might be rendered something like this on a tty device:
A test table with merged cells
/-----------------------------------------\
|
|
Average
|
Red
|
|
|-------------------| eyes
|
|
| height | weight |
|
|-----------------------------------------|
| Males
| 1.9
| 0.003
|
40%
|
|-----------------------------------------|
| Females | 1.7
| 0.002
|
43%
|
\-----------------------------------------/
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or like this by a graphical user agent:
11.2 Elements for constructing tables
11.2.1 The TABLE element
<!ELEMENT TABLE - (CAPTION?, (COL*|COLGROUP*), THEAD?,
<!ATTLIST TABLE
-%attrs;
-summary
%Text;
#IMPLIED -width
%Length;
#IMPLIED -border
%Pixels;
#IMPLIED -frame
%TFrame;
#IMPLIED -rules
%TRules;
#IMPLIED -cellspacing %Length;
#IMPLIED -cellpadding %Length;
#IMPLIED ->
TFOOT?, TBODY+)>
table element -%coreattrs, %i18n, %events -purpose/structure for speech output-table width -controls frame width around table -which parts of frame to render -rulings between rows and cols -spacing between cells -spacing within cells --
Start tag: required, End tag: required
Attribute definitions
summary = text [p.50] [CS] [p.49]
This attribute provides a summary of the table’s purpose and structure for user
agents rendering to non-visual media such as speech and Braille.
align = left|center|right [CI] [p.49]
Deprecated. [p.38] This attribute specifies the position of the table with respect
to the document. Permitted values:
left: The table is to the left of the document.
center: The table is to the center of the document.
right: The table is to the right of the document.
width = length [p.52] [CN] [p.49]
This attribute specifies the desired width of the entire table and is intended for
visual user agents. When the value is a percentage value, the value is relative
to the user agent’s available horizontal space. In the absence of any width
specification, table width is determined by the user agent.
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Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
bgcolor (background color [p.195] )
frame, rules, border (borders and rules [p.130] )
cellspacing, cellpadding (cell margins [p.134] )
The TABLE element contains all other elements that specify caption, rows,
content, and formatting.
The following informative list describes what operations user agents may carry out
when rendering a table:
Make the table summary available to the user. Authors should provide a
summary of a table’s content and structure so that people using non-visual user
agents may better understand it.
Render the caption, if one is defined.
Render the table header, if one is specified. Render the table footer, if one is
specified. User agents must know where to render the header and footer. For
instance, if the output medium is paged, user agents may put the header at the
top of each page and the footer at the bottom. Similarly, if the user agent
provides a mechanism to scroll the rows, the header may appear at the top of
the scrolled area and the footer at the bottom.
Calculate the number of columns [p.121] in the table. Note that the number of
rows in a table is equal to the number of TR elements contained by the TABLE
element.
Group the columns according to any column group [p.118] specifications.
Render the cells, row by row and grouped in appropriate columns, between the
header and footer. Visual user agents should format the table [p.130] according
to HTML attributes and style sheet specification.
The HTML table model has been designed so that, with author assistance, user
agents may render tables incrementally (i.e., as table rows arrive) rather than having
to wait for all the data before beginning to render.
In order for a user agent to format a table in one pass, authors must tell the user
agent:
The number of columns in the table. Please consult the section on calculating
the number of columns in a table [p.121] for details on how to supply this
information.
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The widths of these columns. Please consult the section on calculating the width
of columns [p.122] for details on how to supply this information.
More precisely, a user agent may render a table in a single pass when the column
widths are specified using a combination of COLGROUP and COL elements. If any of
the columns are specified in relative or percentage terms (see the section on
calculating the width of columns [p.122] ), authors must also specify the width of the
table itself.
Table directionality
The directionality of a table is either the inherited directionality (the default is
left-to-right) or that specified by the dir attribute for the TABLE element.
For a left-to-right table, column zero is on the left side and row zero is at the top.
For a right-to-left table, column zero is on the right side and row zero is at the top.
When a user agent allots extra cells to a row (see the section on calculating the
number of columns in a table [p.121] ), extra row cells are added to the right of the
table for left-to-right tables and to the left side for right-to-left tables.
Note that TABLE is the only element on which dir reverses the visual order of the
columns; a single table row (TR) or a group of columns (COLGROUP) cannot be
independently reversed.
When set for the TABLE element, the dir attribute also affects the direction of text
within table cells (since the dir attribute is inherited by block-level elements).
To specify a right-to-left table, set the dir attribute as follows:
<TABLE dir="RTL">
...the rest of the table...
</TABLE>
The direction of text in individual cells can be changed by setting the dir attribute
in an element that defines the cell. Please consult the section on bidirectional text
[p.82] for more information on text direction issues.
11.2.2 Table Captions: The CAPTION element
<!ELEMENT CAPTION
- - (%inline;)*
<!ATTLIST CAPTION
%attrs;
>
-- table caption -->
-- %coreattrs, %i18n, %events --
Start tag: required, End tag: required
Attribute definitions
align = top|bottom|left|right [CI] [p.49]
Deprecated. [p.38] For visual user agents, this attribute specifies the position of
the caption with respect to the table. Possible values:
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top: The caption is at the top of the table. This is the default value.
bottom: The caption is at the bottom of the table.
left: The caption is at the left of the table.
right: The caption is at the right of the table.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
When present, the CAPTION element’s text should describe the nature of the
table. The CAPTION element is only permitted immediately after the TABLE start tag.
A TABLE element may only contain one CAPTION element.
Visual user agents allow sighted people to quickly grasp the structure of the table
from the headings as well as the caption. A consequence of this is that captions will
often be inadequate as a summary of the purpose and structure of the table from the
perspective of people relying on non-visual user agents.
Authors should therefore take care to provide additional information summarizing
the purpose and structure of the table using the summary attribute of the TABLE
element. This is especially important for tables without captions. Examples below
illustrate the use of the summary attribute.
Visual user agents should avoid clipping any part of the table including the
caption, unless a means is provided to access all parts, e.g., by horizontal or vertical
scrolling. We recommend that the caption text be wrapped to the same width as the
table. (See also the section on recommended layout algorithms [p.344] .)
11.2.3 Row groups: the THEAD, TFOOT, and TBODY elements
<!ELEMENT THEAD
<!ELEMENT TFOOT
- O (TR)+
- O (TR)+
-- table header -->
-- table footer -->
Start tag: required, End tag: optional
<!ELEMENT TBODY
O O (TR)+
-- table body -->
Start tag: optional, End tag: optional
<!ATTLIST (THEAD|TBODY|TFOOT)
%attrs;
%cellhalign;
%cellvalign;
>
24 Dec 1999 18:26
-----
table section -%coreattrs, %i18n, %events -horizontal alignment in cells -vertical alignment in cells --
116
Tables in HTML documents
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
align, char, charoff, valign (cell alignment [p.132] )
Table rows may be grouped into a table head, table foot, and one or more table
body sections, using the THEAD, TFOOT and TBODY elements, respectively. This
division enables user agents to support scrolling of table bodies independently of the
table head and foot. When long tables are printed, the table head and foot
information may be repeated on each page that contains table data.
The table head and table foot should contain information about the table’s
columns. The table body should contain rows of table data.
When present, each THEAD, TFOOT, and TBODY contains a row group. Each row
group must contain at least one row, defined by the TR element.
This example illustrates the order and structure of table heads, feet, and bodies.
<TABLE>
<THEAD>
<TR>
</THEAD>
<TFOOT>
<TR>
</TFOOT>
<TBODY>
<TR>
<TR>
</TBODY>
<TBODY>
<TR>
<TR>
<TR>
</TBODY>
</TABLE>
...header information...
...footer information...
...first row of block one data...
...second row of block one data...
...first row of block two data...
...second row of block two data...
...third row of block two data...
TFOOT must appear before TBODY within a TABLE definition so that user agents
can render the foot before receiving all of the (potentially numerous) rows of data.
The following summarizes which tags are required and which may be omitted:
The TBODY start tag is always required except when the table contains only one
table body and no table head or foot sections. The TBODY end tag may always
be safely omitted.
The start tags for THEAD and TFOOT are required when the table head and foot
sections are present respectively, but the corresponding end tags may always
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be safely omitted.
Conforming user agent parsers must obey these rules for reasons of backward
compatibility.
The table of the previous example could be shortened by removing certain end
tags, as in:
<TABLE>
<THEAD>
<TR>
<TFOOT>
<TR>
<TBODY>
<TR>
<TR>
<TBODY>
<TR>
<TR>
<TR>
</TABLE>
...header information...
...footer information...
...first row of block one data...
...second row of block one data...
...first row of block two data...
...second row of block two data...
...third row of block two data...
The THEAD, TFOOT, and TBODY sections must contain the same number of
columns.
11.2.4 Column groups: the COLGROUP and COL elements
Column groups allow authors to create structural divisions within a table. Authors
may highlight this structure through style sheets or HTML attributes (e.g., the rules
attribute for the TABLE element). For an example of the visual presentation of
column groups, please consult the sample table [p.143] .
A table may either contain a single implicit column group (no COLGROUP element
delimits the columns) or any number of explicit column groups (each delimited by an
instance of the COLGROUP element).
The COL element allows authors to share attributes among several columns
without implying any structural grouping. The "span" of the COL element is the
number of columns that will share the element’s attributes.
The COLGROUP element
<!ELEMENT COLGROUP - O (COL)*
<!ATTLIST COLGROUP
%attrs;
span
NUMBER
1
width
%MultiLength; #IMPLIED
%cellhalign;
%cellvalign;
>
-- table column group -->
------
%coreattrs, %i18n, %events -default number of columns in group -default width for enclosed COLs -horizontal alignment in cells -vertical alignment in cells --
Start tag: required, End tag: optional
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Attribute definitions
span = number [p.50] [CN] [p.49]
This attribute, which must be an integer > 0, specifies the number of columns in
a column group. Values mean the following:
In the absence of a span attribute, each COLGROUP defines a column
group containing one column.
If the span attribute is set to N > 0, the current COLGROUP element defines
a column group containing N columns.
User agents must ignore this attribute if the COLGROUP element contains one
or more COL elements.
width = multi-length [p.52] [CN] [p.49]
This attribute specifies a default width for each column in the current column
group. In addition to the standard pixel, percentage, and relative values, this
attribute allows the special form "0*" (zero asterisk) which means that the width
of the each column in the group should be the minimum width necessary to hold
the column’s contents. This implies that a column’s entire contents must be
known before its width may be correctly computed. Authors should be aware
that specifying "0*" will prevent visual user agents from rendering a table
incrementally.
This attribute is overridden for any column in the column group whose width
is specified via a COL element.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
align, char, charoff, valign (cell alignment [p.132] )
The COLGROUP element creates an explicit column group. The number of columns
in the column group may be specified in two, mutually exclusive ways:
1. The element’s span attribute (default value 1) specifies the number of columns
in the group.
2. Each COL element in the COLGROUP represents one or more columns in the
group.
The advantage of using the span attribute is that authors may group together
information about column widths. Thus, if a table contains forty columns, all of which
have a width of 20 pixels, it is easier to write:
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<COLGROUP span="40" width="20">
</COLGROUP>
than:
<COLGROUP>
<COL width="20">
<COL width="20">
...a total of forty COL elements...
</COLGROUP>
When it is necessary to single out a column (e.g., for style information, to specify
width information, etc.) within a group, authors must identify that column with a COL
element. Thus, to apply special style information to the last column of the previous
table, we single it out as follows:
<COLGROUP width="20">
<COL span="39">
<COL id="format-me-specially">
</COLGROUP>
The width attribute of the COLGROUP element is inherited by all 40 columns. The
first COL element refers to the first 39 columns (doing nothing special to them) and
the second one assigns an id value to the fortieth column so that style sheets may
refer to it.
The table in the following example contains two column groups. The first column
group contains 10 columns and the second contains 5 columns. The default width for
each column in the first column group is 50 pixels. The width of each column in the
second column group will be the minimum required for that column.
<TABLE>
<COLGROUP span="10" width="50">
<COLGROUP span="5" width="0*">
<THEAD>
<TR><TD> ...
</TABLE>
The COL element
<!ELEMENT COL
- O EMPTY
<!ATTLIST COL
%attrs;
span
NUMBER
1
width
%MultiLength; #IMPLIED
%cellhalign;
%cellvalign;
>
--------
table column -->
column groups and properties -%coreattrs, %i18n, %events -COL attributes affect N columns -column width specification -horizontal alignment in cells -vertical alignment in cells --
Start tag: required, End tag: forbidden
Attribute definitions
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Tables in HTML documents
span = number [p.50] [CN] [p.49]
This attribute, whose value must be an integer > 0, specifies the number of
columns "spanned" by the COL element; the COL element shares its attributes
with all the columns it spans. The default value for this attribute is 1 (i.e., the
COL element refers to a single column). If the span attribute is set to N > 1, the
current COL element shares its attributes with the next N-1 columns.
width = multi-length [p.52] [CN] [p.49]
This attribute specifies a default width for each column spanned by the current
COL element. It has the same meaning as the width attribute for the COLGROUP
element and overrides it.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
align, char, charoff, valign (cell alignment [p.132] )
The COL element allows authors to group together attribute specifications for table
columns. The COL does not group columns together structurally -- that is the role of
the COLGROUP element. COL elements are empty and serve only as a support for
attributes. They may appear inside or outside an explicit column group (i.e.,
COLGROUP element).
The width attribute for COL refers to the width of each column in the element’s
span.
Calculating the number of columns in a table
There are two ways to determine the number of columns in a table (in order of
precedence):
1. If the TABLE element contains any COLGROUP or COL elements, user agents
should calculate the number of columns by summing the following:
For each COL element, take the value of its span attribute (default value 1).
For each COLGROUP element containing at least one COL element, ignore
the span attribute for the COLGROUP element. For each COL element,
perform the calculation of step 1.
For each empty COLGROUP element, take the value of its span attribute
(default value 1).
2. Otherwise, if the TABLE element contains no COLGROUP or COL elements, user
agents should base the number of columns on what is required by the rows. The
number of columns is equal to the number of columns required by the row with
the most columns, including cells that span multiple columns. For any row that
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has fewer than this number of columns, the end of that row should be padded
with empty cells. The "end" of a row depends on the table directionality [p.115] .
It is an error if a table contains COLGROUP or COL elements and the two
calculations do not result in the same number of columns.
Once the user agent has calculated the number of columns in the table, it may
group them into column groups. [p.118]
For example, for each of the following tables, the two column calculation methods
should result in three columns. The first three tables may be rendered incrementally.
<TABLE>
<COLGROUP span="3"></COLGROUP>
<TR><TD> ...
...rows...
</TABLE>
<TABLE>
<COLGROUP>
<COL>
<COL span="2">
</COLGROUP>
<TR><TD> ...
...rows...
</TABLE>
<TABLE>
<COLGROUP>
<COL>
</COLGROUP>
<COLGROUP span="2">
<TR><TD> ...
...rows...
</TABLE>
<TABLE>
<TR>
<TD><TD><TD>
</TR>
</TABLE>
Calculating the width of columns
Authors may specify column widths in three ways:
Fixed
A fixed width specification is given in pixels (e.g., width="30"). A fixed-width
specification enables incremental rendering.
Percentage
A percentage specification (e.g., width="20%") is based on the percentage of
the horizontal space available to the table (between the current left and right
margins, including floats). Note that this space does not depend on the table
itself, and thus percentage specifications enable incremental rendering.
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Tables in HTML documents
Proportional
Proportional specifications (e.g., width="3*") refer to portions of the horizontal
space required by a table. If the table width is given a fixed value via the width
attribute of the TABLE element, user agents may render the table incrementally
even with proportional columns.
However, if the table does not have a fixed width, user agents must receive all
table data before they can determine the horizontal space required by the table.
Only then may this space be allotted to proportional columns.
If an author specifies no width information for a column, a user agent may not be
able to incrementally format the table since it must wait for the entire column of data
to arrive in order to allot an appropriate width.
If column widths prove to be too narrow for the contents of a particular table cell,
user agents may choose to reflow the table.
The table in this example contains six columns. The first one does not belong to
an explicit column group. The next three belong to the first explicit column group and
the last two belong to the second explicit column group. This table cannot be
formatted incrementally since it contains proportional column width specifications
and no value for the width attribute for the TABLE element.
Once the (visual) user agent has received the table’s data: the available horizontal
space will be alloted by the user agent as follows: First the user agent will allot 30
pixels to columns one and two. Then, the minimal space required for the third
column will be reserved. The remaining horizontal space will be divided into six
equal portions (since 2* + 1* + 3* = 6 portions). Column four (2*) will receive two of
these portions, column five (1*) will receive one, and column six (3*) will receive
three.
<TABLE>
<COLGROUP>
<COL width="30">
<COLGROUP>
<COL width="30">
<COL width="0*">
<COL width="2*">
<COLGROUP align="center">
<COL width="1*">
<COL width="3*" align="char" char=":">
<THEAD>
<TR><TD> ...
...rows...
</TABLE>
We have set the value of the align attribute in the third column group to "center".
All cells in every column in this group will inherit this value, but may override it. In
fact, the final COL does just that, by specifying that every cell in the column it
governs will be aligned along the ":" character.
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In the following table, the column width specifications allow the user agent to
format the table incrementally:
<TABLE width="200">
<COLGROUP span="10" width="15">
<COLGROUP width="*">
<COL id="penultimate-column">
<COL id="last-column">
<THEAD>
<TR><TD> ...
...rows...
</TABLE>
The first ten columns will be 15 pixels wide each. The last two columns will each
receive half of the remaining 50 pixels. Note that the COL elements appear only so
that an id value may be specified for the last two columns.
Note. Although the width attribute on the TABLE element is not deprecated,
authors are encouraged to use style sheets to specify table widths.
11.2.5 Table rows: The TR element
<!ELEMENT TR
<!ATTLIST TR
%attrs;
%cellhalign;
%cellvalign;
>
- O (TH|TD)+
------
table row -->
table row -%coreattrs, %i18n, %events -horizontal alignment in cells -vertical alignment in cells --
Start tag: required, End tag: optional
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
bgcolor (background color [p.195] )
align, char, charoff, valign (cell alignment [p.132] )
The TR elements acts as a container for a row of table cells. The end tag may be
omitted.
This sample table contains three rows, each begun by the TR element:
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<TABLE summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR> ...A header row...
<TR> ...First row of data...
<TR> ...Second row of data...
...the rest of the table...
</TABLE>
11.2.6 Table cells: The TH and TD elements
<!ELEMENT (TH|TD)
- O (%flow;)*
-- table header cell, table data cell-->
<!-- Scope is simpler than headers attribute for common tables -->
<!ENTITY % Scope "(row|col|rowgroup|colgroup)">
<!-- TH is for headers, TD for data, but for cells acting as both use TD -->
<!ATTLIST (TH|TD)
-- header or data cell -%attrs;
-- %coreattrs, %i18n, %events -abbr
%Text;
#IMPLIED -- abbreviation for header cell -axis
CDATA
#IMPLIED -- comma-separated list of related headers-headers
IDREFS
#IMPLIED -- list of id’s for header cells -scope
%Scope;
#IMPLIED -- scope covered by header cells -rowspan
NUMBER
1
-- number of rows spanned by cell -colspan
NUMBER
1
-- number of cols spanned by cell -%cellhalign;
-- horizontal alignment in cells -%cellvalign;
-- vertical alignment in cells ->
Start tag: required, End tag: optional
Attribute definitions
headers = idrefs [p.50] [CS] [p.49]
This attribute specifies the list of header cells that provide header information for
the current data cell. The value of this attribute is a space-separated list of cell
names; those cells must be named by setting their id attribute. Authors
generally use the headers attribute to help non-visual user agents render
header information about data cells (e.g., header information is spoken prior to
the cell data), but the attribute may also be used in conjunction with style
sheets. See also the scope attribute.
scope = scope-name [CI] [p.49]
This attribute specifies the set of data cells for which the current header cell
provides header information. This attribute may be used in place of the
headers attribute, particularly for simple tables. When specified, this attribute
must have one of the following values:
row: The current cell provides header information for the rest of the row
that contains it (see also the section on table directionality [p.115] ).
col: The current cell provides header information for the rest of the column
that contains it.
rowgroup: The header cell provides header information for the rest of the
row group [p.116] that contains it.
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colgroup: The header cell provides header information for the rest of the
column group [p.118] that contains it.
abbr = text [p.50] [CS] [p.49]
This attribute should be used to provide an abbreviated form of the cell’s
content, and may be rendered by user agents when appropriate in place of the
cell’s content. Abbreviated names should be short since user agents may render
them repeatedly. For instance, speech synthesizers may render the abbreviated
headers relating to a particular cell before rendering that cell’s content.
axis = cdata [p.50] [CI] [p.49]
This attribute may be used to place a cell into conceptual categories that can be
considered to form axes in an n-dimensional space. User agents may give users
access to these categories (e.g., the user may query the user agent for all cells
that belong to certain categories, the user agent may present a table in the form
of a table of contents, etc.). Please consult the section on categorizing cells
[p.139] for more information. The value of this attribute is a comma-separated
list of category names.
rowspan = number [p.50] [CN] [p.49]
This attribute specifies the number of rows spanned by the current cell. The
default value of this attribute is one ("1"). The value zero ("0") means that the
cell spans all rows from the current row to the last row of the table section
(THEAD, TBODY, or TFOOT) in which the cell is defined.
colspan = number [p.50] [CN] [p.49]
This attribute specifies the number of columns spanned by the current cell. The
default value of this attribute is one ("1"). The value zero ("0") means that the
cell spans all columns from the current column to the last column of the column
group (COLGROUP) in which the cell is defined.
nowrap [CI] [p.49]
Deprecated. [p.38] When present, this boolean attribute tells visual user agents
to disable automatic text wrapping for this cell. Style sheets [p.183] should be
used instead of this attribute to achieve wrapping effects. Note. if used
carelessly, this attribute may result in excessively wide cells.
width = length [p.52] [CN] [p.49]
Deprecated. [p.38] This attribute supplies user agents with a recommended cell
width.
height = length [p.52] [CN] [p.49]
Deprecated. [p.38] This attribute supplies user agents with a recommended cell
height.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
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bgcolor (background color [p.195] )
align, char, charoff, valign (cell alignment [p.132] )
Table cells may contain two types of information: header information and data.
This distinction enables user agents to render header and data cells distinctly, even
in the absence of style sheets. For example, visual user agents may present header
cell text with a bold font. Speech synthesizers may render header information with a
distinct voice inflection.
The TH element defines a cell that contains header information. User agents have
two pieces of header information available: the contents of the TH element and the
value of the abbr attribute. User agents must render either the contents of the cell or
the value of the abbr attribute. For visual media, the latter may be appropriate when
there is insufficient space to render the full contents of the cell. For non-visual media
abbr may be used as an abbreviation for table headers when these are rendered
along with the contents of the cells to which they apply.
The headers and scope attributes also allow authors to help non-visual user
agents process header information. Please consult the section on labeling cells for
non-visual user agents [p.136] for information and examples.
The TD element defines a cell that contains data.
Cells may be empty (i.e., contain no data).
For example, the following table contains four columns of data, each headed by a
column description.
<TABLE summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH>Name</TH>
<TH>Cups</TH>
<TH>Type of Coffee</TH>
<TH>Sugar?</TH>
<TR>
<TD>T. Sexton</TD>
<TD>10</TD>
<TD>Espresso</TD>
<TD>No</TD>
<TR>
<TD>J. Dinnen</TD>
<TD>5</TD>
<TD>Decaf</TD>
<TD>Yes</TD>
</TABLE>
A user agent rendering to a tty device might display this as follows:
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Name
T. Sexton
J. Dinnen
Cups
10
5
Type of Coffee
Espresso
Decaf
Sugar?
No
Yes
Cells that span several rows or columns
Cells may span several rows or columns. The number of rows or columns spanned
by a cell is set by the rowspan and colspan attributes for the TH and TD elements.
In this table definition, we specify that the cell in row four, column two should span
a total of three columns, including the current column.
<TABLE border="1">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR><TH>Name<TH>Cups<TH>Type of Coffee<TH>Sugar?
<TR><TD>T. Sexton<TD>10<TD>Espresso<TD>No
<TR><TD>J. Dinnen<TD>5<TD>Decaf<TD>Yes
<TR><TD>A. Soria<TD colspan="3"><em>Not available</em>
</TABLE>
This table might be rendered on a tty device by a visual user agent as follows:
Cups of coffee consumed by each senator
-------------------------------------|
Name |Cups|Type of Coffee|Sugar?|
-------------------------------------|T. Sexton|10 |Espresso
|No
|
-------------------------------------|J. Dinnen|5
|Decaf
|Yes
|
-------------------------------------|A. Soria |Not available
|
--------------------------------------
The next example illustrates (with the help of table borders) how cell definitions
that span more than one row or column affect the definition of later cells. Consider
the following table definition:
<TABLE border="1">
<TR><TD>1 <TD rowspan="2">2 <TD>3
<TR><TD>4 <TD>6
<TR><TD>7 <TD>8 <TD>9
</TABLE>
As cell "2" spans the first and second rows, the definition of the second row will
take it into account. Thus, the second TD in row two actually defines the row’s third
cell. Visually, the table might be rendered to a tty device as:
------------| 1 | 2 | 3 |
----|
|---| 4 |
| 6 |
----|---|---| 7 | 8 | 9 |
-------------
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while a graphical user agent might render this as:
Note that if the TD defining cell "6" had been omitted, an extra empty cell would
have been added by the user agent to complete the row.
Similarly, in the following table definition:
<TABLE border="1">
<TR><TD>1 <TD>2 <TD>3
<TR><TD colspan="2">4 <TD>6
<TR><TD>7 <TD>8 <TD>9
</TABLE>
cell "4" spans two columns, so the second TD in the row actually defines the third
cell ("6"):
------------| 1 | 2 | 3 |
--------|---| 4
| 6 |
--------|---| 7 | 8 | 9 |
-------------
A graphical user agent might render this as:
Defining overlapping cells is an error. User agents may vary in how they handle
this error (e.g., rendering may vary).
The following illegal example illustrates how one might create overlapping cells. In
this table, cell "5" spans two rows and cell "7" spans two columns, so there is overlap
in the cell between "7" and "9":
<TABLE border="1">
<TR><TD>1 <TD>2 <TD>3
<TR><TD>4 <TD rowspan="2">5 <TD>6
<TR><TD colspan="2">7 <TD>9
</TABLE>
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11.3 Table formatting by visual user agents
Note. The following sections describe the HTML table attributes that concern visual
formatting. When this specification was first published in 1997, [CSS1] [p.353] did
not offer mechanisms to control all aspects of visual table formatting. Since then,
[CSS2] [p.355] has added properties to allow visual formatting of tables.
HTML 4 includes mechanisms to control:
border styles [p.130]
horizontal and vertical alignment [p.132] of cell contents
and cell margins [p.134]
11.3.1 Borders and rules
The following attributes affect a table’s external frame and internal rules.
Attribute definitions
frame = void|above|below|hsides|lhs|rhs|vsides|box|border [CI]
[p.49]
This attribute specifies which sides of the frame surrounding a table will be
visible. Possible values:
void: No sides. This is the default value.
above: The top side only.
below: The bottom side only.
hsides: The top and bottom sides only.
vsides: The right and left sides only.
lhs: The left-hand side only.
rhs: The right-hand side only.
box: All four sides.
border: All four sides.
rules = none|groups|rows|cols|all [CI] [p.49]
This attribute specifies which rules will appear between cells within a table. The
rendering of rules is user agent dependent. Possible values:
none: No rules. This is the default value.
groups: Rules will appear between row groups (see THEAD, TFOOT, and
TBODY) and column groups (see COLGROUP and COL) only.
rows: Rules will appear between rows only.
cols: Rules will appear between columns only.
all: Rules will appear between all rows and columns.
border = pixels [p.52] [CN] [p.49]
This attributes specifies the width (in pixels only) of the frame around a table
(see the Note below for more information about this attribute).
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To help distinguish the cells of a table, we can set the border attribute of the
TABLE element. Consider a previous example:
<TABLE border="1"
summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH>Name</TH>
<TH>Cups</TH>
<TH>Type of Coffee</TH>
<TH>Sugar?</TH>
<TR>
<TD>T. Sexton</TD>
<TD>10</TD>
<TD>Espresso</TD>
<TD>No</TD>
<TR>
<TD>J. Dinnen</TD>
<TD>5</TD>
<TD>Decaf</TD>
<TD>Yes</TD>
</TABLE>
In the following example, the user agent should show borders five pixels thick on
the left-hand and right-hand sides of the table, with rules drawn between each
column.
<TABLE border="5" frame="vsides" rules="cols">
<TR> <TD>1 <TD>2 <TD>3
<TR> <TD>4 <TD>5 <TD>6
<TR> <TD>7 <TD>8 <TD>9
</TABLE>
The following settings should be observed by user agents for backwards
compatibility.
Setting border="0" implies frame="void" and, unless otherwise specified,
rules="none".
Other values of border imply frame="border" and, unless otherwise specified,
rules="all".
The value "border" in the start tag of the TABLE element should be interpreted
as the value of the frame attribute. It implies rules="all" and some default
(non-zero) value for the border attribute.
For example, the following definitions are equivalent:
<TABLE border="2">
<TABLE border="2" frame="border" rules="all">
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as are the following:
<TABLE border>
<TABLE frame="border" rules="all">
Note. The border attribute also defines the border behavior for the OBJECT and
IMG elements, but takes different values for those elements.
11.3.2 Horizontal and vertical alignment
The following attributes may be set for different table elements (see their definitions).
<!-- horizontal alignment attributes for cell contents -->
<!ENTITY % cellhalign
"align
(left|center|right|justify|char) #IMPLIED
char
%Character;
#IMPLIED -- alignment char, e.g. char=’:’ -charoff
%Length;
#IMPLIED -- offset for alignment char --"
>
<!-- vertical alignment attributes for cell contents -->
<!ENTITY % cellvalign
"valign
(top|middle|bottom|baseline) #IMPLIED"
>
Attribute definitions
align = left|center|right|justify|char [CI] [p.49]
This attribute specifies the alignment of data and the justification of text in a cell.
Possible values:
left: Left-flush data/Left-justify text. This is the default value for table
data.
center: Center data/Center-justify text. This is the default value for table
headers.
right: Right-flush data/Right-justify text.
justify: Double-justify text.
char: Align text around a specific character. If a user agent doesn’t
support character alignment, behavior in the presence of this value is
unspecified.
valign = top|middle|bottom|baseline [CI] [p.49]
This attribute specifies the vertical position of data within a cell. Possible values:
top: Cell data is flush with the top of the cell.
middle: Cell data is centered vertically within the cell. This is the default
value.
bottom: Cell data is flush with the bottom of the cell.
baseline: All cells in the same row as a cell whose valign attribute has
this value should have their textual data positioned so that the first text line
occurs on a baseline common to all cells in the row. This constraint does
not apply to subsequent text lines in these cells.
char = character [p.53] [CN] [p.49]
This attribute specifies a single character within a text fragment to act as an axis
for alignment. The default value for this attribute is the decimal point character
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for the current language as set by the lang attribute (e.g., the period (".") in
English and the comma (",") in French). User agents are not required to support
this attribute.
charoff = length [p.52] [CN] [p.49]
When present, this attribute specifies the offset to the first occurrence of the
alignment character on each line. If a line doesn’t include the alignment
character, it should be horizontally shifted to end at the alignment position.
When charoff is used to set the offset of an alignment character, the
direction of offset is determined by the current text direction (set by the dir
attribute). In left-to-right texts (the default), offset is from the left margin. In
right-to-left texts, offset is from the right margin. User agents are not required to
support this attribute.
The table in this example aligns a row of currency values along a decimal point.
We set the alignment character to "." explicitly.
<TABLE border="1">
<COLGROUP>
<COL><COL align="char" char=".">
<THEAD>
<TR><TH>Vegetable <TH>Cost per kilo
<TBODY>
<TR><TD>Lettuce
<TD>$1
<TR><TD>Silver carrots <TD>$10.50
<TR><TD>Golden turnips <TD>$100.30
</TABLE>
The formatted table may resemble the following:
-----------------------------|
Vegetable |Cost per kilo|
|--------------|-------------|
|Lettuce
|
$1
|
|--------------|-------------|
|Silver carrots|
$10.50|
|--------------|-------------|
|Golden turnips|
$100.30|
------------------------------
When the contents of a cell contain more than one instance of the alignment
character specified by char and the contents wrap, user agent behavior is
undefined. Authors should therefore be attentive in their use of char.
Note. Visual user agents typically render TH elements vertically and horizontally
centered within the cell and with a bold font weight.
Inheritance of alignment specifications
The alignment of cell contents can be specified on a cell by cell basis, or inherited
from enclosing elements, such as the row, column or the table itself.
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The order of precedence (from highest to lowest) for the attributes align, char,
and charoff is the following:
1. An alignment attribute set on an element within a cell’s data (e.g., P).
2. An alignment attribute set on a cell (TH and TD).
3. An alignment attribute set on a column grouping element (COL and COLGROUP).
When a cell is part of a multi-column span, the alignment property is inherited
from the cell definition at the beginning of the span.
4. An alignment attribute set on a row or row grouping element (TR, THEAD,
TFOOT, and TBODY). When a cell is part of a multi-row span, the alignment
property is inherited from the cell definition at the beginning of the span.
5. An alignment attribute set on the table (TABLE).
6. The default alignment value.
The order of precedence (from highest to lowest) for the attribute valign (as well
as the other inherited attributes lang, dir, and style) is the following:
1. An attribute set on an element within a cell’s data (e.g., P).
2. An attribute set on a cell (TH and TD).
3. An attribute set on a row or row grouping element (TR, THEAD, TFOOT, and
TBODY). When a cell is part of a multi-row span, the attribute value is inherited
from the cell definition at the beginning of the span.
4. An attribute set on a column grouping element (COL and COLGROUP). When a
cell is part of a multi-column span, the attribute value is inherited from the cell
definition at the beginning of the span.
5. An attribute set on the table (TABLE).
6. The default attribute value.
Furthermore, when rendering cells, horizontal alignment is determined by columns
in preference to rows, while for vertical alignment, rows are given preference over
columns.
The default alignment for cells depends on the user agent. However, user agents
should substitute the default attribute for the current directionality (i.e., not just "left"
in all cases).
User agents that do not support the "justify" value of the align attribute should
use the value of the inherited directionality in its place.
Note. Note that a cell may inherit an attribute not from its parent but from the first cell
in a span. This is an exception to the general attribute inheritance rules.
11.3.3 Cell margins
Attribute definitions
cellspacing = length [p.52] [CN] [p.49]
This attribute specifies how much space the user agent should leave between
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the left side of the table and the left-hand side of the leftmost column, the top of
the table and the top side of the topmost row, and so on for the right and bottom
of the table. The attribute also specifies the amount of space to leave between
cells.
cellpadding = length [p.52] [CN] [p.49]
This attribute specifies the amount of space between the border of the cell and
its contents. If the value of this attribute is a pixel length, all four margins should
be this distance from the contents. If the value of the attribute is a percentage
length, the top and bottom margins should be equally separated from the
content based on a percentage of the available vertical space, and the left and
right margins should be equally separated from the content based on a
percentage of the available horizontal space.
These two attributes control spacing between and within cells. The following
illustration explains how they relate:
In the following example, the cellspacing attribute specifies that cells should be
separated from each other and from the table frame by twenty pixels. The
cellpadding attribute specifies that the top margin of the cell and the bottom
margin of the cell will each be separated from the cell’s contents by 10% of the
available vertical space (the total being 20%). Similarly, the left margin of the cell
and the right margin of the cell will each be separated from the cell’s contents by
10% of the available horizontal space (the total being 20%).
<TABLE cellspacing="20" cellpadding="20%">
<TR> <TD>Data1 <TD>Data2 <TD>Data3
</TABLE>
If a table or given column has a fixed width, cellspacing and cellpadding
may demand more space than assigned. User agents may give these attributes
precedence over the width attribute when a conflict occurs, but are not required to.
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11.4 Table rendering by non-visual user agents
11.4.1 Associating header information with data cells
Non-visual user agents such as speech synthesizers and Braille-based devices may
use the following TD and TH element attributes to render table cells more intuitively:
For a given data cell, the headers attribute lists which cells provide pertinent
header information. For this purpose, each header cell must be named using the
id attribute. Note that it’s not always possible to make a clean division of cells
into headers or data. You should use the TD element for such cells together with
the id or scope attributes as appropriate.
For a given header cell, the scope attribute tells the user agent the data cells
for which this header provides information. Authors may choose to use this
attribute instead of headers according to which is more convenient; the two
attributes fulfill the same function. The headers attribute is generally needed
when headers are placed in irregular positions with respect to the data they
apply to.
The abbr attribute specifies an abbreviated header for header cells so that user
agents may render header information more rapidly.
In the following example, we assign header information to cells by setting the
headers attribute. Each cell in the same column refers to the same header cell (via
the id attribute).
<TABLE border="1"
summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH id="t1">Name</TH>
<TH id="t2">Cups</TH>
<TH id="t3" abbr="Type">Type of Coffee</TH>
<TH id="t4">Sugar?</TH>
<TR>
<TD headers="t1">T. Sexton</TD>
<TD headers="t2">10</TD>
<TD headers="t3">Espresso</TD>
<TD headers="t4">No</TD>
<TR>
<TD headers="t1">J. Dinnen</TD>
<TD headers="t2">5</TD>
<TD headers="t3">Decaf</TD>
<TD headers="t4">Yes</TD>
</TABLE>
A speech synthesizer might render this table as follows:
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Caption: Cups of coffee consumed by each senator
Summary: This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.
Name: T. Sexton,
Cups: 10,
Type: Espresso,
Sugar: No
Name: J. Dinnen,
Cups: 5,
Type: Decaf,
Sugar: Yes
Note how the header "Type of Coffee" is abbreviated to "Type" using the abbr
attribute.
Here is the same example substituting the scope attribute for the headers
attribute. Note the value "col" for the scope attribute, meaning "all cells in the
current column":
<TABLE border="1"
summary="This table charts the number of cups
of coffee consumed by each senator, the type
of coffee (decaf or regular), and whether
taken with sugar.">
<CAPTION>Cups of coffee consumed by each senator</CAPTION>
<TR>
<TH scope="col">Name</TH>
<TH scope="col">Cups</TH>
<TH scope="col" abbr="Type">Type of Coffee</TH>
<TH scope="col">Sugar?</TH>
<TR>
<TD>T. Sexton</TD>
<TD>10</TD>
<TD>Espresso</TD>
<TD>No</TD>
<TR>
<TD>J. Dinnen</TD>
<TD>5</TD>
<TD>Decaf</TD>
<TD>Yes</TD>
</TABLE>
Here’s a somewhat more complex example illustrating other values for the scope
attribute:
<TABLE border="1" cellpadding="5" cellspacing="2"
summary="History courses offered in the community of
Bath arranged by course name, tutor, summary,
code, and fee">
<TR>
<TH colspan="5" scope="colgroup">Community Courses -- Bath Autumn 1997</TH>
</TR>
<TR>
<TH scope="col" abbr="Name">Course Name</TH>
<TH scope="col" abbr="Tutor">Course Tutor</TH>
<TH scope="col">Summary</TH>
<TH scope="col">Code</TH>
<TH scope="col">Fee</TH>
</TR>
<TR>
<TD scope="row">After the Civil War</TD>
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<TD>Dr. John Wroughton</TD>
<TD>
The course will examine the turbulent years in England
after 1646. <EM>6 weekly meetings starting Monday 13th
October.</EM>
</TD>
<TD>H27</TD>
<TD>&pound;32</TD>
</TR>
<TR>
<TD scope="row">An Introduction to Anglo-Saxon England</TD>
<TD>Mark Cottle</TD>
<TD>
One day course introducing the early medieval
period reconstruction the Anglo-Saxons and
their society. <EM>Saturday 18th October.</EM>
</TD>
<TD>H28</TD>
<TD>&pound;18</TD>
</TR>
<TR>
<TD scope="row">The Glory that was Greece</TD>
<TD>Valerie Lorenz</TD>
<TD>
Birthplace of democracy, philosophy, heartland of theater, home of
argument. The Romans may have done it but the Greeks did it
first. <EM>Saturday day school 25th October 1997</EM>
</TD>
<TD>H30</TD>
<TD>&pound;18</TD>
</TR>
</TABLE>
A graphical user agent might render this as:
Note the use of the scope attribute with the "row" value. Although the first cell in
each row contains data, not header information, the scope attribute makes the data
cell behave like a row header cell. This allows speech synthesizers to provide the
relevant course name upon request or to state it immediately before each cell’s
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content.
11.4.2 Categorizing cells
Users browsing a table with a speech-based user agent may wish to hear an
explanation of a cell’s contents in addition to the contents themselves. One way the
user might provide an explanation is by speaking associated header information
before speaking the data cell’s contents (see the section on associating header
information with data cells [p.136] ).
Users may also want information about more than one cell, in which case header
information provided at the cell level (by headers, scope, and abbr) may not
provide adequate context. Consider the following table, which classifies expenses for
meals, hotels, and transport in two locations (San Jose and Seattle) over several
days:
Users might want to extract information from the table in the form of queries:
"What did I spend for all my meals?"
"What did I spend for meals on 25 August?"
"What did I spend for all expenses in San Jose?"
Each query involves a computation by the user agent that may involve zero or
more cells. In order to determine, for example, the costs of meals on 25 August, the
user agent must know which table cells refer to "Meals" (all of them) and which refer
to "Dates" (specifically, 25 August), and find the intersection of the two sets.
To accommodate this type of query, the HTML 4 table model allows authors to
place cell headers and data into categories. For example, for the travel expense
table, an author could group the header cells "San Jose" and "Seattle" into the
category "Location", the headers "Meals", "Hotels", and "Transport" in the category
"Expenses", and the four days into the category "Date". The previous three
questions would then have the following meanings:
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"What did I spend for all my meals?" means "What are all the data cells in the
"Expenses=Meals" category?
"What did I spend for meals on 25 August?" means "What are all the data cells
in the "Expenses=Meals" and "Date=Aug-25-1997" categories?
"What did I spend for all expenses in San Jose?" means "What are all the data
cells in the "Expenses=Meals, Hotels, Transport" and "Location=San Jose"
categories?
Authors categorize a header or data cell by setting the axis attribute for the cell.
For instance, in the travel expense table, the cell containing the information "San
Jose" could be placed in the "Location" category as follows:
<TH id="a6" axis="location">San Jose</TH>
Any cell containing information related to "San Jose" should refer to this header
cell via either the headers or the scope attribute. Thus, meal expenses for
25-Aug-1997 should be marked up to refer to id attribute (whose value here is "a6")
of the "San Jose" header cell:
<TD headers="a6">37.74</TD>
Each headers attribute provides a list of id references. Authors may thus
categorize a given cell in any number of ways (or, along any number of "headers",
hence the name).
Below we mark up the travel expense table with category information:
<TABLE border="1"
summary="This table summarizes travel expenses
incurred during August trips to
San Jose and Seattle">
<CAPTION>
Travel Expense Report
</CAPTION>
<TR>
<TH></TH>
<TH id="a2" axis="expenses">Meals</TH>
<TH id="a3" axis="expenses">Hotels</TH>
<TH id="a4" axis="expenses">Transport</TH>
<TD>subtotals</TD>
</TR>
<TR>
<TH id="a6" axis="location">San Jose</TH>
<TH></TH>
<TH></TH>
<TH></TH>
<TD></TD>
</TR>
<TR>
<TD id="a7" axis="date">25-Aug-97</TD>
<TD headers="a6 a7 a2">37.74</TD>
<TD headers="a6 a7 a3">112.00</TD>
<TD headers="a6 a7 a4">45.00</TD>
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Tables in HTML documents
<TD></TD>
</TR>
<TR>
<TD id="a8" axis="date">26-Aug-97</TD>
<TD headers="a6 a8 a2">27.28</TD>
<TD headers="a6 a8 a3">112.00</TD>
<TD headers="a6 a8 a4">45.00</TD>
<TD></TD>
</TR>
<TR>
<TD>subtotals</TD>
<TD>65.02</TD>
<TD>224.00</TD>
<TD>90.00</TD>
<TD>379.02</TD>
</TR>
<TR>
<TH id="a10" axis="location">Seattle</TH>
<TH></TH>
<TH></TH>
<TH></TH>
<TD></TD>
</TR>
<TR>
<TD id="a11" axis="date">27-Aug-97</TD>
<TD headers="a10 a11 a2">96.25</TD>
<TD headers="a10 a11 a3">109.00</TD>
<TD headers="a10 a11 a4">36.00</TD>
<TD></TD>
</TR>
<TR>
<TD id="a12" axis="date">28-Aug-97</TD>
<TD headers="a10 a12 a2">35.00</TD>
<TD headers="a10 a12 a3">109.00</TD>
<TD headers="a10 a12 a4">36.00</TD>
<TD></TD>
</TR>
<TR>
<TD>subtotals</TD>
<TD>131.25</TD>
<TD>218.00</TD>
<TD>72.00</TD>
<TD>421.25</TD>
</TR>
<TR>
<TH>Totals</TH>
<TD>196.27</TD>
<TD>442.00</TD>
<TD>162.00</TD>
<TD>800.27</TD>
</TR>
</TABLE>
Note that marking up the table this way also allows user agents to avoid confusing
the user with unwanted information. For instance, if a speech synthesizer were to
speak all of the figures in the "Meals" column of this table in response to the query
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"What were all my meal expenses?", a user would not be able to distinguish a day’s
expenses from subtotals or totals. By carefully categorizing cell data, authors allow
user agents to make important semantic distinctions when rendering.
Of course, there is no limit to how authors may categorize information in a table. In
the travel expense table, for example, we could add the additional categories
"subtotals" and "totals".
This specification does not require user agents to handle information provided by
the axis attribute, nor does it make any recommendations about how user agents
may present axis information to users or how users may query the user agent
about this information.
However, user agents, particularly speech synthesizers, may want to factor out
information common to several cells that are the result of a query. For instance, if the
user asks "What did I spend for meals in San Jose?", the user agent would first
determine the cells in question (25-Aug-1997: 37.74, 26-Aug-1997:27.28), then
render this information. A user agent speaking this information might read it:
Location: San Jose. Date: 25-Aug-1997. Expenses, Meals: 37.74
Location: San Jose. Date: 26-Aug-1997. Expenses, Meals: 27.28
or, more compactly:
San Jose, 25-Aug-1997, Meals: 37.74
San Jose, 26-Aug-1997, Meals: 27.28
An even more economical rendering would factor the common information and
reorder it:
San Jose, Meals, 25-Aug-1997: 37.74
26-Aug-1997: 27.28
User agents that support this type of rendering should allow user agents a means
to customize rendering (e.g., through style sheets).
11.4.3 Algorithm to find heading information
In the absence of header information from either the scope or headers attribute,
user agents may construct header information according to the following algorithm.
The goal of the algorithm is to find an ordered list of headers. (In the following
description of the algorithm the table directionality [p.115] is assumed to be
left-to-right.)
First, search left from the cell’s position to find row header cells. Then search
upwards to find column header cells. The search in a given direction stops when
the edge of the table is reached or when a data cell is found after a header cell.
Row headers are inserted into the list in the order they appear in the table. For
left-to-right tables, headers are inserted from left to right.
Column headers are inserted after row headers, in the order they appear in the
table, from top to bottom.
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If a header cell has the headers attribute set, then the headers referenced by
this attribute are inserted into the list and the search stops for the current
direction.
TD cells that set the axis attribute are also treated as header cells.
11.5 Sample table
This sample illustrates grouped rows and columns. The example is adapted from
"Developing International Software", by Nadine Kano.
In "ascii art", the following table:
<TABLE border="2" frame="hsides" rules="groups"
summary="Code page support in different versions
of MS Windows.">
<CAPTION>CODE-PAGE SUPPORT IN MICROSOFT WINDOWS</CAPTION>
<COLGROUP align="center">
<COLGROUP align="left">
<COLGROUP align="center" span="2">
<COLGROUP align="center" span="3">
<THEAD valign="top">
<TR>
<TH>Code-Page<BR>ID
<TH>Name
<TH>ACP
<TH>OEMCP
<TH>Windows<BR>NT 3.1
<TH>Windows<BR>NT 3.51
<TH>Windows<BR>95
<TBODY>
<TR><TD>1200<TD>Unicode (BMP of ISO/IEC-10646)<TD><TD><TD>X<TD>X<TD>*
<TR><TD>1250<TD>Windows 3.1 Eastern European<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1251<TD>Windows 3.1 Cyrillic<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1252<TD>Windows 3.1 US (ANSI)<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1253<TD>Windows 3.1 Greek<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1254<TD>Windows 3.1 Turkish<TD>X<TD><TD>X<TD>X<TD>X
<TR><TD>1255<TD>Hebrew<TD>X<TD><TD><TD><TD>X
<TR><TD>1256<TD>Arabic<TD>X<TD><TD><TD><TD>X
<TR><TD>1257<TD>Baltic<TD>X<TD><TD><TD><TD>X
<TR><TD>1361<TD>Korean (Johab)<TD>X<TD><TD><TD>**<TD>X
<TBODY>
<TR><TD>437<TD>MS-DOS United States<TD><TD>X<TD>X<TD>X<TD>X
<TR><TD>708<TD>Arabic (ASMO 708)<TD><TD>X<TD><TD><TD>X
<TR><TD>709<TD>Arabic (ASMO 449+, BCON V4)<TD><TD>X<TD><TD><TD>X
<TR><TD>710<TD>Arabic (Transparent Arabic)<TD><TD>X<TD><TD><TD>X
<TR><TD>720<TD>Arabic (Transparent ASMO)<TD><TD>X<TD><TD><TD>X
</TABLE>
would be rendered something like this:
CODE-PAGE SUPPORT IN MICROSOFT WINDOWS
===============================================================================
Code-Page | Name
| ACP OEMCP | Windows Windows Windows
ID
|
|
| NT 3.1 NT 3.51
95
-------------------------------------------------------------------------------
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1200
| Unicode (BMP of ISO 10646)
|
|
X
X
*
1250
| Windows 3.1 Eastern European | X
|
X
X
X
1251
| Windows 3.1 Cyrillic
| X
|
X
X
X
1252
| Windows 3.1 US (ANSI)
| X
|
X
X
X
1253
| Windows 3.1 Greek
| X
|
X
X
X
1254
| Windows 3.1 Turkish
| X
|
X
X
X
1255
| Hebrew
| X
|
X
1256
| Arabic
| X
|
X
1257
| Baltic
| X
|
X
1361
| Korean (Johab)
| X
|
**
X
------------------------------------------------------------------------------437
| MS-DOS United States
|
X
|
X
X
X
708
| Arabic (ASMO 708)
|
X
|
X
709
| Arabic (ASMO 449+, BCON V4) |
X
|
X
710
| Arabic (Transparent Arabic) |
X
|
X
720
| Arabic (Transparent ASMO)
|
X
|
X
===============================================================================
A graphical user agent might render this as:
This example illustrates how COLGROUP can be used to group columns and set the
default column alignment. Similarly, TBODY is used to group rows. The frame and
rules attributes tell the user agent which borders and rules to render.
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12 Links
Contents
1. Introduction to links and anchors .
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4. Unavailable and unidentifiable resources
3. Document relationships: the LINK element
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12.1 Introduction to links and anchors
HTML offers many of the conventional publishing idioms for rich text and structured
documents, but what separates it from most other markup languages is its features
for hypertext and interactive documents. This section introduces the link (or
hyperlink, or Web link), the basic hypertext construct. A link is a connection from one
Web resource to another. Although a simple concept, the link has been one of the
primary forces driving the success of the Web.
A link has two ends -- called anchors -- and a direction. The link starts at the
"source" anchor and points to the "destination" anchor, which may be any Web
resource (e.g., an image, a video clip, a sound bite, a program, an HTML document,
an element within an HTML document, etc.).
12.1.1 Visiting a linked resource
The default behavior associated with a link is the retrieval of another Web resource.
This behavior is commonly and implicitly obtained by selecting the link (e.g., by
clicking, through keyboard input, etc.).
The following HTML excerpt contains two links, one whose destination anchor is
an HTML document named "chapter2.html" and the other whose destination anchor
is a GIF image in the file "forest.gif":
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<BODY>
...some text...
<P>You’ll find a lot more in <A href="chapter2.html">chapter two</A>.
See also this <A href="../images/forest.gif">map of the enchanted forest.</A>
</BODY>
By activating these links (by clicking with the mouse, through keyboard input,
voice commands, etc.), users may visit these resources. Note that the href attribute
in each source anchor specifies the address of the destination anchor with a URI.
The destination anchor of a link may be an element within an HTML document.
The destination anchor must be given an anchor name and any URI addressing this
anchor must include the name as its fragment identifier [p.20] .
Destination anchors in HTML documents may be specified either by the A element
(naming it with the name attribute), or by any other element (naming with the id
attribute).
Thus, for example, an author might create a table of contents whose entries link to
header elements H2, H3, etc., in the same document. Using the A element to create
destination anchors, we would write:
<H1>Table of Contents</H1>
<P><A href="#section1">Introduction</A><BR>
<A href="#section2">Some background</A><BR>
<A href="#section2.1">On a more personal note</A><BR>
...the rest of the table of contents...
...the document body...
<H2><A name="section1">Introduction</A></H2>
...section 1...
<H2><A name="section2">Some background</A></H2>
...section 2...
<H3><A name="section2.1">On a more personal note</A></H3>
...section 2.1...
We may achieve the same effect by making the header elements themselves the
anchors:
<H1>Table of Contents</H1>
<P><A href="#section1">Introduction</A><BR>
<A href="#section2">Some background</A><BR>
<A href="#section2.1">On a more personal note</A><BR>
...the rest of the table of contents...
...the document body...
<H2 id="section1">Introduction</H2>
...section 1...
<H2 id="section2">Some background</H2>
...section 2...
<H3 id="section2.1">On a more personal note</H3>
...section 2.1...
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12.1.2 Other link relationships
By far the most common use of a link is to retrieve another Web resource, as
illustrated in the previous examples. However, authors may insert links in their
documents that express other relationships between resources than simply "activate
this link to visit that related resource". Links that express other types of relationships
have one or more link types [p.54] specified in their source anchor.
The roles of a link defined by A or LINK are specified via the rel and rev
attributes.
For instance, links defined by the LINK element may describe the position of a
document within a series of documents. In the following excerpt, links within the
document entitled "Chapter 5" point to the previous and next chapters:
<HEAD>
...other head information...
<TITLE>Chapter 5</TITLE>
<LINK rel="prev" href="chapter4.html">
<LINK rel="next" href="chapter6.html">
</HEAD>
The link type of the first link is "prev" and that of the second is "next" (two of
several recognized link types [p.54] ). Links specified by LINK are not rendered with
the document’s contents, although user agents may render them in other ways (e.g.,
as navigation tools).
Even if they are not used for navigation, these links may be interpreted in
interesting ways. For example, a user agent that prints a series of HTML documents
as a single document may use this link information as the basis of forming a
coherent linear document. Further information is given below on using links for the
benefit of search engines. [p.155]
12.1.3 Specifying anchors and links
Although several HTML elements and attributes create links to other resources (e.g.,
the IMG element, the FORM element, etc.), this chapter discusses links and anchors
created by the LINK and A elements. The LINK element may only appear in the
head of a document. The A element may only appear in the body.
When the A element’s href attribute is set, the element defines a source anchor
for a link that may be activated by the user to retrieve a Web resource. The source
anchor is the location of the A instance and the destination anchor is the Web
resource.
The retrieved resource may be handled by the user agent in several ways: by
opening a new HTML document in the same user agent window, opening a new
HTML document in a different window, starting a new program to handle the
resource, etc. Since the A element has content (text, images, etc.), user agents may
render this content in such a way as to indicate the presence of a link (e.g., by
underlining the content).
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When the name or id attributes of the A element are set, the element defines an
anchor that may be the destination of other links.
Authors may set the name and href attributes simultaneously in the same A
instance.
The LINK element defines a relationship between the current document and
another resource. Although LINK has no content, the relationships it defines may be
rendered by some user agents.
12.1.4 Link titles
The title attribute may be set for both A and LINK to add information about the
nature of a link. This information may be spoken by a user agent, rendered as a tool
tip, cause a change in cursor image, etc.
Thus, we may augment a previous example [p.145] by supplying a title for each
link:
<BODY>
...some text...
<P>You’ll find a lot more in <A href="chapter2.html"
title="Go to chapter two">chapter two</A>.
<A href="./chapter2.html"
title="Get chapter two.">chapter two</A>.
See also this <A href="../images/forest.gif"
title="GIF image of enchanted forest">map of
the enchanted forest.</A>
</BODY>
12.1.5 Internationalization and links
Since links may point to documents encoded with different character encodings
[p.41] , the A and LINK elements support the charset attribute. This attribute
allows authors to advise user agents about the encoding of data at the other end of
the link.
The hreflang attribute provides user agents with information about the language
of a resource at the end of a link, just as the lang attribute provides information
about the language of an element’s content or attribute values.
Armed with this additional knowledge, user agents should be able to avoid
presenting "garbage" to the user. Instead, they may either locate resources
necessary for the correct presentation of the document or, if they cannot locate the
resources, they should at least warn the user that the document will be unreadable
and explain the cause.
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12.2 The A element
<!ELEMENT A - - (%inline;)* -(A)
<!ATTLIST A
%attrs;
charset
%Charset;
#IMPLIED
type
%ContentType; #IMPLIED
name
CDATA
#IMPLIED
href
%URI;
#IMPLIED
hreflang
%LanguageCode; #IMPLIED
rel
%LinkTypes;
#IMPLIED
rev
%LinkTypes;
#IMPLIED
accesskey
%Character;
#IMPLIED
shape
%Shape;
rect
coords
%Coords;
#IMPLIED
tabindex
NUMBER
#IMPLIED
onfocus
%Script;
#IMPLIED
onblur
%Script;
#IMPLIED
>
-- anchor -->
---------------
%coreattrs, %i18n, %events -char encoding of linked resource -advisory content type -named link end -URI for linked resource -language code -forward link types -reverse link types -accessibility key character -for use with client-side image maps -for use with client-side image maps -position in tabbing order -the element got the focus -the element lost the focus --
Start tag: required, End tag: required
Attribute definitions
name = cdata [p.50] [CS] [p.49]
This attribute names the current anchor so that it may be the destination of
another link. The value of this attribute must be a unique anchor name. The
scope of this name is the current document. Note that this attribute shares the
same name space as the id attribute.
href = uri [p.51] [CT] [p.49]
This attribute specifies the location of a Web resource, thus defining a link
between the current element (the source anchor) and the destination anchor
defined by this attribute.
hreflang = langcode [p.53] [CI] [p.49]
This attribute specifies the base language of the resource designated by href
and may only be used when href is specified.
type = content-type [p.53] [CI] [p.49]
This attribute gives an advisory hint as to the content type of the content
available at the link target address. It allows user agents to opt to use a fallback
mechanism rather than fetch the content if they are advised that they will get
content in a content type they do not support.
Authors who use this attribute take responsibility to manage the risk that it may
become inconsistent with the content available at the link target address.
For the current list of registered content types, please consult [MIMETYPES]
[p.354] .
rel = link-types [p.54] [CI] [p.49]
This attribute describes the relationship from the current document to the anchor
specified by the href attribute. The value of this attribute is a space-separated
list of link types.
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rev = link-types [p.54] [CI] [p.49]
This attribute is used to describe a reverse link [p.155] from the anchor specified
by the href attribute to the current document. The value of this attribute is a
space-separated list of link types.
charset = charset [p.53] [CI] [p.49]
This attribute specifies the character encoding of the resource designated by the
link. Please consult the section on character encodings [p.41] for more details.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
shape and coords (image maps [p.173] )
onfocus, onblur, onclick, ondblclick, onmousedown, onmouseup,
onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
onkeyup (intrinsic events [p.254] )
target (target frame information [p.212] )
tabindex (tabbing navigation [p.241] )
accesskey (access keys [p.242] )
Each A element defines an anchor
1. The A element’s content defines the position of the anchor.
2. The name attribute names the anchor so that it may be the destination of zero or
more links (see also anchors with id [p.152] ).
3. The href attribute makes this anchor the source anchor of exactly one link.
Authors may also create an A element that specifies no anchors, i.e., that doesn’t
specify href, name, or id. Values for these attributes may be set at a later time
through scripts. [p.251]
In the example that follows, the A element defines a link. The source anchor is the
text "W3C Web site" and the destination anchor is "http://www.w3.org/":
For more information about W3C, please consult the
<A href="http://www.w3.org/">W3C Web site</A>.
This link designates the home page of the World Wide Web Consortium. When a
user activates this link in a user agent, the user agent will retrieve the resource, in
this case, an HTML document.
User agents generally render links in such a way as to make them obvious to
users (underlining, reverse video, etc.). The exact rendering depends on the user
agent. Rendering may vary according to whether the user has already visited the link
or not. A possible visual rendering of the previous link might be:
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For more information about W3C, please consult the W3C Web site.
~~~~~~~~~~~~
To tell user agents explicitly what the character encoding of the destination page
is, set the charset attribute:
For more information about W3C, please consult the
<A href="http://www.w3.org/" charset="ISO-8859-1">W3C Web site</A>
Suppose we define an anchor named "anchor-one" in the file "one.html".
...text before the anchor...
<A name="anchor-one">This is the location of anchor one.</A>
...text after the anchor...
This creates an anchor around the text "This is the location of anchor one.".
Usually, the contents of A are not rendered in any special way when A defines an
anchor only.
Having defined the anchor, we may link to it from the same or another document.
URIs that designate anchors contain a "#" character followed by the anchor name
(the fragment identifier [p.20] ). Here are some examples of such URIs:
An absolute URI: http://www.mycompany.com/one.html#anchor-one
A relative URI: ./one.html#anchor-one or one.html#anchor-one
When the link is defined in the same document: #anchor-one
Thus, a link defined in the file "two.html" in the same directory as "one.html" would
refer to the anchor as follows:
...text before the link...
For more information, please consult <A href="./one.html#anchor-one"> anchor one</A>.
...text after the link...
The A element in the following example specifies a link (with href) and creates a
named anchor (with name) simultaneously:
I just returned from vacation! Here’s a
<A name="anchor-two"
href="http://www.somecompany.com/People/Ian/vacation/family.png">
photo of my family at the lake.</A>.
This example contains a link to a different type of Web resource (a PNG image).
Activating the link should cause the image resource to be retrieved from the Web
(and possibly displayed if the system has been configured to do so).
Note. User agents should be able to find anchors created by empty A elements,
but some fail to do so. For example, some user agents may not find the
"empty-anchor" in the following HTML fragment:
<A name="empty-anchor"></A>
<EM>...some HTML...</EM>
<A href="#empty-anchor">Link to empty anchor</A>
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12.2.1 Syntax of anchor names
An anchor name is the value of either the name or id attribute when used in the
context of anchors. Anchor names must observe the following rules:
Uniqueness: Anchor names must be unique within a document. Anchor names
that differ only in case may not appear in the same document.
String matching: Comparisons between fragment identifiers [p.20] and anchor
names must be done by exact (case-sensitive) match.
Thus, the following example is correct with respect to string matching and must be
considered a match by user agents:
<P><A href="#xxx">...</A>
...more document...
<P><A name="xxx">...</A>
ILLEGAL EXAMPLE:
The following example is illegal with respect to uniqueness since the two names are
the same except for case:
<P><A name="xxx">...</A>
<P><A name="XXX">...</A>
Although the following excerpt is legal HTML, the behavior of the user agent is not
defined; some user agents may (incorrectly) consider this a match and others may
not.
<P><A href="#xxx">...</A>
...more document...
<P><A name="XXX">...</A>
Anchor names should be restricted to ASCII characters. Please consult the
appendix for more information about non-ASCII characters in URI attribute values
[p.334] .
12.2.2 Nested links are illegal
Links and anchors defined by the A element must not be nested; an A element must
not contain any other A elements.
Since the DTD defines the LINK element to be empty, LINK elements may not be
nested either.
12.2.3 Anchors with the id attribute
The id attribute may be used to create an anchor at the start tag of any element
(including the A element).
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This example illustrates the use of the id attribute to position an anchor in an H2
element. The anchor is linked to via the A element.
You may read more about this in <A href="#section2">Section Two</A>.
...later in the document
<H2 id="section2">Section Two</H2>
...later in the document
<P>Please refer to <A href="#section2">Section Two</A> above
for more details.
The following example names a destination anchor with the id attribute:
I just returned from vacation! Here’s a
<A id="anchor-two">photo of my family at the lake.</A>.
The id and name attributes share the same name space. This means that they
cannot both define an anchor with the same name in the same document. It is
permissible to use both attributes to specify an element’s unique identifier for the
following elements: A, APPLET, FORM, FRAME, IFRAME, IMG, and MAP. When both
attributes are used on a single element, their values must be identical.
ILLEGAL EXAMPLE:
The following excerpt is illegal HTML since these attributes declare the same name
twice in the same document.
<A href="#a1">...</A>
...
<H1 id="a1">
...pages and pages...
<A name="a1"></A>
The following example illustrates that id and name must be the same when both
appear in an element’s start tag:
<P><A name="a1" id="a1" href="#a1">...</A>
Because of its specification in the HTML DTD, the name attribute may contain
character references [p.45] . Thus, the value D&#xfc;rst is a valid name attribute
value, as is D&uuml;rst . The id attribute, on the other hand, may not contain
character references.
Use id or name? Authors should consider the following issues when deciding
whether to use id or name for an anchor name:
The id attribute can act as more than just an anchor name (e.g., style sheet
selector, processing identifier, etc.).
Some older user agents don’t support anchors created with the id attribute.
The name attribute allows richer anchor names (with entities [p.45] ).
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12.2.4 Unavailable and unidentifiable resources
A reference to an unavailable or unidentifiable resource is an error. Although user
agents may vary in how they handle such an error, we recommend the following
behavior:
If a user agent cannot locate a linked resource, it should alert the user.
If a user agent cannot identify the type of a linked resource, it should still
attempt to process it. It should alert the user and may allow the user to intervene
and identify the document type.
12.3 Document relationships: the LINK element
<!ELEMENT LINK - O EMPTY
<!ATTLIST LINK
%attrs;
charset
%Charset;
href
%URI;
hreflang
%LanguageCode;
type
%ContentType;
rel
%LinkTypes;
rev
%LinkTypes;
media
%MediaDesc;
>
-- a media-independent link -->
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
---------
%coreattrs, %i18n, %events -char encoding of linked resource -URI for linked resource -language code -advisory content type -forward link types -reverse link types -for rendering on these media --
Start tag: required, End tag: forbidden
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
href, hreflang, type, rel, rev (links and anchors [p.145] )
target (target frame information [p.212] )
media (header style information [p.187] )
charset(character encodings [p.41] )
This element defines a link. Unlike A, it may only appear in the HEAD section of a
document, although it may appear any number of times. Although LINK has no
content, it conveys relationship information that may be rendered by user agents in a
variety of ways (e.g., a tool-bar with a drop-down menu of links).
This example illustrates how several LINK definitions may appear in the HEAD
section of a document. The current document is "Chapter2.html". The rel attribute
specifies the relationship of the linked document with the current document. The
values "Index", "Next", and "Prev" are explained in the section on link types [p.54] .
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>Chapter 2</TITLE>
<LINK rel="Index" href="../index.html">
<LINK rel="Next" href="Chapter3.html">
<LINK rel="Prev" href="Chapter1.html">
</HEAD>
...the rest of the document...
12.3.1 Forward and reverse links
The rel and rev attributes play complementary roles -- the rel attribute specifies a
forward link and the rev attribute specifies a reverse link.
Consider two documents A and B.
Document A:
<LINK href="docB" rel="foo">
Has exactly the same meaning as:
Document B:
<LINK href="docA" rev="foo">
Both attributes may be specified simultaneously.
12.3.2 Links and external style sheets
When the LINK element links an external style sheet to a document, the type
attribute specifies the style sheet language and the media attribute specifies the
intended rendering medium or media. User agents may save time by retrieving from
the network only those style sheets that apply to the current device.
Media types [p.189] are further discussed in the section on style sheets.
12.3.3 Links and search engines
Authors may use the LINK element to provide a variety of information to search
engines, including:
Links to alternate versions of a document, written in another human language.
Links to alternate versions of a document, designed for different media, for
instance a version especially suited for printing.
Links to the starting page of a collection of documents.
The examples below illustrate how language information, media types, and link
types may be combined to improve document handling by search engines.
In the following example, we use the hreflang attribute to tell search engines
where to find Dutch, Portuguese, and Arabic versions of a document. Note the use
of the charset attribute for the Arabic manual. Note also the use of the lang
attribute to indicate that the value of the title attribute for the LINK element
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designating the French manual is in French.
<HEAD>
<TITLE>The manual in English</TITLE>
<LINK title="The manual in Dutch"
type="text/html"
rel="alternate"
hreflang="nl"
href="http://someplace.com/manual/dutch.html">
<LINK title="The manual in Portuguese"
type="text/html"
rel="alternate"
hreflang="pt"
href="http://someplace.com/manual/portuguese.html">
<LINK title="The manual in Arabic"
type="text/html"
rel="alternate"
charset="ISO-8859-6"
hreflang="ar"
href="http://someplace.com/manual/arabic.html">
<LINK lang="fr" title="La documentation en Fran&ccedil;ais"
type="text/html"
rel="alternate"
hreflang="fr"
href="http://someplace.com/manual/french.html">
</HEAD>
In the following example, we tell search engines where to find the printed version
of a manual.
<HEAD>
<TITLE>Reference manual</TITLE>
<LINK media="print" title="The manual in postscript"
type="application/postscript"
rel="alternate"
href="http://someplace.com/manual/postscript.ps">
</HEAD>
In the following example, we tell search engines where to find the front page of a
collection of documents.
<HEAD>
<TITLE>Reference manual -- Page 5</TITLE>
<LINK rel="Start" title="The first page of the manual"
type="text/html"
href="http://someplace.com/manual/start.html">
</HEAD>
Further information is given in the notes in the appendix on helping search
engines index your Web site [p.339] .
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12.4 Path information: the BASE element
<!ELEMENT BASE - O EMPTY
<!ATTLIST BASE
href
%URI;
>
-- document base URI -->
#REQUIRED -- URI that acts as base URI --
Start tag: required, End tag: forbidden
Attribute definitions
href = uri [p.51] [CT] [p.49]
This attribute specifies an absolute URI that acts as the base URI for resolving
relative URIs.
Attributes defined elsewhere
target (target frame information [p.212] )
In HTML, links and references to external images, applets, form-processing
programs, style sheets, etc. are always specified by a URI. Relative URIs are
resolved [p.158] according to a base URI, which may come from a variety of
sources. The BASE element allows authors to specify a document’s base URI
explicitly.
When present, the BASE element must appear in the HEAD section of an HTML
document, before any element that refers to an external source. The path
information specified by the BASE element only affects URIs in the document where
the element appears.
For example, given the following BASE declaration and A declaration:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>Our Products</TITLE>
<BASE href="http://www.aviary.com/products/intro.html">
</HEAD>
<BODY>
<P>Have you seen our <A href="../cages/birds.gif">Bird Cages</A>?
</BODY>
</HTML>
the relative URI "../cages/birds.gif" would resolve to:
http://www.aviary.com/cages/birds.gif
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12.4.1 Resolving relative URIs
User agents must calculate the base URI for resolving relative URIs according to
[RFC1808] [p.354] , section 3. The following describes how [RFC1808] [p.354]
applies specifically to HTML.
User agents must calculate the base URI according to the following precedences
(highest priority to lowest):
1. The base URI is set by the BASE element.
2. The base URI is given by meta data discovered during a protocol interaction,
such as an HTTP header (see [RFC2616] [p.354] ).
3. By default, the base URI is that of the current document. Not all HTML
documents have a base URI (e.g., a valid HTML document may appear in an
email and may not be designated by a URI). Such HTML documents are
considered erroneous if they contain relative URIs and rely on a default base
URI.
Additionally, the OBJECT and APPLET elements define attributes that take
precedence over the value set by the BASE element. Please consult the definitions of
these elements for more information about URI issues specific to them.
Note. For versions of HTTP that define a Link header, user agents should handle
these headers exactly as LINK elements in the document. HTTP 1.1 as defined by
[RFC2616] [p.354] does not include a Link header field (refer to section 19.6.3).
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13 Objects, Images, and Applets
Contents
1. Introduction to objects, images, and applets .
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2. Including an image: the IMG element .
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3. Generic inclusion: the OBJECT element .
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2. Object initialization: the PARAM element .
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3. Global naming schemes for objects .
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4. Object declarations and instantiations
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4. Including an applet: the APPLET element .
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5. Notes on embedded documents .
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6. Image maps
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1. Client-side image maps: the MAP and AREA elements
Client-side image map examples
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2. Server-side image maps .
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7. Visual presentation of images, objects, and applets .
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1. Width and height
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2. White space around images and objects .
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3. Borders
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4. Alignment .
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8. How to specify alternate text .
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13.1 Introduction to objects, images, and applets
HTML’s multimedia features allow authors to include images, applets (programs that
are automatically downloaded and run on the user’s machine), video clips, and other
HTML documents in their pages.
For example, to include a PNG image in a document, authors may write:
<BODY>
<P>Here’s a closeup of the Grand Canyon:
<OBJECT data="canyon.png" type="image/png">
This is a <EM>closeup</EM> of the Grand Canyon.
</OBJECT>
</BODY>
Previous versions of HTML allowed authors to include images (via IMG) and
applets (via APPLET). These elements have several limitations:
They fail to solve the more general problem of how to include new and future
media types.
The APPLET element only works with Java-based applets. This element is
deprecated [p.38] in favor of OBJECT.
They pose accessibility problems.
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To address these issues, HTML 4 introduces the OBJECT element, which offers an
all-purpose solution to generic object inclusion. The OBJECT element allows HTML
authors to specify everything required by an object for its presentation by a user
agent: source code, initial values, and run-time data. In this specification, the term
"object" is used to describe the things that people want to place in HTML documents;
other commonly used terms for these things are: applets, plug-ins, media handlers,
etc.
The new OBJECT element thus subsumes some of the tasks carried out by
existing elements. Consider the following chart of functionalities:
Type of inclusion
Specific element
Generic element
Image
IMG
Applet
APPLET (Deprecated [p.38] .) OBJECT
Another HTML document IFRAME
OBJECT
OBJECT
The chart indicates that each type of inclusion has a specific and a general
solution. The generic OBJECT element will serve as the solution for implementing
future media types.
To include images, authors may use the OBJECT element or the IMG element.
To include applets, authors should use the OBJECT element as the APPLET
element is deprecated [p.38] .
To include one HTML document in another, authors may use either the new
IFRAME element or the OBJECT element. In both cases, the embedded document
remains independent of the main document. Visual user agents may present the
embedded document in a distinct window within the main document. Please consult
the notes on embedded documents [p.173] for a comparison of OBJECT and
IFRAME for document inclusion.
Images and other included objects may have hyperlinks associated with them,
both through the standard linking mechanisms [p.145] , but also via image maps
[p.173] . An image map specifies active geometric regions of an included object and
assigns a link to each region. When activated, these links may cause a document to
be retrieved, may run a program on the server, etc.
In the following sections, we discuss the various mechanisms available to authors
for multimedia inclusions and creating image maps for those inclusions.
13.2 Including an image: the IMG element
<!-- To avoid problems with text-only UAs as well as
to make image content understandable and navigable
to users of non-visual UAs, you need to provide
a description with ALT, and avoid server-side image maps -->
<!ELEMENT IMG - O EMPTY
-- Embedded image -->
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<!ATTLIST IMG
%attrs;
src
%URI;
alt
%Text;
longdesc
%URI;
name
height
width
usemap
ismap
>
CDATA
%Length;
%Length;
%URI;
(ismap)
-- %coreattrs, %i18n, %events -#REQUIRED -- URI of image to embed -#REQUIRED -- short description -#IMPLIED -- link to long description
(complements alt) -#IMPLIED -- name of image for scripting -#IMPLIED -- override height -#IMPLIED -- override width -#IMPLIED -- use client-side image map -#IMPLIED -- use server-side image map --
Start tag: required, End tag: forbidden
Attribute definitions
src = uri [p.51] [CT] [p.49]
This attribute specifies the location of the image resource. Examples of widely
recognized image formats include GIF, JPEG, and PNG.
longdesc = uri [p.51] [CT] [p.49]
This attribute specifies a link to a long description of the image. This description
should supplement the short description provided using the alt attribute. When
the image has an associated image map [p.173] , this attribute should provide
information about the image map’s contents. This is particularly important for
server-side image maps. Since an IMG element may be within the content of an
A element, the user agent’s mechanism in the user interface for accessing the
"longdesc" resource of the former must be different than the mechanism for
accessing the href resource of the latter.
name = cdata [p.50] [CI] [p.49]
This attribute names the element so that it may be referred to from style sheets
or scripts. Note. This attribute has been included for backwards compatibility.
Applications should use the id attribute to identify elements.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
alt (alternate text [p.181] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
ismap, usemap (client side image maps [p.174] )
align, width, height, border, hspace, vspace (visual presentation of
objects, images, and applets [p.179] )
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The IMG element embeds an image in the current document at the location of the
element’s definition. The IMG element has no content; it is usually replaced inline by
the image designated by the src attribute, the exception being for left or
right-aligned images that are "floated" [p.197] out of line.
In an earlier example, we defined a link to a family photo. Here, we insert the
photo directly into the current document:
<BODY>
<P>I just returned from vacation! Here’s a photo of my family at the lake:
<IMG src="http://www.somecompany.com/People/Ian/vacation/family.png"
alt="A photo of my family at the lake.">
</BODY>
This inclusion may also be achieved with the OBJECT element as follows:
<BODY>
<P>I just returned from vacation! Here’s a photo of my family at the lake:
<OBJECT data="http://www.somecompany.com/People/Ian/vacation/family.png"
type="image/png">
A photo of my family at the lake.
</OBJECT>
</BODY>
The alt attribute specifies alternate text that is rendered when the image cannot
be displayed (see below for information on how to specify alternate text [p.181] ).
User agents must render alternate text when they cannot support images, they
cannot support a certain image type or when they are configured not to display
images.
The following example shows how the longdesc attribute can be used to link to a
richer description:
<BODY>
<P>
<IMG src="sitemap.gif"
alt="HP Labs Site Map"
longdesc="sitemap.html">
</BODY>
The alt attribute provides a short description of the image. This should be
sufficient to allow users to decide whether they want to follow the link given by the
longdesc attribute to the longer description, here "sitemap.html".
Please consult the section on the visual presentation of objects, images, and
applets [p.179] for information about image size, alignment, and borders.
13.3 Generic inclusion: the OBJECT element
<!ELEMENT OBJECT - - (PARAM | %flow;)*
-- generic embedded object -->
<!ATTLIST OBJECT
%attrs;
-- %coreattrs, %i18n, %events -declare
(declare)
#IMPLIED -- declare but don’t instantiate flag --
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classid
codebase
data
type
codetype
archive
standby
height
width
usemap
name
tabindex
>
%URI;
%URI;
%URI;
%ContentType;
%ContentType;
CDATA
%Text;
%Length;
%Length;
%URI;
CDATA
NUMBER
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
-------------
identifies an implementation -base URI for classid, data, archive-reference to object’s data -content type for data -content type for code -space-separated list of URIs -message to show while loading -override height -override width -use client-side image map -submit as part of form -position in tabbing order --
Start tag: required, End tag: required
Attribute definitions
classid = uri [p.51] [CT] [p.49]
This attribute may be used to specify the location of an object’s implementation
via a URI. It may be used together with, or as an alternative to the data
attribute, depending on the type of object involved.
codebase = uri [p.51] [CT] [p.49]
This attribute specifies the base path used to resolve relative URIs specified by
the classid, data, and archive attributes. When absent, its default value is
the base URI of the current document.
codetype = content-type [p.53] [CI] [p.49]
This attribute specifies the content type of data expected when downloading the
object specified by classid. This attribute is optional but recommended when
classid is specified since it allows the user agent to avoid loading information
for unsupported content types. When absent, it defaults to the value of the type
attribute.
data = uri [p.51] [CT] [p.49]
This attribute may be used to specify the location of the object’s data, for
instance image data for objects defining images, or more generally, a serialized
form of an object which can be used to recreate it. If given as a relative URI, it
should be interpreted relative to the codebase attribute.
type = content-type [p.53] [CI] [p.49]
This attribute specifies the content type for the data specified by data. This
attribute is optional but recommended when data is specified since it allows the
user agent to avoid loading information for unsupported content types. If the
value of this attribute differs from the HTTP Content-Type returned by the server
when the object is retrieved, the HTTP Content-Type takes precedence.
archive = uri-list [p.51] [CT] [p.49]
This attribute may be used to specify a space-separated list of URIs for archives
containing resources relevant to the object, which may include the resources
specified by the classid and data attributes. Preloading archives will
generally result in reduced load times for objects. Archives specified as relative
URIs should be interpreted relative to the codebase attribute.
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declare [CI] [p.49]
When present, this boolean attribute makes the current OBJECT definition a
declaration only. The object must be instantiated by a subsequent OBJECT
definition referring to this declaration.
standby = text [p.50] [CS] [p.49]
This attribute specifies a message that a user agent may render while loading
the object’s implementation and data.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
tabindex (tabbing navigation [p.241] )
usemap (client side image maps [p.174] )
name (form submission [p.245] )
align, width, height, border, hspace, vspace (visual presentation of
objects, images, and applets [p.179] )
Most user agents have built-in mechanisms for rendering common data types
such as text, GIF images, colors, fonts, and a handful of graphic elements. To render
data types they don’t support natively, user agents generally run external
applications. The OBJECT element allows authors to control whether data should be
rendered externally or by some program, specified by the author, that renders the
data within the user agent.
In the most general case, an author may need to specify three types of
information:
The implementation of the included object. For instance, if the included object is
a clock applet, the author must indicate the location of the applet’s executable
code.
The data to be rendered. For instance, if the included object is a program that
renders font data, the author must indicate the location of that data.
Additional values required by the object at run-time. For example, some applets
may require initial values for parameters.
The OBJECT element allows authors to specify all three types of data, but authors
may not have to specify all three at once. For example, some objects may not
require data (e.g., a self-contained applet that performs a small animation). Others
may not require run-time initialization. Still others may not require additional
implementation information, i.e., the user agent itself may already know how to
render that type of data (e.g., GIF images).
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Authors specify an object’s implementation and the location of the data to be
rendered via the OBJECT element. To specify run-time values, however, authors use
the PARAM element, which is discussed in the section on object initialization. [p.167]
The OBJECT element may also appear in the content of the HEAD element. Since
user agents generally do not render elements in the HEAD, authors should ensure
that any OBJECT elements in the HEAD do not specify content that may be rendered.
Please consult the section on sharing frame data [p.208] for an example of including
the OBJECT element in the HEAD element.
Please consult the section on form controls [p.220] for information about OBJECT
elements in forms.
This document does not specify the behavior of OBJECT elements that use both
the classid attribute to identify an implementation and the data attribute to specify
data for that implementation. In order to ensure portability, authors should use the
PARAM element to tell implementations where to retrieve additional data.
13.3.1 Rules for rendering objects
A user agent must interpret an OBJECT element according to the following
precedence rules:
1. The user agent must first try to render the object. It should not render the
element’s contents, but it must examine them in case the element contains any
direct children that are PARAM elements (see object initialization [p.167] ) or MAP
elements (see client-side image maps [p.174] ).
2. If the user agent is not able to render the object for whatever reason (configured
not to, lack of resources, wrong architecture, etc.), it must try to render its
contents.
Authors should not include content in OBJECT elements that appear in the HEAD
element.
In the following example, we insert an analog clock applet in a document via the
OBJECT element. The applet, written in the Python language, requires no additional
data or run-time values. The classid attribute specifies the location of the applet:
<P><OBJECT classid="http://www.miamachina.it/analogclock.py">
</OBJECT>
Note that the clock will be rendered as soon as the user agent interprets this
OBJECT declaration. It is possible to delay rendering of an object by first declaring
the object (described below).
Authors should complete this declaration by including alternate text as the
contents of OBJECT in case the user agent cannot render the clock.
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<P><OBJECT classid="http://www.miamachina.it/analogclock.py">
An animated clock.
</OBJECT>
One significant consequence of the OBJECT element’s design is that it offers a
mechanism for specifying alternate object renderings; each embedded OBJECT
declaration may specify alternate content types. If a user agent cannot render the
outermost OBJECT, it tries to render the contents, which may be another OBJECT
element, etc.
In the following example, we embed several OBJECT declarations to illustrate how
alternate renderings work. A user agent will attempt to render the first OBJECT
element it can, in the following order: (1) an Earth applet written in the Python
language, (2) an MPEG animation of the Earth, (3) a GIF image of the Earth, (4)
alternate text.
<P>
<!-- First, try the Python applet -->
<OBJECT title="The Earth as seen from space"
classid="http://www.observer.mars/TheEarth.py">
<!-- Else, try the MPEG video -->
<OBJECT data="TheEarth.mpeg" type="application/mpeg">
<!-- Else, try the GIF image -->
<OBJECT data="TheEarth.gif" type="image/gif">
<!-- Else render the text -->
The <STRONG>Earth</STRONG> as seen from space.
</OBJECT>
</OBJECT>
</OBJECT>
The outermost declaration specifies an applet that requires no data or initial
values. The second declaration specifies an MPEG animation and, since it does not
define the location of an implementation to handle MPEG, relies on the user agent to
handle the animation. We also set the type attribute so that a user agent that knows
it cannot render MPEG will not bother to retrieve "TheEarth.mpeg" from the network.
The third declaration specifies the location of a GIF file and furnishes alternate text in
case all other mechanisms fail.
Inline vs. external data. Data to be rendered may be supplied in two ways: inline
and from an external resource. While the former method will generally lead to faster
rendering, it is not convenient when rendering large quantities of data.
Here’s an example that illustrates how inline data may be fed to an OBJECT:
<P>
<OBJECT id="clock1"
classid="clsid:663C8FEF-1EF9-11CF-A3DB-080036F12502"
data="data:application/x-oleobject;base64, ...base64 data...">
A clock.
</OBJECT>
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Please consult the section on the visual presentation of objects, images, and
applets [p.179] for information about object size, alignment, and borders.
13.3.2 Object initialization: the PARAM element
<!ELEMENT PARAM - O EMPTY
<!ATTLIST PARAM
id
ID
#IMPLIED
name
CDATA
#REQUIRED
value
CDATA
#IMPLIED
valuetype
(DATA|REF|OBJECT) DATA
type
%ContentType; #IMPLIED
-- named property value -->
------
document-wide unique id -property name -property value -How to interpret value -content type for value
when valuetype=ref --
>
Start tag: required, End tag: forbidden
Attribute definitions
name = cdata [p.50]
This attribute defines the name of a run-time parameter, assumed to be known
by the inserted object. Whether the property name is case-sensitive depends on
the specific object implementation.
value = cdata [p.50]
This attribute specifies the value of a run-time parameter specified by name.
Property values have no meaning to HTML; their meaning is determined by the
object in question.
valuetype = data|ref|object [CI] [p.49]
This attribute specifies the type of the value attribute. Possible values:
data: This is default value for the attribute. It means that the value
specified by value will be evaluated and passed to the object’s
implementation as a string.
ref: The value specified by value is a URI that designates a resource
where run-time values are stored. This allows support tools to identify URIs
given as parameters. The URI must be passed to the object as is, i.e.,
unresolved.
object: The value specified by value is an identifier that refers to an
OBJECT declaration in the same document. The identifier must be the value
of the id attribute set for the declared OBJECT element.
type = content-type [p.53] [CI] [p.49]
This attribute specifies the content type of the resource designated by the
value attribute only in the case where valuetype is set to "ref". This attribute
thus specifies for the user agent, the type of values that will be found at the URI
designated by value.
Attributes defined elsewhere
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id (document-wide identifiers [p.71] )
PARAM elements specify a set of values that may be required by an object at
run-time. Any number of PARAM elements may appear in the content of an OBJECT
or APPLET element, in any order, but must be placed at the start of the content of
the enclosing OBJECT or APPLET element.
The syntax of names and values is assumed to be understood by the object’s
implementation. This document does not specify how user agents should retrieve
name/value pairs nor how they should interpret parameter names that appear twice.
We return to the clock example to illustrate the use of PARAM: suppose that the
applet is able to handle two run-time parameters that define its initial height and
width. We can set the initial dimensions to 40x40 pixels with two PARAM elements.
<P><OBJECT classid="http://www.miamachina.it/analogclock.py">
<PARAM name="height" value="40" valuetype="data">
<PARAM name="width" value="40" valuetype="data">
This user agent cannot render Python applications.
</OBJECT>
In the following example, run-time data for the object’s "Init_values" parameter is
specified as an external resource (a GIF file). The value of the valuetype attribute
is thus set to "ref" and the value is a URI designating the resource.
<P><OBJECT classid="http://www.gifstuff.com/gifappli"
standby="Loading Elvis...">
<PARAM name="Init_values"
value="./images/elvis.gif">
valuetype="ref">
</OBJECT>
Note that we have also set the standby attribute so that the user agent may
display a message while the rendering mechanism loads.
When an OBJECT element is rendered, user agents must search the content for
only those PARAM elements that are direct children and "feed" them to the OBJECT.
Thus, in the following example, if "obj1" is rendered, "param1" applies to "obj1"
(and not "obj2"). If "obj1" is not rendered and "obj2" is, "param1" is ignored, and
"param2" applies to "obj2". If neither OBJECT is rendered, neither PARAM applies.
<P>
<OBJECT id="obj1">
<PARAM name="param1">
<OBJECT id="obj2">
<PARAM name="param2">
</OBJECT>
</OBJECT>
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13.3.3 Global naming schemes for objects
The location of an object’s implementation is given by a URI. As we discussed in the
introduction to URIs [p.19] , the first segment of an absolute URI specifies the
naming scheme used to transfer the data designated by the URI. For HTML
documents, this scheme is frequently "http". Some applets might employ other
naming schemes. For instance, when specifying a Java applet, authors may use
URIs that begin with "java" and for ActiveX applets, authors may use "clsid".
In the following example, we insert a Java applet into an HTML document.
<P><OBJECT classid="java:program.start">
</OBJECT>
By setting the codetype attribute, a user agent can decide whether to retrieve the
Java application based on its ability to do so.
<OBJECT codetype="application/java-archive"
classid="java:program.start">
</OBJECT>
Some rendering schemes require additional information to identify their
implementation and must be told where to find that information. Authors may give
path information to the object’s implementation via the codebase attribute.
<OBJECT codetype="application/java-archive"
classid="java:program.start">
codebase="http://foooo.bar.com/java/myimplementation/"
</OBJECT>
The following example specifies (with the classid attribute) an ActiveX object via
a URI that begins with the naming scheme "clsid". The data attribute locates the
data to render (another clock).
<P><OBJECT classid="clsid:663C8FEF-1EF9-11CF-A3DB-080036F12502"
data="http://www.acme.com/ole/clock.stm">
This application is not supported.
</OBJECT>
13.3.4 Object declarations and instantiations
The preceding examples have only illustrated isolated object definitions. When a
document is to contain more than one instance of the same object, it is possible to
separate the declaration of the object from its instantiations. Doing so has several
advantages:
Data may be retrieved from the network by the user agent one time (during the
declaration) and reused for each instantiation.
It is possible to instantiate an object from a location other than the object’s
declaration, for example, from a link.
It is possible to specify objects as run-time data for other objects.
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To declare an object so that it is not executed when read by the user agent, set
the boolean declare attribute in the OBJECT element. At the same time, authors
must identify the declaration by setting the id attribute in the OBJECT element to a
unique value. Later instantiations of the object will refer to this identifier.
A declared OBJECT must appear in a document before the first instance of that
OBJECT.
An object defined with the declare attribute is instantiated every time an element
that refers to that object requires it to be rendered (e.g., a link that refers to it is
activated, an object that refers to it is activated, etc.).
In the following example, we declare an OBJECT and cause it to be instantiated by
referring to it from a link. Thus, the object can be activated by clicking on some
highlighted text, for example.
<P><OBJECT declare
id="earth.declaration"
data="TheEarth.mpeg"
type="application/mpeg">
The <STRONG>Earth</STRONG> as seen from space.
</OBJECT>
...later in the document...
<P>A neat <A href="#earth.declaration"> animation of The Earth!</A>
The following example illustrates how to specify run-time values that are other
objects. In this example, we send text (a poem, in fact) to a hypothetical mechanism
for viewing poems. The object recognizes a run-time parameter named "font" (say,
for rendering the poem text in a certain font). The value for this parameter is itself an
object that inserts (but does not render) the font object. The relationship between the
font object and the poem viewer object is achieved by (1) assigning the id "tribune"
to the font object declaration and (2) referring to it from the PARAM element of the
poem viewer object (with valuetype and value).
<P><OBJECT declare
id="tribune"
type="application/x-webfont"
data="tribune.gif">
</OBJECT>
...view the poem in KublaKhan.txt here...
<P><OBJECT classid="http://foo.bar.com/poem_viewer"
data="KublaKhan.txt">
<PARAM name="font" valuetype="object" value="#tribune">
<P>You’re missing a really cool poem viewer ...
</OBJECT>
User agents that don’t support the declare attribute must render the contents of
the OBJECT declaration.
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13.4 Including an applet: the APPLET element
APPLET is deprecated (with all its attributes) [p.38] in favor of OBJECT.
See the Transitional DTD [p.286] for the formal definition.
Attribute definitions
codebase = uri [p.51] [CT] [p.49]
This attribute specifies the base URI for the applet. If this attribute is not
specified, then it defaults the same base URI as for the current document.
Values for this attribute may only refer to subdirectories of the directory
containing the current document. Note. While the restriction on subdirectories is
a departure from common practice and the HTML 3.2 specification, the HTML
Working Group has chosen to leave the restriction in this version of the
specification for security reasons.
code = cdata [p.50] [CS] [p.49]
This attribute specifies either the name of the class file that contains the applet’s
compiled applet subclass or the path to get the class, including the class file
itself. It is interpreted with respect to the applet’s codebase. One of code or
object must be present.
name = cdata [p.50] [CS] [p.49]
This attribute specifies a name for the applet instance, which makes it possible
for applets on the same page to find (and communicate with) each other.
archive = uri-list [p.51] [CT] [p.49]
This attribute specifies a comma-separated list of URIs for archives containing
classes and other resources that will be "preloaded". The classes are loaded
using an instance of an AppletClassLoader with the given codebase. Relative
URIs for archives are interpreted with respect to the applet’s codebase.
Preloading resources can significantly improve the performance of applets.
object = cdata [p.50] [CS] [p.49]
This attribute names a resource containing a serialized representation of an
applet’s state. It is interpreted relative to the applet’s codebase. The serialized
data contains the applet’s class name but not the implementation. The class
name is used to retrieve the implementation from a class file or archive.
When the applet is "deserialized" the start() method is invoked but not the
init() method. Attributes valid when the original object was serialized are not
restored. Any attributes passed to this APPLET instance will be available to the
applet. Authors should use this feature with extreme caution. An applet should
be stopped before it is serialized.
Either code or object must be present. If both code and object are given,
it is an error if they provide different class names.
width = length [p.52] [CI] [p.49]
This attribute specifies the initial width of the applet’s display area (excluding
any windows or dialogs that the applet creates).
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height = length [p.52] [CI] [p.49]
This attribute specifies the initial height of the applet’s display area (excluding
any windows or dialogs that the applet creates).
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
title (element title [p.63] )
style (inline style information [p.186] )
alt (alternate text [p.181] )
align, hspace, vspace (visual presentation of objects, images, and applets
[p.179] )
This element, supported by all Java-enabled browsers, allows designers to embed
a Java applet in an HTML document. It has been deprecated [p.38] in favor of the
OBJECT element.
The content of the APPLET acts as alternate information for user agents that don’t
support this element or are currently configured not to support applets. User agents
must ignore the content otherwise.
DEPRECATED EXAMPLE:
In the following example, the APPLET element includes a Java applet in the
document. Since no codebase is supplied, the applet is assumed to be in the same
directory as the current document.
<APPLET code="Bubbles.class" width="500" height="500">
Java applet that draws animated bubbles.
</APPLET>
This example may be rewritten with OBJECT as follows:
<P><OBJECT codetype="application/java"
classid="java:Bubbles.class"
width="500" height="500">
Java applet that draws animated bubbles.
</OBJECT>
Initial values may be supplied to the applet via the PARAM element.
DEPRECATED EXAMPLE:
The following sample Java applet:
<APPLET code="AudioItem" width="15" height="15">
<PARAM name="snd" value="Hello.au|Welcome.au">
Java applet that plays a welcoming sound.
</APPLET>
may be rewritten as follows with OBJECT:
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<OBJECT codetype="application/java"
classid="AudioItem"
width="15" height="15">
<PARAM name="snd" value="Hello.au|Welcome.au">
Java applet that plays a welcoming sound.
</OBJECT>
13.5 Notes on embedded documents
Sometimes, rather than linking [p.145] to a document, an author may want to embed
it directly into a primary HTML document. Authors may use either the IFRAME
element or the OBJECT element for this purpose, but the elements differ in some
ways. Not only do the two elements have different content models, the IFRAME
element may be a target frame (see the section on specifying target frame
information [p.212] for details) and may be "selected" by a user agent as the focus
for printing, viewing HTML source, etc. User agents may render selected frames
elements in ways that distinguish them from unselected frames (e.g., by drawing a
border around the selected frame).
An embedded document is entirely independent of the document in which it is
embedded. For instance, relative URIs within the embedded document resolve
[p.158] according to the base URI of the embedded document, not that of the main
document. An embedded document is only rendered within another document (e.g.,
in a subwindow); it remains otherwise independent.
For instance, the following line embeds the contents of embed_me.html at the
location where the OBJECT definition occurs.
...text before...
<OBJECT data="embed_me.html">
Warning: embed_me.html could not be embedded.
</OBJECT>
...text after...
Recall that the contents of OBJECT must only be rendered if the file specified by
the data attribute cannot be loaded.
The behavior of a user agent in cases where a file includes itself is not defined.
13.6 Image maps
Image maps allow authors to specify regions of an image or object and assign a
specific action to each region (e.g., retrieve a document, run a program, etc.) When
the region is activated by the user, the action is executed.
An image map is created by associating an object with a specification of sensitive
geometric areas on the object.
There are two types of image maps:
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Client-side. When a user activates a region of a client-side image map with a
mouse, the pixel coordinates are interpreted by the user agent. The user agent
selects a link that was specified for the activated region and follows it.
Server-side. When a user activates a region of a server-side image map with a
mouse, the pixel coordinates of the click are sent to the server-side agent
specified by the href attribute of the A element. The server-side agent
interprets the coordinates and performs some action.
Client-side image maps are preferred over server-side image maps for at least two
reasons: they are accessible to people browsing with non-graphical user agents and
they offer immediate feedback as to whether or not the pointer is over an active
region.
13.6.1 Client-side image maps: the MAP and AREA elements
<!ELEMENT MAP - - ((%block;) | AREA)+ -- client-side image map -->
<!ATTLIST MAP
%attrs;
-- %coreattrs, %i18n, %events -name
CDATA
#REQUIRED -- for reference by usemap ->
Start tag: required, End tag: required
<!ELEMENT AREA - O EMPTY
<!ATTLIST AREA
%attrs;
shape
%Shape;
coords
%Coords;
href
%URI;
nohref
(nohref)
alt
%Text;
tabindex
NUMBER
accesskey
%Character;
onfocus
%Script;
onblur
%Script;
>
-- client-side image map area -->
rect
#IMPLIED
#IMPLIED
#IMPLIED
#REQUIRED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
-----------
%coreattrs, %i18n, %events -controls interpretation of coords -comma-separated list of lengths -URI for linked resource -this region has no action -short description -position in tabbing order -accessibility key character -the element got the focus -the element lost the focus --
Start tag: required, End tag: forbidden
MAP attribute definitions
name = cdata [p.50] [CI] [p.49]
This attribute assigns a name to the image map defined by a MAP element.
AREA attribute definitions
shape = default|rect|circle|poly [CI] [p.49]
This attribute specifies the shape of a region. Possible values:
default: Specifies the entire region.
rect: Define a rectangular region.
circle: Define a circular region.
poly: Define a polygonal region.
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coords = coordinates [CN] [p.49]
This attribute specifies the position and shape on the screen. The number and
order of values depends on the shape being defined. Possible combinations:
rect: left-x, top-y, right-x, bottom-y.
circle: center-x, center-y, radius. Note. When the radius value is a
percentage value, user agents should calculate the final radius value based
on the associated object’s width and height. The radius should be the
smaller value of the two.
poly: x1, y1, x2, y2, ..., xN, yN. The first x and y coordinate pair and the
last should be the same to close the polygon. When these coordinate
values are not the same, user agents should infer an additional coordinate
pair to close the polygon.
Coordinates are relative to the top, left corner of the object. All values are
lengths [p.52] . All values are separated by commas.
nohref [CI] [p.49]
When set, this boolean attribute specifies that a region has no associated link.
Attribute to associate an image map with an element
usemap = uri [p.51] [CT] [p.49]
This attribute associates an image map with an element. The image map is
defined by a MAP element. The value of usemap must match the value of the
name attribute of the associated MAP element.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
name (submitting objects with forms [p.245] )
alt (alternate text [p.181] )
href (anchor reference [p.149] ) target (frame target information [p.212] )
tabindex (tabbing navigation [p.241] )
accesskey (access keys [p.242] )
shape (image maps [p.173] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup, onfocus,
onblur (intrinsic events [p.254] )
The MAP element specifies a client-side image map (or other navigation
mechanism) that may be associated with another elements (IMG, OBJECT, or
INPUT). An image map is associated with an element via the element’s usemap
attribute. The MAP element may be used without an associated image for general
navigation mechanisms.
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The presence of the usemap attribute for an OBJECT implies that the object being
included is an image. Furthermore, when the OBJECT element has an associated
client-side image map, user agents may implement user interaction with the OBJECT
solely in terms of the client-side image map. This allows user agents (such as an
audio browser or robot) to interact with the OBJECT without having to process it; the
user agent may even elect not to retrieve (or process) the object. When an OBJECT
has an associated image map, authors should not expect that the object will be
retrieved or processed by every user agent.
The MAP element content model allows authors to combine the following:
1. One or more AREA elements. These elements have no content but specify the
geometric regions of the image map and the link associated with each region.
Note that user agents do not generally render AREA elements. Therefore,
authors must provide alternate text for each AREA with the alt attribute (see
below for information on how to specify alternate text [p.181] ).
2. Block-level content. This content should include A elements that specify the
geometric regions of the image map and the link associated with each region.
Note that the user agent should render block-level content of a MAP element.
Authors should use this method to create more accessible documents.
When a MAP element contains mixed content (both AREA elements and block-level
content), user agents must ignore the AREA elements.
Authors should specify an image maps’s geometry completely with AREA
elements, or completely with A elements, or completely with both if content is mixed.
Authors may wish to mix content so that older user agents will handle map
geometries specified by AREA elements and new user agents will take advantage of
richer block content.
If two or more defined regions overlap, the region-defining element that appears
earliest in the document takes precedence (i.e., responds to user input).
User agents and authors should offer textual alternates to graphical image maps
for cases when graphics are not available or the user cannot access them. For
example, user agents may use alt text to create textual links in place of a graphical
image map. Such links may be activated in a variety of ways (keyboard, voice
activation, etc.).
Note. MAP is not backwards compatible with HTML 2.0 user agents.
Client-side image map examples
In the following example, we create a client-side image map for the OBJECT
element. We do not want to render the image map’s contents when the OBJECT is
rendered, so we "hide" the MAP element within the OBJECT element’s content.
Consequently, the MAP element’s contents will only be rendered if the OBJECT
cannot be rendered.
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<HTML>
<HEAD>
<TITLE>The cool site!</TITLE>
</HEAD>
<BODY>
<P><OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
<MAP name="map1">
<P>Navigate the site:
<A href="guide.html" shape="rect" coords="0,0,118,28">Access Guide</a> |
<A href="shortcut.html" shape="rect" coords="118,0,184,28">Go</A> |
<A href="search.html" shape="circle" coords="184,200,60">Search</A> |
<A href="top10.html" shape="poly" coords="276,0,276,28,100,200,50,50,276,0">Top Ten</A>
</MAP>
</OBJECT>
</BODY>
</HTML>
We may want to render the image map’s contents even when a user agent can
render the OBJECT. For instance, we may want to associate an image map with an
OBJECT element and include a text navigation bar at the bottom of the page. To do
so, we define the MAP element outside the OBJECT:
<HTML>
<HEAD>
<TITLE>The cool site!</TITLE>
</HEAD>
<BODY>
<P><OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
</OBJECT>
...the rest of the page here...
<MAP name="map1">
<P>Navigate the site:
<A href="guide.html" shape="rect" coords="0,0,118,28">Access Guide</a> |
<A href="shortcut.html" shape="rect" coords="118,0,184,28">Go</A> |
<A href="search.html" shape="circle" coords="184,200,60">Search</A> |
<A href="top10.html" shape="poly" coords="276,0,276,28,100,200,50,50,276,0">Top Ten</A>
</MAP>
</BODY>
</HTML>
In the following example, we create a similar image map, this time using the AREA
element. Note the use of alt text:
<P><OBJECT data="navbar1.gif" type="image/gif" usemap="#map1">
<P>This is a navigation bar.
</OBJECT>
<MAP name="map1">
<AREA href="guide.html"
alt="Access Guide"
shape="rect"
coords="0,0,118,28">
<AREA href="search.html"
alt="Search"
shape="rect"
coords="184,0,276,28">
<AREA href="shortcut.html"
alt="Go"
shape="circle"
coords="184,200,60">
<AREA href="top10.html"
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alt="Top Ten"
shape="poly"
coords="276,0,276,28,100,200,50,50,276,0">
</MAP>
Here is a similar version using the IMG element instead of OBJECT (with the same
MAP declaration):
<P><IMG src="navbar1.gif" usemap="#map1" alt="navigation bar">
The following example illustrates how image maps may be shared.
Nested OBJECT elements are useful for providing fallbacks in case a user agent
doesn’t support certain formats. For example:
<P>
<OBJECT data="navbar.png" type="image/png">
<OBJECT data="navbar.gif" type="image/gif">
text describing the image...
</OBJECT>
</OBJECT>
If the user agent doesn’t support the PNG format, it tries to render the GIF image.
If it doesn’t support GIF (e.g., it’s a speech-based user agent), it defaults to the text
description provided as the content of the inner OBJECT element. When OBJECT
elements are nested this way, authors may share image maps among them:
<P>
<OBJECT data="navbar.png" type="image/png" usemap="#map1">
<OBJECT data="navbar.gif" type="image/gif" usemap="#map1">
<MAP name="map1">
<P>Navigate the site:
<A href="guide.html" shape="rect" coords="0,0,118,28">Access Guide</a> |
<A href="shortcut.html" shape="rect" coords="118,0,184,28">Go</A> |
<A href="search.html" shape="circle" coords="184,200,60">Search</A> |
<A href="top10.html" shape="poly" coords="276,0,276,28,100,200,50,50,276,0">Top Ten</A>
</MAP>
</OBJECT>
</OBJECT>
The following example illustrates how anchors may be specified to create inactive
zones within an image map. The first anchor specifies a small circular region with no
associated link. The second anchor specifies a larger circular region with the same
center coordinates. Combined, the two form a ring whose center is inactive and
whose rim is active. The order of the anchor definitions is important, since the
smaller circle must override the larger circle.
<MAP name="map1">
<P>
<A shape="circle" coords="100,200,50">I’m inactive.</A>
<A href="outer-ring-link.html" shape="circle" coords="100,200,250">I’m active.</A>
</MAP>
Similarly, the nohref attribute for the AREA element declares that geometric
region has no associated link.
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13.6.2 Server-side image maps
Server-side image maps may be interesting in cases where the image map is too
complicated for a client-side image map.
It is only possible to define a server-side image map for the IMG and INPUT
elements. In the case of IMG, the IMG must be inside an A element and the boolean
attribute ismap ([CI] [p.49] ) must be set. In the case of INPUT, the INPUT must be
of type "image".
When the user activates the link by clicking on the image, the screen coordinates
are sent directly to the server where the document resides. Screen coordinates are
expressed as screen pixel values relative to the image. For normative information
about the definition of a pixel and how to scale it, please consult [CSS1] [p.353] .
In the following example, the active region defines a server-side link. Thus, a click
anywhere on the image will cause the click’s coordinates to be sent to the server.
<P><A href="http://www.acme.com/cgi-bin/competition">
<IMG src="game.gif" ismap alt="target"></A>
The location clicked is passed to the server as follows. The user agent derives a
new URI from the URI specified by the href attribute of the A element, by
appending ‘?’ followed by the x and y coordinates, separated by a comma. The link
is then followed using the new URI. For instance, in the given example, if the user
clicks at the location x=10, y=27 then the derived URI is
"http://www.acme.com/cgi-bin/competition?10,27".
User agents that do not offer the user a means to select specific coordinates (e.g.,
non-graphical user agents that rely on keyboard input, speech-based user agents,
etc.) should send the coordinates "0,0" to the server when the link is activated.
13.7 Visual presentation of images, objects, and
applets
All IMG and OBJECT attributes that concern visual alignment and presentation have
been deprecated [p.38] in favor of style sheets.
13.7.1 Width and height
Attribute definitions
width = length [p.52] [CN] [p.49]
Image and object width override.
height = length [p.52] [CN] [p.49]
Image and object height override.
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When specified, the width and height attributes tell user agents to override the
natural image or object size in favor of these values.
When the object is an image, it is scaled. User agents should do their best to scale
an object or image to match the width and height specified by the author. Note that
lengths expressed as percentages are based on the horizontal or vertical space
currently available, not on the natural size of the image, object, or applet.
The height and width attributes give user agents an idea of the size of an
image or object so that they may reserve space for it and continue rendering the
document while waiting for the image data.
13.7.2 White space around images and objects
Attribute definitions
hspace = pixels [p.52] [CN] [p.49]
Deprecated. [p.38] This attribute specifies the amount of white space to be
inserted to the left and right of an IMG, APPLET, or OBJECT. The default value is
not specified, but is generally a small, non-zero length.
vspace = pixels [p.52] [CN] [p.49]
Deprecated. [p.38] This attribute specifies the amount of white space to be
inserted above and below an IMG, APPLET, or OBJECT. The default value is not
specified, but is generally a small, non-zero length.
13.7.3 Borders
An image or object may be surrounded by a border (e.g., when a border is specified
by the user or when the image is the content of an A element).
Attribute definitions
border = pixels [p.52] [CN] [p.49]
Deprecated. [p.38] This attribute specifies the width of an IMG or OBJECT
border, in pixels. The default value for this attribute depends on the user agent.
13.7.4 Alignment
Attribute definitions
align = bottom|middle|top|left|right
Deprecated. [p.38] This attribute specifies the position of an IMG, OBJECT, or
APPLET with respect to its context.
The following values for align concern the object’s position with respect to
surrounding text:
bottom: means that the bottom of the object should be vertically aligned with
the current baseline. This is the default value.
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middle: means that the center of the object should be vertically aligned with
the current baseline.
top: means that the top of the object should be vertically aligned with the top of
the current text line.
Two other values, left and right, cause the image to float to the current left or
right margin. They are discussed in the section on floating objects [p.197] .
Differing interpretations of align. User agents vary in their interpretation of the
align attribute. Some only take into account what has occurred on the text line prior
to the element, some take into account the text on both sides of the element.
13.8 How to specify alternate text
Attribute definitions
alt = text [p.50] [CS] [p.49]
For user agents that cannot display images, forms, or applets, this attribute
specifies alternate text. The language of the alternate text is specified by the
lang attribute.
Several non-textual elements (IMG, AREA, APPLET, and INPUT) let authors
specify alternate text to serve as content when the element cannot be rendered
normally. Specifying alternate text assists users without graphic display terminals,
users whose browsers don’t support forms, visually impaired users, those who use
speech synthesizers, those who have configured their graphical user agents not to
display images, etc.
The alt attribute must be specified for the IMG and AREA elements. It is optional
for the INPUT and APPLET elements.
While alternate text may be very helpful, it must be handled with care. Authors
should observe the following guidelines:
Do not specify irrelevant alternate text when including images intended to format
a page, for instance, alt="red ball" would be inappropriate for an image
that adds a red ball for decorating a heading or paragraph. In such cases, the
alternate text should be the empty string (""). Authors are in any case advised to
avoid using images to format pages; style sheets should be used instead.
Do not specify meaningless alternate text (e.g., "dummy text"). Not only will this
frustrate users, it will slow down user agents that must convert text to speech or
braille output.
Implementors should consult the section on accessibility [p.350] for information
about how to handle cases of omitted alternate text.
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14 Style Sheets
Contents
1. Introduction to style sheets .
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14.1 Introduction to style sheets
Style sheets represent a major breakthrough for Web page designers, expanding
their ability to improve the appearance of their pages. In the scientific environments
in which the Web was conceived, people are more concerned with the content of
their documents than the presentation. As people from wider walks of life discovered
the Web, the limitations of HTML became a source of continuing frustration and
authors were forced to sidestep HTML’s stylistic limitations. While the intentions
have been good -- to improve the presentation of Web pages -- the techniques for
doing so have had unfortunate side effects. These techniques work for some of the
people, some of the time, but not for all of the people, all of the time. They include:
Using proprietary HTML extensions
Converting text into images
Using images for white space control
Use of tables for page layout
Writing a program instead of using HTML
These techniques considerably increase the complexity of Web pages, offer
limited flexibility, suffer from interoperability problems, and create hardships for
people with disabilities.
Style sheets solve these problems at the same time they supersede the limited
range of presentation mechanisms in HTML. Style sheets make it easy to specify the
amount of white space between text lines, the amount lines are indented, the colors
used for the text and the backgrounds, the font size and style, and a host of other
details.
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For example, the following short CSS style sheet (stored in the file "special.css"),
sets the text color of a paragraph to green and surrounds it with a solid red border:
P.special {
color : green;
border: solid red;
}
Authors may link this style sheet to their source HTML document with the LINK
element:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<LINK href="special.css" rel="stylesheet" type="text/css">
</HEAD>
<BODY>
<P class="special">This paragraph should have special green text.
</BODY>
</HTML>
HTML 4 provides support for the following style sheet features:
Flexible placement of style information
Placing style sheets in separate files makes them easy to reuse. Sometimes it’s
useful to include rendering instructions within the document to which they apply,
either grouped at the start of the document, or in attributes of the elements
throughout the body of the document. To make it easier to manage style on a
site basis, this specification describes how to use HTTP headers to set the style
sheets to be applied to a document.
Independence from specific style sheet languages
This specification doesn’t tie HTML to any particular style sheet language. This
allows for a range of such languages to be used, for instance simple ones for
the majority of users and much more complex ones for the minority of users with
highly specialized needs. The examples included below all use the CSS
(Cascading Style Sheets) language [CSS1] [p.353] , but other style sheet
languages would be possible.
Cascading
This is the capability provided by some style sheet languages such as CSS to
allow style information from several sources to be blended together. These
could be, for instance, corporate style guidelines, styles common to a group of
documents, and styles specific to a single document. By storing these
separately, style sheets can be reused, simplifying authoring and making more
effective use of network caching. The cascade defines an ordered sequence of
style sheets where rules in later sheets have greater precedence than earlier
ones. Not all style sheet languages support cascading.
Media dependencies
HTML allows authors to specify documents in a media-independent way. This
allows users to access Web pages using a wide variety of devices and media,
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e.g., graphical displays for computers running Windows, Macintosh OS, and
X11, devices for television sets, specially adapted phones and PDA-based
portable devices, speech-based browsers, and braille-based tactile devices.
Style sheets, by contrast, apply to specific media or media groups. A style
sheet intended for screen use may be applicable when printing, but is of little
use for speech-based browsers. This specification allows you to define the
broad categories of media a given style sheet is applicable to. This allows user
agents to avoid retrieving inappropriate style sheets. Style sheet languages may
include features for describing media dependencies within the same style sheet.
Alternate styles
Authors may wish to offer readers several ways to view a document. For
instance, a style sheet for rendering compact documents with small fonts, or
one that specifies larger fonts for increased legibility. This specification allows
authors to specify a preferred style sheet as well as alternates that target
specific users or media. User agents should give users the opportunity to select
from among alternate style sheets or to switch off style sheets altogether.
Performance concerns
Some people have voiced concerns over performance issues for style sheets.
For instance, retrieving an external style sheet may delay the full presentation
for the user. A similar situation arises if the document head includes a lengthy
set of style rules.
The current proposal addresses these issues by allowing authors to include
rendering instructions within each HTML element. The rendering information is
then always available by the time the user agent wants to render each element.
In many cases, authors will take advantage of a common style sheet for a
group of documents. In this case, distributing style rules throughout the
document will actually lead to worse performance than using a linked style
sheet, since for most documents, the style sheet will already be present in the
local cache. The public availability of good style sheets will encourage this
effect.
14.2 Adding style to HTML
Note. The sample default style sheet for HTML 4 that is included in [CSS2] [p.355]
expresses generally accepted default style information for each element. Authors
and implementors alike might find this a useful resource.
HTML documents may contain style sheet rules directly in them or they may
import style sheets.
Any style sheet language may be used with HTML. A simple style sheet language
may suffice for the needs of most users, but other languages may be more suited to
highly specialized needs. This specification uses the style language "Cascading
Style Sheets" ([CSS1] [p.353] ), abbreviated CSS, for examples.
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The syntax of style data [p.57] depends on the style sheet language.
14.2.1 Setting the default style sheet language
Authors must specify the style sheet language of style information associated with
an HTML document.
Authors should use the META element to set the default style sheet language for a
document. For example, to set the default to CSS, authors should put the following
declaration in the HEAD of their documents:
<META http-equiv="Content-Style-Type" content="text/css">
The default style sheet language may also be set with HTTP headers. The above
META declaration is equivalent to the HTTP header:
Content-Style-Type: text/css
User agents should determine the default style sheet language for a document
according to the following steps (highest to lowest priority):
1. If any META declarations specify the "Content-Style-Type", the last one in the
character stream determines the default style sheet language.
2. Otherwise, if any HTTP headers specify the "Content-Style-Type", the last one
in the character stream determines the default style sheet language.
3. Otherwise, the default style sheet language is "text/css".
Documents that include elements that set the style attribute but which don’t
define a default style sheet language are incorrect. Authoring tools should generate
default style sheet language information (typically a META declaration) so that user
agents do not have to rely on a default of "text/css".
14.2.2 Inline style information
Attribute definitions
style = style [p.57] [CN] [p.49]
This attribute specifies style information for the current element.
The syntax [p.57] of the value of the style attribute is determined by the default
style sheet language [p.186] . For example, for [[CSS2]] inline style, use the
declaration block syntax described in section 4.1.8 (without curly brace delimiters).
This CSS example sets color and font size information for the text in a specific
paragraph.
<P style="font-size: 12pt; color: fuchsia">Aren’t style sheets wonderful?
In CSS, property declarations have the form "name : value" and are separated by
a semi-colon.
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To specify style information for more than one element, authors should use the
STYLE element. For optimal flexibility, authors should define styles in external style
sheets.
14.2.3 Header style information: the STYLE element
<!ELEMENT STYLE - - %StyleSheet
<!ATTLIST STYLE
%i18n;
type
%ContentType; #REQUIRED
media
%MediaDesc;
#IMPLIED
title
%Text;
#IMPLIED
>
-- style info -->
-----
lang, dir, for use with title -content type of style language -designed for use with these media -advisory title --
Start tag: required, End tag: required
Attribute definitions
type = content-type [p.53] [CI] [p.49]
This attribute specifies the style sheet language of the element’s contents and
overrides the default style sheet language. The style sheet language is specified
as a content type (e.g., "text/css"). Authors must supply a value for this attribute;
there is no default value for this attribute.
media = media-descriptors [p.56] [CI] [p.49]
This attribute specifies the intended destination medium for style information. It
may be a single media descriptor or a comma-separated list. The default value
for this attribute is "screen".
Attributes defined elsewhere
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
The STYLE element allows authors to put style sheet rules in the head of the
document. HTML permits any number of STYLE elements in the HEAD section of a
document.
User agents that don’t support style sheets, or don’t support the specific style
sheet language used by a STYLE element, must hide the contents of the STYLE
element. It is an error to render the content as part of the document’s text. Some
style sheet languages support syntax for hiding the content [p.193] from
non-conforming user agents.
The syntax of style data [p.57] depends on the style sheet language.
Some style sheet implementations may allow a wider variety of rules in the STYLE
element than in the style attribute. For example, with CSS, rules may be declared
within a STYLE element for:
All instances of a specific HTML element (e.g., all P elements, all H1 elements,
etc.)
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All instances of an HTML element belonging to a specific class (i.e., whose
class attribute is set to some value).
Single instances of an HTML element (i.e., whose id attribute is set to some
value).
Rules for style rule precedences and inheritance depend on the style sheet
language.
The following CSS STYLE declaration puts a border around every H1 element in
the document and centers it on the page.
<HEAD>
<STYLE type="text/css">
H1 {border-width: 1; border: solid; text-align: center}
</STYLE>
</HEAD>
To specify that this style information should only apply to H1 elements of a specific
class, we modify it as follows:
<HEAD>
<STYLE type="text/css">
H1.myclass {border-width: 1; border: solid; text-align: center}
</STYLE>
</HEAD>
<BODY>
<H1 class="myclass"> This H1 is affected by our style </H1>
<H1> This one is not affected by our style </H1>
</BODY>
Finally, to limit the scope of the style information to a single instance of H1, set the
id attribute:
<HEAD>
<STYLE type="text/css">
#myid {border-width: 1; border: solid; text-align: center}
</STYLE>
</HEAD>
<BODY>
<H1 class="myclass"> This H1 is not affected </H1>
<H1 id="myid"> This H1 is affected by style </H1>
<H1> This H1 is not affected </H1>
</BODY>
Although style information may be set for almost every HTML element, two
elements, DIV and SPAN, are particularly useful in that they do not impose any
presentation semantics (besides block-level vs. inline [p.73] ). When combined with
style sheets, these elements allow users to extend HTML indefinitely, particularly
when used with the class and id attributes.
In the following example, we use the SPAN element to set the font style of the first
few words of a paragraph to small caps.
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<HEAD>
<STYLE type="text/css">
SPAN.sc-ex { font-variant: small-caps }
</STYLE>
</HEAD>
<BODY>
<P><SPAN class="sc-ex">The first</SPAN> few words of
this paragraph are in small-caps.
</BODY>
In the following example, we use DIV and the class attribute to set the text
justification for a series of paragraphs that make up the abstract section of a
scientific article. This style information could be reused for other abstract sections by
setting the class attribute elsewhere in the document.
<HEAD>
<STYLE type="text/css">
DIV.Abstract { text-align: justify }
</STYLE>
</HEAD>
<BODY>
<DIV class="Abstract">
<P>The Chieftain product range is our market winner for
the coming year. This report sets out how to position
Chieftain against competing products.
<P>Chieftain replaces the Commander range, which will
remain on the price list until further notice.
</DIV>
</BODY>
14.2.4 Media types
HTML allows authors to design documents that take advantage of the characteristics
of the media where the document is to be rendered (e.g., graphical displays,
television screens, handheld devices, speech-based browsers, braille-based tactile
devices, etc.). By specifying the media attribute, authors allow user agents to load
and apply style sheets selectively. Please consult the list of recognized media
descriptors [p.56] .
The following sample declarations apply to H1 elements. When projected in a
business meeting, all instances will be blue. When printed, all instances will be
centered.
<HEAD>
<STYLE type="text/css" media="projection">
H1 { color: blue}
</STYLE>
<STYLE type="text/css" media="print">
H1 { text-align: center }
</STYLE>
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This example adds sound effects to anchors for use in speech output:
<STYLE type="text/css" media="aural">
A { cue-before: uri(bell.aiff); cue-after: uri(dong.wav)}
</STYLE>
</HEAD>
Media control is particularly interesting when applied to external style sheets since
user agents can save time by retrieving from the network only those style sheets that
apply to the current device. For instance, speech-based browsers can avoid
downloading style sheets designed for visual rendering. See the section on
media-dependent cascades [p.192] for more information.
14.3 External style sheets
Authors may separate style sheets from HTML documents. This offers several
benefits:
Authors and Web site managers may share style sheets across a number of
documents (and sites).
Authors may change the style sheet without requiring modifications to the
document.
User agents may load style sheets selectively (based on media descriptions).
14.3.1 Preferred and alternate style sheets
HTML allows authors to associate any number of external style sheets with a
document. The style sheet language defines how multiple external style sheets
interact (for example, the CSS "cascade" rules).
Authors may specify a number of mutually exclusive style sheets called alternate
style sheets. Users may select their favorite among these depending on their
preferences. For instance, an author may specify one style sheet designed for small
screens and another for users with weak vision (e.g., large fonts). User agents
should allow users to select from alternate style sheets.
The author may specify that one of the alternates is a preferred style sheet. User
agents should apply the author’s preferred style sheet unless the user has selected
a different alternate.
Authors may group several alternate style sheets (including the author’s preferred
style sheets) under a single style name. When a user selects a named style, the
user agent must apply all style sheets with that name. User agents must not apply
alternate style sheets with a different style name. The section on specifying external
style sheets [p.191] explains how to name a group of style sheets.
Authors may also specify persistent style sheets that user agents must apply in
addition to any alternate style sheet.
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User agents must respect media descriptors [p.56] when applying any style sheet.
User agents should also allow users to disable the author’s style sheets entirely, in
which case the user agent must not apply any persistent or alternate style sheets.
14.3.2 Specifying external style sheets
Authors specify external style sheets with the following attributes of the LINK
element:
Set the value of href to the location of the style sheet file. The value of href is
a URI [p.51] .
Set the value of the type attribute to indicate the language of the linked (style
sheet) resource. This allows the user agent to avoid downloading a style sheet
for an unsupported style sheet language.
Specify that the style sheet is persistent, preferred, or alternate:
To make a style sheet persistent, set the rel attribute to "stylesheet" and
don’t set the title attribute.
To make a style sheet preferred, set the rel attribute to "stylesheet" and
name the style sheet with the title attribute.
To specify an alternate style sheet, set the rel attribute to "alternate
stylesheet" and name the style sheet with the title attribute.
User agents should provide a means for users to view and pick from the list of
alternate styles. The value of the title attribute is recommended as the name of
each choice.
In this example, we first specify a persistent style sheet located in the file
mystyle.css:
<LINK href="mystyle.css" rel="stylesheet" type="text/css">
Setting the title attribute makes this the author’s preferred style sheet:
<LINK href="mystyle.css" title="compact" rel="stylesheet" type="text/css">
Adding the keyword "alternate" to the rel attribute makes it an alternate style
sheet:
<LINK href="mystyle.css" title="Medium" rel="alternate stylesheet" type="text/css">
For more information on external style sheets, please consult the section on links
and external style sheets. [p.155]
Authors may also use the META element to set the document’s preferred style
sheet. For example, to set the preferred style sheet to "compact" (see the preceding
example), authors may include the following line in the HEAD:
<META http-equiv="Default-Style" content="compact">
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The preferred style sheet may also be specified with HTTP headers. The above
META declaration is equivalent to the HTTP header:
Default-Style: "compact"
If two or more META declarations or HTTP headers specify the preferred style
sheet, the last one takes precedence. HTTP headers are considered to occur earlier
than the document HEAD for this purpose.
If two or more LINK elements specify a preferred style sheet, the first one takes
precedence.
Preferred style sheets specified with META or HTTP headers have precedence
over those specified with the LINK element.
14.4 Cascading style sheets
Cascading style sheet languages such as CSS allow style information from several
sources to be blended together. However, not all style sheet languages support
cascading. To define a cascade, authors specify a sequence of LINK and/or STYLE
elements. The style information is cascaded in the order the elements appear in the
HEAD.
Note. This specification does not specify how style sheets from different style
languages cascade. Authors should avoid mixing style sheet languages.
In the following example, we specify two alternate style sheets named "compact".
If the user selects the "compact" style, the user agent must apply both external style
sheets, as well as the persistent "common.css" style sheet. If the user selects the
"big print" style, only the alternate style sheet "bigprint.css" and the persistent
"common.css" will be applied.
<LINK
<LINK
<LINK
<LINK
rel="alternate stylesheet" title="compact" href="small-base.css" type="text/css">
rel="alternate stylesheet" title="compact" href="small-extras.css" type="text/css">
rel="alternate stylesheet" title="big print" href="bigprint.css" type="text/css">
rel="stylesheet" href="common.css" type="text/css">
Here is a cascade example that involves both the LINK and STYLE elements.
<LINK rel="stylesheet" href="corporate.css" type="text/css">
<LINK rel="stylesheet" href="techreport.css" type="text/css">
<STYLE type="text/css">
p.special { color: rgb(230, 100, 180) }
</STYLE>
14.4.1 Media-dependent cascades
A cascade may include style sheets applicable to different media. Both LINK and
STYLE may be used with the media attribute. The user agent is then responsible for
filtering out those style sheets that do not apply to the current medium.
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In the following example, we define a cascade where the "corporate" style sheet is
provided in several versions: one suited to printing, one for screen use and one for
speech-based browsers (useful, say, when reading email in the car). The
"techreport" stylesheet applies to all media. The color rule defined by the STYLE
element is used for print and screen but not for aural rendering.
<LINK rel="stylesheet" media="aural" href="corporate-aural.css" type="text/css">
<LINK rel="stylesheet" media="screen" href="corporate-screen.css" type="text/css">
<LINK rel="stylesheet" media="print" href="corporate-print.css" type="text/css">
<LINK rel="stylesheet" href="techreport.css" type="text/css">
<STYLE media="screen, print" type="text/css">
p.special { color: rgb(230, 100, 180) }
</STYLE>
14.4.2 Inheritance and cascading
When the user agent wants to render a document, it needs to find values for style
properties, e.g. the font family, font style, size, line height, text color and so on. The
exact mechanism depends on the style sheet language, but the following description
is generally applicable:
The cascading mechanism is used when a number of style rules all apply directly
to an element. The mechanism allows the user agent to sort the rules by specificity,
to determine which rule to apply. If no rule can be found, the next step depends on
whether the style property can be inherited or not. Not all properties can be inherited.
For these properties the style sheet language provides default values for use when
there are no explicit rules for a particular element.
If the property can be inherited, the user agent examines the immediately
enclosing element to see if a rule applies to that. This process continues until an
applicable rule is found. This mechanism allows style sheets to be specified
compactly. For instance, authors may specify the font family for all elements within
the BODY by a single rule that applies to the BODY element.
14.5 Hiding style data from user agents
Some style sheet languages support syntax intended to allow authors to hide the
content of STYLE elements from non-conforming user agents.
This example illustrates for CSS how to comment out the content of STYLE
elements to ensure that older, non-conforming user agents will not render them as
text.
<STYLE type="text/css">
<!-H1 { color: red }
P { color: blue}
-->
</STYLE>
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14.6 Linking to style sheets with HTTP headers
This section only applies to user agents conforming to versions of HTTP that define
a Link header field. Note that HTTP 1.1 as defined by [RFC2616] [p.354] does not
include a Link header field (refer to section 19.6.3).
Web server managers may find it convenient to configure a server so that a style
sheet will be applied to a group of pages. The HTTP Link header has the same
effect as a LINK element with the same attributes and values. Multiple Link
headers correspond to multiple LINK elements occurring in the same order. For
instance,
Link: <http://www.acme.com/corporate.css>; REL=stylesheet
corresponds to:
<LINK rel="stylesheet" href="http://www.acme.com/corporate.css">
It is possible to specify several alternate styles using multiple Link headers, and
then use the rel attribute to determine the default style.
In the following example, "compact" is applied by default since it omits the
"alternate" keyword for the rel attribute.
Link: <compact.css>; rel="stylesheet"; title="compact"
Link: <bigprint.css>; rel="alternate stylesheet"; title="big print"
This should also work when HTML documents are sent by email. Some email
agents can alter the ordering of [RFC822] [p.356] headers. To protect against this
affecting the cascading order for style sheets specified by Link headers, authors
can use header concatenation to merge several instances of the same header field.
The quote marks are only needed when the attribute values include whitespace. Use
SGML entities to reference characters that are otherwise not permitted within HTTP
or email headers, or that are likely to be affected by transit through gateways.
LINK and META elements implied by HTTP headers are defined as occurring
before any explicit LINK and META elements in the document’s HEAD.
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15 Alignment, font styles, and horizontal rules
Contents
1. Formatting .
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1. Background color
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2. Alignment .
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3. Floating objects .
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Float an object .
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Float text around an object .
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2. Fonts
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1. Font style elements: the TT, I, B, BIG, SMALL, STRIKE, S, and U elements
199
2. Font modifier elements: FONT and BASEFONT
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3. Rules: the HR element
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This section of the specification discusses some HTML elements and attributes
that may be used for visual formatting of elements. Many of them are deprecated
[p.38] .
15.1 Formatting
15.1.1 Background color
Attribute definitions
bgcolor = color [p.51] [CI] [p.49]
Deprecated. [p.38] This attribute sets the background color for the document
body or table cells.
This attribute sets the background color of the canvas for the document body (the
BODY element) or for tables (the TABLE, TR, TH, and TD elements). Additional
attributes for specifying text color can be used with the BODY element.
This attribute has been deprecated [p.38] in favor of style sheets for specifying
background color information.
15.1.2 Alignment
It is possible to align block elements (tables, images, objects, paragraphs, etc.) on
the canvas with the align attribute. Although this attribute may be set for many
HTML elements, its range of possible values sometimes differs from element to
element. Here we only discuss the meaning of the align attribute for text.
Attribute definitions
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align = left|center|right|justify [CI] [p.49]
Deprecated. [p.38] This attribute specifies the horizontal alignment of its
element with respect to the surrounding context. Possible values:
left: text lines are rendered flush left.
center: text lines are centered.
right: text lines are rendered flush right.
justify: text lines are justified to both margins.
The default depends on the base text direction. For left to right text, the default is
align=left, while for right to left text, the default is align=right.
DEPRECATED EXAMPLE:
This example centers a heading on the canvas.
<H1 align="center"> How to Carve Wood </H1>
Using CSS, for example, you could achieve the same effect as follows:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
H1 { text-align: center}
</STYLE>
<BODY>
<H1> How to Carve Wood </H1>
Note that this would center all H1 declarations. You could reduce the scope of the
style by setting the class attribute on the element:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
H1.wood {text-align: center}
</STYLE>
<BODY>
<H1 class="wood"> How to Carve Wood </H1>
DEPRECATED EXAMPLE:
Similarly, to right align a paragraph on the canvas with HTML’s align attribute you
could have:
<P align="right">...Lots of paragraph text...
which, with CSS, would be:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
P.mypar {text-align: right}
</STYLE>
<BODY>
<P class="mypar">...Lots of paragraph text...
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DEPRECATED EXAMPLE:
To right align a series of paragraphs, group them with the DIV element:
<DIV align="right">
<P>...text in first paragraph...
<P>...text in second paragraph...
<P>...text in third paragraph...
</DIV>
With CSS, the text-align property is inherited from the parent element, you can
therefore use:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
DIV.mypars {text-align: right}
</STYLE>
<BODY>
<DIV class="mypars">
<P>...text in first paragraph...
<P>...text in second paragraph...
<P>...text in third paragraph...
</DIV>
To center the entire document with CSS:
<HEAD>
<TITLE>How to Carve Wood</TITLE>
<STYLE type="text/css">
BODY {text-align: center}
</STYLE>
<BODY>
...the body is centered...
</BODY>
The CENTER element is exactly equivalent to specifying the DIV element with the
align attribute set to "center". The CENTER element is deprecated [p.38] .
15.1.3 Floating objects
Images and objects may appear directly "in-line" or may be floated to one side of the
page, temporarily altering the margins of text that may flow on either side of the
object.
Float an object
The align attribute for objects, images, tables, frames, etc., causes the object to
float to the left or right margin. Floating objects generally begin a new line. This
attribute takes the following values:
left: Floats the object to the current left margin. Subsequent text flows along
the image’s right side.
right: Floats the object to the current right margin. Subsequent text flows
along the image’s left side.
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DEPRECATED EXAMPLE:
The following example shows how to float an IMG element to the current left margin
of the canvas.
<IMG align="left" src="http://foo.com/animage.gif" alt="my boat">
Some alignment attributes also permit the "center" value, which does not cause
floating, but centers the object within the current margins. However, for P and DIV,
the value "center" causes the contents of the element to be centered.
Float text around an object
Another attribute, defined for the BR element, controls text flow around floating
objects.
Attribute definitions
clear = none|left|right|all [CI] [p.49]
Deprecated. [p.38] Specifies where the next line should appear in a visual
browser after the line break caused by this element. This attribute takes into
account floating objects (images, tables, etc.). Possible values:
none: The next line will begin normally. This is the default value.
left: The next line will begin at nearest line below any floating objects on
the left-hand margin.
right: The next line will begin at nearest line below any floating objects
on the right-hand margin.
all: The next line will begin at nearest line below any floating objects on
either margin.
Consider the following visual scenario, where text flows to the right of an image
until a line is broken by a BR:
*********
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| image |
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*********
--------------<BR>
If the clear attribute is set to none, the line following BR will begin immediately
below it at the right margin of the image:
*********
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| image |
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*********
--------------<BR>
------
DEPRECATED EXAMPLE:
If the clear attribute is set to left or all, the next line will appear as follows:
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********* ------|
| ------| image | --<BR clear="left">
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*********
-----------------
Using style sheets, you could specify that all line breaks should behave this way
for objects (images, tables, etc.) floating against the left margin. With CSS, you could
achieve this as follows:
<STYLE type="text/css">
BR { clear: left }
</STYLE>
To specify this behavior for a specific instance of the BR element, you could
combine style information and the id attribute:
<HEAD>
...
<STYLE type="text/css">
BR#mybr { clear: left }
</STYLE>
</HEAD>
<BODY>
<P>...
********* ------|
| ------| table | --<BR id="mybr">
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*********
----------------...
</BODY>
15.2 Fonts
The following HTML elements specify font information. Although they are not all
deprecated [p.38] , their use is discouraged in favor of style sheets.
15.2.1 Font style elements: the TT, I, B, BIG, SMALL,
STRIKE, S, and U elements
<!ENTITY % fontstyle
"TT | I | B | BIG | SMALL">
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
%attrs;
-- %coreattrs, %i18n, %events ->
Start tag: required, End tag: required
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Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown onkeyup (intrinsic
events [p.254] )
Rendering of font style elements depends on the user agent. The following is an
informative description only.
TT: Renders as teletype or monospaced text.
I: Renders as italic text style.
B: Renders as bold text style.
BIG: Renders text in a "large" font.
SMALL: Renders text in a "small" font.
STRIKE and S: Deprecated. [p.38] Render strike-through style text.
U: Deprecated. [p.38] Renders underlined text.
The following sentence shows several types of text:
<P><b>bold</b>,
<i>italic</i>, <b><i>bold italic</i></b>, <tt>teletype text</tt>, and
<big>big</big> and <small>small</small> text.
These words might be rendered as follows:
It is possible to achieve a much richer variety of font effects using style sheets. To
specify blue, italic text in a paragraph with CSS:
<HEAD>
<STYLE type="text/css">
P#mypar {font-style: italic; color: blue}
</STYLE>
</HEAD>
<P id="mypar">...Lots of blue italic text...
Font style elements must be properly nested. Rendering of nested font style
elements depends on the user agent.
15.2.2 Font modifier elements: FONT and BASEFONT
FONT and BASEFONT are deprecated [p.38] .
See the Transitional DTD [p.283] for the formal definition.
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Attribute definitions
size = cdata [p.50] [CN] [p.49]
Deprecated. [p.38] This attribute sets the size of the font. Possible values:
An integer between 1 and 7. This sets the font to some fixed size, whose
rendering depends on the user agent. Not all user agents may render all
seven sizes.
A relative increase in font size. The value "+1" means one size larger. The
value "-3" means three sizes smaller. All sizes belong to the scale of 1 to 7.
color = color [p.51] [CI] [p.49]
Deprecated. [p.38] This attribute sets the text color.
face = cdata [p.50] [CI] [p.49]
Deprecated. [p.38] This attribute defines a comma-separated list of font names
the user agent should search for in order of preference.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
The FONT element changes the font size and color for text in its contents.
The BASEFONT element sets the base font size (using the size attribute). Font
size changes achieved with FONT are relative to the base font size set by
BASEFONT. If BASEFONT is not used, the default base font size is 3.
DEPRECATED EXAMPLE:
The following example will show the difference between the seven font sizes
available with FONT:
<P><font size=1>size=1</font>
<font size=2>size=2</font>
<font size=3>size=3</font>
<font size=4>size=4</font>
<font size=5>size=5</font>
<font size=6>size=6</font>
<font size=7>size=7</font>
This might be rendered as:
The following shows an example of the effect of relative font sizes using a base
font size of 3:
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The base font size does not apply to headings, except where these are modified
using the FONT element with a relative font size change.
15.3 Rules: the HR element
<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ATTLIST HR
%attrs;
-- %coreattrs, %i18n, %events ->
Start tag: required, End tag: forbidden
Attribute definitions
align = left|center|right [CI] [p.49]
Deprecated. [p.38] This attribute specifies the horizontal alignment of the rule
with respect to the surrounding context. Possible values:
left: the rule is rendered flush left.
center: the rule is centered.
right: the rule is rendered flush right.
The default is align=center.
noshade [CI] [p.49]
Deprecated. [p.38] When set, this boolean attribute requests that the user
agent render the rule in a solid color rather than as the traditional two-color
"groove".
size = pixels [p.52] [CI] [p.49]
Deprecated. [p.38] This attribute specifies the height of the rule. The default
value for this attribute depends on the user agent.
width = length [p.52] [CI] [p.49]
Deprecated. [p.38] This attribute specifies the width of the rule. The default
width is 100%, i.e., the rule extends across the entire canvas.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
The HR element causes a horizontal rule to be rendered by visual user agents.
The amount of vertical space inserted between a rule and the content that
surrounds it depends on the user agent.
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DEPRECATED EXAMPLE:
This example centers the rules, sizing them to half the available width between the
margins. The top rule has the default thickness while the bottom two are set to 5
pixels. The bottom rule should be rendered in a solid color without shading:
<HR width="50%" align="center">
<HR size="5" width="50%" align="center">
<HR noshade size="5" width="50%" align="center">
These rules might be rendered as follows:
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Frames in HTML documents
16 Frames
Contents
1. Introduction to frames
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2. Layout of frames
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1. The FRAMESET element .
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Rows and columns .
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Nested frame sets .
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Sharing data among frames .
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2. The FRAME element .
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Setting the initial contents of a frame
Visual rendering of a frame .
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3. Specifying target frame information .
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1. Setting the default target for links
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2. Target semantics
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4. Alternate content
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1. The NOFRAMES element .
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2. Long descriptions of frames .
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5. Inline frames: the IFRAME element .
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16.1 Introduction to frames
HTML frames allow authors to present documents in multiple views, which may be
independent windows or subwindows. Multiple views offer designers a way to keep
certain information visible, while other views are scrolled or replaced. For example,
within the same window, one frame might display a static banner, a second a
navigation menu, and a third the main document that can be scrolled through or
replaced by navigating in the second frame.
Here is a simple frame document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A simple frameset document</TITLE>
</HEAD>
<FRAMESET cols="20%, 80%">
<FRAMESET rows="100, 200">
<FRAME src="contents_of_frame1.html">
<FRAME src="contents_of_frame2.gif">
</FRAMESET>
<FRAME src="contents_of_frame3.html">
<NOFRAMES>
<P>This frameset document contains:
<UL>
<LI><A href="contents_of_frame1.html">Some neat contents</A>
<LI><IMG src="contents_of_frame2.gif" alt="A neat image">
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<LI><A href="contents_of_frame3.html">Some other neat contents</A>
</UL>
</NOFRAMES>
</FRAMESET>
</HTML>
that might create a frame layout something like this:
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If the user agent can’t display frames or is configured not to, it will render the
contents of the NOFRAMES element.
16.2 Layout of frames
An HTML document that describes frame layout (called a frameset document) has a
different makeup than an HTML document without frames. A standard document has
one HEAD section and one BODY. A frameset document has a HEAD, and a
FRAMESET in place of the BODY.
The FRAMESET section of a document specifies the layout of views in the main
user agent window. In addition, the FRAMESET section can contain a NOFRAMES
element to provide alternate content [p.214] for user agents that do not support
frames or are configured not to display frames.
Elements that might normally be placed in the BODY element must not appear
before the first FRAMESET element or the FRAMESET will be ignored.
16.2.1 The FRAMESET element
<![ %HTML.Frameset; [
<!ELEMENT FRAMESET - - ((FRAMESET|FRAME)+ & NOFRAMES?) -- window subdivision-->
<!ATTLIST FRAMESET
%coreattrs;
-- id, class, style, title -rows
%MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 row) -cols
%MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 col) --
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onload
onunload
>
]]>
%Script;
%Script;
#IMPLIED
#IMPLIED
-- all the frames have been loaded --- all the frames have been removed --
Attribute definitions
rows = multi-length-list [p.52] [CN] [p.49]
This attribute specifies the layout of horizontal frames. It is a comma-separated
list of pixels, percentages, and relative lengths. The default value is 100%,
meaning one row.
cols = multi-length-list [p.52] [CN] [p.49]
This attribute specifies the layout of vertical frames. It is a comma-separated list
of pixels, percentages, and relative lengths. The default value is 100%, meaning
one column.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
title (element title [p.63] )
style (inline style information [p.186] )
onload, onunload (intrinsic events [p.254] )
The FRAMESET element specifies the layout of the main user window in terms of
rectangular subspaces.
Rows and columns
Setting the rows attribute defines the number of horizontal subspaces in a frameset.
Setting the cols attribute defines the number of vertical subspaces. Both attributes
may be set simultaneously to create a grid.
If the rows attribute is not set, each column extends the entire length of the page.
If the cols attribute is not set, each row extends the entire width of the page. If
neither attribute is set, the frame takes up exactly the size of the page.
Frames are created left-to-right for columns and top-to-bottom for rows. When
both attributes are specified, views are created left-to-right in the top row, left-to-right
in the second row, etc.
The first example divides the screen vertically in two (i.e., creates a top half and a
bottom half).
<FRAMESET rows="50%, 50%">
...the rest of the definition...
</FRAMESET>
The next example creates three columns: the second has a fixed width of 250
pixels (useful, for example, to hold an image with a known size). The first receives
25% of the remaining space and the third 75% of the remaining space.
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<FRAMESET cols="1*,250,3*">
...the rest of the definition...
</FRAMESET>
The next example creates a 2x3 grid of subspaces.
<FRAMESET rows="30%,70%" cols="33%,34%,33%">
...the rest of the definition...
</FRAMESET>
For the next example, suppose the browser window is currently 1000 pixels high.
The first view is allotted 30% of the total height (300 pixels). The second view is
specified to be exactly 400 pixels high. This leaves 300 pixels to be divided between
the other two frames. The fourth frame’s height is specified as "2*", so it is twice as
high as the third frame, whose height is only "*" (equivalent to 1*). Therefore the third
frame will be 100 pixels high and the fourth will be 200 pixels high.
<FRAMESET rows="30%,400,*,2*">
...the rest of the definition...
</FRAMESET>
Absolute lengths that do not sum to 100% of the real available space should be
adjusted by the user agent. When underspecified, remaining space should be
allotted proportionally to each view. When overspecified, each view should be
reduced according to its specified proportion of the total space.
Nested frame sets
Framesets may be nested to any level.
In the following example, the outer FRAMESET divides the available space into
three equal columns. The inner FRAMESET then divides the second area into two
rows of unequal height.
<FRAMESET cols="33%, 33%, 34%">
...contents of first frame...
<FRAMESET rows="40%, 50%">
...contents of second frame, first row...
...contents of second frame, second row...
</FRAMESET>
...contents of third frame...
</FRAMESET>
Sharing data among frames
Authors may share data among several frames by including this data via an OBJECT
element. Authors should include the OBJECT element in the HEAD element of a
frameset document and name it with the id attribute. Any document that is the
contents of a frame in the frameset may refer to this identifier.
The following example illustrates how a script might refer to an OBJECT element
defined for an entire frameset:
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>This is a frameset with OBJECT in the HEAD</TITLE>
<!-- This OBJECT is not rendered! -->
<OBJECT id="myobject" data="data.bar"></OBJECT>
</HEAD>
<FRAMESET>
<FRAME src="bianca.html" name="bianca">
</FRAMESET>
</HTML>
<!-- In bianca.html -->
<HTML>
<HEAD>
<TITLE>Bianca’s page</TITLE>
</HEAD>
<BODY>
...the beginning of the document...
<P>
<SCRIPT type="text/javascript">
parent.myobject.myproperty
</SCRIPT>
...the rest of the document...
</BODY>
</HTML>
16.2.2 The FRAME element
<![ %HTML.Frameset; [
<!-- reserved frame names start with "_" otherwise starts with letter -->
<!ELEMENT FRAME - O EMPTY
-- subwindow -->
<!ATTLIST FRAME
%coreattrs;
-- id, class, style, title -longdesc
%URI;
#IMPLIED -- link to long description
(complements title) -name
CDATA
#IMPLIED -- name of frame for targetting -src
%URI;
#IMPLIED -- source of frame content -frameborder (1|0)
1
-- request frame borders? -marginwidth %Pixels;
#IMPLIED -- margin widths in pixels -marginheight %Pixels;
#IMPLIED -- margin height in pixels -noresize
(noresize)
#IMPLIED -- allow users to resize frames? -scrolling
(yes|no|auto) auto
-- scrollbar or none ->
]]>
Attribute definitions
name = cdata [p.50] [CI] [p.49]
This attribute assigns a name to the current frame. This name may be used as
the target of subsequent links.
longdesc = uri [p.51] [CT] [p.49]
This attribute specifies a link to a long description of the frame. This description
should supplement the short description provided using the title attribute, and
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may be particularly useful for non-visual user agents.
src = uri [p.51] [CT] [p.49]
This attribute specifies the location of the initial contents to be contained in the
frame.
noresize [CI] [p.49]
When present, this boolean attribute tells the user agent that the frame window
must not be resizeable.
scrolling = auto|yes|no [CI] [p.49]
This attribute specifies scroll information for the frame window. Possible values
auto: This value tells the user agent to provide scrolling devices for the
frame window when necessary. This is the default value.
yes: This value tells the user agent to always provide scrolling devices for
the frame window.
no: This value tells the user agent not to provide scrolling devices for the
frame window.
frameborder = 1|0 [CN] [p.49]
This attribute provides the user agent with information about the frame border.
Possible values:
1: This value tells the user agent to draw a separator between this frame
and every adjoining frame. This is the default value.
0: This value tells the user agent not to draw a separator between this
frame and every adjoining frame. Note that separators may be drawn next
to this frame nonetheless if specified by other frames.
marginwidth = pixels [p.52] [CN] [p.49]
This attribute specifies the amount of space to be left between the frame’s
contents in its left and right margins. The value must be greater than zero
(pixels). The default value depends on the user agent.
marginheight = pixels [p.52] [CN] [p.49]
This attribute specifies the amount of space to be left between the frame’s
contents in its top and bottom margins. The value must be greater than zero
(pixels). The default value depends on the user agent.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
title (element title [p.63] )
style (inline style information [p.186] )
The FRAME element defines the contents and appearance of a single frame.
Setting the initial contents of a frame
The src attribute specifies the initial document the frame will contain.
The following example HTML document:
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Frames in HTML documents
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET cols="33%,33%,33%">
<FRAMESET rows="*,200">
<FRAME src="contents_of_frame1.html">
<FRAME src="contents_of_frame2.gif">
</FRAMESET>
<FRAME src="contents_of_frame3.html">
<FRAME src="contents_of_frame4.html">
</FRAMESET>
</HTML>
should create a frame layout something like this:
-----------------------------------------|Frame 1
|Frame 3
|Frame 4
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-------------|
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------------------------------------------
and cause the user agent to load each file into a separate view.
The contents of a frame must not be in the same document as the frame’s
definition.
ILLEGAL EXAMPLE:
The following frameset definition is not legal HTML since the contents of the second
frame are in the same document as the frameset.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET cols="50%,50%">
<FRAME src="contents_of_frame1.html">
<FRAME src="#anchor_in_same_document">
<NOFRAMES>
...some text...
<H2><A name="anchor_in_same_document">Important section</A></H2>
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...some text...
</NOFRAMES>
</FRAMESET>
</HTML>
Visual rendering of a frame
The following example illustrates the usage of the decorative FRAME attributes. We
specify that frame 1 will allow no scroll bars. Frame 2 will leave white space around
its contents (initially, an image file) and the frame will not be resizeable. No border
will be drawn between frames 3 and 4. Borders will be drawn (by default) between
frames 1, 2, and 3.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET cols="33%,33%,33%">
<FRAMESET rows="*,200">
<FRAME src="contents_of_frame1.html" scrolling="no">
<FRAME src="contents_of_frame2.gif"
marginwidth="10" marginheight="15"
noresize>
</FRAMESET>
<FRAME src="contents_of_frame3.html" frameborder="0">
<FRAME src="contents_of_frame4.html" frameborder="0">
</FRAMESET>
</HTML>
16.3 Specifying target frame information
Note. For information about current practice in determining the target of a frame,
please consult the notes on frames [p.350] in the appendix.
Attribute definitions
target = frame-target [p.57] [CI] [p.49]
This attribute specifies the name of a frame where a document is to be opened.
By assigning a name to a frame via the name attribute, authors can refer to it as the
"target" of links defined by other elements. The target attribute may be set for
elements that create links (A, LINK), image maps (AREA), and forms (FORM).
Please consult the section on target frame names [p.57] for information about
recognized frame names.
This example illustrates how targets allow the dynamic modification of a frame’s
contents. First we define a frameset in the document frameset.html, shown here:
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document</TITLE>
</HEAD>
<FRAMESET rows="50%,50%">
<FRAME name="fixed" src="init_fixed.html">
<FRAME name="dynamic" src="init_dynamic.html">
</FRAMESET>
</HTML>
Then, in init_dynamic.html, we link to the frame named "dynamic".
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<TITLE>A document with anchors with specific targets</TITLE>
</HEAD>
<BODY>
...beginning of the document...
<P>Now you may advance to
<A href="slide2.html" target="dynamic">slide 2.</A>
...more document...
<P>You’re doing great. Now on to
<A href="slide3.html" target="dynamic">slide 3.</A>
</BODY>
</HTML>
Activating either link opens a new document in the frame named "dynamic" while
the other frame, "fixed", maintains its initial contents.
Note. A frameset definition never changes, but the contents of one of its frames
can. Once the initial contents of a frame change, the frameset definition no longer
reflects the current state of its frames.
There is currently no way to encode the entire state of a frameset in a URI.
Therefore, many user agents do not allow users to assign a bookmark to a frameset.
Framesets may make navigation forward and backward through your user agent’s
history more difficult for users.
16.3.1 Setting the default target for links
When many links in the same document designate the same target, it is possible to
specify the target once and dispense with the target attribute of each element.
This is done by setting the target attribute of the BASE element.
We return to the previous example, this time factoring the target information by
defining it in the BASE element and removing it from the A elements.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
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<TITLE>A document with BASE with a specific target</TITLE>
<BASE href="http://www.mycom.com/Slides" target="dynamic">
</HEAD>
<BODY>
...beginning of the document...
<P>Now you may advance to <A href="slide2.html">slide 2.</A>
...more document...
<P>You’re doing great. Now on to
<A href="slide3.html">slide 3.</A>
</BODY>
</HTML>
16.3.2 Target semantics
User agents should determine the target frame in which to load a linked resource
according to the following precedences (highest priority to lowest):
1. If an element has its target attribute set to a known frame, when the element
is activated (i.e., a link is followed or a form is processed), the resource
designated by the element should be loaded into the target frame.
2. If an element does not have the target attribute set but the BASE element
does, the BASE element’s target attribute determines the frame.
3. If neither the element nor the BASE element refers to a target, the resource
designated by the element should be loaded into the frame containing the
element.
4. If any target attribute refers to an unknown frame F, the user agent should
create a new window and frame, assign the name F to the frame, and load the
resource designated by the element in the new frame.
User agents may provide users with a mechanism to override the target
attribute.
16.4 Alternate content
Authors should supply alternate content for those user agents that do not support
frames or are configured not to display frames.
16.4.1 The NOFRAMES element
<![ %HTML.Frameset; [
<!ENTITY % noframes.content "(BODY) -(NOFRAMES)">
]]>
<!ENTITY % noframes.content "(%flow;)*">
<!ELEMENT NOFRAMES - - %noframes.content;
-- alternate content container for non frame-based rendering -->
<!ATTLIST NOFRAMES
%attrs;
-- %coreattrs, %i18n, %events ->
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Frames in HTML documents
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
The NOFRAMES element specifies content that should be displayed only by user
agents that do not support frames or are configured not to display frames. User
agents that support frames must only display the contents of a NOFRAMES
declaration when configured not to display frames. User agents that do not support
frames must display the contents of NOFRAMES in any case.
The NOFRAMES element is part of both the transitional and frameset DTDs. [p.60]
In a document that uses the frameset DTD, NOFRAMES may be used at the end of
the FRAMESET section of the document.
For example:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A frameset document with NOFRAMES</TITLE>
</HEAD>
<FRAMESET cols="50%, 50%">
<FRAME src="main.html">
<FRAME src="table_of_contents.html">
<NOFRAMES>
<P>Here is the <A href="main-noframes.html">
non-frame based version of the document.</A>
</NOFRAMES>
</FRAMESET>
</HTML>
NOFRAMES may be used, for example, in a document that is the source of a frame
and that uses the transitional DTD. This allows authors to explain the document’s
purpose in cases when it is viewed out of the frameset or with a user agent that
doesn’t support frames.
16.4.2 Long descriptions of frames
The longdesc attribute allows authors to make frame documents more accessible
to people using non-visual user agents. This attribute designates a resource that
provides a long description of the frame. Authors should note that long descriptions
associated with frames are attached to the frame, not the frame’s contents. Since
the contents may vary over time, the initial long description is likely to become
inappropriate for the frame’s later contents. In particular, authors should not include
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an image as the sole content of a frame.
The following frameset document describes two frames. The left frame contains a
table of contents and the right frame initially contains an image of an ostrich:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A poorly-designed frameset document</TITLE>
</HEAD>
<FRAMESET cols="20%, 80%">
<FRAME src="table_of_contents.html">
<FRAME src="ostrich.gif" longdesc="ostrich-desc.html">
</FRAMESET>
</HTML>
Note that the image has been included in the frame independently of any HTML
element, so the author has no means of specifying alternate text other than via the
longdesc attribute. If the contents of the right frame change (e.g., the user selects
a rattlesnake from the table of contents), users will have no textual access to the
frame’s new content.
Thus, authors should not put an image directly in a frame. Instead, the image
should be specified in a separate HTML document, and therein annotated with the
appropriate alternate text:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<HTML>
<HEAD>
<TITLE>A well-designed frameset document</TITLE>
</HEAD>
<FRAMESET cols="20%, 80%">
<FRAME src="table_of_contents.html">
<FRAME src="ostrich-container.html">
</FRAMESET>
</HTML>
<!-- In ostrich-container.html: -->
<HTML>
<HEAD>
<TITLE>The fast and powerful ostrich</TITLE>
</HEAD>
<P>
<OBJECT data="ostrich.gif" type="image/gif">
These ostriches sure taste good!
</OBJECT>
</HTML>
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16.5 Inline frames: the IFRAME element
<!ELEMENT IFRAME - - (%flow;)*
<!ATTLIST IFRAME
%coreattrs;
longdesc
%URI;
#IMPLIED
name
CDATA
src
%URI;
frameborder (1|0)
marginwidth %Pixels;
marginheight %Pixels;
scrolling
(yes|no|auto)
align
%IAlign;
height
%Length;
width
%Length;
>
#IMPLIED
#IMPLIED
1
#IMPLIED
#IMPLIED
auto
#IMPLIED
#IMPLIED
#IMPLIED
-- inline subwindow -->
-- id, class, style, title --- link to long description
(complements title) --- name of frame for targetting --- source of frame content --- request frame borders? --- margin widths in pixels --- margin height in pixels --- scrollbar or none --- vertical or horizontal alignment --- frame height --- frame width --
Attribute definitions
longdesc = uri [p.51] [CT] [p.49]
This attribute specifies a link to a long description of the frame. This description
should supplement the short description provided using the title attribute, and
is particularly useful for non-visual user agents.
name = cdata [p.50] [CI] [p.49]
This attribute assigns a name to the current frame. This name may be used as
the target of subsequent links.
width = length [p.52] [CN] [p.49]
The width of the inline frame.
height = length [p.52] [CN] [p.49]
The height of the inline frame.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
title (element title [p.63] )
style (inline style information [p.186] )
name, src, frameborder, marginwidth, marginheight, scrolling
(frame controls and decoration [p.209] )
align (alignment [p.195] )
The IFRAME element allows authors to insert a frame within a block of text. Inserting
an inline frame within a section of text is much like inserting an object via the
OBJECT element: they both allow you to insert an HTML document in the middle of
another, they may both be aligned with surrounding text, etc.
The information to be inserted inline is designated by the src attribute of this
element. The contents of the IFRAME element, on the other hand, should only be
displayed by user agents that do not support frames or are configured not to display
frames.
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For user agents that support frames, the following example will place an inline
frame surrounded by a border in the middle of the text.
<IFRAME src="foo.html" width="400" height="500"
scrolling="auto" frameborder="1">
[Your user agent does not support frames or is currently configured
not to display frames. However, you may visit
<A href="foo.html">the related document.</A>]
</IFRAME>
Inline frames may not be resized (and thus, they do not take the noresize
attribute).
Note. HTML documents may also be embedded in other HTML documents with
the OBJECT element. See the section on embedded documents [p.173] for details.
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17 Forms
Contents
1. Introduction to forms
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10. Adding structure to forms: the FIELDSET and LEGEND elements
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Step two: Build a form data set .
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Step three: Encode the form data set
Step four: Submit the encoded form data set .
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application/x-www-form-urlencoded .
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17.1 Introduction to forms
An HTML form is a section of a document containing normal content, markup,
special elements called controls [p.220] (checkboxes, radio buttons, menus, etc.),
and labels on those controls. Users generally "complete" a form by modifying its
controls (entering text, selecting menu items, etc.), before submitting the form to an
agent for processing (e.g., to a Web server, to a mail server, etc.)
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Here’s a simple form that includes labels, radio buttons, and push buttons (reset
the form or submit it):
<FORM action="http://somesite.com/prog/adduser" method="post">
<P>
<LABEL for="firstname">First name: </LABEL>
<INPUT type="text" id="firstname"><BR>
<LABEL for="lastname">Last name: </LABEL>
<INPUT type="text" id="lastname"><BR>
<LABEL for="email">email: </LABEL>
<INPUT type="text" id="email"><BR>
<INPUT type="radio" name="sex" value="Male"> Male<BR>
<INPUT type="radio" name="sex" value="Female"> Female<BR>
<INPUT type="submit" value="Send"> <INPUT type="reset">
</P>
</FORM>
Note. This specification includes more detailed information about forms in the
subsections on form display issues [p.347] .
17.2 Controls
Users interact with forms through named controls.
A control’s "control name" is given by its name attribute. The scope of the name
attribute for a control within a FORM element is the FORM element.
Each control has both an initial value and a current value, both of which are
character strings. Please consult the definition of each control for information about
initial values and possible constraints on values imposed by the control. In general, a
control’s "initial value" may be specified with the control element’s value attribute.
However, the initial value of a TEXTAREA element is given by its contents, and the
initial value of an OBJECT element in a form is determined by the object
implementation (i.e., it lies outside the scope of this specification).
The control’s "current value" is first set to the initial value. Thereafter, the control’s
current value may be modified through user interaction and scripts. [p.251]
A control’s initial value does not change. Thus, when a form is reset, each
control’s current value is reset to its initial value. If a control does not have an initial
value, the effect of a form reset on that control is undefined.
When a form is submitted for processing, some controls have their name paired
with their current value and these pairs are submitted [p.245] with the form. Those
controls for which name/value pairs are submitted are called successful controls
[p.245] .
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17.2.1 Control types
HTML defines the following control types:
buttons
Authors may create three types of buttons:
submit buttons: When activated, a submit button submits a form. [p.245] A
form may contain more than one submit button.
reset buttons: When activated, a reset button resets all controls to their
initial values. [p.220]
push buttons: Push buttons have no default behavior. Each push button
may have client-side scripts [p.251] associated with the element’s event
[p.254] attributes. When an event occurs (e.g., the user presses the button,
releases it, etc.), the associated script is triggered.
Authors should specify the scripting language of a push button script
through a default script declaration [p.253] (with the META element).
Authors create buttons with the BUTTON element or the INPUT element.
Please consult the definitions of these elements for details about specifying
different button types.
Note. Authors should note that the BUTTON element offers richer rendering
capabilities than the INPUT element.
checkboxes
Checkboxes (and radio buttons) are on/off switches that may be toggled by the
user. A switch is "on" when the control element’s checked attribute is set.
When a form is submitted, only "on" checkbox controls can become successful
[p.245] .
Several checkboxes in a form may share the same control name. [p.220]
Thus, for example, checkboxes allow users to select several values for the
same property. The INPUT element is used to create a checkbox control.
radio buttons
Radio buttons are like checkboxes except that when several share the same
control name [p.220] , they are mutually exclusive: when one is switched "on",
all others with the same name are switched "off". The INPUT element is used to
create a radio button control.
If no radio button in a set sharing the same control name is initially "on", user
agent behavior for choosing which control is initially "on" is undefined. Note.
Since existing implementations handle this case differently, the current
specification differs from RFC 1866 ([RFC1866] [p.356] section 8.1.2.4), which
states:
At all times, exactly one of the radio buttons in a set is checked. If none of
the <INPUT> elements of a set of radio buttons specifies ‘CHECKED’, then
the user agent must check the first radio button of the set initially.
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Since user agent behavior differs, authors should ensure that in each set of
radio buttons that one is initially "on".
menus
Menus offer users options from which to choose. The SELECT element creates
a menu, in combination with the OPTGROUP and OPTION elements.
text input
Authors may create two types of controls that allow users to input text. The
INPUT element creates a single-line input control and the TEXTAREA element
creates a multi-line input control. In both cases, the input text becomes the
control’s current value [p.220] .
file select
This control type allows the user to select files so that their contents may be
submitted with a form. The INPUT element is used to create a file select control.
hidden controls
Authors may create controls that are not rendered but whose values are
submitted with a form. Authors generally use this control type to store
information between client/server exchanges that would otherwise be lost due to
the stateless nature of HTTP (see [RFC2616] [p.354] ). The INPUT element is
used to create a hidden control.
object controls
Authors may insert generic objects in forms such that associated values are
submitted along with other controls. Authors create object controls with the
OBJECT element.
The elements used to create controls generally appear inside a FORM element, but
may also appear outside of a FORM element declaration when they are used to build
user interfaces. This is discussed in the section on intrinsic events. [p.254] Note that
controls outside a form cannot be successful controls [p.245] .
17.3 The FORM element
<!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM) -- interactive form -->
<!ATTLIST FORM
%attrs;
-- %coreattrs, %i18n, %events -action
%URI;
#REQUIRED -- server-side form handler -method
(GET|POST)
GET
-- HTTP method used to submit the form-enctype
%ContentType; "application/x-www-form-urlencoded"
accept
%ContentTypes; #IMPLIED -- list of MIME types for file upload -name
CDATA
#IMPLIED -- name of form for scripting -onsubmit
%Script;
#IMPLIED -- the form was submitted -onreset
%Script;
#IMPLIED -- the form was reset -accept-charset %Charsets; #IMPLIED -- list of supported charsets ->
Start tag: required, End tag: required
Attribute definitions
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action = uri [p.51] [CT] [p.49]
This attribute specifies a form processing agent. User agent behavior for a value
other than an HTTP URI is undefined.
method = get|post [CI] [p.49]
This attribute specifies which HTTP method will be used to submit the form data
set [p.246] . Possible (case-insensitive) values are "get" (the default) and "post".
See the section on form submission [p.245] for usage information.
enctype = content-type [p.53] [CI] [p.49]
This attribute specifies the content type [p.247] used to submit the form to the
server (when the value of method is "post"). The default value for this attribute
is "application/x-www-form-urlencoded". The value "multipart/form-data" should
be used in combination with the INPUT element, type="file".
accept-charset = charset list [p.53] [CI] [p.49]
This attribute specifies the list of character encodings [p.41] for input data that is
accepted by the server processing this form. The value is a space- and/or
comma-delimited list of charset [p.53] values. The client must interpret this list
as an exclusive-or list, i.e., the server is able to accept any single character
encoding per entity received.
The default value for this attribute is the reserved string "UNKNOWN". User
agents may interpret this value as the character encoding that was used to
transmit the document containing this FORM element.
accept = content-type-list [p.53] [CI] [p.49]
This attribute specifies a comma-separated list of content types that a server
processing this form will handle correctly. User agents may use this information
to filter out non-conforming files when prompting a user to select files to be sent
to the server (cf. the INPUT element when type="file").
name = cdata [p.50] [CI] [p.49]
This attribute names the element so that it may be referred to from style sheets
or scripts. Note. This attribute has been included for backwards compatibility.
Applications should use the id attribute to identify elements.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
style (inline style information [p.186] )
title (element title [p.63] )
target (target frame information [p.212] )
onsubmit, onreset, onclick, ondblclick, onmousedown, onmouseup,
onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
onkeyup (intrinsic events [p.254] )
The FORM element acts as a container for controls [p.220] . It specifies:
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The layout of the form (given by the contents of the element).
The program that will handle the completed and submitted form (the action
attribute). The receiving program must be able to parse name/value pairs in
order to make use of them.
The method by which user data will be sent to the server (the method attribute).
A character encoding that must be accepted by the server in order to handle this
form (the accept-charset attribute). User agents may advise the user of the
value of the accept-charset attribute and/or restrict the user’s ability to enter
unrecognized characters.
A form can contain text and markup (paragraphs, lists, etc.) in addition to form
controls. [p.220]
The following example shows a form that is to be processed by the "adduser"
program when submitted. The form will be sent to the program using the HTTP
"post" method.
<FORM action="http://somesite.com/prog/adduser" method="post">
...form contents...
</FORM>
Please consult the section on form submission [p.245] for information about how
user agents must prepare form data for servers and how user agents should handle
expected responses.
Note. Further discussion on the behavior of servers that receive form data is
beyond the scope of this specification.
17.4 The INPUT element
<!ENTITY % InputType
"(TEXT | PASSWORD | CHECKBOX |
RADIO | SUBMIT | RESET |
FILE | HIDDEN | IMAGE | BUTTON)"
>
<!-- attribute name required
<!ELEMENT INPUT - O EMPTY
<!ATTLIST INPUT
%attrs;
type
%InputType;
name
CDATA
value
CDATA
checked
(checked)
disabled
(disabled)
readonly
(readonly)
size
CDATA
maxlength
NUMBER
src
%URI;
alt
CDATA
usemap
%URI;
ismap
(ismap)
tabindex
NUMBER
accesskey
%Character;
onfocus
%Script;
onblur
%Script;
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for all but submit and reset -->
-- form control -->
TEXT
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
------------------
%coreattrs, %i18n, %events -what kind of widget is needed -submit as part of form -Specify for radio buttons and checkboxes -for radio buttons and check boxes -unavailable in this context -for text and passwd -specific to each type of field -max chars for text fields -for fields with images -short description -use client-side image map -use server-side image map -position in tabbing order -accessibility key character -the element got the focus -the element lost the focus --
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onselect
onchange
accept
>
%Script;
#IMPLIED
%Script;
#IMPLIED
%ContentTypes; #IMPLIED
-- some text was selected --- the element value was changed --- list of MIME types for file upload --
Start tag: required, End tag: forbidden
Attribute definitions
type =
text|password|checkbox|radio|submit|reset|file|hidden|image|button
[CI] [p.49]
This attribute specifies the type of control [p.226] to create. The default value for
this attribute is "text".
name = cdata [p.50] [CI] [p.49]
This attribute assigns the control name [p.220] .
value = cdata [p.50] [CA] [p.49]
This attribute specifies the initial value [p.220] of the control. It is optional except
when the type attribute has the value "radio" or "checkbox".
size = cdata [p.50] [CN] [p.49]
This attribute tells the user agent the initial width of the control. The width is
given in pixels [p.52] except when type attribute has the value "text" or
"password". In that case, its value refers to the (integer) number of characters.
maxlength = number [p.50] [CN] [p.49]
When the type attribute has the value "text" or "password", this attribute
specifies the maximum number of characters the user may enter. This number
may exceed the specified size, in which case the user agent should offer a
scrolling mechanism. The default value for this attribute is an unlimited number.
checked [CI] [p.49]
When the type attribute has the value "radio" or "checkbox", this boolean
attribute specifies that the button is on. User agents must ignore this attribute for
other control types.
src = uri [p.51] [CT] [p.49]
When the type attribute has the value "image", this attribute specifies the
location of the image to be used to decorate the graphical submit button.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
alt (alternate text [p.181] )
align (alignment [p.195] )
accept (legal content types for a server [p.222] )
readonly (read-only input controls [p.244] )
disabled (disabled input controls [p.244] )
tabindex (tabbing navigation [p.241] )
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accesskey (access keys [p.242] )
usemap (client-side image maps [p.174] )
ismap (server-side image maps [p.179] )
onfocus, onblur, onselect, onchange, onclick, ondblclick,
onmousedown, onmouseup, onmouseover, onmousemove, onmouseout,
onkeypress, onkeydown, onkeyup (intrinsic events [p.254] )
17.4.1 Control types created with INPUT
The control type [p.220] defined by the INPUT element depends on the value of the
type attribute:
text
Creates a single-line text input [p.222] control.
password
Like "text", but the input text is rendered in such a way as to hide the characters
(e.g., a series of asterisks). This control type is often used for sensitive input
such as passwords. Note that the current value [p.220] is the text entered by the
user, not the text rendered by the user agent.
Note. Application designers should note that this mechanism affords only light
security protection. Although the password is masked by user agents from
casual observers, it is transmitted to the server in clear text, and may be read by
anyone with low-level access to the network.
checkbox
Creates a checkbox. [p.221]
radio
Creates a radio button. [p.221]
submit
Creates a submit button. [p.221]
image
Creates a graphical submit button. [p.221] The value of the src attribute
specifies the URI of the image that will decorate the button. For accessibility
reasons, authors should provide alternate text [p.181] for the image via the alt
attribute.
When a pointing device is used to click on the image, the form is submitted
and the click coordinates passed to the server. The x value is measured in
pixels [p.52] from the left of the image, and the y value in pixels [p.52] from the
top of the image. The submitted data includes name.x=x-value and
name.y=y-value where "name" is the value of the name attribute, and x-value
and y-value are the x and y coordinate values, respectively.
If the server takes different actions depending on the location clicked, users of
non-graphical browsers will be disadvantaged. For this reason, authors should
consider alternate approaches:
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Use multiple submit buttons (each with its own image) in place of a single
graphical submit button. Authors may use style sheets to control the
positioning of these buttons.
Use a client-side image map [p.173] together with scripting.
reset
Creates a reset button. [p.221]
button
Creates a push button. [p.221] User agents should use the value of the value
attribute as the button’s label.
hidden
Creates a hidden control. [p.222]
file
Creates a file select [p.222] control. User agents may use the value of the
value attribute as the initial file name.
17.4.2 Examples of forms containing INPUT controls
The following sample HTML fragment defines a simple form that allows the user to
enter a first name, last name, email address, and gender. When the submit button is
activated, the form will be sent to the program specified by the action attribute.
<FORM action="http://somesite.com/prog/adduser" method="post">
<P>
First name: <INPUT type="text" name="firstname"><BR>
Last name: <INPUT type="text" name="lastname"><BR>
email: <INPUT type="text" name="email"><BR>
<INPUT type="radio" name="sex" value="Male"> Male<BR>
<INPUT type="radio" name="sex" value="Female"> Female<BR>
<INPUT type="submit" value="Send"> <INPUT type="reset">
</P>
</FORM>
This form might be rendered as follows:
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In the section on the LABEL element, we discuss marking up labels such as "First
name".
In this next example, the JavaScript function name verify is triggered when the
"onclick" event occurs:
<HEAD>
<META http-equiv="Content-Script-Type" content="text/javascript">
</HEAD>
<BODY>
<FORM action="..." method="post">
<P>
<INPUT type="button" value="Click Me" onclick="verify()">
</FORM>
</BODY>
Please consult the section on intrinsic events [p.254] for more information about
scripting and events.
The following example shows how the contents of a user-specified file may be
submitted with a form. The user is prompted for his or her name and a list of file
names whose contents should be submitted with the form. By specifying the
enctype value of "multipart/form-data", each file’s contents will be packaged for
submission in a separate section of a multipart document.
<FORM action="http://server.dom/cgi/handle"
enctype="multipart/form-data"
method="post">
<P>
What is your name? <INPUT type="text" name="name_of_sender">
What files are you sending? <INPUT type="file" name="name_of_files">
</P>
</FORM>
17.5 The BUTTON element
<!ELEMENT BUTTON - (%flow;)* -(A|%formctrl;|FORM|FIELDSET)
-- push button -->
<!ATTLIST BUTTON
%attrs;
-- %coreattrs, %i18n, %events -name
CDATA
#IMPLIED
value
CDATA
#IMPLIED -- sent to server when submitted -type
(button|submit|reset) submit -- for use as form button -disabled
(disabled)
#IMPLIED -- unavailable in this context -tabindex
NUMBER
#IMPLIED -- position in tabbing order -accesskey
%Character;
#IMPLIED -- accessibility key character -onfocus
%Script;
#IMPLIED -- the element got the focus -onblur
%Script;
#IMPLIED -- the element lost the focus ->
Start tag: required, End tag: required
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Attribute definitions
name = cdata [p.50] [CI] [p.49]
This attribute assigns the control name. [p.220]
value = cdata [p.50] [CS] [p.49]
This attribute assigns the initial value [p.220] to the button.
type = submit|button|reset [CI] [p.49]
This attribute declares the type of the button. Possible values:
submit: Creates a submit button. [p.221] This is the default value.
reset: Creates a reset button. [p.221]
button: Creates a push button. [p.221]
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
disabled (disabled input controls [p.244] )
accesskey (access keys [p.242] )
tabindex (tabbing navigation [p.241] )
onfocus, onblur, onclick, ondblclick, onmousedown, onmouseup,
onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
onkeyup (intrinsic events [p.254] )
Buttons created with the BUTTON element function just like buttons created with
the INPUT element, but they offer richer rendering possibilities: the BUTTON element
may have content. For example, a BUTTON element that contains an image functions
like and may resemble an INPUT element whose type is set to "image", but the
BUTTON element type allows content.
Visual user agents may render BUTTON buttons with relief and an up/down motion
when clicked, while they may render INPUT buttons as "flat" images.
The following example expands a previous example, but creates submit [p.221]
and reset [p.221] buttons with BUTTON instead of INPUT. The buttons contain
images by way of the IMG element.
<FORM action="http://somesite.com/prog/adduser" method="post">
<P>
First name: <INPUT type="text" name="firstname"><BR>
Last name: <INPUT type="text" name="lastname"><BR>
email: <INPUT type="text" name="email"><BR>
<INPUT type="radio" name="sex" value="Male"> Male<BR>
<INPUT type="radio" name="sex" value="Female"> Female<BR>
<BUTTON name="submit" value="submit" type="submit">
Send<IMG src="/icons/wow.gif" alt="wow"></BUTTON>
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<BUTTON name="reset" type="reset">
Reset<IMG src="/icons/oops.gif" alt="oops"></BUTTON>
</P>
</FORM>
Recall that authors must provide alternate text [p.181] for an IMG element.
It is illegal to associate an image map with an IMG that appears as the contents of
a BUTTON element.
ILLEGAL EXAMPLE:
The following is not legal HTML.
<BUTTON>
<IMG src="foo.gif" usemap="...">
</BUTTON>
17.6 The SELECT, OPTGROUP, and OPTION elements
<!ELEMENT SELECT - - (OPTGROUP|OPTION)+ -- option selector -->
<!ATTLIST SELECT
%attrs;
-- %coreattrs, %i18n, %events -name
CDATA
#IMPLIED -- field name -size
NUMBER
#IMPLIED -- rows visible -multiple
(multiple)
#IMPLIED -- default is single selection -disabled
(disabled)
#IMPLIED -- unavailable in this context -tabindex
NUMBER
#IMPLIED -- position in tabbing order -onfocus
%Script;
#IMPLIED -- the element got the focus -onblur
%Script;
#IMPLIED -- the element lost the focus -onchange
%Script;
#IMPLIED -- the element value was changed ->
Start tag: required, End tag: required
SELECT Attribute definitions
name = cdata [p.50] [CI] [p.49]
This attribute assigns the control name. [p.220]
size = number [p.50] [CN] [p.49]
If a SELECT element is presented as a scrolled list box, this attribute specifies
the number of rows in the list that should be visible at the same time. Visual
user agents are not required to present a SELECT element as a list box; they
may use any other mechanism, such as a drop-down menu.
multiple [CI] [p.49]
If set, this boolean attribute allows multiple selections. If not set, the SELECT
element only permits single selections.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
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disabled (disabled input controls [p.244] )
tabindex (tabbing navigation [p.241] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
The SELECT element creates a menu [p.222] . Each choice offered by the menu is
represented by an OPTION element. A SELECT element must contain at least one
OPTION element.
The OPTGROUP element allows authors to group choices logically. This is
particularly helpful when the user must choose from a long list of options; groups of
related choices are easier to grasp and remember than a single long list of options.
In HTML 4, all OPTGROUP elements must be specified directly within a SELECT
element (i.e., groups may not be nested).
17.6.1 Pre-selected options
Zero or more choices may be pre-selected for the user. User agents should
determine which choices are pre-selected as follows:
If no OPTION element has the selected attribute set, user agent behavior for
choosing which option is initially selected is undefined. Note. Since existing
implementations handle this case differently, the current specification differs
from RFC 1866 ([RFC1866] [p.356] section 8.1.3), which states:
The initial state has the first option selected, unless a SELECTED attribute
is present on any of the <OPTION> elements.
Since user agent behavior differs, authors should ensure that each menu
includes a default pre-selected OPTION.
If one OPTION element has the selected attribute set, it should be
pre-selected.
If the SELECT element has the multiple attribute set and more than one
OPTION element has the selected attribute set, they should all be
pre-selected.
It is considered an error if more than one OPTION element has the selected
attribute set and the SELECT element does not have the multiple attribute
set. User agents may vary in how they handle this error, but should not
pre-select more than one choice.
<!ELEMENT OPTGROUP - - (OPTION)+ -- option group -->
<!ATTLIST OPTGROUP
%attrs;
-- %coreattrs, %i18n, %events -disabled
(disabled)
#IMPLIED -- unavailable in this context -label
%Text;
#REQUIRED -- for use in hierarchical menus ->
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Start tag: required, End tag: required
OPTGROUP Attribute definitions
label = text [p.50] [CS] [p.49]
This attribute specifies the label for the option group.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
disabled (disabled input controls [p.244] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
Note. Implementors are advised that future versions of HTML may extend the
grouping mechanism to allow for nested groups (i.e., OPTGROUP elements may
nest). This will allow authors to represent a richer hierarchy of choices.
<!ELEMENT OPTION - O (#PCDATA)
<!ATTLIST OPTION
%attrs;
selected
(selected)
#IMPLIED
disabled
(disabled)
#IMPLIED
label
%Text;
#IMPLIED
value
CDATA
#IMPLIED
>
-- selectable choice -->
-- %coreattrs, %i18n, %events --- unavailable in this context --- for use in hierarchical menus --- defaults to element content --
Start tag: required, End tag: optional
OPTION Attribute definitions
selected [CI] [p.49]
When set, this boolean attribute specifies that this option is pre-selected.
value = cdata [p.50] [CS] [p.49]
This attribute specifies the initial value [p.220] of the control. If this attribute is
not set, the initial value [p.220] is set to the contents of the OPTION element.
label = text [p.50] [CS] [p.49]
This attribute allows authors to specify a shorter label for an option than the
content of the OPTION element. When specified, user agents should use the
value of this attribute rather than the content of the OPTION element as the
option label.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
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title (element title [p.63] )
style (inline style information [p.186] )
disabled (disabled input controls [p.244] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
When rendering a menu choice, user agents should use the value of the label
attribute of the OPTION element as the choice. If this attribute is not specified, user
agents should use the contents of the OPTION element.
The label attribute of the OPTGROUP element specifies the label for a group of
choices.
In this example, we create a menu that allows the user to select which of seven
software components to install. The first and second components are pre-selected
but may be deselected by the user. The remaining components are not pre-selected.
The size attribute states that the menu should only have 4 rows even though the
user may select from among 7 options. The other options should be made available
through a scrolling mechanism.
The SELECT is followed by submit and reset buttons.
<FORM action="http://somesite.com/prog/component-select" method="post">
<P>
<SELECT multiple size="4" name="component-select">
<OPTION selected value="Component_1_a">Component_1</OPTION>
<OPTION selected value="Component_1_b">Component_2</OPTION>
<OPTION>Component_3</OPTION>
<OPTION>Component_4</OPTION>
<OPTION>Component_5</OPTION>
<OPTION>Component_6</OPTION>
<OPTION>Component_7</OPTION>
</SELECT>
<INPUT type="submit" value="Send"><INPUT type="reset">
</P>
</FORM>
Only selected options will be successful [p.245] (using the control name [p.220]
"component-select"). When no options are selected, the control is not successful and
neither the name nor any values are submitted to the server when the form is
submitted. Note that where the value attribute is set, it determines the control’s
initial value [p.220] , otherwise it’s the element’s contents.
In this example we use the OPTGROUP element to group choices. The following
markup:
<FORM action="http://somesite.com/prog/someprog" method="post">
<P>
<SELECT name="ComOS">
<OPTION selected label="none" value="none">None</OPTION>
<OPTGROUP label="PortMaster 3">
<OPTION label="3.7.1" value="pm3_3.7.1">PortMaster 3 with ComOS 3.7.1</OPTION>
<OPTION label="3.7" value="pm3_3.7">PortMaster 3 with ComOS 3.7</OPTION>
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<OPTION label="3.5" value="pm3_3.5">PortMaster
</OPTGROUP>
<OPTGROUP label="PortMaster 2">
<OPTION label="3.7" value="pm2_3.7">PortMaster
<OPTION label="3.5" value="pm2_3.5">PortMaster
</OPTGROUP>
<OPTGROUP label="IRX">
<OPTION label="3.7R" value="IRX_3.7R">IRX with
<OPTION label="3.5R" value="IRX_3.5R">IRX with
</OPTGROUP>
</SELECT>
</FORM>
3 with ComOS 3.5</OPTION>
2 with ComOS 3.7</OPTION>
2 with ComOS 3.5</OPTION>
ComOS 3.7R</OPTION>
ComOS 3.5R</OPTION>
represents the following grouping:
None
PortMaster 3
3.7.1
3.7
3.5
PortMaster 2
3.7
3.5
IRX
3.7R
3.5R
Visual user agents may allow users to select from option groups through a
hierarchical menu or some other mechanism that reflects the structure of choices.
A graphical user agent might render this as:
This image shows a SELECT element rendered as cascading menus. The top
label of the menu displays the currently selected value (PortMaster 3, 3.7.1). The
user has unfurled two cascading menus, but has not yet selected the new value
(PortMaster 2, 3.7). Note that each cascading menu displays the label of an
OPTGROUP or OPTION element.
17.7 The TEXTAREA element
<!ELEMENT TEXTAREA - - (#PCDATA)
<!ATTLIST TEXTAREA
%attrs;
name
CDATA
#IMPLIED
rows
NUMBER
#REQUIRED
cols
NUMBER
#REQUIRED
disabled
(disabled)
#IMPLIED
readonly
(readonly)
#IMPLIED
tabindex
NUMBER
#IMPLIED
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-- multi-line text field -->
-- %coreattrs, %i18n, %events --
-- unavailable in this context --- position in tabbing order --
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accesskey
onfocus
onblur
onselect
onchange
>
%Character;
%Script;
%Script;
%Script;
%Script;
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
------
accessibility key character -the element got the focus -the element lost the focus -some text was selected -the element value was changed --
Start tag: required, End tag: required
Attribute definitions
name = cdata [p.50] [CI] [p.49]
This attribute assigns the control name. [p.220]
rows = number [p.50] [CN] [p.49]
This attribute specifies the number of visible text lines. Users should be able to
enter more lines than this, so user agents should provide some means to scroll
through the contents of the control when the contents extend beyond the visible
area.
cols = number [p.50] [CN] [p.49]
This attribute specifies the visible width in average character widths. Users
should be able to enter longer lines than this, so user agents should provide
some means to scroll through the contents of the control when the contents
extend beyond the visible area. User agents may wrap visible text lines to keep
long lines visible without the need for scrolling.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
readonly (read-only input controls [p.244] )
disabled (disabled input controls [p.244] )
tabindex (tabbing navigation [p.241] )
onfocus, onblur, onselect, onchange, onclick, ondblclick,
onmousedown, onmouseup, onmouseover, onmousemove, onmouseout,
onkeypress, onkeydown, onkeyup (intrinsic events [p.254] )
The TEXTAREA element creates a multi-line text input [p.222] control. User agents
should use the contents of this element as the initial value [p.220] of the control and
should render this text initially.
This example creates a TEXTAREA control that is 20 rows by 80 columns and
contains two lines of text initially. The TEXTAREA is followed by submit and reset
buttons.
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<FORM action="http://somesite.com/prog/text-read" method="post">
<P>
<TEXTAREA name="thetext" rows="20" cols="80">
First line of initial text.
Second line of initial text.
</TEXTAREA>
<INPUT type="submit" value="Send"><INPUT type="reset">
</P>
</FORM>
Setting the readonly attribute allows authors to display unmodifiable text in a
TEXTAREA. This differs from using standard marked-up text in a document because
the value of TEXTAREA is submitted with the form.
17.8 The ISINDEX element
ISINDEX is deprecated [p.38] . This element creates a single-line text input [p.222]
control. Authors should use the INPUT element to create text input [p.222] controls.
See the Transitional DTD [p.294] for the formal definition.
Attribute definitions
prompt = text [p.50] [CS] [p.49]
Deprecated. [p.38] This attribute specifies a prompt string for the input field.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
The ISINDEX element creates a single-line text input [p.222] control that allows
any number of characters. User agents may use the value of the prompt attribute
as a title for the prompt.
DEPRECATED EXAMPLE:
The following ISINDEX declaration:
<ISINDEX prompt="Enter your search phrase: ">
could be rewritten with INPUT as follows:
<FORM action="..." method="post">
<P>Enter your search phrase: <INPUT type="text"></P>
</FORM>
Semantics of ISINDEX. Currently, the semantics for ISINDEX are only
well-defined when the base URI for the enclosing document is an HTTP URI. In
practice, the input string is restricted to Latin-1 as there is no mechanism for the URI
to specify a different character set.
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17.9 Labels
Some form controls automatically have labels associated with them (press buttons)
while most do not (text fields, checkboxes and radio buttons, and menus).
For those controls that have implicit labels, user agents should use the value of
the value attribute as the label string.
The LABEL element is used to specify labels for controls that do not have implicit
labels,
17.9.1 The LABEL element
<!ELEMENT LABEL - - (%inline;)* -(LABEL) -- form field label text -->
<!ATTLIST LABEL
%attrs;
-- %coreattrs, %i18n, %events -for
IDREF
#IMPLIED -- matches field ID value -accesskey
%Character;
#IMPLIED -- accessibility key character -onfocus
%Script;
#IMPLIED -- the element got the focus -onblur
%Script;
#IMPLIED -- the element lost the focus ->
Start tag: required, End tag: required
Attribute definitions
for = idref [p.50] [CS] [p.49]
This attribute explicitly associates the label being defined with another control.
When present, the value of this attribute must be the same as the value of the
id attribute of some other control in the same document. When absent, the
label being defined is associated with the element’s contents.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
accesskey (access keys [p.242] )
onfocus, onblur, onclick, ondblclick, onmousedown, onmouseup,
onmouseover, onmousemove, onmouseout, onkeypress, onkeydown,
onkeyup (intrinsic events [p.254] )
The LABEL element may be used to attach information to controls. Each LABEL
element is associated with exactly one form control.
The for attribute associates a label with another control explicitly: the value of the
for attribute must be the same as the value of the id attribute of the associated
control element. More than one LABEL may be associated with the same control by
creating multiple references via the for attribute.
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This example creates a table that is used to align two text input [p.222] controls
and their associated labels. Each label is associated explicitly with one text input
[p.222] :
<FORM action="..." method="post">
<TABLE>
<TR>
<TD><LABEL for="fname">First Name</LABEL>
<TD><INPUT type="text" name="firstname" id="fname">
<TR>
<TD><LABEL for="lname">Last Name</LABEL>
<TD><INPUT type="text" name="lastname" id="lname">
</TABLE>
</FORM>
This example extends a previous example form to include LABEL elements.
<FORM action="http://somesite.com/prog/adduser" method="post">
<P>
<LABEL for="firstname">First name: </LABEL>
<INPUT type="text" id="firstname"><BR>
<LABEL for="lastname">Last name: </LABEL>
<INPUT type="text" id="lastname"><BR>
<LABEL for="email">email: </LABEL>
<INPUT type="text" id="email"><BR>
<INPUT type="radio" name="sex" value="Male"> Male<BR>
<INPUT type="radio" name="sex" value="Female"> Female<BR>
<INPUT type="submit" value="Send"> <INPUT type="reset">
</P>
</FORM>
To associate a label with another control implicitly, the control element must be
within the contents of the LABEL element. In this case, the LABEL may only contain
one control element. The label itself may be positioned before or after the associated
control.
In this example, we implicitly associate two labels with two text input [p.222]
controls:
<FORM action="..." method="post">
<P>
<LABEL>
First Name
<INPUT type="text" name="firstname">
</LABEL>
<LABEL>
<INPUT type="text" name="lastname">
Last Name
</LABEL>
</P>
</FORM>
Note that this technique cannot be used when a table is being used for layout, with
the label in one cell and its associated control in another cell.
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When a LABEL element receives focus [p.241] , it passes the focus on to its
associated control. See the section below on access keys [p.242] for examples.
Labels may be rendered by user agents in a number of ways (e.g., visually, read
by speech synthesizers, etc.)
17.10 Adding structure to forms: the FIELDSET and
LEGEND elements
<!-#PCDATA is to solve the mixed content problem,
per specification only whitespace is allowed there!
-->
<!ELEMENT FIELDSET - - (#PCDATA,LEGEND,(%flow;)*) -- form control group -->
<!ATTLIST FIELDSET
%attrs;
-- %coreattrs, %i18n, %events ->
<!ELEMENT LEGEND - - (%inline;)*
-- fieldset legend -->
<!ATTLIST LEGEND
%attrs;
accesskey
%Character;
>
-- %coreattrs, %i18n, %events --- accessibility key character --
#IMPLIED
Start tag: required, End tag: required
LEGEND Attribute definitions
align = top|bottom|left|right [CI] [p.49]
Deprecated. [p.38] This attribute specifies the position of the legend with
respect to the fieldset. Possible values:
top: The legend is at the top of the fieldset. This is the default value.
bottom: The legend is at the bottom of the fieldset.
left: The legend is at the left side of the fieldset.
right: The legend is at the right side of the fieldset.
Attributes defined elsewhere
id, class (document-wide identifiers [p.71] )
lang (language information [p.79] ), dir (text direction [p.82] )
title (element title [p.63] )
style (inline style information [p.186] )
accesskey (access keys [p.242] )
onclick, ondblclick, onmousedown, onmouseup, onmouseover,
onmousemove, onmouseout, onkeypress, onkeydown, onkeyup (intrinsic
events [p.254] )
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The FIELDSET element allows authors to group thematically related controls and
labels. Grouping controls makes it easier for users to understand their purpose while
simultaneously facilitating tabbing navigation for visual user agents and speech
navigation for speech-oriented user agents. The proper use of this element makes
documents more accessible.
The LEGEND element allows authors to assign a caption to a FIELDSET. The
legend improves accessibility when the FIELDSET is rendered non-visually.
In this example, we create a form that one might fill out at the doctor’s office. It is
divided into three sections: personal information, medical history, and current
medication. Each section contains controls for inputting the appropriate information.
<FORM action="..." method="post">
<P>
<FIELDSET>
<LEGEND>Personal Information</LEGEND>
Last Name: <INPUT name="personal_lastname" type="text" tabindex="1">
First Name: <INPUT name="personal_firstname" type="text" tabindex="2">
Address: <INPUT name="personal_address" type="text" tabindex="3">
...more personal information...
</FIELDSET>
<FIELDSET>
<LEGEND>Medical History</LEGEND>
<INPUT name="history_illness"
type="checkbox"
value="Smallpox" tabindex="20"> Smallpox
<INPUT name="history_illness"
type="checkbox"
value="Mumps" tabindex="21"> Mumps
<INPUT name="history_illness"
type="checkbox"
value="Dizziness" tabindex="22"> Dizziness
<INPUT name="history_illness"
type="checkbox"
value="Sneezing" tabindex="23"> Sneezing
...more medical history...
</FIELDSET>
<FIELDSET>
<LEGEND>Current Medication</LEGEND>
Are you currently taking any medication?
<INPUT name="medication_now"
type="radio"
value="Yes" tabindex="35">Yes
<INPUT name="medication_now"
type="radio"
value="No" tabindex="35">No
If you are currently taking medication, please indicate
it in the space below:
<TEXTAREA name="current_medication"
rows="20" cols="50"
tabindex="40">
</TEXTAREA>
</FIELDSET>
</FORM>
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Note that in this example, we might improve the visual presentation of the form by
aligning elements within each FIELDSET (with style sheets), adding color and font
information (with style sheets), adding scripting (say, to only open the "current
medication" text area if the user indicates he or she is currently on medication), etc.
17.11 Giving focus to an element
In an HTML document, an element must receive focus from the user in order to
become active and perform its tasks. For example, users must activate a link
specified by the A element in order to follow the specified link. Similarly, users must
give a TEXTAREA focus in order to enter text into it.
There are several ways to give focus to an element:
Designate the element with a pointing device.
Navigate from one element to the next with the keyboard. The document’s
author may define a tabbing order that specifies the order in which elements will
receive focus if the user navigates the document with the keyboard (see tabbing
navigation [p.241] ). Once selected, an element may be activated by some other
key sequence.
Select an element through an access key [p.242] (sometimes called "keyboard
shortcut" or "keyboard accelerator").
17.11.1 Tabbing navigation
Attribute definitions
tabindex = number [p.50] [CN] [p.49]
This attribute specifies the position of the current element in the tabbing order
for the current document. This value must be a number between 0 and 32767.
User agents should ignore leading zeros.
The tabbing order defines the order in which elements will receive focus when
navigated by the user via the keyboard. The tabbing order may include elements
nested within other elements.
Elements that may receive focus should be navigated by user agents according to
the following rules:
1. Those elements that support the tabindex attribute and assign a positive
value to it are navigated first. Navigation proceeds from the element with the
lowest tabindex value to the element with the highest value. Values need not
be sequential nor must they begin with any particular value. Elements that have
identical tabindex values should be navigated in the order they appear in the
character stream.
2. Those elements that do not support the tabindex attribute or support it and
assign it a value of "0" are navigated next. These elements are navigated in the
order they appear in the character stream.
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3. Elements that are disabled [p.244] do not participate in the tabbing order.
The following elements support the tabindex attribute: A, AREA, BUTTON,
INPUT, OBJECT, SELECT, and TEXTAREA.
In this example, the tabbing order will be the BUTTON, the INPUT elements in
order (note that "field1" and the button share the same tabindex, but "field1" appears
later in the character stream), and finally the link created by the A element.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A document with FORM</TITLE>
</HEAD>
<BODY>
...some text...
<P>Go to the
<A tabindex="10" href="http://www.w3.org/">W3C Web site.</A>
...some more...
<BUTTON type="button" name="get-database"
tabindex="1" onclick="get-database">
Get the current database.
</BUTTON>
...some more...
<FORM action="..." method="post">
<P>
<INPUT tabindex="1" type="text" name="field1">
<INPUT tabindex="2" type="text" name="field2">
<INPUT tabindex="3" type="submit" name="submit">
</P>
</FORM>
</BODY>
</HTML>
Tabbing keys. The actual key sequence that causes tabbing navigation or
element activation depends on the configuration of the user agent (e.g., the "tab" key
is used for navigation and the "enter" key is used to activate a selected element).
User agents may also define key sequences to navigate the tabbing order in
reverse. When the end (or beginning) of the tabbing order is reached, user agents
may circle back to the beginning (or end).
17.11.2 Access keys
Attribute definitions
accesskey = character [p.53] [CN] [p.49]
This attribute assigns an access key to an element. An access key is a single
character from the document character set. Note. Authors should consider the
input method of the expected reader when specifying an accesskey.
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Forms in HTML documents
Pressing an access key assigned to an element gives focus to the element. The
action that occurs when an element receives focus depends on the element. For
example, when a user activates a link defined by the A element, the user agent
generally follows the link. When a user activates a radio button, the user agent
changes the value of the radio button. When the user activates a text field, it allows
input, etc.
The following elements support the accesskey attribute: A, AREA, BUTTON,
INPUT, LABEL, and LEGEND, and TEXTAREA.
This example assigns the access key "U" to a label associated with an INPUT
control. Typing the access key gives focus to the label which in turn gives it to the
associated control. The user may then enter text into the INPUT area.
<FORM action="..." method="post">
<P>
<LABEL for="fuser" accesskey="U">
User Name
</LABEL>
<INPUT type="text" name="user" id="fuser">
</P>
</FORM>
In this example, we assign an access key to a link defined by the A element.
Typing this access key takes the user to another document, in this case, a table of
contents.
<P><A accesskey="C"
rel="contents"
href="http://someplace.com/specification/contents.html">
Table of Contents</A>
The invocation of access keys depends on the underlying system. For instance,
on machines running MS Windows, one generally has to press the "alt" key in
addition to the access key. On Apple systems, one generally has to press the "cmd"
key in addition to the access key.
The rendering of access keys depends on the user agent. We recommend that
authors include the access key in label text or wherever the access key is to apply.
User agents should render the value of an access key in such a way as to
emphasize its role and to distinguish it from other characters (e.g., by underlining it).
17.12 Disabled and read-only controls
In contexts where user input is either undesirable or irrelevant, it is important to be
able to disable a control or render it read-only. For example, one may want to
disable a form’s submit button until the user has entered some required data.
Similarly, an author may want to include a piece of read-only text that must be
submitted as a value along with the form. The following sections describe disabled
and read-only controls.
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17.12.1 Disabled controls
Attribute definitions
disabled [CI] [p.49]
When set for a form control, this boolean attribute disables the control for user
input.
When set, the disabled attribute has the following effects on an element:
Disabled controls do not receive focus [p.241] .
Disabled controls are skipped in tabbing navigation [p.241] .
Disabled controls cannot be successful [p.245] .
The following elements support the disabled attribute: BUTTON, INPUT,
OPTGROUP, OPTION, SELECT, and TEXTAREA.
This attribute is inherited but local declarations override the inherited value.
How disabled elements are rendered depends on the user agent. For example,
some user agents "gray out" disabled menu items, button labels, etc.
In this example, the INPUT element is disabled. Therefore, it cannot receive user
input nor will its value be submitted with the form.
<INPUT disabled name="fred" value="stone">
Note. The only way to modify dynamically the value of the disabled attribute is
through a script. [p.251]
17.12.2 Read-only controls
Attribute definitions
readonly [CI] [p.49]
When set for a form control, this boolean attribute prohibits changes to the
control.
The readonly attribute specifies whether the control may be modified by the
user.
When set, the readonly attribute has the following effects on an element:
Read-only elements receive focus [p.241] but cannot be modified by the user.
Read-only elements are included in tabbing navigation [p.241] .
Read-only elements may be successful [p.245] .
The following elements support the readonly attribute: INPUT and TEXTAREA.
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Forms in HTML documents
How read-only elements are rendered depends on the user agent.
Note. The only way to modify dynamically the value of the readonly attribute is
through a script. [p.251]
17.13 Form submission
The following sections explain how user agents submit form data to form processing
agents.
17.13.1 Form submission method
The method attribute of the FORM element specifies the HTTP method used to send
the form to the processing agent. This attribute may take two values:
get: With the HTTP "get" method, the form data set [p.246] is appended to the
URI specified by the action attribute (with a question-mark ("?") as separator)
and this new URI is sent to the processing agent.
post: With the HTTP "post" method, the form data set [p.246] is included in the
body of the form and sent to the processing agent.
The "get" method should be used when the form is idempotent (i.e., causes no
side-effects). Many database searches have no visible side-effects and make ideal
applications for the "get" method.
If the service associated with the processing of a form causes side effects (for
example, if the form modifies a database or subscription to a service), the "post"
method should be used.
Note. The "get" method restricts form data set [p.246] values to ASCII characters.
Only the "post" method (with enctype="multipart/form-data") is specified to cover
the entire [ISO10646] [p.353] character set.
17.13.2 Successful controls
A successful control is "valid" for submission. Every successful control has its control
name [p.220] paired with its current value [p.220] as part of the submitted form data
set [p.246] . A successful control must be defined within a FORM element and must
have a control name. [p.220]
However:
Controls that are disabled [p.244] cannot be successful.
If a form contains more than one submit button [p.221] , only the activated
submit button is successful.
All "on" checkboxes [p.221] may be successful.
For radio buttons [p.221] that share the same value of the name attribute, only
the "on" radio button may be successful.
For menus [p.222] , the control name [p.220] is provided by a SELECT element
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and values are provided by OPTION elements. Only selected options may be
successful. When no options are selected, the control is not successful and
neither the name nor any values are submitted to the server when the form is
submitted.
The current value [p.220] of a file select [p.222] is a list of one or more file
names. Upon submission of the form, the contents of each file are submitted
with the rest of the form data. The file contents are packaged according to the
form’s content type [p.247] .
The current value of an object control is determined by the object’s
implementation.
If a control doesn’t have a current value [p.220] when the form is submitted, user
agents are not required to treat it as a successful control.
Furthermore, user agents should not consider the following controls successful:
Reset buttons. [p.221]
OBJECT elements whose declare attribute has been set.
Hidden controls [p.222] and controls that are not rendered because of style sheet
[p.183] settings may still be successful. For example:
<FORM action="..." method="post">
<P>
<INPUT type="password" style="display:none"
name="invisible-password"
value="mypassword">
</FORM>
will still cause a value to be paired with the name "invisible-password" and
submitted with the form.
17.13.3 Processing form data
When the user submits a form (e.g., by activating a submit button [p.221] ), the user
agent processes it as follows.
Step one: Identify the successful controls
Step two: Build a form data set
A form data set is a sequence of control-name [p.220] /current-value [p.220] pairs
constructed from successful controls [p.245]
Step three: Encode the form data set
The form data set is then encoded according to the content type [p.247] specified by
the enctype attribute of the FORM element.
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Step four: Submit the encoded form data set
Finally, the encoded data is sent to the processing agent designated by the action
attribute using the protocol specified by the method attribute.
This specification does not specify all valid submission methods or content types
[p.247] that may be used with forms. However, HTML 4 user agents must support
the established conventions in the following cases:
If the method is "get" and the action is an HTTP URI, the user agent takes the
value of action, appends a ‘?’ to it, then appends the form data set [p.246] ,
encoded using the "application/x-www-form-urlencoded" content type [p.247] .
The user agent then traverses the link to this URI. In this scenario, form data are
restricted to ASCII codes.
If the method is "post" and the action is an HTTP URI, the user agent
conducts an HTTP "post" transaction using the value of the action attribute
and a message created according to the content type [p.247] specified by the
enctype attribute.
For any other value of action or method, behavior is unspecified.
User agents should render the response from the HTTP "get" and "post"
transactions.
17.13.4 Form content types
The enctype attribute of the FORM element specifies the content type [p.53] used to
encode the form data set [p.246] for submission to the server. User agents must
support the content types listed below. Behavior for other content types is
unspecified.
Please also consult the section on escaping ampersands in URI attribute values
[p.335] .
application/x-www-form-urlencoded
This is the default content type. Forms submitted with this content type must be
encoded as follows:
1. Control names and values are escaped. Space characters are replaced by ‘+’,
and then reserved characters are escaped as described in [RFC1738] [p.354] ,
section 2.2: Non-alphanumeric characters are replaced by ‘%HH’, a percent
sign and two hexadecimal digits representing the ASCII code of the character.
Line breaks are represented as "CR LF" pairs (i.e., ‘%0D%0A’).
2. The control names/values are listed in the order they appear in the document.
The name is separated from the value by ‘=’ and name/value pairs are
separated from each other by ‘&’.
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multipart/form-data
Note. Please consult [RFC2388] [p.356] for additional information about file uploads,
including backwards compatibility issues, the relationship between
"multipart/form-data" and other content types, performance issues, etc.
Please consult the appendix for information about security issues for forms [p.350]
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The content type "application/x-www-form-urlencoded" is inefficient for sending
large quantities of binary data or text containing non-ASCII characters. The content
type "multipart/form-data" should be used for submitting forms that contain files,
non-ASCII data, and binary data.
The content "multipart/form-data" follows the rules of all multipart MIME data
streams as outlined in [RFC2045] [p.354] . The definition of "multipart/form-data" is
available at the [IANA] [p.353] registry.
A "multipart/form-data" message contains a series of parts, each representing a
successful control [p.245] . The parts are sent to the processing agent in the same
order the corresponding controls appear in the document stream. Part boundaries
should not occur in any of the data; how this is done lies outside the scope of this
specification.
As with all multipart MIME types, each part has an optional "Content-Type" header
that defaults to "text/plain". User agents should supply the "Content-Type" header,
accompanied by a "charset" parameter.
Each part is expected to contain:
1. a "Content-Disposition" header whose value is "form-data".
2. a name attribute specifying the control name [p.220] of the corresponding
control. Control names originally encoded in non-ASCII character sets [p.41]
may be encoded using the method outlined in [RFC2045] [p.354] .
Thus, for example, for a control named "mycontrol", the corresponding part would
be specified:
Content-Disposition: form-data; name="mycontrol"
As with all MIME transmissions, "CR LF" (i.e., ‘%0D%0A’) is used to separate
lines of data.
Each part may be encoded and the "Content-Transfer-Encoding" header supplied
if the value of that part does not conform to the default (7BIT) encoding (see
[RFC2045] [p.354] , section 6)
If the contents of a file are submitted with a form, the file input should be identified
by the appropriate content type [p.53] (e.g., "application/octet-stream"). If multiple
files are to be returned as the result of a single form entry, they should be returned
as "multipart/mixed" embedded within the "multipart/form-data".
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The user agent should attempt to supply a file name for each submitted file. The
file name may be specified with the "filename" parameter of the ’Content-Disposition:
form-data’ header, or, in the case of multiple files, in a ’Content-Disposition: file’
header of the subpart. If the file name of the client’s operating system is not in
US-ASCII, the file name might be approximated or encoded using the method of
[RFC2045] [p.354] . This is convenient for those cases where, for example, the
uploaded files might contain references to each other (e.g., a TeX file and its ".sty"
auxiliary style description).
The following example illustrates "multipart/form-data" encoding. Suppose we
have the following form:
<FORM action="http://server.com/cgi/handle"
enctype="multipart/form-data"
method="post">
<P>
What is your name? <INPUT type="text" name="submit-name"><BR>
What files are you sending? <INPUT type="file" name="files"><BR>
<INPUT type="submit" value="Send"> <INPUT type="reset">
</FORM>
If the user enters "Larry" in the text input, and selects the text file "file1.txt", the
user agent might send back the following data:
Content-Type: multipart/form-data; boundary=AaB03x
--AaB03x
Content-Disposition: form-data; name="submit-name"
Larry
--AaB03x
Content-Disposition: form-data; name="files"; filename="file1.txt"
Content-Type: text/plain
... contents of file1.txt ...
--AaB03x--
If the user selected a second (image) file "file2.gif", the user agent might construct
the parts as follows:
Content-Type: multipart/form-data; boundary=AaB03x
--AaB03x
Content-Disposition: form-data; name="submit-name"
Larry
--AaB03x
Content-Disposition: form-data; name="files"
Content-Type: multipart/mixed; boundary=BbC04y
--BbC04y
Content-Disposition: file; filename="file1.txt"
Content-Type: text/plain
... contents of file1.txt ...
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--BbC04y
Content-Disposition: file; filename="file2.gif"
Content-Type: image/gif
Content-Transfer-Encoding: binary
...contents of file2.gif...
--BbC04y---AaB03x--
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18 Scripts
Contents
1. Introduction to scripts
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2. Designing documents for user agents that support scripting .
1. The SCRIPT element
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2. Specifying the scripting language
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The default scripting language .
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Local declaration of a scripting language
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References to HTML elements from a script .
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3. Intrinsic events .
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4. Dynamic modification of documents .
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3. Designing documents for user agents that don’t support scripting
1. The NOSCRIPT element .
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18.1 Introduction to scripts
A client-side script is a program that may accompany an HTML document or be
embedded directly in it. The program executes on the client’s machine when the
document loads, or at some other time such as when a link is activated. HTML’s
support for scripts is independent of the scripting language.
Scripts offer authors a means to extend HTML documents in highly active and
interactive ways. For example:
Scripts may be evaluated as a document loads to modify the contents of the
document dynamically.
Scripts may accompany a form to process input as it is entered. Designers may
dynamically fill out parts of a form based on the values of other fields. They may
also ensure that input data conforms to predetermined ranges of values, that
fields are mutually consistent, etc.
Scripts may be triggered by events that affect the document, such as loading,
unloading, element focus, mouse movement, etc.
Scripts may be linked to form controls (e.g., buttons) to produce graphical user
interface elements.
There are two types of scripts authors may attach to an HTML document:
Those that are executed one time when the document is loaded by the user
agent. Scripts that appear within a SCRIPT element are executed when the
document is loaded. For user agents that cannot or will not handle scripts,
authors may include alternate content via the NOSCRIPT element.
Those that are executed every time a specific event occurs. These scripts may
be assigned to a number of elements via the intrinsic event [p.254] attributes.
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Note. This specification includes more detailed information about scripting in
sections on script macros [p.348] .
18.2 Designing documents for user agents that
support scripting
The following sections discuss issues that concern user agents that support
scripting.
18.2.1 The SCRIPT element
<!ELEMENT SCRIPT - - %Script;
<!ATTLIST SCRIPT
charset
%Charset;
#IMPLIED
type
%ContentType; #REQUIRED
src
%URI;
#IMPLIED
defer
(defer)
#IMPLIED
>
-- script statements -->
-----
char encoding of linked resource -content type of script language -URI for an external script -UA may defer execution of script --
Start tag: required, End tag: required
Attribute definitions
src = uri [p.51] [CT] [p.49]
This attribute specifies the location of an external script.
type = content-type [p.53] [CI] [p.49]
This attribute specifies the scripting language of the element’s contents and
overrides the default scripting language. The scripting language is specified as a
content type (e.g., "text/javascript"). Authors must supply a value for this
attribute. There is no default value for this attribute.
language = cdata [p.50] [CI] [p.49]
Deprecated. [p.38] This attribute specifies the scripting language of the
contents of this element. Its value is an identifier for the language, but since
these identifiers are not standard, this attribute has been deprecated [p.38] in
favor of type.
defer [CI] [p.49]
When set, this boolean attribute provides a hint to the user agent that the script
is not going to generate any document content (e.g., no "document.write" in
javascript) and thus, the user agent can continue parsing and rendering.
Attributes defined elsewhere
charset(character encodings [p.41] )
The SCRIPT element places a script within a document. This element may appear
any number of times in the HEAD or BODY of an HTML document.
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The script may be defined within the contents of the SCRIPT element or in an
external file. If the src attribute is not set, user agents must interpret the contents of
the element as the script. If the src has a URI value, user agents must ignore the
element’s contents and retrieve the script via the URI. Note that the charset
attribute refers to the character encoding [p.41] of the script designated by the src
attribute; it does not concern the content of the SCRIPT element.
Scripts are evaluated by script engines that must be known to a user agent.
The syntax of script data [p.57] depends on the scripting language.
18.2.2 Specifying the scripting language
As HTML does not rely on a specific scripting language, document authors must
explicitly tell user agents the language of each script. This may be done either
through a default declaration or a local declaration.
The default scripting language
Authors should specify the default scripting language for all scripts in a document by
including the following META declaration in the HEAD:
<META http-equiv="Content-Script-Type" content="type">
where "type" is a content type [p.53] naming the scripting language. Examples of
values include "text/tcl", "text/javascript", "text/vbscript".
In the absence of a META declaration, the default can be set by a
"Content-Script-Type" HTTP header.
Content-Script-Type: type
where "type" is again a content type [p.53] naming the scripting language.
User agents should determine the default scripting language for a document
according to the following steps (highest to lowest priority):
1. If any META declarations specify the "Content-Script-Type", the last one in the
character stream determines the default scripting language.
2. Otherwise, if any HTTP headers specify the "Content-Script-Type", the last one
in the character stream determines the default scripting language.
Documents that do not specify default scripting language information and that
contain elements that specify an intrinsic event [p.254] script are incorrect. User
agents may still attempt to interpret incorrectly specified scripts but are not required
to. Authoring tools should generate default scripting language information to help
authors avoid creating incorrect documents.
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Local declaration of a scripting language
The type attribute must be specified for each SCRIPT element instance in a
document. The value of the type attribute for a SCRIPT element overrides the
default scripting language for that element.
In this example, we declare the default scripting language to be "text/tcl". We
include one SCRIPT in the header, whose script is located in an external file and is
in the scripting language "text/vbscript". We also include one SCRIPT in the body,
which contains its own script written in "text/javascript".
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<HTML>
<HEAD>
<TITLE>A document with SCRIPT</TITLE>
<META http-equiv="Content-Script-Type" content="text/tcl">
<SCRIPT type="text/vbscript" src="http://someplace.com/progs/vbcalc">
</SCRIPT>
</HEAD>
<BODY>
<SCRIPT type="text/javascript">
...some JavaScript...
</SCRIPT>
</BODY>
</HTML>
References to HTML elements from a script
Each scripting language has its own conventions for referring to HTML objects from
within a script. This specification does not define a standard mechanism for referring
to HTML objects.
However, scripts should refer to an element according to its assigned name.
Scripting engines should observe the following precedence rules when identifying an
element: a name attribute takes precedence over an id if both are set. Otherwise,
one or the other may be used.
18.2.3 Intrinsic events
Note. Authors of HTML documents are advised that changes are likely to occur in
the realm of intrinsic events (e.g., how scripts are bound to events). Research in this
realm is carried on by members of the W3C Document Object Model Working Group
(see the W3C Web Site at http://www.w3.org/ for more information).
Attribute definitions
onload = script [p.57] [CT] [p.49]
The onload event occurs when the user agent finishes loading a window or all
frames within a FRAMESET. This attribute may be used with BODY and
FRAMESET elements.
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Scripts in HTML documents
onunload = script [p.57] [CT] [p.49]
The onunload event occurs when the user agent removes a document from a
window or frame. This attribute may be used with BODY and FRAMESET
elements.
onclick = script [p.57] [CT] [p.49]
The onclick event occurs when the pointing device button is clicked over an
element. This attribute may be used with most elements.
ondblclick = script [p.57] [CT] [p.49]
The ondblclick event occurs when the pointing device button is double
clicked over an element. This attribute may be used with most elements.
onmousedown = script [p.57] [CT] [p.49]
The onmousedown event occurs when the pointing device button is pressed
over an element. This attribute may be used with most elements.
onmouseup = script [p.57] [CT] [p.49]
The onmouseup event occurs when the pointing device button is released over
an element. This attribute may be used with most elements.
onmouseover = script [p.57] [CT] [p.49]
The onmouseover event occurs when the pointing device is moved onto an
element. This attribute may be used with most elements.
onmousemove = script [p.57] [CT] [p.49]
The onmousemove event occurs when the pointing device is moved while it is
over an element. This attribute may be used with most elements.
onmouseout = script [p.57] [CT] [p.49]
The onmouseout event occurs when the pointing device is moved away from
an element. This attribute may be used with most elements.
onfocus = script [p.57] [CT] [p.49]
The onfocus event occurs when an element receives focus either by the
pointing device or by tabbing navigation. This attribute may be used with the
following elements: A, AREA, LABEL, INPUT, SELECT, TEXTAREA, and BUTTON.
onblur = script [p.57] [CT] [p.49]
The onblur event occurs when an element loses focus either by the pointing
device or by tabbing navigation. It may be used with the same elements as
onfocus.
onkeypress = script [p.57] [CT] [p.49]
The onkeypress event occurs when a key is pressed and released over an
element. This attribute may be used with most elements.
onkeydown = script [p.57] [CT] [p.49]
The onkeydown event occurs when a key is pressed down over an element.
This attribute may be used with most elements.
onkeyup = script [p.57] [CT] [p.49]
The onkeyup event occurs when a key is released over an element. This
attribute may be used with most elements.
onsubmit = script [p.57] [CT] [p.49]
The onsubmit event occurs when a form is submitted. It only applies to the
FORM element.
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onreset = script [p.57] [CT] [p.49]
The onreset event occurs when a form is reset. It only applies to the FORM
element.
onselect = script [p.57] [CT] [p.49]
The onselect event occurs when a user selects some text in a text field. This
attribute may be used with the INPUT and TEXTAREA elements.
onchange = script [p.57] [CT] [p.49]
The onchange event occurs when a control loses the input focus and its value
has been modified since gaining focus. This attribute applies to the following
elements: INPUT, SELECT, and TEXTAREA.
It is possible to associate an action with a certain number of events that occur
when a user interacts with a user agent. Each of the "intrinsic events" listed above
takes a value that is a script. The script is executed whenever the event occurs for
that element. The syntax of script data [p.57] depends on the scripting language.
Control elements such as INPUT, SELECT, BUTTON, TEXTAREA, and LABEL all
respond to certain intrinsic events. When these elements do not appear within a
form, they may be used to augment the graphical user interface of the document.
For instance, authors may want to include press buttons in their documents that
do not submit a form but still communicate with a server when they are activated.
The following examples show some possible control and user interface behavior
based on intrinsic events.
In the following example, userName is a required text field. When a user attempts
to leave the field, the onblur event calls a JavaScript function to confirm that
userName has an acceptable value.
<INPUT NAME="userName" onblur="validUserName(this.value)">
Here is another JavaScript example:
<INPUT NAME="num"
onchange="if (!checkNum(this.value, 1, 10))
{this.focus();this.select();} else {thanks()}"
VALUE="0">
Here is a VBScript example of an event handler for a text field:
<INPUT name="edit1" size="50">
<SCRIPT type="text/vbscript">
Sub edit1_changed()
If edit1.value = "abc" Then
button1.enabled = True
Else
button1.enabled = False
End If
End Sub
</SCRIPT>
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Here is the same example using Tcl:
<INPUT name="edit1" size="50">
<SCRIPT type="text/tcl">
proc edit1_changed {} {
if {[edit value] == abc} {
button1 enable 1
} else {
button1 enable 0
}
}
edit1 onChange edit1_changed
</SCRIPT>
Here is a JavaScript example for event binding within a script. First, here’s a
simple click handler:
<BUTTON type="button" name="mybutton" value="10">
<SCRIPT type="text/javascript">
function my_onclick() {
. . .
}
document.form.mybutton.onclick = my_onclick
</SCRIPT>
</BUTTON>
Here’s a more interesting window handler:
<SCRIPT type="text/javascript">
function my_onload() {
. . .
}
var win = window.open("some/other/URI")
if (win) win.onload = my_onload
</SCRIPT>
In Tcl this looks like:
<SCRIPT type="text/tcl">
proc my_onload {} {
. . .
}
set win [window open "some/other/URI"]
if {$win != ""} {
$win onload my_onload
}
</SCRIPT>
Note that "document.write" or equivalent statements in intrinsic event handlers
create and write to a new document rather than modifying the current one.
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18.2.4 Dynamic modification of documents
Scripts that are executed when a document is loaded may be able to modify the
document’s contents dynamically. The ability to do so depends on the scripting
language itself (e.g., the "document.write" statement in the HTML object model
supported by some vendors).
The dynamic modification of a document may be modeled as follows:
1. All SCRIPT elements are evaluated in order as the document is loaded.
2. All script constructs within a given SCRIPT element that generate SGML
CDATA are evaluated. Their combined generated text is inserted in the
document in place of the SCRIPT element.
3. The generated CDATA is re-evaluated.
HTML documents are constrained to conform to the HTML DTD both before and
after processing any SCRIPT elements.
The following example illustrates how scripts may modify a document dynamically.
The following script:
<TITLE>Test Document</TITLE>
<SCRIPT type="text/javascript">
document.write("<p><b>Hello World!<\/b>")
</SCRIPT>
Has the same effect as this HTML markup:
<TITLE>Test Document</TITLE>
<P><B>Hello World!</B>
18.3 Designing documents for user agents that don’t
support scripting
The following sections discuss how authors may create documents that work for
user agents that don’t support scripting.
18.3.1 The NOSCRIPT element
<!ELEMENT NOSCRIPT - - (%block;)+
-- alternate content container for non script-based rendering -->
<!ATTLIST NOSCRIPT
%attrs;
-- %coreattrs, %i18n, %events ->
Start tag: required, End tag: required
The NOSCRIPT element allows authors to provide alternate content when a script is
not executed. The content of a NOSCRIPT element should only be rendered by a
script-aware user agent in the following cases:
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The user agent is configured not to evaluate scripts.
The user agent doesn’t support a scripting language invoked by a SCRIPT
element earlier in the document.
User agents that do not support client-side scripts must render this element’s
contents.
In the following example, a user agent that executes the SCRIPT will include some
dynamically created data in the document. If the user agent doesn’t support scripts,
the user may still retrieve the data through a link.
<SCRIPT type="text/tcl">
...some Tcl script to insert data...
</SCRIPT>
<NOSCRIPT>
<P>Access the <A href="http://someplace.com/data">data.</A>
</NOSCRIPT>
18.3.2 Hiding script data from user agents
User agents that don’t recognize the SCRIPT element will likely render that
element’s contents as text. Some scripting engines, including those for languages
JavaScript, VBScript, and Tcl allow the script statements to be enclosed in an SGML
comment. User agents that don’t recognize the SCRIPT element will thus ignore the
comment while smart scripting engines will understand that the script in comments
should be executed.
Another solution to the problem is to keep scripts in external documents and refer
to them with the src attribute.
Commenting scripts in JavaScript
The JavaScript engine allows the string "<!--" to occur at the start of a SCRIPT
element, and ignores further characters until the end of the line. JavaScript interprets
"//" as starting a comment extending to the end of the current line. This is needed to
hide the string "-->" from the JavaScript parser.
<SCRIPT type="text/javascript">
<!-- to hide script contents from old browsers
function square(i) {
document.write("The call passed ", i ," to the function.","<BR>")
return i * i
}
document.write("The function returned ",square(5),".")
// end hiding contents from old browsers -->
</SCRIPT>
Commenting scripts in VBScript
In VBScript, a single quote character causes the rest of the current line to be treated
as a comment. It can therefore be used to hide the string "-->" from VBScript, for
instance:
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<SCRIPT type="text/vbscript">
<!-Sub foo()
...
End Sub
’ -->
</SCRIPT>
Commenting scripts in TCL
In Tcl, the "#" character comments out the rest of the line:
<SCRIPT type="text/tcl">
<!-- to hide script contents from old browsers
proc square {i} {
document write "The call passed $i to the function.<BR>"
return [expr $i * $i]
}
document write "The function returned [square 5]."
# end hiding contents from old browsers -->
</SCRIPT>
Note. Some browsers close comments on the first ">" character, so to hide script
content from such browsers, you can transpose operands for relational and shift
operators (e.g., use "y < x" rather than "x > y") or use scripting language-dependent
escapes for ">".
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SGML reference information for HTML
19 SGML reference information for HTML
Contents
1. Document Validation
2. Sample SGML catalog
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The following sections contain the formal SGML definition of HTML 4. It includes
the SGML declaration [p.263] , the Document Type Definition [p.265] (DTD), and the
Character entity references [p.299] , as well as a sample SGML catalog [p.262] .
These files are also available in ASCII format as listed below:
Default DTD:
strict.dtd
Transitional DTD:
loose.dtd
Frameset DTD:
frameset.dtd
SGML declaration:
HTML4.decl
Entity definition files:
HTMLspecial.ent
HTMLsymbol.ent
HTMLlat1.ent
A sample catalog:
HTML4.cat
19.1 Document Validation
Many authors rely on a limited set of browsers to check on the documents they
produce, assuming that if the browsers can render their documents they are valid.
Unfortunately, this is a very ineffective means of verifying a document’s validity
precisely because browsers are designed to cope with invalid documents by
rendering them as well as they can to avoid frustrating users.
For better validation, you should check your document against an SGML parser
such as nsgmls (see [SP] [p.357] ), to verify that HTML documents conform to the
HTML 4 DTD. If the document type declaration [p.60] of your document includes a
URI and your SGML parser supports this type of system identifier, it will get the DTD
directly. Otherwise you can use the following sample SGML catalog. It assumes that
the DTD has been saved as the file "strict.dtd" and that the entities are in the files
"HTMLlat1.ent", "HTMLsymbol.ent" and "HTMLspecial.ent". In any case, make sure
your SGML parser is capable of handling [ISO10646]. [p.353] See your validation
tool documentation for further details.
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Beware that such validation, although useful and highly recommended, does not
guarantee that a document fully conforms to the HTML 4 specification. This is
because an SGML parser relies solely on the given SGML DTD which does not
express all aspects of a valid HTML 4 document. Specifically, an SGML parser
ensures that the syntax, the structure, the list of elements, and their attributes are
valid. But for instance, it cannot catch errors such as setting the width attribute of
an IMG element to an invalid value (i.e., "foo" or "12.5"). Although the specification
restricts the value for this attribute to an "integer representing a length in pixels," the
DTD only defines it to be CDATA [p.50] , which actually allows any value. Only a
specialized program could capture the complete specification of HTML 4.
Nevertheless, this type of validation is still highly recommended since it permits
the detection of a large set of errors that make documents invalid.
19.2 Sample SGML catalog
This catalog includes the override directive to ensure that processing software such
as nsgmls uses public identifiers in preference to system identifiers. This means that
users do not have to be connected to the Web when retrieving URI-based system
identifiers.
OVERRIDE YES
PUBLIC
PUBLIC
PUBLIC
PUBLIC
PUBLIC
PUBLIC
"-//W3C//DTD HTML
"-//W3C//DTD HTML
"-//W3C//DTD HTML
"-//W3C//ENTITIES
"-//W3C//ENTITIES
"-//W3C//ENTITIES
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4.01//EN" strict.dtd
4.01 Transitional//EN" loose.dtd
4.01 Frameset//EN" frameset.dtd
Latin1//EN//HTML" HTMLlat1.ent
Special//EN//HTML" HTMLspecial.ent
Symbols//EN//HTML" HTMLsymbol.ent
262
SGML Declaration of HTML 4
20 SGML Declaration of HTML 4
Note. The total number of codepoints allowed in the document character set of this
SGML declaration includes the first 17 planes of [ISO10646] [p.353] (17 times
65536). This limitation has been made because this number is limited to a length of
8 digits in the current version of the SGML standard. It does not imply any statement
about the feasibility of a long-term restriction of characters in UCS to the first 17
planes. Chances are very high that the limitation to 8 digits in SGML will be removed
before, and that this specification will be updated before, the first assignment of a
character beyond the first 17 planes.
Note. Strictly speaking, ISO Registration Number 177 refers to the original state of
[ISO10646] [p.353] in 1993. Changes since 1993 have been the addition of
characters and a one-time operation reallocating a large number of codepoints for
Korean Hangul (Amendment 5). Revisions of the HTML 4 specification may update
the reference to ISO 10646 to include additional changes.
20.1 SGML Declaration
<!SGML
--
"ISO 8879:1986 (WWW)"
SGML Declaration for HyperText Markup Language version HTML 4
With support for the first 17 planes of ISO 10646 and
increased limits for tag and literal lengths etc.
-CHARSET
BASESET
"ISO Registration Number 177//CHARSET
ISO/IEC 10646-1:1993 UCS-4 with
implementation level 3//ESC 2/5 2/15 4/6"
DESCSET 0
9
UNUSED
9
2
9
11
2
UNUSED
13
1
13
14
18
UNUSED
32
95
32
127
1
UNUSED
128
32
UNUSED
160
55136
160
55296
2048
UNUSED -- SURROGATES -57344
1056768 57344
CAPACITY
SCOPE
SYNTAX
SGMLREF
TOTALCAP
GRPCAP
ENTCAP
150000
150000
150000
DOCUMENT
SHUNCHAR CONTROLS 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 127
BASESET "ISO 646IRV:1991//CHARSET
263
24 Dec 1999 18:26
SGML Declaration of HTML 4
DESCSET
International Reference Version
(IRV)//ESC 2/8 4/2"
0 128 0
FUNCTION
RE
RS
SPACE
TAB SEPCHAR
NAMING
13
10
32
9
LCNMSTRT
UCNMSTRT
LCNMCHAR
UCNMCHAR
NAMECASE
""
""
".-_:"
".-_:"
GENERAL YES
ENTITY NO
DELIM
GENERAL SGMLREF
HCRO "&#38;#x" -- 38 is the number for ampersand
SHORTREF SGMLREF
NAMES
SGMLREF
QUANTITY SGMLREF
ATTCNT
60
-- increased -ATTSPLEN 65536
-- These are the largest values
LITLEN
65536
-- permitted in the declaration
NAMELEN 65536
-- Avoid fixed limits in actual
PILEN
65536
-- implementations of HTML UA’s
TAGLVL
100
TAGLEN
65536
GRPGTCNT 150
GRPCNT
64
--
-----
FEATURES
MINIMIZE
DATATAG NO
OMITTAG YES
RANK
NO
SHORTTAG YES
LINK
SIMPLE
NO
IMPLICIT NO
EXPLICIT NO
OTHER
CONCUR
NO
SUBDOC
NO
FORMAL
YES
APPINFO NONE
>
24 Dec 1999 18:26
264
HTML 4 Document Type Definition
21 Document Type Definition
<!-This is HTML 4.01 Strict DTD, which excludes the presentation
attributes and elements that W3C expects to phase out as
support for style sheets matures. Authors should use the Strict
DTD when possible, but may use the Transitional DTD when support
for presentation attribute and elements is required.
HTML 4 includes mechanisms for style sheets, scripting,
embedding objects, improved support for right to left and mixed
direction text, and enhancements to forms for improved
accessibility for people with disabilities.
Draft: $Date: 1999/12/24 22:40:35 $
Authors:
Dave Raggett <dsr@w3.org>
Arnaud Le Hors <lehors@w3.org>
Ian Jacobs <ij@w3.org>
Further information about HTML 4.01 is available at:
http://www.w3.org/TR/1999/REC-html401-19991224
The HTML 4.01 specification includes additional
syntactic constraints that cannot be expressed within
the DTDs.
-->
<!-Typical usage:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
...
</head>
<body>
...
</body>
</html>
The URI used as a system identifier with the public identifier allows
the user agent to download the DTD and entity sets as needed.
The FPI for the Transitional HTML 4.01 DTD is:
"-//W3C//DTD HTML 4.01 Transitional//EN"
This version of the transitional DTD is:
http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd
If you are writing a document that includes frames, use
the following FPI:
"-//W3C//DTD HTML 4.01 Frameset//EN"
This version of the frameset DTD is:
265
24 Dec 1999 18:26
HTML 4 Document Type Definition
http://www.w3.org/TR/1999/REC-html401-19991224/frameset.dtd
Use the following (relative) URIs to refer to
the DTDs and entity definitions of this specification:
"strict.dtd"
"loose.dtd"
"frameset.dtd"
"HTMLlat1.ent"
"HTMLsymbol.ent"
"HTMLspecial.ent"
-->
<!--================== Imported Names ====================================-->
<!-- Feature Switch for frameset documents -->
<!ENTITY % HTML.Frameset "IGNORE">
<!ENTITY % ContentType "CDATA"
-- media type, as per [RFC2045]
-->
<!ENTITY % ContentTypes "CDATA"
-- comma-separated list of media types, as per [RFC2045]
-->
<!ENTITY % Charset "CDATA"
-- a character encoding, as per [RFC2045]
-->
<!ENTITY % Charsets "CDATA"
-- a space-separated list of character encodings, as per [RFC2045]
-->
<!ENTITY % LanguageCode "NAME"
-- a language code, as per [RFC1766]
-->
<!ENTITY % Character "CDATA"
-- a single character from [ISO10646]
-->
<!ENTITY % LinkTypes "CDATA"
-- space-separated list of link types
-->
<!ENTITY % MediaDesc "CDATA"
-- single or comma-separated list of media descriptors
-->
<!ENTITY % URI "CDATA"
-- a Uniform Resource Identifier,
see [URI]
-->
<!ENTITY % Datetime "CDATA" -- date and time information. ISO date format -->
<!ENTITY % Script "CDATA" -- script expression -->
<!ENTITY % StyleSheet "CDATA" -- style sheet data -->
<!ENTITY % Text "CDATA">
24 Dec 1999 18:26
266
HTML 4 Document Type Definition
<!-- Parameter Entities -->
<!ENTITY % head.misc "SCRIPT|STYLE|META|LINK|OBJECT" -- repeatable head elements -->
<!ENTITY % heading "H1|H2|H3|H4|H5|H6">
<!ENTITY % list "UL | OL">
<!ENTITY % preformatted "PRE">
<!--================ Character mnemonic entities =========================-->
<!ENTITY % HTMLlat1 PUBLIC
"-//W3C//ENTITIES Latin1//EN//HTML"
"HTMLlat1.ent">
%HTMLlat1;
<!ENTITY % HTMLsymbol PUBLIC
"-//W3C//ENTITIES Symbols//EN//HTML"
"HTMLsymbol.ent">
%HTMLsymbol;
<!ENTITY % HTMLspecial PUBLIC
"-//W3C//ENTITIES Special//EN//HTML"
"HTMLspecial.ent">
%HTMLspecial;
<!--=================== Generic Attributes ===============================-->
<!ENTITY % coreattrs
"id
ID
class
CDATA
style
%StyleSheet;
title
%Text;
>
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
-----
document-wide unique id -space-separated list of classes -associated style info -advisory title --"
<!ENTITY % i18n
"lang
%LanguageCode; #IMPLIED
dir
(ltr|rtl)
#IMPLIED
>
-- language code --- direction for weak/neutral text --"
<!ENTITY % events
"onclick
%Script;
ondblclick %Script;
onmousedown %Script;
onmouseup
%Script;
onmouseover %Script;
onmousemove %Script;
onmouseout %Script;
onkeypress %Script;
onkeydown
%Script;
onkeyup
%Script;
>
-----------
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
a
a
a
a
a
a
a
a
a
a
pointer
pointer
pointer
pointer
pointer
pointer
pointer
key was
key was
key was
button was clicked -button was double clicked-button was pressed down -button was released -was moved onto -was moved within -was moved away -pressed and released -pressed down -released --"
<!-- Reserved Feature Switch -->
<!ENTITY % HTML.Reserved "IGNORE">
<!-- The following attributes are reserved for possible future use -->
<![ %HTML.Reserved; [
<!ENTITY % reserved
"datasrc
%URI;
#IMPLIED -- a single or tabular Data Source -datafld
CDATA
#IMPLIED -- the property or column name -dataformatas (plaintext|html) plaintext -- text or html --"
>
267
24 Dec 1999 18:26
HTML 4 Document Type Definition
]]>
<!ENTITY % reserved "">
<!ENTITY % attrs "%coreattrs; %i18n; %events;">
<!--=================== Text Markup ======================================-->
<!ENTITY % fontstyle
"TT | I | B | BIG | SMALL">
<!ENTITY % phrase "EM | STRONG | DFN | CODE |
SAMP | KBD | VAR | CITE | ABBR | ACRONYM" >
<!ENTITY % special
"A | IMG | OBJECT | BR | SCRIPT | MAP | Q | SUB | SUP | SPAN | BDO">
<!ENTITY % formctrl "INPUT | SELECT | TEXTAREA | LABEL | BUTTON">
<!-- %inline; covers inline or "text-level" elements -->
<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
%attrs;
-- %coreattrs, %i18n, %events ->
<!ELEMENT (SUB|SUP) - - (%inline;)*
<!ATTLIST (SUB|SUP)
%attrs;
>
-- subscript, superscript -->
-- %coreattrs, %i18n, %events --
<!ELEMENT SPAN - - (%inline;)*
-- generic language/style container -->
<!ATTLIST SPAN
%attrs;
-- %coreattrs, %i18n, %events -%reserved;
-- reserved for possible future use ->
<!ELEMENT BDO - - (%inline;)*
<!ATTLIST BDO
%coreattrs;
lang
%LanguageCode; #IMPLIED
dir
(ltr|rtl)
#REQUIRED
>
<!ELEMENT BR - O EMPTY
<!ATTLIST BR
%coreattrs;
>
-- I18N BiDi over-ride -->
-- id, class, style, title --- language code --- directionality --
-- forced line break -->
-- id, class, style, title --
<!--================== HTML content models ===============================-->
<!-HTML has two basic content models:
%inline;
%block;
character level elements and text strings
block-like elements e.g. paragraphs and lists
-->
<!ENTITY % block
"P | %heading; | %list; | %preformatted; | DL | DIV | NOSCRIPT |
BLOCKQUOTE | FORM | HR | TABLE | FIELDSET | ADDRESS">
24 Dec 1999 18:26
268
HTML 4 Document Type Definition
<!ENTITY % flow "%block; | %inline;">
<!--=================== Document Body ====================================-->
<!ELEMENT BODY O O (%block;|SCRIPT)+ +(INS|DEL) -- document body -->
<!ATTLIST BODY
%attrs;
-- %coreattrs, %i18n, %events -onload
%Script;
#IMPLIED -- the document has been loaded -onunload
%Script;
#IMPLIED -- the document has been removed ->
<!ELEMENT ADDRESS - - (%inline;)* -- information on author -->
<!ATTLIST ADDRESS
%attrs;
-- %coreattrs, %i18n, %events ->
<!ELEMENT DIV - - (%flow;)*
<!ATTLIST DIV
%attrs;
%reserved;
>
-- generic language/style container -->
-- %coreattrs, %i18n, %events --- reserved for possible future use --
<!--================== The Anchor Element ================================-->
<!ENTITY % Shape "(rect|circle|poly|default)">
<!ENTITY % Coords "CDATA" -- comma-separated list of lengths -->
<!ELEMENT A - - (%inline;)* -(A)
<!ATTLIST A
%attrs;
charset
%Charset;
#IMPLIED
type
%ContentType; #IMPLIED
name
CDATA
#IMPLIED
href
%URI;
#IMPLIED
hreflang
%LanguageCode; #IMPLIED
rel
%LinkTypes;
#IMPLIED
rev
%LinkTypes;
#IMPLIED
accesskey
%Character;
#IMPLIED
shape
%Shape;
rect
coords
%Coords;
#IMPLIED
tabindex
NUMBER
#IMPLIED
onfocus
%Script;
#IMPLIED
onblur
%Script;
#IMPLIED
>
-- anchor -->
---------------
%coreattrs, %i18n, %events -char encoding of linked resource -advisory content type -named link end -URI for linked resource -language code -forward link types -reverse link types -accessibility key character -for use with client-side image maps -for use with client-side image maps -position in tabbing order -the element got the focus -the element lost the focus --
<!--================== Client-side image maps ============================-->
<!-- These can be placed in the same document or grouped in a
separate document although this isn’t yet widely supported -->
<!ELEMENT MAP - - ((%block;) | AREA)+ -- client-side image map -->
<!ATTLIST MAP
%attrs;
-- %coreattrs, %i18n, %events -name
CDATA
#REQUIRED -- for reference by usemap ->
<!ELEMENT AREA - O EMPTY
<!ATTLIST AREA
%attrs;
shape
%Shape;
coords
%Coords;
href
%URI;
nohref
(nohref)
alt
%Text;
269
-- client-side image map area -->
rect
#IMPLIED
#IMPLIED
#IMPLIED
#REQUIRED
-------
%coreattrs, %i18n, %events -controls interpretation of coords -comma-separated list of lengths -URI for linked resource -this region has no action -short description --
24 Dec 1999 18:26
HTML 4 Document Type Definition
tabindex
accesskey
onfocus
onblur
>
NUMBER
%Character;
%Script;
%Script;
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
-----
position in tabbing order -accessibility key character -the element got the focus -the element lost the focus --
<!--================== The LINK Element ==================================-->
<!-Relationship values can be used in principle:
a) for document specific toolbars/menus when used
with the LINK element in document head e.g.
start, contents, previous, next, index, end, help
b) to link to a separate style sheet (rel=stylesheet)
c) to make a link to a script (rel=script)
d) by stylesheets to control how collections of
html nodes are rendered into printed documents
e) to make a link to a printable version of this document
e.g. a postscript or pdf version (rel=alternate media=print)
-->
<!ELEMENT LINK - O EMPTY
<!ATTLIST LINK
%attrs;
charset
%Charset;
href
%URI;
hreflang
%LanguageCode;
type
%ContentType;
rel
%LinkTypes;
rev
%LinkTypes;
media
%MediaDesc;
>
-- a media-independent link -->
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
---------
%coreattrs, %i18n, %events -char encoding of linked resource -URI for linked resource -language code -advisory content type -forward link types -reverse link types -for rendering on these media --
<!--=================== Images ===========================================-->
<!-- Length defined in strict DTD for cellpadding/cellspacing -->
<!ENTITY % Length "CDATA" -- nn for pixels or nn% for percentage length -->
<!ENTITY % MultiLength "CDATA" -- pixel, percentage, or relative -->
<![ %HTML.Frameset; [
<!ENTITY % MultiLengths "CDATA" -- comma-separated list of MultiLength -->
]]>
<!ENTITY % Pixels "CDATA" -- integer representing length in pixels -->
<!-- To avoid problems with text-only UAs as well as
to make image content understandable and navigable
to users of non-visual UAs, you need to provide
a description with ALT, and avoid server-side image maps -->
<!ELEMENT IMG - O EMPTY
-- Embedded image -->
<!ATTLIST IMG
%attrs;
-- %coreattrs, %i18n, %events -src
%URI;
#REQUIRED -- URI of image to embed -alt
%Text;
#REQUIRED -- short description -longdesc
%URI;
#IMPLIED -- link to long description
(complements alt) -name
CDATA
#IMPLIED -- name of image for scripting -height
%Length;
#IMPLIED -- override height -width
%Length;
#IMPLIED -- override width -usemap
%URI;
#IMPLIED -- use client-side image map -ismap
(ismap)
#IMPLIED -- use server-side image map ->
24 Dec 1999 18:26
270
HTML 4 Document Type Definition
<!-- USEMAP points to a MAP element which may be in this document
or an external document, although the latter is not widely supported -->
<!--==================== OBJECT ======================================-->
<!-OBJECT is used to embed objects as part of HTML pages
PARAM elements should precede other content. SGML mixed content
model technicality precludes specifying this formally ...
-->
<!ELEMENT OBJECT - - (PARAM | %flow;)*
-- generic embedded object -->
<!ATTLIST OBJECT
%attrs;
declare
(declare)
#IMPLIED
classid
%URI;
#IMPLIED
codebase
%URI;
#IMPLIED
data
%URI;
#IMPLIED
type
%ContentType; #IMPLIED
codetype
%ContentType; #IMPLIED
archive
CDATA
#IMPLIED
standby
%Text;
#IMPLIED
height
%Length;
#IMPLIED
width
%Length;
#IMPLIED
usemap
%URI;
#IMPLIED
name
CDATA
#IMPLIED
tabindex
NUMBER
#IMPLIED
%reserved;
>
<!ELEMENT PARAM - O EMPTY
<!ATTLIST PARAM
id
ID
#IMPLIED
name
CDATA
#REQUIRED
value
CDATA
#IMPLIED
valuetype
(DATA|REF|OBJECT) DATA
type
%ContentType; #IMPLIED
----------------
%coreattrs, %i18n, %events -declare but don’t instantiate flag -identifies an implementation -base URI for classid, data, archive-reference to object’s data -content type for data -content type for code -space-separated list of URIs -message to show while loading -override height -override width -use client-side image map -submit as part of form -position in tabbing order -reserved for possible future use --
-- named property value -->
------
document-wide unique id -property name -property value -How to interpret value -content type for value
when valuetype=ref --
>
<!--=================== Horizontal Rule ==================================-->
<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ATTLIST HR
%attrs;
-- %coreattrs, %i18n, %events ->
<!--=================== Paragraphs =======================================-->
<!ELEMENT P - O (%inline;)*
<!ATTLIST P
%attrs;
>
-- paragraph -->
-- %coreattrs, %i18n, %events --
<!--=================== Headings =========================================-->
<!-There are six levels of headings from H1 (the most important)
to H6 (the least important).
-->
<!ELEMENT (%heading;)
<!ATTLIST (%heading;)
%attrs;
271
- - (%inline;)* -- heading -->
-- %coreattrs, %i18n, %events --
24 Dec 1999 18:26
HTML 4 Document Type Definition
>
<!--=================== Preformatted Text ================================-->
<!-- excludes markup for images and changes in font size -->
<!ENTITY % pre.exclusion "IMG|OBJECT|BIG|SMALL|SUB|SUP">
<!ELEMENT PRE - - (%inline;)* -(%pre.exclusion;) -- preformatted text -->
<!ATTLIST PRE
%attrs;
-- %coreattrs, %i18n, %events ->
<!--===================== Inline Quotes ==================================-->
<!ELEMENT Q - - (%inline;)*
<!ATTLIST Q
%attrs;
cite
%URI;
>
-- short inline quotation -->
#IMPLIED
-- %coreattrs, %i18n, %events --- URI for source document or msg --
<!--=================== Block-like Quotes ================================-->
<!ELEMENT BLOCKQUOTE - - (%block;|SCRIPT)+ -- long quotation -->
<!ATTLIST BLOCKQUOTE
%attrs;
-- %coreattrs, %i18n, %events -cite
%URI;
#IMPLIED -- URI for source document or msg ->
<!--=================== Inserted/Deleted Text ============================-->
<!-- INS/DEL are handled by inclusion on BODY -->
<!ELEMENT (INS|DEL) - - (%flow;)*
-- inserted text, deleted text -->
<!ATTLIST (INS|DEL)
%attrs;
-- %coreattrs, %i18n, %events -cite
%URI;
#IMPLIED -- info on reason for change -datetime
%Datetime;
#IMPLIED -- date and time of change ->
<!--=================== Lists ============================================-->
<!-- definition lists - DT for term, DD for its definition -->
<!ELEMENT DL - - (DT|DD)+
<!ATTLIST DL
%attrs;
>
-- definition list -->
<!ELEMENT DT - O (%inline;)*
<!ELEMENT DD - O (%flow;)*
<!ATTLIST (DT|DD)
%attrs;
>
-- definition term -->
-- definition description -->
<!ELEMENT OL - - (LI)+
<!ATTLIST OL
%attrs;
>
-- %coreattrs, %i18n, %events --
-- %coreattrs, %i18n, %events --
-- ordered list -->
-- %coreattrs, %i18n, %events --
<!-- Unordered Lists (UL) bullet styles -->
<!ELEMENT UL - - (LI)+
-- unordered list -->
<!ATTLIST UL
%attrs;
-- %coreattrs, %i18n, %events ->
24 Dec 1999 18:26
272
HTML 4 Document Type Definition
<!ELEMENT LI - O (%flow;)*
<!ATTLIST LI
%attrs;
>
-- list item -->
-- %coreattrs, %i18n, %events --
<!--================ Forms ===============================================-->
<!ELEMENT FORM - - (%block;|SCRIPT)+ -(FORM) -- interactive form -->
<!ATTLIST FORM
%attrs;
-- %coreattrs, %i18n, %events -action
%URI;
#REQUIRED -- server-side form handler -method
(GET|POST)
GET
-- HTTP method used to submit the form-enctype
%ContentType; "application/x-www-form-urlencoded"
accept
%ContentTypes; #IMPLIED -- list of MIME types for file upload -name
CDATA
#IMPLIED -- name of form for scripting -onsubmit
%Script;
#IMPLIED -- the form was submitted -onreset
%Script;
#IMPLIED -- the form was reset -accept-charset %Charsets; #IMPLIED -- list of supported charsets ->
<!-- Each label must not contain more than ONE field -->
<!ELEMENT LABEL - - (%inline;)* -(LABEL) -- form field label text -->
<!ATTLIST LABEL
%attrs;
-- %coreattrs, %i18n, %events -for
IDREF
#IMPLIED -- matches field ID value -accesskey
%Character;
#IMPLIED -- accessibility key character -onfocus
%Script;
#IMPLIED -- the element got the focus -onblur
%Script;
#IMPLIED -- the element lost the focus ->
<!ENTITY % InputType
"(TEXT | PASSWORD | CHECKBOX |
RADIO | SUBMIT | RESET |
FILE | HIDDEN | IMAGE | BUTTON)"
>
<!-- attribute name required
<!ELEMENT INPUT - O EMPTY
<!ATTLIST INPUT
%attrs;
type
%InputType;
name
CDATA
value
CDATA
checked
(checked)
disabled
(disabled)
readonly
(readonly)
size
CDATA
maxlength
NUMBER
src
%URI;
alt
CDATA
usemap
%URI;
ismap
(ismap)
tabindex
NUMBER
accesskey
%Character;
onfocus
%Script;
onblur
%Script;
onselect
%Script;
onchange
%Script;
accept
%ContentTypes;
%reserved;
>
for all but submit and reset -->
-- form control -->
TEXT
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
----------------------
%coreattrs, %i18n, %events -what kind of widget is needed -submit as part of form -Specify for radio buttons and checkboxes -for radio buttons and check boxes -unavailable in this context -for text and passwd -specific to each type of field -max chars for text fields -for fields with images -short description -use client-side image map -use server-side image map -position in tabbing order -accessibility key character -the element got the focus -the element lost the focus -some text was selected -the element value was changed -list of MIME types for file upload -reserved for possible future use --
<!ELEMENT SELECT - - (OPTGROUP|OPTION)+ -- option selector -->
<!ATTLIST SELECT
%attrs;
-- %coreattrs, %i18n, %events --
273
24 Dec 1999 18:26
HTML 4 Document Type Definition
name
size
multiple
disabled
tabindex
onfocus
onblur
onchange
%reserved;
>
CDATA
NUMBER
(multiple)
(disabled)
NUMBER
%Script;
%Script;
%Script;
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
----------
field name -rows visible -default is single selection -unavailable in this context -position in tabbing order -the element got the focus -the element lost the focus -the element value was changed -reserved for possible future use --
<!ELEMENT OPTGROUP - - (OPTION)+ -- option group -->
<!ATTLIST OPTGROUP
%attrs;
-- %coreattrs, %i18n, %events -disabled
(disabled)
#IMPLIED -- unavailable in this context -label
%Text;
#REQUIRED -- for use in hierarchical menus ->
<!ELEMENT OPTION - O (#PCDATA)
<!ATTLIST OPTION
%attrs;
selected
(selected)
#IMPLIED
disabled
(disabled)
#IMPLIED
label
%Text;
#IMPLIED
value
CDATA
#IMPLIED
>
<!ELEMENT TEXTAREA - - (#PCDATA)
<!ATTLIST TEXTAREA
%attrs;
name
CDATA
#IMPLIED
rows
NUMBER
#REQUIRED
cols
NUMBER
#REQUIRED
disabled
(disabled)
#IMPLIED
readonly
(readonly)
#IMPLIED
tabindex
NUMBER
#IMPLIED
accesskey
%Character;
#IMPLIED
onfocus
%Script;
#IMPLIED
onblur
%Script;
#IMPLIED
onselect
%Script;
#IMPLIED
onchange
%Script;
#IMPLIED
%reserved;
>
-- selectable choice -->
-- %coreattrs, %i18n, %events --- unavailable in this context --- for use in hierarchical menus --- defaults to element content --
-- multi-line text field -->
-- %coreattrs, %i18n, %events --
-- unavailable in this context ---------
position in tabbing order -accessibility key character -the element got the focus -the element lost the focus -some text was selected -the element value was changed -reserved for possible future use --
<!-#PCDATA is to solve the mixed content problem,
per specification only whitespace is allowed there!
-->
<!ELEMENT FIELDSET - - (#PCDATA,LEGEND,(%flow;)*) -- form control group -->
<!ATTLIST FIELDSET
%attrs;
-- %coreattrs, %i18n, %events ->
<!ELEMENT LEGEND - - (%inline;)*
-- fieldset legend -->
<!ATTLIST LEGEND
%attrs;
accesskey
%Character;
>
-- %coreattrs, %i18n, %events --- accessibility key character --
#IMPLIED
<!ELEMENT BUTTON - (%flow;)* -(A|%formctrl;|FORM|FIELDSET)
-- push button -->
<!ATTLIST BUTTON
%attrs;
-- %coreattrs, %i18n, %events --
24 Dec 1999 18:26
274
HTML 4 Document Type Definition
name
value
type
disabled
tabindex
accesskey
onfocus
onblur
%reserved;
>
CDATA
#IMPLIED
CDATA
#IMPLIED -- sent to server when submitted -(button|submit|reset) submit -- for use as form button -(disabled)
#IMPLIED -- unavailable in this context -NUMBER
#IMPLIED -- position in tabbing order -%Character;
#IMPLIED -- accessibility key character -%Script;
#IMPLIED -- the element got the focus -%Script;
#IMPLIED -- the element lost the focus --- reserved for possible future use --
<!--======================= Tables =======================================-->
<!-- IETF HTML table standard, see [RFC1942] -->
<!-The BORDER attribute sets the thickness of the frame around the
table. The default units are screen pixels.
The FRAME attribute specifies which parts of the frame around
the table should be rendered. The values are not the same as
CALS to avoid a name clash with the VALIGN attribute.
The value "border" is included for backwards compatibility with
<TABLE BORDER> which yields frame=border and border=implied
For <TABLE BORDER=1> you get border=1 and frame=implied. In this
case, it is appropriate to treat this as frame=border for backwards
compatibility with deployed browsers.
-->
<!ENTITY % TFrame "(void|above|below|hsides|lhs|rhs|vsides|box|border)">
<!-The RULES attribute defines which rules to draw between cells:
If RULES is absent then assume:
"none" if BORDER is absent or BORDER=0 otherwise "all"
-->
<!ENTITY % TRules "(none | groups | rows | cols | all)">
<!-- horizontal placement of table relative to document -->
<!ENTITY % TAlign "(left|center|right)">
<!-- horizontal alignment attributes for cell contents -->
<!ENTITY % cellhalign
"align
(left|center|right|justify|char) #IMPLIED
char
%Character;
#IMPLIED -- alignment char, e.g. char=’:’ -charoff
%Length;
#IMPLIED -- offset for alignment char --"
>
<!-- vertical alignment attributes for cell contents -->
<!ENTITY % cellvalign
"valign
(top|middle|bottom|baseline) #IMPLIED"
>
<!ELEMENT TABLE - (CAPTION?, (COL*|COLGROUP*), THEAD?,
<!ELEMENT CAPTION - - (%inline;)*
-<!ELEMENT THEAD
- O (TR)+
-<!ELEMENT TFOOT
- O (TR)+
-<!ELEMENT TBODY
O O (TR)+
-<!ELEMENT COLGROUP - O (COL)*
-<!ELEMENT COL
- O EMPTY
-<!ELEMENT TR
- O (TH|TD)+
-<!ELEMENT (TH|TD) - O (%flow;)*
--
275
TFOOT?, TBODY+)>
table caption -->
table header -->
table footer -->
table body -->
table column group -->
table column -->
table row -->
table header cell, table data cell-->
24 Dec 1999 18:26
HTML 4 Document Type Definition
<!ATTLIST TABLE
%attrs;
summary
%Text;
width
%Length;
border
%Pixels;
frame
%TFrame;
rules
%TRules;
cellspacing %Length;
cellpadding %Length;
%reserved;
datapagesize CDATA
>
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
<!ATTLIST CAPTION
%attrs;
>
------------
table element -%coreattrs, %i18n, %events -purpose/structure for speech output-table width -controls frame width around table -which parts of frame to render -rulings between rows and cols -spacing between cells -spacing within cells -reserved for possible future use -reserved for possible future use --
-- %coreattrs, %i18n, %events --
<!-COLGROUP groups a set of COL
several semantically related
-->
<!ATTLIST COLGROUP
%attrs;
span
NUMBER
width
%MultiLength;
%cellhalign;
%cellvalign;
>
elements. It allows you to group
columns together.
1
#IMPLIED
------
%coreattrs, %i18n, %events -default number of columns in group -default width for enclosed COLs -horizontal alignment in cells -vertical alignment in cells --
<!-COL elements define the alignment properties for cells in
one or more columns.
The WIDTH attribute specifies the width of the columns, e.g.
width=64
width=0.5*
width in screen pixels
relative width of 0.5
The SPAN attribute causes the attributes of one
COL element to apply to more than one column.
-->
<!ATTLIST COL
-- column groups and properties -%attrs;
-- %coreattrs, %i18n, %events -span
NUMBER
1
-- COL attributes affect N columns -width
%MultiLength; #IMPLIED -- column width specification -%cellhalign;
-- horizontal alignment in cells -%cellvalign;
-- vertical alignment in cells ->
<!-Use THEAD to duplicate headers when breaking table
across page boundaries, or for static headers when
TBODY sections are rendered in scrolling panel.
Use TFOOT to duplicate footers when breaking table
across page boundaries, or for static footers when
TBODY sections are rendered in scrolling panel.
Use multiple TBODY sections when rules are needed
between groups of table rows.
-->
<!ATTLIST (THEAD|TBODY|TFOOT)
%attrs;
24 Dec 1999 18:26
-- table section --- %coreattrs, %i18n, %events --
276
HTML 4 Document Type Definition
%cellhalign;
%cellvalign;
>
-- horizontal alignment in cells --- vertical alignment in cells --
<!ATTLIST TR
%attrs;
%cellhalign;
%cellvalign;
>
-----
table row -%coreattrs, %i18n, %events -horizontal alignment in cells -vertical alignment in cells --
<!-- Scope is simpler than headers attribute for common tables -->
<!ENTITY % Scope "(row|col|rowgroup|colgroup)">
<!-- TH is for headers, TD for data, but for cells acting as both use TD -->
<!ATTLIST (TH|TD)
-- header or data cell -%attrs;
-- %coreattrs, %i18n, %events -abbr
%Text;
#IMPLIED -- abbreviation for header cell -axis
CDATA
#IMPLIED -- comma-separated list of related headers-headers
IDREFS
#IMPLIED -- list of id’s for header cells -scope
%Scope;
#IMPLIED -- scope covered by header cells -rowspan
NUMBER
1
-- number of rows spanned by cell -colspan
NUMBER
1
-- number of cols spanned by cell -%cellhalign;
-- horizontal alignment in cells -%cellvalign;
-- vertical alignment in cells ->
<!--================ Document Head =======================================-->
<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & BASE?">
<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
%i18n;
-- lang, dir -profile
%URI;
#IMPLIED -- named dictionary of meta info ->
<!-- The TITLE element is not considered part of the flow of text.
It should be displayed, for example as the page header or
window title. Exactly one title is required per document.
-->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>
<!ELEMENT BASE - O EMPTY
<!ATTLIST BASE
href
%URI;
>
<!ELEMENT META - O EMPTY
<!ATTLIST META
%i18n;
http-equiv NAME
name
NAME
content
CDATA
scheme
CDATA
>
-- document base URI -->
#REQUIRED -- URI that acts as base URI --
-- generic metainformation -->
#IMPLIED
#IMPLIED
#REQUIRED
#IMPLIED
------
lang, dir, for use with content -HTTP response header name -metainformation name -associated information -select form of content --
<!ELEMENT STYLE - - %StyleSheet
-- style info -->
<!ATTLIST STYLE
%i18n;
-- lang, dir, for use with title -type
%ContentType; #REQUIRED -- content type of style language --
277
24 Dec 1999 18:26
HTML 4 Document Type Definition
media
title
>
%MediaDesc;
%Text;
#IMPLIED
#IMPLIED
<!ELEMENT SCRIPT - - %Script;
<!ATTLIST SCRIPT
charset
%Charset;
#IMPLIED
type
%ContentType; #REQUIRED
src
%URI;
#IMPLIED
defer
(defer)
#IMPLIED
event
CDATA
#IMPLIED
for
%URI;
#IMPLIED
>
-- designed for use with these media --- advisory title --
-- script statements -->
-------
char encoding of linked resource -content type of script language -URI for an external script -UA may defer execution of script -reserved for possible future use -reserved for possible future use --
<!ELEMENT NOSCRIPT - - (%block;)+
-- alternate content container for non script-based rendering -->
<!ATTLIST NOSCRIPT
%attrs;
-- %coreattrs, %i18n, %events ->
<!--================ Document Structure ==================================-->
<!ENTITY % html.content "HEAD, BODY">
<!ELEMENT HTML O O (%html.content;)
<!ATTLIST HTML
%i18n;
>
24 Dec 1999 18:26
-- document root element -->
-- lang, dir --
278
HTML 4 Transitional Document Type Definition
22 Transitional Document Type Definition
<!-This is the HTML 4.01 Transitional DTD, which includes
presentation attributes and elements that W3C expects to phase out
as support for style sheets matures. Authors should use the Strict
DTD when possible, but may use the Transitional DTD when support
for presentation attribute and elements is required.
HTML 4 includes mechanisms for style sheets, scripting,
embedding objects, improved support for right to left and mixed
direction text, and enhancements to forms for improved
accessibility for people with disabilities.
Draft: $Date: 1999/12/24 22:40:35 $
Authors:
Dave Raggett <dsr@w3.org>
Arnaud Le Hors <lehors@w3.org>
Ian Jacobs <ij@w3.org>
Further information about HTML 4.01 is available at:
http://www.w3.org/TR/1999/REC-html401-19991224
The HTML 4.01 specification includes additional
syntactic constraints that cannot be expressed within
the DTDs.
-->
<!ENTITY % HTML.Version "-//W3C//DTD HTML 4.01 Transitional//EN"
-- Typical usage:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
...
</head>
<body>
...
</body>
</html>
The URI used as a system identifier with the public identifier allows
the user agent to download the DTD and entity sets as needed.
The FPI for the Strict HTML 4.01 DTD is:
"-//W3C//DTD HTML 4.01//EN"
This version of the strict DTD is:
http://www.w3.org/TR/1999/REC-html401-19991224/strict.dtd
Authors should use the Strict DTD unless they need the
presentation control for user agents that don’t (adequately)
support style sheets.
If you are writing a document that includes frames, use
the following FPI:
279
24 Dec 1999 18:26
HTML 4 Transitional Document Type Definition
"-//W3C//DTD HTML 4.01 Frameset//EN"
This version of the frameset DTD is:
http://www.w3.org/TR/1999/REC-html401-19991224/frameset.dtd
Use the following (relative) URIs to refer to
the DTDs and entity definitions of this specification:
"strict.dtd"
"loose.dtd"
"frameset.dtd"
"HTMLlat1.ent"
"HTMLsymbol.ent"
"HTMLspecial.ent"
-->
<!--================== Imported Names ====================================-->
<!-- Feature Switch for frameset documents -->
<!ENTITY % HTML.Frameset "IGNORE">
<!ENTITY % ContentType "CDATA"
-- media type, as per [RFC2045]
-->
<!ENTITY % ContentTypes "CDATA"
-- comma-separated list of media types, as per [RFC2045]
-->
<!ENTITY % Charset "CDATA"
-- a character encoding, as per [RFC2045]
-->
<!ENTITY % Charsets "CDATA"
-- a space-separated list of character encodings, as per [RFC2045]
-->
<!ENTITY % LanguageCode "NAME"
-- a language code, as per [RFC1766]
-->
<!ENTITY % Character "CDATA"
-- a single character from [ISO10646]
-->
<!ENTITY % LinkTypes "CDATA"
-- space-separated list of link types
-->
<!ENTITY % MediaDesc "CDATA"
-- single or comma-separated list of media descriptors
-->
<!ENTITY % URI "CDATA"
-- a Uniform Resource Identifier,
see [URI]
-->
<!ENTITY % Datetime "CDATA" -- date and time information. ISO date format -->
<!ENTITY % Script "CDATA" -- script expression -->
<!ENTITY % StyleSheet "CDATA" -- style sheet data -->
24 Dec 1999 18:26
280
HTML 4 Transitional Document Type Definition
<!ENTITY % FrameTarget "CDATA" -- render in this frame -->
<!ENTITY % Text "CDATA">
<!-- Parameter Entities -->
<!ENTITY % head.misc "SCRIPT|STYLE|META|LINK|OBJECT" -- repeatable head elements -->
<!ENTITY % heading "H1|H2|H3|H4|H5|H6">
<!ENTITY % list "UL | OL |
DIR | MENU">
<!ENTITY % preformatted "PRE">
<!ENTITY % Color "CDATA" -- a color using sRGB: #RRGGBB as Hex values -->
<!-- There are also 16 widely known color names with their sRGB values:
Black =
Silver =
Gray
=
White =
Maroon =
Red
=
Purple =
Fuchsia=
#000000
#C0C0C0
#808080
#FFFFFF
#800000
#FF0000
#800080
#FF00FF
Green
Lime
Olive
Yellow
Navy
Blue
Teal
Aqua
=
=
=
=
=
=
=
=
#008000
#00FF00
#808000
#FFFF00
#000080
#0000FF
#008080
#00FFFF
-->
<!ENTITY % bodycolors "
bgcolor
%Color;
text
%Color;
link
%Color;
vlink
%Color;
alink
%Color;
">
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
------
document
document
color of
color of
color of
background color -text color -links -visited links -selected links --
<!--================ Character mnemonic entities =========================-->
<!ENTITY % HTMLlat1 PUBLIC
"-//W3C//ENTITIES Latin1//EN//HTML"
"HTMLlat1.ent">
%HTMLlat1;
<!ENTITY % HTMLsymbol PUBLIC
"-//W3C//ENTITIES Symbols//EN//HTML"
"HTMLsymbol.ent">
%HTMLsymbol;
<!ENTITY % HTMLspecial PUBLIC
"-//W3C//ENTITIES Special//EN//HTML"
"HTMLspecial.ent">
%HTMLspecial;
<!--=================== Generic Attributes ===============================-->
<!ENTITY % coreattrs
"id
ID
class
CDATA
style
%StyleSheet;
title
%Text;
>
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
-----
document-wide unique id -space-separated list of classes -associated style info -advisory title --"
<!ENTITY % i18n
281
24 Dec 1999 18:26
HTML 4 Transitional Document Type Definition
"lang
dir
>
%LanguageCode; #IMPLIED
(ltr|rtl)
#IMPLIED
<!ENTITY % events
"onclick
%Script;
ondblclick %Script;
onmousedown %Script;
onmouseup
%Script;
onmouseover %Script;
onmousemove %Script;
onmouseout %Script;
onkeypress %Script;
onkeydown
%Script;
onkeyup
%Script;
>
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
-- language code --- direction for weak/neutral text --"
-----------
a
a
a
a
a
a
a
a
a
a
pointer
pointer
pointer
pointer
pointer
pointer
pointer
key was
key was
key was
button was clicked -button was double clicked-button was pressed down -button was released -was moved onto -was moved within -was moved away -pressed and released -pressed down -released --"
<!-- Reserved Feature Switch -->
<!ENTITY % HTML.Reserved "IGNORE">
<!-- The following attributes are reserved for possible future use -->
<![ %HTML.Reserved; [
<!ENTITY % reserved
"datasrc
%URI;
#IMPLIED -- a single or tabular Data Source -datafld
CDATA
#IMPLIED -- the property or column name -dataformatas (plaintext|html) plaintext -- text or html --"
>
]]>
<!ENTITY % reserved "">
<!ENTITY % attrs "%coreattrs; %i18n; %events;">
<!ENTITY % align "align (left|center|right|justify) #IMPLIED"
-- default is left for ltr paragraphs, right for rtl ->
<!--=================== Text Markup ======================================-->
<!ENTITY % fontstyle
"TT | I | B | U | S | STRIKE | BIG | SMALL">
<!ENTITY % phrase "EM | STRONG | DFN | CODE |
SAMP | KBD | VAR | CITE | ABBR | ACRONYM" >
<!ENTITY % special
"A | IMG | APPLET | OBJECT | FONT | BASEFONT | BR | SCRIPT |
MAP | Q | SUB | SUP | SPAN | BDO | IFRAME">
<!ENTITY % formctrl "INPUT | SELECT | TEXTAREA | LABEL | BUTTON">
<!-- %inline; covers inline or "text-level" elements -->
<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">
<!ELEMENT (%fontstyle;|%phrase;) - - (%inline;)*>
<!ATTLIST (%fontstyle;|%phrase;)
%attrs;
-- %coreattrs, %i18n, %events ->
<!ELEMENT (SUB|SUP) - - (%inline;)*
<!ATTLIST (SUB|SUP)
%attrs;
>
<!ELEMENT SPAN - - (%inline;)*
24 Dec 1999 18:26
-- subscript, superscript -->
-- %coreattrs, %i18n, %events --
-- generic language/style container -->
282
HTML 4 Transitional Document Type Definition
<!ATTLIST SPAN
%attrs;
%reserved;
>
-- %coreattrs, %i18n, %events --- reserved for possible future use --
<!ELEMENT BDO - - (%inline;)*
<!ATTLIST BDO
%coreattrs;
lang
%LanguageCode; #IMPLIED
dir
(ltr|rtl)
#REQUIRED
>
<!ELEMENT BASEFONT - O EMPTY
<!ATTLIST BASEFONT
id
ID
#IMPLIED
size
CDATA
#REQUIRED
color
%Color;
#IMPLIED
face
CDATA
#IMPLIED
>
-- I18N BiDi over-ride -->
-- id, class, style, title --- language code --- directionality --
-- base font size -->
-----
document-wide unique id -base font size for FONT elements -text color -comma-separated list of font names --
<!ELEMENT FONT - - (%inline;)*
-- local change to font -->
<!ATTLIST FONT
%coreattrs;
-- id, class, style, title -%i18n;
-- lang, dir -size
CDATA
#IMPLIED -- [+|-]nn e.g. size="+1", size="4" -color
%Color;
#IMPLIED -- text color -face
CDATA
#IMPLIED -- comma-separated list of font names ->
<!ELEMENT BR - O EMPTY
-- forced line break -->
<!ATTLIST BR
%coreattrs;
-- id, class, style, title -clear
(left|all|right|none) none -- control of text flow ->
<!--================== HTML content models ===============================-->
<!-HTML has two basic content models:
%inline;
%block;
character level elements and text strings
block-like elements e.g. paragraphs and lists
-->
<!ENTITY % block
"P | %heading; | %list; | %preformatted; | DL | DIV | CENTER |
NOSCRIPT | NOFRAMES | BLOCKQUOTE | FORM | ISINDEX | HR |
TABLE | FIELDSET | ADDRESS">
<!ENTITY % flow "%block; | %inline;">
<!--=================== Document Body ====================================-->
<!ELEMENT BODY O O (%flow;)*
<!ATTLIST BODY
%attrs;
onload
%Script;
onunload
%Script;
background
%URI;
+(INS|DEL) -- document body -->
#IMPLIED
#IMPLIED
#IMPLIED
%bodycolors;
>
<!ELEMENT ADDRESS - - ((%inline;)|P)*
<!ATTLIST ADDRESS
283
-----
%coreattrs, %i18n, %events -the document has been loaded -the document has been removed -texture tile for document
background --- bgcolor, text, link, vlink, alink --
-- information on author -->
24 Dec 1999 18:26
HTML 4 Transitional Document Type Definition
%attrs;
>
-- %coreattrs, %i18n, %events --
<!ELEMENT DIV - - (%flow;)*
<!ATTLIST DIV
%attrs;
%align;
%reserved;
>
-- generic language/style container -->
-- %coreattrs, %i18n, %events --- align, text alignment --- reserved for possible future use --
<!ELEMENT CENTER - - (%flow;)*
<!ATTLIST CENTER
%attrs;
>
-- shorthand for DIV align=center -->
-- %coreattrs, %i18n, %events --
<!--================== The Anchor Element ================================-->
<!ENTITY % Shape "(rect|circle|poly|default)">
<!ENTITY % Coords "CDATA" -- comma-separated list of lengths -->
<!ELEMENT A - - (%inline;)* -(A)
<!ATTLIST A
%attrs;
charset
%Charset;
#IMPLIED
type
%ContentType; #IMPLIED
name
CDATA
#IMPLIED
href
%URI;
#IMPLIED
hreflang
%LanguageCode; #IMPLIED
target
%FrameTarget; #IMPLIED
rel
%LinkTypes;
#IMPLIED
rev
%LinkTypes;
#IMPLIED
accesskey
%Character;
#IMPLIED
shape
%Shape;
rect
coords
%Coords;
#IMPLIED
tabindex
NUMBER
#IMPLIED
onfocus
%Script;
#IMPLIED
onblur
%Script;
#IMPLIED
>
-- anchor -->
----------------
%coreattrs, %i18n, %events -char encoding of linked resource -advisory content type -named link end -URI for linked resource -language code -render in this frame -forward link types -reverse link types -accessibility key character -for use with client-side image maps -for use with client-side image maps -position in tabbing order -the element got the focus -the element lost the focus --
<!--================== Client-side image maps ============================-->
<!-- These can be placed in the same document or grouped in a
separate document although this isn’t yet widely supported -->
<!ELEMENT MAP - - ((%block;) | AREA)+ -- client-side image map -->
<!ATTLIST MAP
%attrs;
-- %coreattrs, %i18n, %events -name
CDATA
#REQUIRED -- for reference by usemap ->
<!ELEMENT AREA - O EMPTY
<!ATTLIST AREA
%attrs;
shape
%Shape;
coords
%Coords;
href
%URI;
target
%FrameTarget;
nohref
(nohref)
alt
%Text;
tabindex
NUMBER
accesskey
%Character;
onfocus
%Script;
onblur
%Script;
>
24 Dec 1999 18:26
-- client-side image map area -->
rect
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#REQUIRED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
------------
%coreattrs, %i18n, %events -controls interpretation of coords -comma-separated list of lengths -URI for linked resource -render in this frame -this region has no action -short description -position in tabbing order -accessibility key character -the element got the focus -the element lost the focus --
284
HTML 4 Transitional Document Type Definition
<!--================== The LINK Element ==================================-->
<!-Relationship values can be used in principle:
a) for document specific toolbars/menus when used
with the LINK element in document head e.g.
start, contents, previous, next, index, end, help
b) to link to a separate style sheet (rel=stylesheet)
c) to make a link to a script (rel=script)
d) by stylesheets to control how collections of
html nodes are rendered into printed documents
e) to make a link to a printable version of this document
e.g. a postscript or pdf version (rel=alternate media=print)
-->
<!ELEMENT LINK - O EMPTY
<!ATTLIST LINK
%attrs;
charset
%Charset;
href
%URI;
hreflang
%LanguageCode;
type
%ContentType;
rel
%LinkTypes;
rev
%LinkTypes;
media
%MediaDesc;
target
%FrameTarget;
>
-- a media-independent link -->
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
----------
%coreattrs, %i18n, %events -char encoding of linked resource -URI for linked resource -language code -advisory content type -forward link types -reverse link types -for rendering on these media -render in this frame --
<!--=================== Images ===========================================-->
<!-- Length defined in strict DTD for cellpadding/cellspacing -->
<!ENTITY % Length "CDATA" -- nn for pixels or nn% for percentage length -->
<!ENTITY % MultiLength "CDATA" -- pixel, percentage, or relative -->
<![ %HTML.Frameset; [
<!ENTITY % MultiLengths "CDATA" -- comma-separated list of MultiLength -->
]]>
<!ENTITY % Pixels "CDATA" -- integer representing length in pixels -->
<!ENTITY % IAlign "(top|middle|bottom|left|right)" -- center? -->
<!-- To avoid problems with text-only UAs as well as
to make image content understandable and navigable
to users of non-visual UAs, you need to provide
a description with ALT, and avoid server-side image maps -->
<!ELEMENT IMG - O EMPTY
-- Embedded image -->
<!ATTLIST IMG
%attrs;
-- %coreattrs, %i18n, %events -src
%URI;
#REQUIRED -- URI of image to embed -alt
%Text;
#REQUIRED -- short description -longdesc
%URI;
#IMPLIED -- link to long description
(complements alt) -name
CDATA
#IMPLIED -- name of image for scripting -height
%Length;
#IMPLIED -- override height -width
%Length;
#IMPLIED -- override width -usemap
%URI;
#IMPLIED -- use client-side image map -ismap
(ismap)
#IMPLIED -- use server-side image map -align
%IAlign;
#IMPLIED -- vertical or horizontal alignment -border
%Pixels;
#IMPLIED -- link border width -hspace
%Pixels;
#IMPLIED -- horizontal gutter -vspace
%Pixels;
#IMPLIED -- vertical gutter ->
285
24 Dec 1999 18:26
HTML 4 Transitional Document Type Definition
<!-- USEMAP points to a MAP element which may be in this document
or an external document, although the latter is not widely supported -->
<!--==================== OBJECT ======================================-->
<!-OBJECT is used to embed objects as part of HTML pages
PARAM elements should precede other content. SGML mixed content
model technicality precludes specifying this formally ...
-->
<!ELEMENT OBJECT - - (PARAM | %flow;)*
-- generic embedded object -->
<!ATTLIST OBJECT
%attrs;
declare
(declare)
#IMPLIED
classid
%URI;
#IMPLIED
codebase
%URI;
#IMPLIED
data
%URI;
#IMPLIED
type
%ContentType; #IMPLIED
codetype
%ContentType; #IMPLIED
archive
CDATA
#IMPLIED
standby
%Text;
#IMPLIED
height
%Length;
#IMPLIED
width
%Length;
#IMPLIED
usemap
%URI;
#IMPLIED
name
CDATA
#IMPLIED
tabindex
NUMBER
#IMPLIED
align
%IAlign;
#IMPLIED
border
%Pixels;
#IMPLIED
hspace
%Pixels;
#IMPLIED
vspace
%Pixels;
#IMPLIED
%reserved;
>
<!ELEMENT PARAM - O EMPTY
<!ATTLIST PARAM
id
ID
#IMPLIED
name
CDATA
#REQUIRED
value
CDATA
#IMPLIED
valuetype
(DATA|REF|OBJECT) DATA
type
%ContentType; #IMPLIED
--------------------
%coreattrs, %i18n, %events -declare but don’t instantiate flag -identifies an implementation -base URI for classid, data, archive-reference to object’s data -content type for data -content type for code -space-separated list of URIs -message to show while loading -override height -override width -use client-side image map -submit as part of form -position in tabbing order -vertical or horizontal alignment -link border width -horizontal gutter -vertical gutter -reserved for possible future use --
-- named property value -->
------
document-wide unique id -property name -property value -How to interpret value -content type for value
when valuetype=ref --
>
<!--=================== Java APPLET ==================================-->
<!-One of code or object attributes must be present.
Place PARAM elements before other content.
-->
<!ELEMENT APPLET - - (PARAM | %flow;)* -- Java applet -->
<!ATTLIST APPLET
%coreattrs;
-- id, class, style, title -codebase
%URI;
#IMPLIED -- optional base URI for applet -archive
CDATA
#IMPLIED -- comma-separated archive list -code
CDATA
#IMPLIED -- applet class file -object
CDATA
#IMPLIED -- serialized applet file -alt
%Text;
#IMPLIED -- short description -name
CDATA
#IMPLIED -- allows applets to find each other -width
%Length;
#REQUIRED -- initial width -height
%Length;
#REQUIRED -- initial height -align
%IAlign;
#IMPLIED -- vertical or horizontal alignment -hspace
%Pixels;
#IMPLIED -- horizontal gutter -vspace
%Pixels;
#IMPLIED -- vertical gutter ->
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HTML 4 Transitional Document Type Definition
<!--=================== Horizontal Rule ==================================-->
<!ELEMENT HR - O EMPTY -- horizontal rule -->
<!ATTLIST HR
%attrs;
-- %coreattrs, %i18n, %events -align
(left|center|right) #IMPLIED
noshade
(noshade)
#IMPLIED
size
%Pixels;
#IMPLIED
width
%Length;
#IMPLIED
>
<!--=================== Paragraphs =======================================-->
<!ELEMENT P - O (%inline;)*
<!ATTLIST P
%attrs;
%align;
>
-- paragraph -->
-- %coreattrs, %i18n, %events --- align, text alignment --
<!--=================== Headings =========================================-->
<!-There are six levels of headings from H1 (the most important)
to H6 (the least important).
-->
<!ELEMENT (%heading;)
<!ATTLIST (%heading;)
%attrs;
%align;
>
- - (%inline;)* -- heading -->
-- %coreattrs, %i18n, %events --- align, text alignment --
<!--=================== Preformatted Text ================================-->
<!-- excludes markup for images and changes in font size -->
<!ENTITY % pre.exclusion "IMG|OBJECT|APPLET|BIG|SMALL|SUB|SUP|FONT|BASEFONT">
<!ELEMENT PRE - - (%inline;)* -(%pre.exclusion;) -- preformatted text -->
<!ATTLIST PRE
%attrs;
-- %coreattrs, %i18n, %events -width
NUMBER
#IMPLIED
>
<!--===================== Inline Quotes ==================================-->
<!ELEMENT Q - - (%inline;)*
<!ATTLIST Q
%attrs;
cite
%URI;
>
-- short inline quotation -->
#IMPLIED
-- %coreattrs, %i18n, %events --- URI for source document or msg --
<!--=================== Block-like Quotes ================================-->
<!ELEMENT BLOCKQUOTE - - (%flow;)*
<!ATTLIST BLOCKQUOTE
%attrs;
cite
%URI;
#IMPLIED
>
-- long quotation -->
-- %coreattrs, %i18n, %events --- URI for source document or msg --
<!--=================== Inserted/Deleted Text ============================-->
<!-- INS/DEL are handled by inclusion on BODY -->
<!ELEMENT (INS|DEL) - - (%flow;)*
-- inserted text, deleted text -->
<!ATTLIST (INS|DEL)
287
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%attrs;
cite
datetime
>
%URI;
%Datetime;
-- %coreattrs, %i18n, %events --- info on reason for change --- date and time of change --
#IMPLIED
#IMPLIED
<!--=================== Lists ============================================-->
<!-- definition lists - DT for term, DD for its definition -->
<!ELEMENT DL - - (DT|DD)+
<!ATTLIST DL
%attrs;
compact
(compact)
>
-- definition list -->
-- %coreattrs, %i18n, %events --- reduced interitem spacing --
#IMPLIED
<!ELEMENT DT - O (%inline;)*
<!ELEMENT DD - O (%flow;)*
<!ATTLIST (DT|DD)
%attrs;
>
-- definition term -->
-- definition description -->
-- %coreattrs, %i18n, %events --
<!-- Ordered lists (OL) Numbering style
1
a
A
i
I
arablic numbers
lower alpha
upper alpha
lower roman
upper roman
1,
a,
A,
i,
I,
2, 3, ...
b, c, ...
B, C, ...
ii, iii, ...
II, III, ...
The style is applied to the sequence number which by default
is reset to 1 for the first list item in an ordered list.
This can’t be expressed directly in SGML due to case folding.
-->
<!ENTITY % OLStyle "CDATA"
<!ELEMENT OL - - (LI)+
<!ATTLIST OL
%attrs;
type
%OLStyle;
compact
(compact)
start
NUMBER
>
-- constrained to: "(1|a|A|i|I)" -->
-- ordered list -->
#IMPLIED
#IMPLIED
#IMPLIED
-----
%coreattrs, %i18n, %events -numbering style -reduced interitem spacing -starting sequence number --
<!-- Unordered Lists (UL) bullet styles -->
<!ENTITY % ULStyle "(disc|square|circle)">
<!ELEMENT UL - - (LI)+
<!ATTLIST UL
%attrs;
type
%ULStyle;
compact
(compact)
>
-- unordered list -->
#IMPLIED
#IMPLIED
-- %coreattrs, %i18n, %events --- bullet style --- reduced interitem spacing --
<!ELEMENT (DIR|MENU) - - (LI)+ -(%block;) -- directory list, menu list -->
<!ATTLIST DIR
%attrs;
-- %coreattrs, %i18n, %events -compact
(compact)
#IMPLIED -- reduced interitem spacing ->
<!ATTLIST MENU
%attrs;
-- %coreattrs, %i18n, %events -compact
(compact)
#IMPLIED -- reduced interitem spacing ->
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<!ENTITY % LIStyle "CDATA" -- constrained to: "(%ULStyle;|%OLStyle;)" -->
<!ELEMENT LI - O (%flow;)*
<!ATTLIST LI
%attrs;
type
%LIStyle;
value
NUMBER
>
-- list item -->
#IMPLIED
#IMPLIED
-- %coreattrs, %i18n, %events --- list item style --- reset sequence number --
<!--================ Forms ===============================================-->
<!ELEMENT FORM - - (%flow;)* -(FORM)
-- interactive form -->
<!ATTLIST FORM
%attrs;
-- %coreattrs, %i18n, %events -action
%URI;
#REQUIRED -- server-side form handler -method
(GET|POST)
GET
-- HTTP method used to submit the form-enctype
%ContentType; "application/x-www-form-urlencoded"
accept
%ContentTypes; #IMPLIED -- list of MIME types for file upload -name
CDATA
#IMPLIED -- name of form for scripting -onsubmit
%Script;
#IMPLIED -- the form was submitted -onreset
%Script;
#IMPLIED -- the form was reset -target
%FrameTarget; #IMPLIED -- render in this frame -accept-charset %Charsets; #IMPLIED -- list of supported charsets ->
<!-- Each label must not contain more than ONE field -->
<!ELEMENT LABEL - - (%inline;)* -(LABEL) -- form field label text -->
<!ATTLIST LABEL
%attrs;
-- %coreattrs, %i18n, %events -for
IDREF
#IMPLIED -- matches field ID value -accesskey
%Character;
#IMPLIED -- accessibility key character -onfocus
%Script;
#IMPLIED -- the element got the focus -onblur
%Script;
#IMPLIED -- the element lost the focus ->
<!ENTITY % InputType
"(TEXT | PASSWORD | CHECKBOX |
RADIO | SUBMIT | RESET |
FILE | HIDDEN | IMAGE | BUTTON)"
>
<!-- attribute name required
<!ELEMENT INPUT - O EMPTY
<!ATTLIST INPUT
%attrs;
type
%InputType;
name
CDATA
value
CDATA
checked
(checked)
disabled
(disabled)
readonly
(readonly)
size
CDATA
maxlength
NUMBER
src
%URI;
alt
CDATA
usemap
%URI;
ismap
(ismap)
tabindex
NUMBER
accesskey
%Character;
onfocus
%Script;
onblur
%Script;
onselect
%Script;
onchange
%Script;
accept
%ContentTypes;
align
%IAlign;
%reserved;
289
for all but submit and reset -->
-- form control -->
TEXT
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
-----------------------
%coreattrs, %i18n, %events -what kind of widget is needed -submit as part of form -Specify for radio buttons and checkboxes -for radio buttons and check boxes -unavailable in this context -for text and passwd -specific to each type of field -max chars for text fields -for fields with images -short description -use client-side image map -use server-side image map -position in tabbing order -accessibility key character -the element got the focus -the element lost the focus -some text was selected -the element value was changed -list of MIME types for file upload -vertical or horizontal alignment -reserved for possible future use --
24 Dec 1999 18:26
HTML 4 Transitional Document Type Definition
>
<!ELEMENT SELECT - - (OPTGROUP|OPTION)+ -- option selector -->
<!ATTLIST SELECT
%attrs;
-- %coreattrs, %i18n, %events -name
CDATA
#IMPLIED -- field name -size
NUMBER
#IMPLIED -- rows visible -multiple
(multiple)
#IMPLIED -- default is single selection -disabled
(disabled)
#IMPLIED -- unavailable in this context -tabindex
NUMBER
#IMPLIED -- position in tabbing order -onfocus
%Script;
#IMPLIED -- the element got the focus -onblur
%Script;
#IMPLIED -- the element lost the focus -onchange
%Script;
#IMPLIED -- the element value was changed -%reserved;
-- reserved for possible future use ->
<!ELEMENT OPTGROUP - - (OPTION)+ -- option group -->
<!ATTLIST OPTGROUP
%attrs;
-- %coreattrs, %i18n, %events -disabled
(disabled)
#IMPLIED -- unavailable in this context -label
%Text;
#REQUIRED -- for use in hierarchical menus ->
<!ELEMENT OPTION - O (#PCDATA)
<!ATTLIST OPTION
%attrs;
selected
(selected)
#IMPLIED
disabled
(disabled)
#IMPLIED
label
%Text;
#IMPLIED
value
CDATA
#IMPLIED
>
<!ELEMENT TEXTAREA - - (#PCDATA)
<!ATTLIST TEXTAREA
%attrs;
name
CDATA
#IMPLIED
rows
NUMBER
#REQUIRED
cols
NUMBER
#REQUIRED
disabled
(disabled)
#IMPLIED
readonly
(readonly)
#IMPLIED
tabindex
NUMBER
#IMPLIED
accesskey
%Character;
#IMPLIED
onfocus
%Script;
#IMPLIED
onblur
%Script;
#IMPLIED
onselect
%Script;
#IMPLIED
onchange
%Script;
#IMPLIED
%reserved;
>
-- selectable choice -->
-- %coreattrs, %i18n, %events --- unavailable in this context --- for use in hierarchical menus --- defaults to element content --
-- multi-line text field -->
-- %coreattrs, %i18n, %events --
-- unavailable in this context ---------
position in tabbing order -accessibility key character -the element got the focus -the element lost the focus -some text was selected -the element value was changed -reserved for possible future use --
<!-#PCDATA is to solve the mixed content problem,
per specification only whitespace is allowed there!
-->
<!ELEMENT FIELDSET - - (#PCDATA,LEGEND,(%flow;)*) -- form control group -->
<!ATTLIST FIELDSET
%attrs;
-- %coreattrs, %i18n, %events ->
<!ELEMENT LEGEND - - (%inline;)*
-- fieldset legend -->
<!ENTITY % LAlign "(top|bottom|left|right)">
<!ATTLIST LEGEND
%attrs;
accesskey
%Character;
align
%LAlign;
24 Dec 1999 18:26
#IMPLIED
#IMPLIED
-- %coreattrs, %i18n, %events --- accessibility key character --- relative to fieldset --
290
HTML 4 Transitional Document Type Definition
>
<!ELEMENT BUTTON - (%flow;)* -(A|%formctrl;|FORM|ISINDEX|FIELDSET|IFRAME)
-- push button -->
<!ATTLIST BUTTON
%attrs;
-- %coreattrs, %i18n, %events -name
CDATA
#IMPLIED
value
CDATA
#IMPLIED -- sent to server when submitted -type
(button|submit|reset) submit -- for use as form button -disabled
(disabled)
#IMPLIED -- unavailable in this context -tabindex
NUMBER
#IMPLIED -- position in tabbing order -accesskey
%Character;
#IMPLIED -- accessibility key character -onfocus
%Script;
#IMPLIED -- the element got the focus -onblur
%Script;
#IMPLIED -- the element lost the focus -%reserved;
-- reserved for possible future use ->
<!--======================= Tables =======================================-->
<!-- IETF HTML table standard, see [RFC1942] -->
<!-The BORDER attribute sets the thickness of the frame around the
table. The default units are screen pixels.
The FRAME attribute specifies which parts of the frame around
the table should be rendered. The values are not the same as
CALS to avoid a name clash with the VALIGN attribute.
The value "border" is included for backwards compatibility with
<TABLE BORDER> which yields frame=border and border=implied
For <TABLE BORDER=1> you get border=1 and frame=implied. In this
case, it is appropriate to treat this as frame=border for backwards
compatibility with deployed browsers.
-->
<!ENTITY % TFrame "(void|above|below|hsides|lhs|rhs|vsides|box|border)">
<!-The RULES attribute defines which rules to draw between cells:
If RULES is absent then assume:
"none" if BORDER is absent or BORDER=0 otherwise "all"
-->
<!ENTITY % TRules "(none | groups | rows | cols | all)">
<!-- horizontal placement of table relative to document -->
<!ENTITY % TAlign "(left|center|right)">
<!-- horizontal alignment attributes for cell contents -->
<!ENTITY % cellhalign
"align
(left|center|right|justify|char) #IMPLIED
char
%Character;
#IMPLIED -- alignment char, e.g. char=’:’ -charoff
%Length;
#IMPLIED -- offset for alignment char --"
>
<!-- vertical alignment attributes for cell contents -->
<!ENTITY % cellvalign
"valign
(top|middle|bottom|baseline) #IMPLIED"
>
<!ELEMENT TABLE - (CAPTION?, (COL*|COLGROUP*), THEAD?, TFOOT?, TBODY+)>
<!ELEMENT CAPTION - - (%inline;)*
-- table caption -->
291
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HTML 4 Transitional Document Type Definition
<!ELEMENT
<!ELEMENT
<!ELEMENT
<!ELEMENT
<!ELEMENT
<!ELEMENT
<!ELEMENT
THEAD
TFOOT
TBODY
COLGROUP
COL
TR
(TH|TD)
O
-
O
O
O
O
O
O
O
(TR)+
(TR)+
(TR)+
(COL)*
EMPTY
(TH|TD)+
(%flow;)*
<!ATTLIST TABLE
%attrs;
summary
%Text;
width
%Length;
border
%Pixels;
frame
%TFrame;
rules
%TRules;
cellspacing %Length;
cellpadding %Length;
align
%TAlign;
bgcolor
%Color;
%reserved;
datapagesize CDATA
>
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
#IMPLIED
--------
table
table
table
table
table
table
table
header -->
footer -->
body -->
column group -->
column -->
row -->
header cell, table data cell-->
--------------
table element -%coreattrs, %i18n, %events -purpose/structure for speech output-table width -controls frame width around table -which parts of frame to render -rulings between rows and cols -spacing between cells -spacing within cells -table position relative to window -background color for cells -reserved for possible future use -reserved for possible future use --
<!ENTITY % CAlign "(top|bottom|left|right)">
<!ATTLIST CAPTION
%attrs;
align
%CAlign;
>
<!-COLGROUP groups a set of COL
several semantically related
-->
<!ATTLIST COLGROUP
%attrs;
span
NUMBER
width
%MultiLength;
%cellhalign;
%cellvalign;
>
#IMPLIED
-- %coreattrs, %i18n, %events --- relative to table --
elements. It allows you to group
columns together.
1
#IMPLIED
------
%coreattrs, %i18n, %events -default number of columns in group -default width for enclosed COLs -horizontal alignment in cells -vertical alignment in cells --
<!-COL elements define the alignment properties for cells in
one or more columns.
The WIDTH attribute specifies the width of the columns, e.g.
width=64
width=0.5*
width in screen pixels
relative width of 0.5
The SPAN attribute causes the attributes of one
COL element to apply to more than one column.
-->
<!ATTLIST COL
-- column groups and properties -%attrs;
-- %coreattrs, %i18n, %events -span
NUMBER
1
-- COL attributes affect N columns -width
%MultiLength; #IMPLIED -- column width specification -%cellhalign;
-- horizontal alignment in cells -%cellvalign;
-- vertical alignment in cells ->
<!-Use THEAD to duplicate headers when breaking table
across page boundaries, or for static headers when
24 Dec 1999 18:26
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HTML 4 Transitional Document Type Definition
TBODY sections are rendered in scrolling panel.
Use TFOOT to duplicate footers when breaking table
across page boundaries, or for static footers when
TBODY sections are rendered in scrolling panel.
Use multiple TBODY sections when rules are needed
between groups of table rows.
-->
<!ATTLIST (THEAD|TBODY|TFOOT)
%attrs;
%cellhalign;
%cellvalign;
>
<!ATTLIST TR
%attrs;
%cellhalign;
%cellvalign;
bgcolor
%Color;
>
#IMPLIED
-----
table section -%coreattrs, %i18n, %events -horizontal alignment in cells -vertical alignment in cells --
------
table row -%coreattrs, %i18n, %events -horizontal alignment in cells -vertical alignment in cells -background color for row --
<!-- Scope is simpler than headers attribute for common tables -->
<!ENTITY % Scope "(row|col|rowgroup|colgroup)">
<!-- TH is for headers, TD for data, but for cells acting as both use TD -->
<!ATTLIST (TH|TD)
-- header or data cell -%attrs;
-- %coreattrs, %i18n, %events -abbr
%Text;
#IMPLIED -- abbreviation for header cell -axis
CDATA
#IMPLIED -- comma-separated list of related headers-headers
IDREFS
#IMPLIED -- list of id’s for header cells -scope
%Scope;
#IMPLIED -- scope covered by header cells -rowspan
NUMBER
1
-- number of rows spanned by cell -colspan
NUMBER
1
-- number of cols spanned by cell -%cellhalign;
-- horizontal alignment in cells -%cellvalign;
-- vertical alignment in cells -nowrap
(nowrap)
#IMPLIED -- suppress word wrap -bgcolor
%Color;
#IMPLIED -- cell background color -width
%Length;
#IMPLIED -- width for cell -height
%Length;
#IMPLIED -- height for cell ->
<!--================== Document Frames ===================================-->
<!-The content model for HTML documents depends on whether the HEAD is
followed by a FRAMESET or BODY element. The widespread omission of
the BODY start tag makes it impractical to define the content model
without the use of a marked section.
-->
<![ %HTML.Frameset; [
<!ELEMENT FRAMESET - - ((FRAMESET|FRAME)+ & NOFRAMES?) -- window subdivision-->
<!ATTLIST FRAMESET
%coreattrs;
-- id, class, style, title -rows
%MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 row) -cols
%MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 col) -onload
%Script;
#IMPLIED -- all the frames have been loaded -onunload
%Script;
#IMPLIED -- all the frames have been removed ->
]]>
293
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<![ %HTML.Frameset; [
<!-- reserved frame names start with "_" otherwise starts with letter -->
<!ELEMENT FRAME - O EMPTY
-- subwindow -->
<!ATTLIST FRAME
%coreattrs;
-- id, class, style, title -longdesc
%URI;
#IMPLIED -- link to long description
(complements title) -name
CDATA
#IMPLIED -- name of frame for targetting -src
%URI;
#IMPLIED -- source of frame content -frameborder (1|0)
1
-- request frame borders? -marginwidth %Pixels;
#IMPLIED -- margin widths in pixels -marginheight %Pixels;
#IMPLIED -- margin height in pixels -noresize
(noresize)
#IMPLIED -- allow users to resize frames? -scrolling
(yes|no|auto) auto
-- scrollbar or none ->
]]>
<!ELEMENT IFRAME - - (%flow;)*
<!ATTLIST IFRAME
%coreattrs;
longdesc
%URI;
#IMPLIED
name
CDATA
src
%URI;
frameborder (1|0)
marginwidth %Pixels;
marginheight %Pixels;
scrolling
(yes|no|auto)
align
%IAlign;
height
%Length;
width
%Length;
>
#IMPLIED
#IMPLIED
1
#IMPLIED
#IMPLIED
auto
#IMPLIED
#IMPLIED
#IMPLIED
-- inline subwindow -->
-- id, class, style, title --- link to long description
(complements title) --- name of frame for targetting --- source of frame content --- request frame borders? --- margin widths in pixels --- margin height in pixels --- scrollbar or none --- vertical or horizontal alignment --- frame height --- frame width --
<![ %HTML.Frameset; [
<!ENTITY % noframes.content "(BODY) -(NOFRAMES)">
]]>
<!ENTITY % noframes.content "(%flow;)*">
<!ELEMENT NOFRAMES - - %noframes.content;
-- alternate content container for non frame-based rendering -->
<!ATTLIST NOFRAMES
%attrs;
-- %coreattrs, %i18n, %events ->
<!--================ Document Head =======================================-->
<!-- %head.misc; defined earlier on as "SCRIPT|STYLE|META|LINK|OBJECT" -->
<!ENTITY % head.content "TITLE & ISINDEX? & BASE?">
<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head -->
<!ATTLIST HEAD
%i18n;
-- lang, dir -profile
%URI;
#IMPLIED -- named dictionary of meta info ->
<!-- The TITLE element is not considered part of the flow of text.
It should be displayed, for example as the page header or
window title. Exactly one title is required per document.
-->
<!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) -- document title -->
<!ATTLIST TITLE %i18n>
<!ELEMENT ISINDEX - O EMPTY
<!ATTLIST ISINDEX
24 Dec 1999 18:26
-- single line prompt -->
294
HTML 4 Transitional Document Type Definition
%coreattrs;
%i18n;
prompt
%Text;
<!ELEMENT BASE - O EMPTY
<!ATTLIST BASE
href
%URI;
target
%FrameTarget;
>
<!ELEMENT META - O EMPTY
<!ATTLIST META
%i18n;
http-equiv NAME
name
NAME
content
CDATA
scheme
CDATA
>
#IMPLIED
-- id, class, style, title --- lang, dir --- prompt message -->
-- document base URI -->
#IMPLIED
#IMPLIED
-- URI that acts as base URI --- render in this frame --
-- generic metainformation -->
#IMPLIED
#IMPLIED
#REQUIRED
#IMPLIED
<!ELEMENT STYLE - - %StyleSheet
<!ATTLIST STYLE
%i18n;
type
%ContentType; #REQUIRED
media
%MediaDesc;
#IMPLIED
title
%Text;
#IMPLIED
>
<!ELEMENT SCRIPT - - %Script;
<!ATTLIST SCRIPT
charset
%Charset;
#IMPLIED
type
%ContentType; #REQUIRED
language
CDATA
#IMPLIED
src
%URI;
#IMPLIED
defer
(defer)
#IMPLIED
event
CDATA
#IMPLIED
for
%URI;
#IMPLIED
>
------
lang, dir, for use with content -HTTP response header name -metainformation name -associated information -select form of content --
-- style info -->
-----
lang, dir, for use with title -content type of style language -designed for use with these media -advisory title --
-- script statements -->
--------
char encoding of linked resource -content type of script language -predefined script language name -URI for an external script -UA may defer execution of script -reserved for possible future use -reserved for possible future use --
<!ELEMENT NOSCRIPT - - (%flow;)*
-- alternate content container for non script-based rendering -->
<!ATTLIST NOSCRIPT
%attrs;
-- %coreattrs, %i18n, %events ->
<!--================ Document Structure ==================================-->
<!ENTITY % version "version CDATA #FIXED ’%HTML.Version;’">
<![ %HTML.Frameset; [
<!ENTITY % html.content "HEAD, FRAMESET">
]]>
<!ENTITY % html.content "HEAD, BODY">
<!ELEMENT HTML O O (%html.content;)
<!ATTLIST HTML
%i18n;
%version;
>
295
-- document root element -->
-- lang, dir --
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HTML 4 Transitional Document Type Definition
24 Dec 1999 18:26
296
HTML 4 Frameset Document Type Definition
23 Frameset Document Type Definition
<!-This is the HTML 4.01 Frameset DTD, which should be
used for documents with frames. This DTD is identical
to the HTML 4.01 Transitional DTD except for the
content model of the "HTML" element: in frameset
documents, the "FRAMESET" element replaces the "BODY"
element.
Draft: $Date: 1999/12/24 23:20:08 $
Authors:
Dave Raggett <dsr@w3.org>
Arnaud Le Hors <lehors@w3.org>
Ian Jacobs <ij@w3.org>
Further information about HTML 4.01 is available at:
http://www.w3.org/TR/1999/REC-html401-19991224.
-->
<!ENTITY % HTML.Version "-//W3C//DTD HTML 4.01 Frameset//EN"
-- Typical usage:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
"http://www.w3.org/TR/html4/frameset.dtd">
<html>
<head>
...
</head>
<frameset>
...
</frameset>
</html>
-->
<!ENTITY % HTML.Frameset "INCLUDE">
<!ENTITY % HTML4.dtd PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
%HTML4.dtd;
297
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HTML 4 Frameset Document Type Definition
24 Dec 1999 18:26
298
Character entity references in HTML 4
24 Character entity references in HTML 4
Contents
1. Introduction to character entity references
.
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2. Character entity references for ISO 8859-1 characters
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1. The list of characters
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3. Character entity references for symbols, mathematical symbols, and Greek
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4. Character entity references for markup-significant and internationalization
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1. The list of characters
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24.1 Introduction to character entity references
A character entity reference [p.45] is an SGML construct that references a character
of the document character set. [p.41]
This version of HTML supports several sets of character entity references:
ISO 8859-1 (Latin-1) characters [p.299] In accordance with section 14 of
[RFC1866] [p.356] , the set of Latin-1 entities has been extended by this
specification to cover the whole right part of ISO-8859-1 (all code positions with
the high-order bit set), including the already commonly used &nbsp;, &copy; and
&reg;. The names of the entities are taken from the appendices of SGML
(defined in [ISO8879] [p.353] ).
symbols, mathematical symbols, and Greek letters [p.303] . These characters
may be represented by glyphs in the Adobe font "Symbol".
markup-significant and internationalization characters [p.308] (e.g., for
bidirectional text).
The following sections present the complete lists of character entity references.
Although, by convention, [ISO10646] [p.353] the comments following each entry are
usually written with uppercase letters, we have converted them to lowercase in this
specification for reasons of readability.
24.2 Character entity references for ISO 8859-1
characters
The character entity references in this section produce characters whose numeric
equivalents should already be supported by conforming HTML 2.0 user agents.
Thus, the character entity reference &divide; is a more convenient form than &#247;
for obtaining the division sign (÷).
299
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To support these named entities, user agents need only recognize the entity
names and convert them to characters that lie within the repertoire of [ISO88591]
[p.354] .
Character 65533 (FFFD hexadecimal) is the last valid character in UCS-2. 65534
(FFFE hexadecimal) is unassigned and reserved as the byte-swapped version of
ZERO WIDTH NON-BREAKING SPACE for byte-order detection purposes. 65535
(FFFF hexadecimal) is unassigned.
24.2.1 The list of characters
<!-- Portions © International Organization for Standardization 1986
Permission to copy in any form is granted for use with
conforming SGML systems and applications as defined in
ISO 8879, provided this notice is included in all copies.
-->
<!-- Character entity set. Typical invocation:
<!ENTITY % HTMLlat1 PUBLIC
"-//W3C//ENTITIES Latin 1//EN//HTML">
%HTMLlat1;
-->
<!ENTITY nbsp
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
iexcl
cent
pound
curren
yen
brvbar
<!ENTITY sect
<!ENTITY uml
<!ENTITY copy
<!ENTITY ordf
<!ENTITY laquo
<!ENTITY not
<!ENTITY shy
<!ENTITY reg
<!ENTITY macr
<!ENTITY deg
<!ENTITY plusmn
<!ENTITY sup2
<!ENTITY sup3
<!ENTITY acute
<!ENTITY micro
<!ENTITY para
<!ENTITY middot
24 Dec 1999 18:26
CDATA "&#160;" -- no-break space = non-breaking space,
U+00A0 ISOnum -->
CDATA "&#161;" -- inverted exclamation mark, U+00A1 ISOnum -->
CDATA "&#162;" -- cent sign, U+00A2 ISOnum -->
CDATA "&#163;" -- pound sign, U+00A3 ISOnum -->
CDATA "&#164;" -- currency sign, U+00A4 ISOnum -->
CDATA "&#165;" -- yen sign = yuan sign, U+00A5 ISOnum -->
CDATA "&#166;" -- broken bar = broken vertical bar,
U+00A6 ISOnum -->
CDATA "&#167;" -- section sign, U+00A7 ISOnum -->
CDATA "&#168;" -- diaeresis = spacing diaeresis,
U+00A8 ISOdia -->
CDATA "&#169;" -- copyright sign, U+00A9 ISOnum -->
CDATA "&#170;" -- feminine ordinal indicator, U+00AA ISOnum -->
CDATA "&#171;" -- left-pointing double angle quotation mark
= left pointing guillemet, U+00AB ISOnum -->
CDATA "&#172;" -- not sign, U+00AC ISOnum -->
CDATA "&#173;" -- soft hyphen = discretionary hyphen,
U+00AD ISOnum -->
CDATA "&#174;" -- registered sign = registered trade mark sign,
U+00AE ISOnum -->
CDATA "&#175;" -- macron = spacing macron = overline
= APL overbar, U+00AF ISOdia -->
CDATA "&#176;" -- degree sign, U+00B0 ISOnum -->
CDATA "&#177;" -- plus-minus sign = plus-or-minus sign,
U+00B1 ISOnum -->
CDATA "&#178;" -- superscript two = superscript digit two
= squared, U+00B2 ISOnum -->
CDATA "&#179;" -- superscript three = superscript digit three
= cubed, U+00B3 ISOnum -->
CDATA "&#180;" -- acute accent = spacing acute,
U+00B4 ISOdia -->
CDATA "&#181;" -- micro sign, U+00B5 ISOnum -->
CDATA "&#182;" -- pilcrow sign = paragraph sign,
U+00B6 ISOnum -->
CDATA "&#183;" -- middle dot = Georgian comma
300
Character entity references in HTML 4
<!ENTITY cedil
<!ENTITY sup1
<!ENTITY ordm
<!ENTITY raquo
<!ENTITY frac14
<!ENTITY frac12
<!ENTITY frac34
<!ENTITY iquest
<!ENTITY Agrave
<!ENTITY Aacute
<!ENTITY Acirc
<!ENTITY Atilde
<!ENTITY Auml
<!ENTITY Aring
<!ENTITY AElig
<!ENTITY Ccedil
<!ENTITY Egrave
<!ENTITY Eacute
<!ENTITY Ecirc
<!ENTITY Euml
<!ENTITY Igrave
<!ENTITY Iacute
<!ENTITY Icirc
<!ENTITY Iuml
<!ENTITY ETH
<!ENTITY Ntilde
<!ENTITY Ograve
<!ENTITY Oacute
<!ENTITY Ocirc
301
= Greek middle dot, U+00B7 ISOnum -->
CDATA "&#184;" -- cedilla = spacing cedilla, U+00B8 ISOdia -->
CDATA "&#185;" -- superscript one = superscript digit one,
U+00B9 ISOnum -->
CDATA "&#186;" -- masculine ordinal indicator,
U+00BA ISOnum -->
CDATA "&#187;" -- right-pointing double angle quotation mark
= right pointing guillemet, U+00BB ISOnum -->
CDATA "&#188;" -- vulgar fraction one quarter
= fraction one quarter, U+00BC ISOnum -->
CDATA "&#189;" -- vulgar fraction one half
= fraction one half, U+00BD ISOnum -->
CDATA "&#190;" -- vulgar fraction three quarters
= fraction three quarters, U+00BE ISOnum -->
CDATA "&#191;" -- inverted question mark
= turned question mark, U+00BF ISOnum -->
CDATA "&#192;" -- latin capital letter A with grave
= latin capital letter A grave,
U+00C0 ISOlat1 -->
CDATA "&#193;" -- latin capital letter A with acute,
U+00C1 ISOlat1 -->
CDATA "&#194;" -- latin capital letter A with circumflex,
U+00C2 ISOlat1 -->
CDATA "&#195;" -- latin capital letter A with tilde,
U+00C3 ISOlat1 -->
CDATA "&#196;" -- latin capital letter A with diaeresis,
U+00C4 ISOlat1 -->
CDATA "&#197;" -- latin capital letter A with ring above
= latin capital letter A ring,
U+00C5 ISOlat1 -->
CDATA "&#198;" -- latin capital letter AE
= latin capital ligature AE,
U+00C6 ISOlat1 -->
CDATA "&#199;" -- latin capital letter C with cedilla,
U+00C7 ISOlat1 -->
CDATA "&#200;" -- latin capital letter E with grave,
U+00C8 ISOlat1 -->
CDATA "&#201;" -- latin capital letter E with acute,
U+00C9 ISOlat1 -->
CDATA "&#202;" -- latin capital letter E with circumflex,
U+00CA ISOlat1 -->
CDATA "&#203;" -- latin capital letter E with diaeresis,
U+00CB ISOlat1 -->
CDATA "&#204;" -- latin capital letter I with grave,
U+00CC ISOlat1 -->
CDATA "&#205;" -- latin capital letter I with acute,
U+00CD ISOlat1 -->
CDATA "&#206;" -- latin capital letter I with circumflex,
U+00CE ISOlat1 -->
CDATA "&#207;" -- latin capital letter I with diaeresis,
U+00CF ISOlat1 -->
CDATA "&#208;" -- latin capital letter ETH, U+00D0 ISOlat1 -->
CDATA "&#209;" -- latin capital letter N with tilde,
U+00D1 ISOlat1 -->
CDATA "&#210;" -- latin capital letter O with grave,
U+00D2 ISOlat1 -->
CDATA "&#211;" -- latin capital letter O with acute,
U+00D3 ISOlat1 -->
CDATA "&#212;" -- latin capital letter O with circumflex,
U+00D4 ISOlat1 -->
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Character entity references in HTML 4
<!ENTITY Otilde CDATA "&#213;" -- latin capital letter O with tilde,
U+00D5 ISOlat1 -->
<!ENTITY Ouml
CDATA "&#214;" -- latin capital letter O with diaeresis,
U+00D6 ISOlat1 -->
<!ENTITY times CDATA "&#215;" -- multiplication sign, U+00D7 ISOnum -->
<!ENTITY Oslash CDATA "&#216;" -- latin capital letter O with stroke
= latin capital letter O slash,
U+00D8 ISOlat1 -->
<!ENTITY Ugrave CDATA "&#217;" -- latin capital letter U with grave,
U+00D9 ISOlat1 -->
<!ENTITY Uacute CDATA "&#218;" -- latin capital letter U with acute,
U+00DA ISOlat1 -->
<!ENTITY Ucirc CDATA "&#219;" -- latin capital letter U with circumflex,
U+00DB ISOlat1 -->
<!ENTITY Uuml
CDATA "&#220;" -- latin capital letter U with diaeresis,
U+00DC ISOlat1 -->
<!ENTITY Yacute CDATA "&#221;" -- latin capital letter Y with acute,
U+00DD ISOlat1 -->
<!ENTITY THORN CDATA "&#222;" -- latin capital letter THORN,
U+00DE ISOlat1 -->
<!ENTITY szlig CDATA "&#223;" -- latin small letter sharp s = ess-zed,
U+00DF ISOlat1 -->
<!ENTITY agrave CDATA "&#224;" -- latin small letter a with grave
= latin small letter a grave,
U+00E0 ISOlat1 -->
<!ENTITY aacute CDATA "&#225;" -- latin small letter a with acute,
U+00E1 ISOlat1 -->
<!ENTITY acirc CDATA "&#226;" -- latin small letter a with circumflex,
U+00E2 ISOlat1 -->
<!ENTITY atilde CDATA "&#227;" -- latin small letter a with tilde,
U+00E3 ISOlat1 -->
<!ENTITY auml
CDATA "&#228;" -- latin small letter a with diaeresis,
U+00E4 ISOlat1 -->
<!ENTITY aring CDATA "&#229;" -- latin small letter a with ring above
= latin small letter a ring,
U+00E5 ISOlat1 -->
<!ENTITY aelig CDATA "&#230;" -- latin small letter ae
= latin small ligature ae, U+00E6 ISOlat1 -->
<!ENTITY ccedil CDATA "&#231;" -- latin small letter c with cedilla,
U+00E7 ISOlat1 -->
<!ENTITY egrave CDATA "&#232;" -- latin small letter e with grave,
U+00E8 ISOlat1 -->
<!ENTITY eacute CDATA "&#233;" -- latin small letter e with acute,
U+00E9 ISOlat1 -->
<!ENTITY ecirc CDATA "&#234;" -- latin small letter e with circumflex,
U+00EA ISOlat1 -->
<!ENTITY euml
CDATA "&#235;" -- latin small letter e with diaeresis,
U+00EB ISOlat1 -->
<!ENTITY igrave CDATA "&#236;" -- latin small letter i with grave,
U+00EC ISOlat1 -->
<!ENTITY iacute CDATA "&#237;" -- latin small letter i with acute,
U+00ED ISOlat1 -->
<!ENTITY icirc CDATA "&#238;" -- latin small letter i with circumflex,
U+00EE ISOlat1 -->
<!ENTITY iuml
CDATA "&#239;" -- latin small letter i with diaeresis,
U+00EF ISOlat1 -->
<!ENTITY eth
CDATA "&#240;" -- latin small letter eth, U+00F0 ISOlat1 -->
<!ENTITY ntilde CDATA "&#241;" -- latin small letter n with tilde,
U+00F1 ISOlat1 -->
<!ENTITY ograve CDATA "&#242;" -- latin small letter o with grave,
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Character entity references in HTML 4
U+00F2 ISOlat1 -->
<!ENTITY oacute CDATA "&#243;" -- latin small letter o with acute,
U+00F3 ISOlat1 -->
<!ENTITY ocirc CDATA "&#244;" -- latin small letter o with circumflex,
U+00F4 ISOlat1 -->
<!ENTITY otilde CDATA "&#245;" -- latin small letter o with tilde,
U+00F5 ISOlat1 -->
<!ENTITY ouml
CDATA "&#246;" -- latin small letter o with diaeresis,
U+00F6 ISOlat1 -->
<!ENTITY divide CDATA "&#247;" -- division sign, U+00F7 ISOnum -->
<!ENTITY oslash CDATA "&#248;" -- latin small letter o with stroke,
= latin small letter o slash,
U+00F8 ISOlat1 -->
<!ENTITY ugrave CDATA "&#249;" -- latin small letter u with grave,
U+00F9 ISOlat1 -->
<!ENTITY uacute CDATA "&#250;" -- latin small letter u with acute,
U+00FA ISOlat1 -->
<!ENTITY ucirc CDATA "&#251;" -- latin small letter u with circumflex,
U+00FB ISOlat1 -->
<!ENTITY uuml
CDATA "&#252;" -- latin small letter u with diaeresis,
U+00FC ISOlat1 -->
<!ENTITY yacute CDATA "&#253;" -- latin small letter y with acute,
U+00FD ISOlat1 -->
<!ENTITY thorn CDATA "&#254;" -- latin small letter thorn,
U+00FE ISOlat1 -->
<!ENTITY yuml
CDATA "&#255;" -- latin small letter y with diaeresis,
U+00FF ISOlat1 -->
24.3 Character entity references for symbols,
mathematical symbols, and Greek letters
The character entity references in this section produce characters that may be
represented by glyphs in the widely available Adobe Symbol font, including Greek
characters, various bracketing symbols, and a selection of mathematical operators
such as gradient, product, and summation symbols.
To support these entities, user agents may support full [ISO10646] [p.353] or use
other means. Display of glyphs for these characters may be obtained by being able
to display the relevant [ISO10646] [p.353] characters or by other means, such as
internally mapping the listed entities, numeric character references, and characters
to the appropriate position in some font that contains the requisite glyphs.
When to use Greek entities. This entity set contains all the letters used in
modern Greek. However, it does not include Greek punctuation, precomposed
accented characters nor the non-spacing accents (tonos, dialytika) required to
compose them. There are no archaic letters, Coptic-unique letters, or precomposed
letters for Polytonic Greek. The entities defined here are not intended for the
representation of modern Greek text and would not be an efficient representation;
rather, they are intended for occasional Greek letters used in technical and
mathematical works.
303
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Character entity references in HTML 4
24.3.1 The list of characters
<!-- Mathematical, Greek and Symbolic characters for HTML -->
<!-- Character entity set. Typical invocation:
<!ENTITY % HTMLsymbol PUBLIC
"-//W3C//ENTITIES Symbols//EN//HTML">
%HTMLsymbol; -->
<!-- Portions © International Organization for Standardization 1986:
Permission to copy in any form is granted for use with
conforming SGML systems and applications as defined in
ISO 8879, provided this notice is included in all copies.
-->
<!-- Relevant ISO entity set is given unless names are newly introduced.
New names (i.e., not in ISO 8879 list) do not clash with any
existing ISO 8879 entity names. ISO 10646 character numbers
are given for each character, in hex. CDATA values are decimal
conversions of the ISO 10646 values and refer to the document
character set. Names are ISO 10646 names.
-->
<!-- Latin Extended-B -->
<!ENTITY fnof
CDATA "&#402;" -- latin small f with hook = function
= florin, U+0192 ISOtech -->
<!-- Greek -->
<!ENTITY Alpha
<!ENTITY Beta
<!ENTITY Gamma
<!ENTITY Chi
CDATA "&#913;" -- greek capital letter alpha, U+0391 -->
CDATA "&#914;" -- greek capital letter beta, U+0392 -->
CDATA "&#915;" -- greek capital letter gamma,
U+0393 ISOgrk3 -->
CDATA "&#916;" -- greek capital letter delta,
U+0394 ISOgrk3 -->
CDATA "&#917;" -- greek capital letter epsilon, U+0395 -->
CDATA "&#918;" -- greek capital letter zeta, U+0396 -->
CDATA "&#919;" -- greek capital letter eta, U+0397 -->
CDATA "&#920;" -- greek capital letter theta,
U+0398 ISOgrk3 -->
CDATA "&#921;" -- greek capital letter iota, U+0399 -->
CDATA "&#922;" -- greek capital letter kappa, U+039A -->
CDATA "&#923;" -- greek capital letter lambda,
U+039B ISOgrk3 -->
CDATA "&#924;" -- greek capital letter mu, U+039C -->
CDATA "&#925;" -- greek capital letter nu, U+039D -->
CDATA "&#926;" -- greek capital letter xi, U+039E ISOgrk3 -->
CDATA "&#927;" -- greek capital letter omicron, U+039F -->
CDATA "&#928;" -- greek capital letter pi, U+03A0 ISOgrk3 -->
CDATA "&#929;" -- greek capital letter rho, U+03A1 -->
Sigmaf, and no U+03A2 character either -->
CDATA "&#931;" -- greek capital letter sigma,
U+03A3 ISOgrk3 -->
CDATA "&#932;" -- greek capital letter tau, U+03A4 -->
CDATA "&#933;" -- greek capital letter upsilon,
U+03A5 ISOgrk3 -->
CDATA "&#934;" -- greek capital letter phi,
U+03A6 ISOgrk3 -->
CDATA "&#935;" -- greek capital letter chi, U+03A7 -->
24 Dec 1999 18:26
304
<!ENTITY Delta
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
Epsilon
Zeta
Eta
Theta
<!ENTITY Iota
<!ENTITY Kappa
<!ENTITY Lambda
<!ENTITY Mu
<!ENTITY Nu
<!ENTITY Xi
<!ENTITY Omicron
<!ENTITY Pi
<!ENTITY Rho
<!-- there is no
<!ENTITY Sigma
<!ENTITY Tau
<!ENTITY Upsilon
<!ENTITY Phi
Character entity references in HTML 4
<!ENTITY Psi
<!ENTITY Omega
CDATA "&#936;" -- greek capital letter psi,
U+03A8 ISOgrk3 -->
CDATA "&#937;" -- greek capital letter omega,
U+03A9 ISOgrk3 -->
<!ENTITY alpha
CDATA "&#945;" -- greek small letter alpha,
U+03B1 ISOgrk3 -->
<!ENTITY beta
CDATA "&#946;" -- greek small letter beta, U+03B2 ISOgrk3 -->
<!ENTITY gamma
CDATA "&#947;" -- greek small letter gamma,
U+03B3 ISOgrk3 -->
<!ENTITY delta
CDATA "&#948;" -- greek small letter delta,
U+03B4 ISOgrk3 -->
<!ENTITY epsilon CDATA "&#949;" -- greek small letter epsilon,
U+03B5 ISOgrk3 -->
<!ENTITY zeta
CDATA "&#950;" -- greek small letter zeta, U+03B6 ISOgrk3 -->
<!ENTITY eta
CDATA "&#951;" -- greek small letter eta, U+03B7 ISOgrk3 -->
<!ENTITY theta
CDATA "&#952;" -- greek small letter theta,
U+03B8 ISOgrk3 -->
<!ENTITY iota
CDATA "&#953;" -- greek small letter iota, U+03B9 ISOgrk3 -->
<!ENTITY kappa
CDATA "&#954;" -- greek small letter kappa,
U+03BA ISOgrk3 -->
<!ENTITY lambda
CDATA "&#955;" -- greek small letter lambda,
U+03BB ISOgrk3 -->
<!ENTITY mu
CDATA "&#956;" -- greek small letter mu, U+03BC ISOgrk3 -->
<!ENTITY nu
CDATA "&#957;" -- greek small letter nu, U+03BD ISOgrk3 -->
<!ENTITY xi
CDATA "&#958;" -- greek small letter xi, U+03BE ISOgrk3 -->
<!ENTITY omicron CDATA "&#959;" -- greek small letter omicron, U+03BF NEW -->
<!ENTITY pi
CDATA "&#960;" -- greek small letter pi, U+03C0 ISOgrk3 -->
<!ENTITY rho
CDATA "&#961;" -- greek small letter rho, U+03C1 ISOgrk3 -->
<!ENTITY sigmaf
CDATA "&#962;" -- greek small letter final sigma,
U+03C2 ISOgrk3 -->
<!ENTITY sigma
CDATA "&#963;" -- greek small letter sigma,
U+03C3 ISOgrk3 -->
<!ENTITY tau
CDATA "&#964;" -- greek small letter tau, U+03C4 ISOgrk3 -->
<!ENTITY upsilon CDATA "&#965;" -- greek small letter upsilon,
U+03C5 ISOgrk3 -->
<!ENTITY phi
CDATA "&#966;" -- greek small letter phi, U+03C6 ISOgrk3 -->
<!ENTITY chi
CDATA "&#967;" -- greek small letter chi, U+03C7 ISOgrk3 -->
<!ENTITY psi
CDATA "&#968;" -- greek small letter psi, U+03C8 ISOgrk3 -->
<!ENTITY omega
CDATA "&#969;" -- greek small letter omega,
U+03C9 ISOgrk3 -->
<!ENTITY thetasym CDATA "&#977;" -- greek small letter theta symbol,
U+03D1 NEW -->
<!ENTITY upsih
CDATA "&#978;" -- greek upsilon with hook symbol,
U+03D2 NEW -->
<!ENTITY piv
CDATA "&#982;" -- greek pi symbol, U+03D6 ISOgrk3 -->
<!-- General Punctuation -->
<!ENTITY bull
CDATA "&#8226;" -- bullet = black small circle,
U+2022 ISOpub -->
<!-- bullet is NOT the same as bullet operator, U+2219 -->
<!ENTITY hellip
CDATA "&#8230;" -- horizontal ellipsis = three dot leader,
U+2026 ISOpub -->
<!ENTITY prime
CDATA "&#8242;" -- prime = minutes = feet, U+2032 ISOtech -->
<!ENTITY Prime
CDATA "&#8243;" -- double prime = seconds = inches,
U+2033 ISOtech -->
<!ENTITY oline
CDATA "&#8254;" -- overline = spacing overscore,
U+203E NEW -->
<!ENTITY frasl
CDATA "&#8260;" -- fraction slash, U+2044 NEW -->
305
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Character entity references in HTML 4
<!-- Letterlike Symbols -->
<!ENTITY weierp
CDATA "&#8472;" -- script capital P = power set
= Weierstrass p, U+2118 ISOamso -->
<!ENTITY image
CDATA "&#8465;" -- blackletter capital I = imaginary part,
U+2111 ISOamso -->
<!ENTITY real
CDATA "&#8476;" -- blackletter capital R = real part symbol,
U+211C ISOamso -->
<!ENTITY trade
CDATA "&#8482;" -- trade mark sign, U+2122 ISOnum -->
<!ENTITY alefsym CDATA "&#8501;" -- alef symbol = first transfinite cardinal,
U+2135 NEW -->
<!-- alef symbol is NOT the same as hebrew letter alef,
U+05D0 although the same glyph could be used to depict both characters -->
<!-- Arrows -->
<!ENTITY larr
<!ENTITY uarr
<!ENTITY rarr
<!ENTITY darr
<!ENTITY harr
<!ENTITY crarr
CDATA
CDATA
CDATA
CDATA
CDATA
CDATA
"&#8592;"
"&#8593;"
"&#8594;"
"&#8595;"
"&#8596;"
"&#8629;"
-------
<!-- Mathematical
<!ENTITY forall
<!ENTITY part
<!ENTITY exist
<!ENTITY empty
Operators -->
CDATA "&#8704;"
CDATA "&#8706;"
CDATA "&#8707;"
CDATA "&#8709;"
-----
leftwards arrow, U+2190 ISOnum -->
upwards arrow, U+2191 ISOnum-->
rightwards arrow, U+2192 ISOnum -->
downwards arrow, U+2193 ISOnum -->
left right arrow, U+2194 ISOamsa -->
downwards arrow with corner leftwards
= carriage return, U+21B5 NEW -->
<!ENTITY lArr
CDATA "&#8656;" -- leftwards double arrow, U+21D0 ISOtech -->
<!-- ISO 10646 does not say that lArr is the same as the ’is implied by’ arrow
but also does not have any other character for that function. So ? lArr can
be used for ’is implied by’ as ISOtech suggests -->
<!ENTITY uArr
CDATA "&#8657;" -- upwards double arrow, U+21D1 ISOamsa -->
<!ENTITY rArr
CDATA "&#8658;" -- rightwards double arrow,
U+21D2 ISOtech -->
<!-- ISO 10646 does not say this is the ’implies’ character but does not have
another character with this function so ?
rArr can be used for ’implies’ as ISOtech suggests -->
<!ENTITY dArr
CDATA "&#8659;" -- downwards double arrow, U+21D3 ISOamsa -->
<!ENTITY hArr
CDATA "&#8660;" -- left right double arrow,
U+21D4 ISOamsa -->
for all, U+2200 ISOtech -->
partial differential, U+2202 ISOtech -->
there exists, U+2203 ISOtech -->
empty set = null set = diameter,
U+2205 ISOamso -->
<!ENTITY nabla
CDATA "&#8711;" -- nabla = backward difference,
U+2207 ISOtech -->
<!ENTITY isin
CDATA "&#8712;" -- element of, U+2208 ISOtech -->
<!ENTITY notin
CDATA "&#8713;" -- not an element of, U+2209 ISOtech -->
<!ENTITY ni
CDATA "&#8715;" -- contains as member, U+220B ISOtech -->
<!-- should there be a more memorable name than ’ni’? -->
<!ENTITY prod
CDATA "&#8719;" -- n-ary product = product sign,
U+220F ISOamsb -->
<!-- prod is NOT the same character as U+03A0 ’greek capital letter pi’ though
the same glyph might be used for both -->
<!ENTITY sum
CDATA "&#8721;" -- n-ary sumation, U+2211 ISOamsb -->
<!-- sum is NOT the same character as U+03A3 ’greek capital letter sigma’
though the same glyph might be used for both -->
<!ENTITY minus
CDATA "&#8722;" -- minus sign, U+2212 ISOtech -->
<!ENTITY lowast
CDATA "&#8727;" -- asterisk operator, U+2217 ISOtech -->
<!ENTITY radic
CDATA "&#8730;" -- square root = radical sign,
U+221A ISOtech -->
<!ENTITY prop
CDATA "&#8733;" -- proportional to, U+221D ISOtech -->
<!ENTITY infin
CDATA "&#8734;" -- infinity, U+221E ISOtech -->
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Character entity references in HTML 4
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
ang
and
or
cap
cup
int
there4
sim
CDATA
CDATA
CDATA
CDATA
CDATA
CDATA
CDATA
CDATA
"&#8736;"
"&#8743;"
"&#8744;"
"&#8745;"
"&#8746;"
"&#8747;"
"&#8756;"
"&#8764;"
---------
angle, U+2220 ISOamso -->
logical and = wedge, U+2227 ISOtech -->
logical or = vee, U+2228 ISOtech -->
intersection = cap, U+2229 ISOtech -->
union = cup, U+222A ISOtech -->
integral, U+222B ISOtech -->
therefore, U+2234 ISOtech -->
tilde operator = varies with = similar to,
U+223C ISOtech -->
<!-- tilde operator is NOT the same character as the tilde, U+007E,
although the same glyph might be used to represent both -->
<!ENTITY cong
CDATA "&#8773;" -- approximately equal to, U+2245 ISOtech -->
<!ENTITY asymp
CDATA "&#8776;" -- almost equal to = asymptotic to,
U+2248 ISOamsr -->
<!ENTITY ne
CDATA "&#8800;" -- not equal to, U+2260 ISOtech -->
<!ENTITY equiv
CDATA "&#8801;" -- identical to, U+2261 ISOtech -->
<!ENTITY le
CDATA "&#8804;" -- less-than or equal to, U+2264 ISOtech -->
<!ENTITY ge
CDATA "&#8805;" -- greater-than or equal to,
U+2265 ISOtech -->
<!ENTITY sub
CDATA "&#8834;" -- subset of, U+2282 ISOtech -->
<!ENTITY sup
CDATA "&#8835;" -- superset of, U+2283 ISOtech -->
<!-- note that nsup, ’not a superset of, U+2283’ is not covered by the Symbol
font encoding and is not included. Should it be, for symmetry?
It is in ISOamsn -->
<!ENTITY nsub
CDATA "&#8836;" -- not a subset of, U+2284 ISOamsn -->
<!ENTITY sube
CDATA "&#8838;" -- subset of or equal to, U+2286 ISOtech -->
<!ENTITY supe
CDATA "&#8839;" -- superset of or equal to,
U+2287 ISOtech -->
<!ENTITY oplus
CDATA "&#8853;" -- circled plus = direct sum,
U+2295 ISOamsb -->
<!ENTITY otimes
CDATA "&#8855;" -- circled times = vector product,
U+2297 ISOamsb -->
<!ENTITY perp
CDATA "&#8869;" -- up tack = orthogonal to = perpendicular,
U+22A5 ISOtech -->
<!ENTITY sdot
CDATA "&#8901;" -- dot operator, U+22C5 ISOamsb -->
<!-- dot operator is NOT the same character as U+00B7 middle dot -->
<!-- Miscellaneous Technical -->
<!ENTITY lceil
CDATA "&#8968;" -- left ceiling = apl upstile,
U+2308 ISOamsc -->
<!ENTITY rceil
CDATA "&#8969;" -- right ceiling, U+2309 ISOamsc -->
<!ENTITY lfloor
CDATA "&#8970;" -- left floor = apl downstile,
U+230A ISOamsc -->
<!ENTITY rfloor
CDATA "&#8971;" -- right floor, U+230B ISOamsc -->
<!ENTITY lang
CDATA "&#9001;" -- left-pointing angle bracket = bra,
U+2329 ISOtech -->
<!-- lang is NOT the same character as U+003C ’less than’
or U+2039 ’single left-pointing angle quotation mark’ -->
<!ENTITY rang
CDATA "&#9002;" -- right-pointing angle bracket = ket,
U+232A ISOtech -->
<!-- rang is NOT the same character as U+003E ’greater than’
or U+203A ’single right-pointing angle quotation mark’ -->
<!-- Geometric Shapes -->
<!ENTITY loz
CDATA "&#9674;" -- lozenge, U+25CA ISOpub -->
<!-- Miscellaneous Symbols -->
<!ENTITY spades
CDATA "&#9824;" -- black spade suit, U+2660 ISOpub -->
<!-- black here seems to mean filled as opposed to hollow -->
<!ENTITY clubs
CDATA "&#9827;" -- black club suit = shamrock,
307
24 Dec 1999 18:26
Character entity references in HTML 4
<!ENTITY hearts
<!ENTITY diams
U+2663 ISOpub -->
CDATA "&#9829;" -- black heart suit = valentine,
U+2665 ISOpub -->
CDATA "&#9830;" -- black diamond suit, U+2666 ISOpub -->
24.4 Character entity references for markup-significant
and internationalization characters
The character entity references in this section are for escaping markup-significant
characters (these are the same as those in HTML 2.0 and 3.2), for denoting spaces
and dashes. Other characters in this section apply to internationalization issues such
as the disambiguation of bidirectional text (see the section on bidirectional text [p.82]
for details).
Entities have also been added for the remaining characters occurring in CP-1252
which do not occur in the HTMLlat1 or HTMLsymbol entity sets. These all occur in
the 128 to 159 range within the CP-1252 charset. These entities permit the
characters to be denoted in a platform-independent manner.
To support these entities, user agents may support full [ISO10646] [p.353] or use
other means. Display of glyphs for these characters may be obtained by being able
to display the relevant [ISO10646] [p.353] characters or by other means, such as
internally mapping the listed entities, numeric character references, and characters
to the appropriate position in some font that contains the requisite glyphs.
24.4.1 The list of characters
<!-- Special characters for HTML -->
<!-- Character entity set. Typical invocation:
<!ENTITY % HTMLspecial PUBLIC
"-//W3C//ENTITIES Special//EN//HTML">
%HTMLspecial; -->
<!-- Portions © International Organization for Standardization 1986:
Permission to copy in any form is granted for use with
conforming SGML systems and applications as defined in
ISO 8879, provided this notice is included in all copies.
-->
<!-- Relevant ISO entity set is given unless names are newly introduced.
New names (i.e., not in ISO 8879 list) do not clash with any
existing ISO 8879 entity names. ISO 10646 character numbers
are given for each character, in hex. CDATA values are decimal
conversions of the ISO 10646 values and refer to the document
character set. Names are ISO 10646 names.
-->
<!-- C0 Controls and Basic Latin -->
<!ENTITY quot
CDATA "&#34;"
-- quotation mark = APL quote,
U+0022 ISOnum -->
<!ENTITY amp
CDATA "&#38;"
-- ampersand, U+0026 ISOnum -->
<!ENTITY lt
CDATA "&#60;"
-- less-than sign, U+003C ISOnum -->
24 Dec 1999 18:26
308
Character entity references in HTML 4
<!ENTITY gt
CDATA "&#62;"
-- greater-than sign, U+003E ISOnum -->
<!-- Latin Extended-A -->
<!ENTITY OElig
CDATA "&#338;"
-- latin capital ligature OE,
U+0152 ISOlat2 -->
<!ENTITY oelig
CDATA "&#339;" -- latin small ligature oe, U+0153 ISOlat2 -->
<!-- ligature is a misnomer, this is a separate character in some languages -->
<!ENTITY Scaron CDATA "&#352;" -- latin capital letter S with caron,
U+0160 ISOlat2 -->
<!ENTITY scaron CDATA "&#353;" -- latin small letter s with caron,
U+0161 ISOlat2 -->
<!ENTITY Yuml
CDATA "&#376;" -- latin capital letter Y with diaeresis,
U+0178 ISOlat2 -->
<!-- Spacing Modifier Letters -->
<!ENTITY circ
CDATA "&#710;" -- modifier letter circumflex accent,
U+02C6 ISOpub -->
<!ENTITY tilde
CDATA "&#732;" -- small tilde, U+02DC ISOdia -->
<!-- General Punctuation -->
<!ENTITY ensp
CDATA "&#8194;"
<!ENTITY emsp
CDATA "&#8195;"
<!ENTITY thinsp CDATA "&#8201;"
<!ENTITY zwnj
CDATA "&#8204;"
-----
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
-------
zwj
lrm
rlm
ndash
mdash
lsquo
CDATA
CDATA
CDATA
CDATA
CDATA
CDATA
"&#8205;"
"&#8206;"
"&#8207;"
"&#8211;"
"&#8212;"
"&#8216;"
<!ENTITY rsquo
CDATA "&#8217;" --
<!ENTITY sbquo
<!ENTITY ldquo
CDATA "&#8218;" -CDATA "&#8220;" --
<!ENTITY rdquo
CDATA "&#8221;" --
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
<!ENTITY
CDATA
CDATA
CDATA
CDATA
CDATA
bdquo
dagger
Dagger
permil
lsaquo
"&#8222;"
"&#8224;"
"&#8225;"
"&#8240;"
"&#8249;"
------
<!-- lsaquo is proposed but not yet
<!ENTITY rsaquo CDATA "&#8250;" -<!-- rsaquo is proposed but not yet
<!ENTITY euro
CDATA "&#8364;" --
309
en space, U+2002 ISOpub -->
em space, U+2003 ISOpub -->
thin space, U+2009 ISOpub -->
zero width non-joiner,
U+200C NEW RFC 2070 -->
zero width joiner, U+200D NEW RFC 2070 -->
left-to-right mark, U+200E NEW RFC 2070 -->
right-to-left mark, U+200F NEW RFC 2070 -->
en dash, U+2013 ISOpub -->
em dash, U+2014 ISOpub -->
left single quotation mark,
U+2018 ISOnum -->
right single quotation mark,
U+2019 ISOnum -->
single low-9 quotation mark, U+201A NEW -->
left double quotation mark,
U+201C ISOnum -->
right double quotation mark,
U+201D ISOnum -->
double low-9 quotation mark, U+201E NEW -->
dagger, U+2020 ISOpub -->
double dagger, U+2021 ISOpub -->
per mille sign, U+2030 ISOtech -->
single left-pointing angle quotation mark,
U+2039 ISO proposed -->
ISO standardized -->
single right-pointing angle quotation mark,
U+203A ISO proposed -->
ISO standardized -->
euro sign, U+20AC NEW -->
24 Dec 1999 18:26
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310
HTML 4 Changes
Appendix A: Changes
Contents
1. Changes between 24 April 1998 HTML 4.0 and 24 December 1999 HTML 4.01
versions
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. 312
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1. Changes to the specification
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. 312
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General changes
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. 312
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On SGML and HTML
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. 312
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HTML Document Representation
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. 312
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Basic HTML data types .
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. 312
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Global structure of an HTML document .
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. 313
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Language information and text direction .
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. 313
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Tables .
Links .
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. 313
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Objects, Images, and Applets .
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. 314
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. 314
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Style Sheets in HTML Documents .
Frames
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. 314
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Forms .
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. 315
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SGML Declaration .
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. 315
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Strict DTD .
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. 315
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. 315
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Notes .
References .
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. 316
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2. Errors that were corrected .
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. 316
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3. Minor typographical errors that were corrected .
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. 318
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4. Clarifications
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. 322
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5. Known Browser problems
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. 322
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2. Changes between 18 December 1997 and 24 April 1998 versions
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. 322
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1. Errors that were corrected .
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. 323
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2. Minor typographical errors that were corrected .
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. 325
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3. Changes between HTML 3.2 and HTML 4.0 (18 December 1997) .
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. 327
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1. Changes to elements
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. 327
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New elements .
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. 327
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Deprecated elements .
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. 327
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Obsolete elements .
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. 328
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2. Changes to attributes
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. 328
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3. Changes for accessibility
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. 328
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4. Changes for meta data .
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. 328
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5. Changes for text
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. 328
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6. Changes for links
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. 328
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7. Changes for tables .
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. 328
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8. Changes for images, objects, and image maps .
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. 329
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9. Changes for forms .
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. 330
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HTML 4 Changes
10.
11.
12.
13.
Changes for style sheets
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Changes for frames .
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Changes for scripting
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Changes for internationalization
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330
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330
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330
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330
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A.1 Changes between 24 April 1998 HTML 4.0 and 24
December 1999 HTML 4.01 versions
This section describes how the 24 December 1999 version of the HTML 4.01
specification differs from the 24 April 1998 version of the HTML 4.0 specification.
A.1.1 Changes to the specification
General changes
New style sheets for the document based on W3C technical report styles.
Added a short table of contents [p.4] .
Updated the copyright.
Fixed document scripts to remove markup causing crashes on some browsers.
Thanks to Shane McCarron added to the acknowledgments [p.17] .
In section 1.4 [p.18] , removed copyright details and refer to W3C site instead.
References to the document character set are all ISO 10646 (and one time to
UNICODE to signal equivalence). References to UNICODE refer only to the
bidirectionality algorithm.
Examples now use dated FPIs.
On SGML and HTML
Section 3.2.2 [p.29] : Attribute values may contain colons and underscores as
well.
HTML Document Representation
The Document Character Set [p.41] : [ISO10646] now used only for references
to the document character set. [UNICODE] is reserved for bidi-related
references.
Basic HTML data types
Media descriptors [p.56] : All characters in examples now described using hex
notation (and reference to ISO 10646 rather than Unicode).
24 Dec 1999 18:26
312
HTML 4 Changes
Global structure of an HTML document
7.2 HTML version information [p.60] : Add a note about the HTML WG’s
commitment that
Any changes to future HTML 4 DTDs will not invalidate documents that
conform to the DTDs of the present specification. The HTML Working
Group reserves the right to correct known bugs.
Software conforming to the DTDs of the present specification may ignore
features of future HTML 4 DTDs that it does not recognize.
7.2 HTML version information [p.60] : Use undated, HTML 4 URIs for system
identifiers. These URIs are also used globally in all examples.
7.4.4 Meta data [p.64] : Removed note about ongoing work at W3C on meta
data and replaced with a note about RDF.
7.4.4.2 Meta data [p.65] : At the end of the section on HTTP headers, removed
the auto-refresh example (since not part of the Recommendation) and added a
note to use server-side redirects.
Language information and text direction
The dir attribute [p.82] : Clarification that dir applies to element content,
attribute values, and table direction.
Tables
11.2.6 Table Cells: [p.125] The definitions of rowspan and colspan changed.
Now spans are bounded by groups (rowgroups or colgroups).
11.3.2 Table Cells: [p.132] When "char=align" not supported by the user agent,
behavior is undefined.
Links
12.2 The A element: [p.149] The description of the type attribute for the A and
(LINK) elements has been modified to emphasize its advisory nature.
12.2.3 Anchors with the id attribute: [p.152] It is legal for "name" and "id" to
appear in the same start tag when they are both defined for an element. They
must have identical values.
12.3.3 Links and search engines: [p.155] Removed reference to dir attribute in
example since it doesn’t apply to linked resources (only element content and
attribute text values).
12.4.1 Resolving relative URIs: [p.158] Since RFC 2616 does not include a Link
header field, the following statement is qualified for earlier versions of HTTP 1.1:
"Link elements specified by HTTP headers are handled exactly as LINK
elements that appear explicitly in a document."
313
24 Dec 1999 18:26
HTML 4 Changes
Objects, Images, and Applets
13.2 The IMG element: [p.160] Addition of the name attribute for backwards
compatibility.
13.2 The IMG element: [p.160] Added a note that user agents must provide
different mechanisms for accessing the "longdesc" URI (of IMG) and the "src"
URI (of A) when an IMG is part of the content of an A element.
13.3 The OBJECT element: [p.162] Added a note that when the value of "type"
for OBJECT and the Content-Type HTTP header differ, the latter takes
precedence.
13.3 The OBJECT element: [p.162] Added a statement to use PARAM instead
of the "data" and "classid" attributes for OBJECT together.
13.4 The APPLET element: [p.171] Added a note that, for security reasons only
subdirectories are searched for the "codebase" attribute of APPLET.
13.6.1 Client-side image maps: [p.174] The definition of the "poly" attribute has
been cleared up. There is a note that if not closed by authors, user agents
should close the polygon for the "coords" attribute of AREA.
13.6.1 Client-side image maps: [p.174]
The content model of the MAP element now allows authors to mix AREA
content and block-level content.
User agents "should" render block-level content (used to be "may").
The MAP element may be used without an image for general purpose
navigation tools.
User agents must ignore AREA elements when content is mixed (AREA and
block level).
Authors should specify geometries completely with either AREA elements,
or A elements in block content, or both.
13.7.2 [p.180] and 13.7.3 [p.180] : The vspace and hspace attribute definitions
now look like the definitions of other attributes.
13.7.2 [p.180] and 13.7.3 [p.180] : The type of vspace, hspace, and border
attribute values was changed from "length" to "pixels".
13.8 Alternate text: [p.181] The last sentence of section now links to notes for
user agent developers for handling empty "alt" attribute text.
Style Sheets in HTML Documents
14.6 Linking to style sheets with HTTP headers: [p.194] Since RFC 2616 does
not include a Link header field, the entire section is qualified to pertain only to
earlier versions of HTTP 1.1.
Frames
16.4.1 NOFRAMES: [p.214] Added text to the NOFRAMES description about
rendering when (1) frames turned off (2) frames not supported.
16.4.1 NOFRAMES: [p.214] Added text about which DTDs may have
NOFRAMES (frames, transitional).
24 Dec 1999 18:26
314
HTML 4 Changes
Forms
17.2.1 Control types: [p.221] In the description of radio buttons, when no radio
button is initially selected, user agent behavior for selecting one is undefined.
This differs from RFC 1866.
17.3 The FORM element: [p.222] Addition of the name attribute for backwards
compatibility.
17.3 The FORM element: [p.222] Removed the reference to the "mailto" URI in
the "action" attribute definition.
17.3 The FORM element: [p.222] Removed "mailto" example near end of
section since behavior not defined in this spec.
17.3 The FORM element: [p.222] The accept attribute is added to the DTD
fragment. Also, the description of the accept-charset attribute is amended.
17.4 The INPUT element: [p.224] Added missing "ismap" for the INPUT
element. Also, in definition of value., add "checkbox" to values of type that
require a value.
17.6.1 [p.231] : When no option is preselected, user agent behavior is
undefined. Authors should supply and explicit none option to cover this case.
This behavior differs from RFC 1866.
SGML Declaration
SGML Declaration of HTML 4: [p.263] Removed text about up-to-date
references to ISO 10646. Replaced with: "Revisions of the HTML 4 specification
may update the reference to ISO 10646 to include additional changes."
Strict DTD
vspace/hspace/border attributes for IMG, OBJECT, APPLET in pixels.
Changed content model of MAP to ((%block;) | AREA)+
Added "ismap" attribute to INPUT
The accept attribute is added to the DTD fragment for the FORM element.
The axis attribute comment has been changed to refer to a comma-separated
list.
The archive attribute for the OBJECT element takes a value of type CDATA
instead of type %URI since the value is a space-separated list of URIs.
Notes
Notes [p.350] Updated notes on accessibility to point to Web Content
Accessibility Guidelines.
315
24 Dec 1999 18:26
HTML 4 Changes
References
Updated links to RFCs to use http://www.ietf.org/rfc
Put links in titles.
Added revised date of 27 Aug 1998 for [DATETIME]
Added revised date of 11 Jan 1999 for [CSS1].
Publication date of [CSS2] fixed.
[UNICODE] has been updated to version 3.0
[ISO10646] has been updated to allow for new character assignments. Note that
amendment five is specifically taken into account.
[RFC1766] expected to be updated.
[RFC2279] obsoletes [RFC2044].
[RFC2616] obsoletes [RFC2068].
[RFC2388] added in addition to [RFC1867].
[LEXHTML] address updated, date added.
[DCORE] address updated.
Updated [WEBSGML]
[HTML3STYLE] address updated.
Added [RDF10] (replaced old RDF)
Changed [WAIGUIDE] -> [WAI]
Added informative references [WCGL], [UAGL], and [ATGL]
Updated URI reference to [URI] (RFC 2396).
A.1.2 Errors that were corrected
Section 13.6.1 [p.174]
Image map examples using "poly" have been fixed to form a closed polygon.
Also, the last pair of coordinates is the same as the first to close the polygon.
Section 14.4.1 [p.192]
In the final example, the STYLE element is missing the attribute assignment
"media=screen, print".
Section 15.2.1 [p.199]
In the example with "mypar", the CSS rule should read
P#mypar {font-style: italic; color: blue}
In CSS, "#" refers to an ID name while the "." refers to a class name. This
example is dealing with the "id" attribute.
Section 16.2.2 [p.209]
Values for marginwidth and marginheight must be 0 pixels or more, not 1
pixel or more.
Section 16.2.2 [p.209]
The FRAME element does not take the target attribute.
24 Dec 1999 18:26
316
HTML 4 Changes
Section 16.5 [p.217]
The IFRAME element does not take the target attribute.
Section 17.2.1 [p.221]
In the description of "checkboxes", change "selected" to "checked" in "when the
control element’s selected attribute is set."
Section 17.6.1 [p.231]
In the "Attributes defined elsewhere" section for the OPTGROUP element, the
attributes onfocus, onblur, and onchange should not be there.
Section 18.2.3 [p.254]
To the list of elements that take onfocus and onblur, add A and AREA.
Section 20 [p.263]
The SGML Declaration for HTML 4 must be modified slightly to support
hexadecimal numeric character references. The lines:
DELIM
GENERAL SGMLREF
SHORTREF SGMLREF
must be changed to:
DELIM
GENERAL SGMLREF
HCRO "&#38;#x" -- 38 is the number for ampersand -SHORTREF SGMLREF
And the initial <!SGML "ISO 8879:1986" must be changed to <!SGML
"ISO 8879:1986 (WWW)".
Section 21 [p.265]
The HR element should also take the lang and dir attributes. These are noted
as being defined elsewhere at the element’s definition, but were left out of the
DTDs.
Section 21 [p.265]
The OBJECT element’s archive attribute is defined in the DTD as taking a
value of type %URI". This is incorrect: the value may be a space-separated list
of URIs (as indicated in the definition of the attribute and in the DTD comment).
The FORM element’s DTD fragment should include a definition for the accept
attribute, which is listed in the element’s definition. The definition should be the
following:
accept
%ContentTypes;
#IMPLIED
-- list of MIME types for file upload --
Section B.4.1 [p.340]
At the end of the section, the following sentences are incorrect: "The list of
terms in the content is ALL, INDEX, NOFOLLOW, NOINDEX. The name and the
content attribute values are case-insensitive." In fact, the META definition
specifies that values for the name and content attributes are case-sensitive.
Section B.4.1.1 [p.340]
The specification reads, "Blank lines are not permitted." Blank lines are
permitted in the robots.txt file, just not within a single "record". Note that the
317
24 Dec 1999 18:26
HTML 4 Changes
specification doesn’t define record.
Further down the page, the specification reads, "There must be exactly one
"User-agent" field per record." In fact, there can be more than one User-Agent
field in the robots.txt file, just not more than one per record.
For information about search robots, please consult, for example:
http://www.kollar.com/robots.html
http://info.webcrawler.com/mak/projects/robots/norobots-rfc.html
http://info.webcrawler.com/mak/projects/robots/robots.html
References [p.353]
The [URI] [p.355] reference should be updated to RFC 2396 as of August
1998. "Uniform Resource Identifiers (URI): Generic Syntax", T.
Berners-Lee, R. Fielding, L. Masinter, August 1998. RFC 2396 updates
[RFC1738] and [RFC1808].
A.1.3 Minor typographical errors that were corrected
Section 2.1.1 [p.19]
The phrase "accessible via the path "/TR/REC-html4/". should end with
"/TR/REC-html40/".
Section 2.1.3 [p.20]
In the third bullet, the word "applets" should be "applet".
Section 3.3 [p.28]
In bullet two, the sentence "Whether the element’s end tag is optional." should
read "Whether the element’s tags are optional."
Section 3.2.1 [p.28]
In the sentence beginning "Please consult the SGML standard", the phrase "an
end tag closes all omitted start tags up to the matching start tag (section 7.5.1)"
should read "an end tag closes, back to the matching start tag, all unclosed
intervening start tags with omitted end tags".
Section 3.2.2 [p.29]
"Attribute names are always case-insensitive" is missing a final period.
Section 3.3.4.2 [p.36]
The example with the OPTION element has an improper end tag; it should be
</OPTION>.
Later in the section, the sentence that begins "Authors should be aware than"
should say "aware that" instead.
Section 5.2.2 [p.43]
Change "ASCII characters" to ASCII-valued bytes".
Section 5.3.1 [p.45]
The second bullet should read "a" instead of "an" in "where H is an hexadecimal
number".
Section 6.5.1 [p.52]
The first sentence needs the indefinite article "a" before the word "document".
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Section 6.10 [p.53]
The first sentence needs the indefinite article "a" before the word "single".
Section 6.12 [p.54]
Under "Next", "in an linear" should read "in a linear" instead.
Section 6.16 [p.57]
Change "cancelling" to "canceling".
Section 7.4.4.3 [p.68]
In the paragraph beginning "The scheme attribute allows...", replace
"Month-Date-Year" with "Month-Day-Year".
Section 7.5.4 [p.73]
In the sentence after the example, make "declaration" plural.
Section 7.5.6 [p.76]
For the ADDRESS element, in the section "Attributes defined elsewhere", style
and title are missing.
Also, after the section on "Attributes defined elsewhere", in "contact
information for document", put "a" before "document".
Section 8.2.3 [p.84]
In "Authors may also use special Unicode characters to achieve multiply"
change to "multiple" at the end.
Section 11.2.4.1 [p.118]
The sentence "The first COL element refers to the first 39 columns (doing
nothing special to them) and the second one assigns an id value to the fortieth
columns so that style sheets may refer to it." should have "fortieth column"
instead.
Section 11.2.5 [p.124]
For the TR element, in the section "Attributes defined elsewhere", bgcolor is
missing.
Section 11.2.6 [p.125]
For the TH and TD elements, the type of the width and height attributes is
changed from "%Pixels;" to "%Length;" to allow for percentage values.
Section 11.3.1 [p.130]
In the first sentence of the frame attribute definition, use "surrounding" instead
of "that surrounds".
Section 11.4.1 [p.136]
First bullet, third sentence. "Note that its not always possible" should have "it’s"
instead.
Section 12.1.2 [p.147]
The last sentence should read "Further information is given below on using links
for..." (change "of" to "on"). This sentence is also missing its closing
punctuation.
Section 12.2.2 [p.152]
The last paragraph should read "Since the DTD defines the LINK element to be
empty..." (insert definite article "the" before "LINK").
Section 12.2.3 [p.152]
Just before section 12.2.4, the third bullet. "richer anchors names" should read
"richer anchor names".
319
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Section 13.3.4 [p.169]
In the paragraph that begins "In the following example...", the phrase "cause it
so be instantiated" should be changed to cause it to be instantiated" (change
"so" to "to").
Section 13.4 [p.171]
Just after the deprecated example, the sentence "This example may be
rewritten as follows with OBJECT as follows:" should say "This example may be
rewritten with OBJECT as follows:".
Section 13.6.1 [p.174]
Under the "coords" attribute, the word "and" should be substituted for the word
"a" so the sentence reads, "This attribute specifies the position and shape on
the screen."
Section 13.7.1 [p.179]
In the definition of the height attribute, the phrase "Image and object override"
should read "Image and object height override".
Section 15.1.3.1 [p.197]
Under the subheading "Float an object", in the first paragraph, the first use of
the word "object" should be "objects".
Section 15.1.3.2 [p.198]
In the "Deprecated" example, the first sentence should read "If the clear
attribute is set to left or all, the next line will appear as follows:" ("the" before
"next line").
Section 15.3 [p.202]
The align attribute for HR is not defined elsewhere.
Section 16.1 [p.205]
In the last sentence of the first paragraph, the word "though" should be
"through".
Section 16.3.1 [p.213]
In the second sentence, the word "factorizing" should be "factoring".
Section 16.4.1 [p.214]
The list of "attributes defined elsewhere" was inadvertently omitted after the
definition of NOFRAMES. These attributes are: class, id, lang, dir, title,
style, and the %events; [p.282] attributes.
Section 17.1 [p.219]
In "(entering text, selecting menu items, etc.)", add the "," after "text".
Section 17.5 [p.228]
In the paragraph that begins "Visual user agents may render...", the indefinite
article "a" should be removed from before the word "flat".
Section 17.12.1 [p.244]
A comma should be added between BUTTON and INPUT in the list of elements
that support the "disabled" attribute.
Section 17.13.4.2 [p.248]
In the examples at the end of the section, change "Content-Disposition:
attachment" to "Content-Disposition: file". Also, in an earlier example, change
"server.dom" to "server.com".
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HTML 4 Changes
Section 18.2.2.1 [p.253]
After the first example, the indefinite article before "content-type" needs to be
"a", not "an". The same applies to "content-type" in the next paragraph.
In the sentence beginning "Documents that do not specify...", the indefinite
article "a" needs to be removed from before "default scripting language
information".
Section 18.2.3 [p.254]
In the first sentence of the first note, the word "realm" should be preceded by
the definite article "the".
Section 18.3.1 [p.258]
In the second sentence of the first paragraph, the word "be" needs to be
inserted between the words "only" and "rendered".
Section 21 [p.265]
In all DTDs, under the COLGROUP element, the content model should
indicate "COL", not "col".
In the comment about the %Scope entity, change "axes" to "headers"
attribute.
Section 24.2.1 [p.300]
At end of definition of "thorn", remove stray final word.
Section 24.4 [p.308]
Change "cp-1252" to "CP-1252".
Appendix: Changes for tables [p.328]
In the paragraph on the COLGROUP element, the last sentence should read:
"The semantics of COLGROUP have been clarified over previous drafts, and
rules="basic" has been replaced by rules="groups"."
Changes to elements [p.327]
The list of deprecated elements should include S.
Section B.3.2 [p.336]
In "delimiter followed by a name character", change to delimiter followed by a
name start character".
Section B.4 [p.339]
Under "Provide keywords and descriptions", the middle of the sentence "The
value of the name attribute sought by a search attribute is not defined by this
specification." should read "search engine" instead.
Section B.4 [p.339]
In the example to indicate the beginning of a collection replace rel="begin"
with rel="start".
Section B.4.1 [p.340]
Remove "The name and the content attribute values are case-insensitive."
Section B.5.1.2 [p.342]
The last sentence of the last paragraph is missing a closing parenthesis.
Section B.7.1.1 [p.348]
In the deprecated example:
321
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<BODY bgcolor=’&{randomrgb};’>
The word "randomrbg" should be "randomrgb".
A.1.4 Clarifications
Section 3.2.1 [p.28]
In seventh paragraph, added "back to the matching start tag" to "(e.g., they must
be properly nested, an end tag closes, back to the matching start tag, all
unclosed intervening start tags with omitted end tags (section 7.5.1), etc.)."
Section 3.2.4 [p.30]
Added a statement that comments are markup.
Section 3.3.3 [p.32]
In the second list item, change "Whether the element’s end tag" to "Whether the
element’s tags".
Section 3.3.3.1 [p.33]
In a content model definition, "A" means that "A" must occur one time and only
one time. Also, added "+(A)" and "-(A)" to the section on content model syntax.
Section 7.4.2 [p.62]
Clarified that TITLE may not include comments.
Section 10.3 [p.106]
All uses of "cracker" in this section and its subsections are replaced with
"hacker". Also, definitions of "hacker" and "nerd" taken from "The Hacker’s
Dictionary".
Section 13.7.2 [p.180]
The hspace and vspace attributes are deprecated.
Section 13.7.4 [p.180]
The align attribute is deprecated for IMG, OBJECT, and APPLET.
A.1.5 Known Browser problems
Some versions of Netscape Navigator 4.0X crash upon reading Chapter 3 of
previous versions of this specification. Netscape is aware of this bug and have
fixed it in version 4.5. To work around this bug, go to the
Edit/Preferences/Advanced submenu and disable Style Sheets (and possibly
JavaScript).
A.2 Changes between 18 December 1997 and 24 April
1998 versions
This section describes how the 24 April 1998 version of the HTML 4.0 specification
differs from the 18 December 1997 version.
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HTML 4 Changes
A.2.1 Errors that were corrected
Section 2.1.1 [p.19]
"http://www.w3.org/TR/PR-html4/cover.html" was said to designate the current
HTML specification. The current HTML specification is actually at
http://www.w3.org/TR/REC-html40.
Section 7.5.2 [p.71]
The hypertext link on name was incorrect. It now links to types.html#type-name
[p.50] .
Section 7.5.4 [p.73]
href was listed as an attribute of the DIV and SPAN elements. It is not.
Section 7.5.6 [p.76]
A P element was used in the example. It is invalid in ADDRESS.
Section 8.1 [p.79]
In the first example, which reads "Her super-powers were the result...", there
was an extra double quote mark before the word "Her".
Section 9.3.4 [p.97]
The attribute width [p.97] was not noted as deprecated [p.38] .
Section 11.2.4, "Calculating the width of columns" [p.122]
The sentence "We have set the value of the align attribute in the third column
group to ’center’" read "second" instead of "third".
Section 11.2.6, "Cells that span several rows or columns" [p.128]
The second paragraph read "In this table definition, we specify that the cell in
row four, column two should span a total of three columns, including the current
row." It now ends "...including the current column."
Section 13.2 [p.160]
The sentence beginning "User agents must render alternate text when they
cannot support ..." read "next", instead of "text".
Section 13.6.2 [p.179]
The last sentence of the second paragraph applied to both the IMG and INPUT
elements. However, the ismap attribute is not defined for INPUT. The sentence
now only applies to IMG.
Section 14.2.3 [p.187]
The title attribute for the STYLE element was not listed as an attribute
defined elsewhere.
Section 14.3.2 [p.191]
The second example set title="Compact". It now sets title="compact".
Section 15.1.2 [p.195]
The sentence ending "the align attribute." read "the align element."
Section 15.1.3.2 [p.198]
The CSS style rule "BR.mybr { clear: left }" was incorrect, since it refers to the
class "mybr" and not the id value. The correct syntax is: "BR#mybr { clear: left }".
Section 16 [p.205]
All the examples containing a Document Type Declaration used something like
"THE_LATEST_VERSION_/frameset.dtd" or "THE_LATEST_VERSION_" as
the system identifier for the Frameset DTD. They now use the proper document
323
24 Dec 1999 18:26
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type declaration indicated in Section 7.2 [p.60]
Section 16.3 [p.212] and Section 16.3.1 [p.213]
The second example of 16.3 and the example of 16.3.1 used the wrong DTD;
they now use the Transitional DTD.
Section 17.5 [p.228]
In "attributes defined elsewhere" for the BUTTON element, id, class, lang,
dir, title, style, and tabindex were missing. Also, usemap has been
removed.
Section 17.6/17.6.1 [p.230]
The "attributes defined elsewhere" for OPTION and OPTGROUP mistakenly listed
onfocus, onblur, and onchange. The "attributes defined elsewhere" section
was missing for the SELECT element (please see the DTD for the full list of
attributes).
Section 17.9.1 [p.237]
The tabindex attribute was said to be defined for the LABEL element. It is not.
Section 17.12.2 [p.244]
The sentence "The following elements support the readonly attribute: INPUT
and TEXTAREA." read "The following elements support the readonly attribute:
INPUT, TEXT, PASSWORD, and TEXTAREA."
Section 18.2.2, "Local declaration of a scripting language" [p.254]
The first paragraph read: "It is also possible to specify the scripting language in
each SCRIPT element via the type attribute. In the absence of a default
scripting language specification, this attribute must be set on each SCRIPT
element." Since the type attribute is required for the SCRIPT element, this
paragraph now reads: "The type attribute must be specified for each SCRIPT
element instance in a document. The value of the type attribute for a SCRIPT
element overrides the default scripting language for that element."
Section 21 [p.265]
Added note that the spec includes some syntactic constraints that cannot be
expressed in the DTD.
Section 24.2.1 [p.300] and file HTMLlat1.ent
The comment for the character reference "not" read "= discretionary hyphen".
This has been removed.
The FPI in comment read "-//W3C//ENTITIES Full Latin 1//EN//HTML", instead
this is now "-//W3C//ENTITIES Latin1//EN//HTML".
Section 24.3.1 [p.304] and file HTMLsymbol.ent
The FPI in comment read "-//W3C//ENTITIES Symbolic//EN//HTML", instead
this is now "-//W3C//ENTITIES Symbols//EN//HTML".
Section A.1.1, "New elements" [p.312] (previously A.1.1) and Section A.1.1,
"Deprecated elements" [p.312] (previously A.1.2)
The S element which is deprecated [p.38] was listed as part of the changes
between HTML 3.2 and HTML 4.0. This element was not actually defined in
HTML 3.2 [p.356] . It is now in the new elements list.
Section A.1.3 (previously A.3) [p.312]
The longdesc attribute was said to be specified for tables. It is not. Instead, the
summary attribute allows authors to give longer descriptions of tables.
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HTML 4 Changes
Section B.4 [p.339]
The sentence "You may help search engines by using the LINK element with
rel="start" along with the title attribute, ..." read "You may help search
engines by using the LINK element with rel="begin" along with a TITLE, ..."
The same stands for the companion example.
Section B.5.1 [p.342]
The sentence "This can be altered by setting the width attribute of the TABLE
element." read "This can be altered by setting the width-TABLE attribute of the
TABLE element."
Section B.5.2 [p.344]
The sentence "Rules for handling objects too large for a column apply when the
explicit or implied alignment results in a situation where the data exceeds the
assigned width of the column." read "too large for column". The meaning of the
sentence was unclear since it referred to "rules" governing an error condition;
user agent behavior in error conditions lies outside the scope of the
specification.
Index of attributes [p.363]
The href attribute for the BASE element was marked as deprecated [p.38] . It
is not. However, it is not defined in the Strict DTD either.
The language attribute for the SCRIPT element was not marked as
deprecated [p.38] . It is now, and it is no longer defined in the Strict DTD.
A.2.2 Minor typographical errors that were corrected
Section 2.1.3 [p.20]
"Relative URIs are resolved ..." was "Relative URIsare resolved ...".
Section 2.2.1 [p.21]
The second word "of" was missing in "Despite never receiving consensus in
standards discussions, these drafts led to the adoption of a range of new
features."
Section 3.3.3 [p.32]
The sentence "Element types that are designed to have no content are called
empty elements." contained one too many "elements". The word "a" was
missing in the sentence "A few HTML element types use an additional SGML
feature to exclude elements from a content model".
Also, in list item two, a period was missing between "optional" and "Two".
Section 3.3.4 [p.34]
In the section on "Boolean attributes", the sentence that begins "In HTML,
boolean attributes may appear in minimized ..." included a bogus word "be".
Section 6.3 [p.50]
The sentence beginning "For introductory information about attributes, ..." read
"For introductory about attributes, ...".
Section 6.6 [p.52]
In the first sentence of the section on Pixels, "is an integer" read "is integer".
325
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Section 7.4.1 [p.62]
The first word "The" was missing at the beginning of the section title.
Section 7.4.4 [p.64]
The last word "a" was missing in the sentence "The meaning of a property and
the set of legal values for that property should be defined in a reference lexicon
called profile."
Section 7.5.2 [p.71]
"Variable déclarée deux fois" read "Variable déclaré deux fois".
Section 9.2.2 [p.92]
The language of the quotations was "en" instead of "en-us", while in British
English, the single quotation marks would delimit the outer quotation.
Section 9.3.2 [p.95]
In the first line, the sixth character of "&#x000A" was the letter ’O’ instead of a
zero.
Section 10.3.1 [p.108]
"(they are case-sensitive)" read "(the are case-sensitive)".
Section 12.1.1 [p.145]
In the sentence beginning "Note that the href attribute in each source ..." the
space was missing between "href" and "attribute".
Section 12.1.2 [p.147]
The sentence "Links that express other types of relationships have one or more
link types specified in their source anchors." read "Links that express other
types of relationships have one or more link type specified in their source
anchor."
Section 12.1.5 [p.148]
The second paragraph reads "the hreflang attribute provides user agents about
the language of a ..." It should read "the hreflang attribute provides user agents
with information about the language of a ..."
Section 13.3.2 [p.167]
In the sentence beginning "Any number of PARAM elements may appear in the
content of an OBJECT or APPLET element, ..." a space was missing between
"APPLET" and "element".
Section 14.2.2 [p.186]
There was a bogus word "style" at the beginning of the sentence "The style
attribute specifies ..."
Section 17.2 [p.220]
In "Those controls for which name/value pairs are submitted are called
successful controls" the word "for" was missing.
Section 17.10 [p.239]
There was a bogus word "/samp" just before section 17.11.
Section 17.11 [p.241]
The first sentence read, "In an HTML document, an element must receive focus
from the user in order to become active and perform their tasks" (instead of "its"
tasks).
Section 18.2.2 [p.253]
Just before section 18.2.3, the sentence that includes "a name attribute takes
24 Dec 1999 18:26
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HTML 4 Changes
precedence over an id if both are set." read "over a id if both are set.".
Section 19.1 [p.261]
The section title read "document Document Validation". It now is "Document
Validation".
Section 21 [p.265]
The FPI for the Transitional HTML 4.0 DTD was missing a closing double quote.
Section B.5.1/B.5.2 [p.342]
This sections referred to a non-existent cols attribute. This attribute is not part
of HTML 4.0. Calculating the number of columns in a table is described in
section Section 11.2.4.3 [p.121] , in the chapter on tables. In sections B.5.1 and
B.5.2, occurrences of cols have been replaced by "the number of columns
specified by the COL and COLGROUP elements".
Section B.5.2 [p.344]
In the sentence "The values for the frame attribute have been chosen to avoid
clashes with the rules, align and valign attributes." a space was missing
between "the" and "frame" and the last attribute was "valign-COLGROUP".
Section B.10.1 [p.350]
The last sentence read "Once a file is uploaded, the processing agent should
process and store the it appropriately." "the it" was changed to "it".
Index of Elements [p.359]
"strike-through" in the description of the S element read "sstrike-through".
A.3 Changes between HTML 3.2 and HTML 4.0 (18
December 1997)
This section describes how the 18 December 1997 specification of HTML 4.0 differs
from HTML 3.2 ([HTML32] [p.356] ).
A.3.1 Changes to elements
New elements
The new elements in HTML 4.0 are: ABBR, ACRONYM, BDO, BUTTON, COL,
COLGROUP, DEL, FIELDSET, FRAME, FRAMESET, IFRAME, INS, LABEL, LEGEND,
NOFRAMES, NOSCRIPT, OBJECT, OPTGROUP, PARAM, S (deprecated), SPAN, TBODY,
TFOOT, THEAD, and Q.
Deprecated elements
The following elements are deprecated [p.38] : APPLET, BASEFONT, CENTER, DIR,
FONT, ISINDEX, MENU, S, STRIKE, and U.
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Obsolete elements
The following elements are obsolete: LISTING, PLAINTEXT, and XMP. For all of
them, authors should use the PRE element instead.
A.3.2 Changes to attributes
Almost all attributes that specify the presentation of an HTML document (e.g.,
colors, alignment, fonts, graphics, etc.) have been deprecated [p.38] in favor of
style sheets. The list of attributes [p.363] in the appendix indicates which
attributes have been deprecated [p.38] .
The id and class attribute allow authors to assign name and class information
[p.71] to elements for style sheets, as anchors, for scripting, for object
declarations, general purpose document processing, etc.
A.3.3 Changes for accessibility
HTML 4.0 features many changes to promote accessibility [p.22] , including:
The title attribute may now be set on virtually every element.
Authors may provide long descriptions of tables (see the summary attribute),
images and frames (see the longdesc attribute).
A.3.4 Changes for meta data
Authors may now specify profiles [p.68] that provide explanations about meta data
specified with the META or LINK elements.
A.3.5 Changes for text
New features for internationalization [p.330] allow authors to specify text
direction and language.
The INS and DEL elements allow authors to mark up changes in their
documents.
The ABBR and ACRONYM elements allow authors to mark up abbreviations and
acronyms in their documents.
A.3.6 Changes for links
The id attribute makes any element the destination anchor of a link.
A.3.7 Changes for tables
The HTML 4.0 table model has grown out of early work on HTML+ and the initial
draft of HTML3.0 [p.355] . The earlier model has been extended in response to
requests from information providers as follows:
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HTML 4 Changes
Authors may specify tables that may be incrementally displayed as the user
agent receives data.
Authors may specify tables that are more accessible to users with non-visual
user agents.
Authors may specify tables with fixed headers and footers. User agents may
take advantage of these when scrolling large tables or rendering tables to paged
media.
The HTML 4.0 table model also satisfies requests for optional column-based
defaults for alignment properties, more flexibility in specifying table frames and rules,
and the ability to align on designated characters. It is expected, however, that style
sheets [p.183] will take over the task of rendering tables in the near future.
In addition, a major goal has been to provide backwards compatibility with the
widely deployed Netscape implementation of tables. Another goal has been to
simplify importing tables conforming to the SGML CALS model. The latest draft
makes the align attribute compatible with the latest versions of the most popular
browsers. Some clarifications have been made to the role of the dir attribute and
recommended behavior when absolute and relative column widths are mixed.
A new element, COLGROUP, has been introduced to allow sets of columns to be
grouped with different width and alignment properties specified by one or more COL
elements. The semantics of COLGROUP have been clarified over previous drafts, and
rules="basic" has been replaced by rules="groups".
The style attribute is included as a means for extending the properties
associated with edges and interiors of groups of cells. For instance, the line style:
dotted, double, thin/thick etc; the color/pattern fill for the interior; cell margins and
font information. This will be the subject for a companion specification on style
sheets.
The frame and rules attributes have been modified to avoid SGML name
clashes with each other, and to avoid clashes with the align and valign
attributes. These changes were additionally motivated by the desire to avoid future
problems if this specification is extended to allow frame and rules attributes with
other table elements.
A.3.8 Changes for images, objects, and image maps
The OBJECT element allows generic inclusion of objects.
The IFRAME and OBJECT elements allow authors to create embedded
documents.
The alt attribute is required on the IMG and AREA elements.
The mechanism for creating image maps [p.173] now allows authors to create
more accessible image maps. The content model of the MAP element has
changed for this reason.
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A.3.9 Changes for forms
This specification introduces several new attributes and elements that affect forms:
The accesskey attribute allows authors to specify direct keyboard access to
form controls.
The disabled attribute allows authors to make a form control initially
insensitive.
The readonly attribute, allows authors to prohibit changes to a form control.
The LABEL element associates a label with a particular form control.
The FIELDSET element groups related fields together and, in association with
the LEGEND element, can be used to name the group. Both of these new
elements allow better rendering and better interactivity. Speech-based browsers
can better describe the form and graphic browsers can make labels sensitive.
A new set of attributes, in combination with scripts [p.251] , allow form providers
to verify user-entered data.
The BUTTON element and INPUT with type set to "button" can be used in
combination with scripts [p.251] to create richer forms.
The OPTGROUP element allows authors to group menu options together in a
SELECT, which is particularly important for form accessibility.
Additional changes for internationalization [p.330] .
A.3.10 Changes for style sheets
HTML 4.0 supports a larger set of media descriptors [p.56] so that authors may write
device-sensitive style sheets.
A.3.11 Changes for frames
HTML 4.0 supports frame documents and inline frames.
A.3.12 Changes for scripting
Many elements now feature event attributes [p.254] that may be coupled with scripts;
the script is executed when the event occurs (e.g., when a document is loaded,
when the mouse is clicked, etc.).
A.3.13 Changes for internationalization
HTML 4.0 integrates the recommendations of [RFC2070] [p.356] for the
internationalization of HTML.
However, this specification and [RFC2070] [p.356] differ as follows:
The accept-charset attribute has been specified for the FORM element rather
than the TEXTAREA and INPUT elements.
The HTML 4.0 specification makes additional clarifications with respect to the
24 Dec 1999 18:26
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HTML 4 Changes
bidirectional algorithm [p.82] .
The use of CDATA [p.50] to define the SCRIPT and STYLE elements does not
preserve the ability to transcode documents, as described in section 2.1 of
[RFC2070] [p.356] .
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Performance, Implementation, and Design Notes
Appendix B: Performance, Implementation, and
Design Notes
Contents
1. Notes on invalid documents .
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2. Special characters in URI attribute values
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1. Non-ASCII characters in URI attribute values
2. Ampersands in URI attribute values .
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3. SGML implementation notes .
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1. Line breaks .
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2. Specifying non-HTML data .
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Element content
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Attribute values .
3. SGML features with limited support .
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4. Boolean attributes .
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5. Marked Sections
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6. Processing Instructions .
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7. Shorthand markup .
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4. Notes on helping search engines index your Web site
1. Search robots .
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The robots.txt file .
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Robots and the META element .
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5. Notes on tables .
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1. Design rationale
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Dynamic reformatting .
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Incremental display .
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Structure and presentation .
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Row and column groups
Accessibility
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2. Recommended Layout Algorithms .
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Fixed Layout Algorithm .
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Autolayout Algorithm
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6. Notes on forms .
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1. Incremental display .
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2. Future projects .
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7. Notes on scripting
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1. Reserved syntax for future script macros
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Current Practice for Script Macros .
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8. Notes on frames
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9. Notes on accessibility
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10. Notes on security
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1. Security issues for forms
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24 Dec 1999 18:26
Performance, Implementation, and Design Notes
The following notes are informative, not normative. Despite the appearance of
words such as "must" and "should", all requirements in this section appear
elsewhere in the specification.
B.1 Notes on invalid documents
This specification does not define how conforming user agents handle general error
conditions, including how user agents behave when they encounter elements,
attributes, attribute values, or entities not specified in this document.
However, to facilitate experimentation and interoperability between
implementations of various versions of HTML, we recommend the following
behavior:
If a user agent encounters an element it does not recognize, it should try to
render the element’s content.
If a user agent encounters an attribute it does not recognize, it should ignore the
entire attribute specification (i.e., the attribute and its value).
If a user agent encounters an attribute value it doesn’t recognize, it should use
the default attribute value.
If it encounters an undeclared entity, the entity should be treated as character
data.
We also recommend that user agents provide support for notifying the user of
such errors.
Since user agents may vary in how they handle error conditions, authors and
users must not rely on specific error recovery behavior.
The HTML 2.0 specification ([RFC1866] [p.356] ) observes that many HTML 2.0
user agents assume that a document that does not begin with a document type
declaration refers to the HTML 2.0 specification. As experience shows that this is a
poor assumption, the current specification does not recommend this behavior.
For reasons of interoperability, authors must not "extend" HTML through the
available SGML mechanisms (e.g., extending the DTD, adding a new set of entity
definitions, etc.).
B.2 Special characters in URI attribute values
B.2.1 Non-ASCII characters in URI attribute values
Although URIs do not contain non-ASCII values (see [URI] [p.355] , section 2.1)
authors sometimes specify them in attribute values expecting URIs (i.e., defined with
%URI; [p.266] in the DTD [p.265] ). For instance, the following href value is illegal:
<A href="http://foo.org/Håkon">...</A>
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Performance, Implementation, and Design Notes
We recommend that user agents adopt the following convention for handling
non-ASCII characters in such cases:
1. Represent each character in UTF-8 (see [RFC2279] [p.354] ) as one or more
bytes.
2. Escape these bytes with the URI escaping mechanism (i.e., by converting each
byte to %HH, where HH is the hexadecimal notation of the byte value).
This procedure results in a syntactically legal URI (as defined in [RFC1738]
[p.354] , section 2.2 or [RFC2141] [p.354] , section 2) that is independent of the
character encoding [p.41] to which the HTML document carrying the URI may have
been transcoded.
Note. Some older user agents trivially process URIs in HTML using the bytes of
the character encoding [p.41] in which the document was received. Some older
HTML documents rely on this practice and break when transcoded. User agents that
want to handle these older documents should, on receiving a URI containing
characters outside the legal set, first use the conversion based on UTF-8. Only if the
resulting URI does not resolve should they try constructing a URI based on the bytes
of the character encoding [p.41] in which the document was received.
Note. The same conversion based on UTF-8 should be applied to values of the
name attribute for the A element.
B.2.2 Ampersands in URI attribute values
The URI that is constructed when a form is submitted [p.245] may be used as an
anchor-style link (e.g., the href attribute for the A element). Unfortunately, the use
of the "&" character to separate form fields interacts with its use in SGML attribute
values to delimit character entity references [p.30] . For example, to use the URI
"http://host/?x=1&y=2" as a linking URI, it must be written <A
href="http://host/?x=1&#38;y=2"> or <A href="http://host/?x=1&amp;y=2">.
We recommend that HTTP server implementors, and in particular, CGI
implementors support the use of ";" in place of "&" to save authors the trouble of
escaping "&" characters in this manner.
B.3 SGML implementation notes
B.3.1 Line breaks
SGML (see [ISO8879] [p.353] , section 7.6.1) specifies that a line break immediately
following a start tag must be ignored, as must a line break immediately before an
end tag. This applies to all HTML elements without exception.
The following two HTML examples must be rendered identically:
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Performance, Implementation, and Design Notes
<P>Thomas is watching TV.</P>
<P>
Thomas is watching TV.
</P>
So must the following two examples:
<A>My favorite Website</A>
<A>
My favorite Website
</A>
B.3.2 Specifying non-HTML data
Script [p.251] and style [p.183] data may appear as element content or attribute
values. The following sections describe the boundary between HTML markup and
foreign data.
Note. The DTD [p.265] defines script and style data to be CDATA for both element
content and attribute values. SGML rules do not allow character references [p.45] in
CDATA element content but do allow them in CDATA attribute values. Authors
should pay particular attention when cutting and pasting script and style data
between element content and attribute values.
This asymmetry also means that when transcoding from a richer to a poorer
character encoding, the transcoder cannot simply replace unconvertible characters
in script or style data with the corresponding numeric character references; it must
parse the HTML document and know about each script and style language’s syntax
in order to process the data correctly.
Element content
When script or style data is the content of an element (SCRIPT and STYLE), the data
begins immediately after the element start tag and ends at the first ETAGO ("</")
delimiter followed by a name start character ([a-zA-Z]); note that this may not be the
element’s end tag. Authors should therefore escape "</" within the content. Escape
mechanisms are specific to each scripting or style sheet language.
ILLEGAL EXAMPLE:
The following script data incorrectly contains a "</" sequence (as part of "</EM>")
before the SCRIPT end tag:
<SCRIPT type="text/javascript">
document.write ("<EM>This won’t work</EM>")
</SCRIPT>
In JavaScript, this code can be expressed legally by hiding the ETAGO delimiter
before an SGML name start character:
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Performance, Implementation, and Design Notes
<SCRIPT type="text/javascript">
document.write ("<EM>This will work<\/EM>")
</SCRIPT>
In Tcl, one may accomplish this as follows:
<SCRIPT type="text/tcl">
document write "<EM>This will work<\/EM>"
</SCRIPT>
In VBScript, the problem may be avoided with the Chr() function:
"<EM>This will work<" & Chr(47) & "EM>"
Attribute values
When script or style data is the value of an attribute (either style or the intrinsic
event [p.254] attributes), authors should escape occurrences of the delimiting single
or double quotation mark within the value according to the script or style language
convention. Authors should also escape occurrences of "&" if the "&" is not meant to
be the beginning of a character reference [p.45] .
’"’ should be written as "&quot;" or "&#34;"
’&’ should be written as "&amp;" or "&#38;"
Thus, for example, one could write:
<INPUT name="num" value="0"
onchange="if (compare(this.value, &quot;help&quot;)) {gethelp()}">
B.3.3 SGML features with limited support
SGML systems conforming to [ISO8879] [p.353] are expected to recognize a number
of features that aren’t widely supported by HTML user agents. We recommend that
authors avoid using all of these features.
B.3.4 Boolean attributes
Authors should be aware that many user agents only recognize the minimized form
of boolean attributes and not the full form.
For instance, authors may want to specify:
<OPTION selected>
instead of
<OPTION selected="selected">
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Performance, Implementation, and Design Notes
B.3.5 Marked Sections
Marked sections play a role similar to the #ifdef construct recognized by C
preprocessors.
<![INCLUDE[
<!-- this will be included -->
]]>
<![IGNORE[
<!-- this will be ignored -->
]]>
SGML also defines the use of marked sections for CDATA content, within which
"<" is not treated as the start of a tag, e.g.,
<![CDATA[
<an> example of <sgml> markup that is
not <painful> to write with < and such.
]]>
The telltale sign that a user agent doesn’t recognize a marked section is the
appearance of "]]>", which is seen when the user agent mistakenly uses the first ">"
character as the end of the tag starting with "<![".
B.3.6 Processing Instructions
Processing instructions are a mechanism to capture platform-specific idioms. A
processing instruction begins with <? and ends with >
<?instruction >
For example:
<?>
<?style tt = font courier>
<?page break>
<?experiment> ... <?/experiment>
Authors should be aware that many user agents render processing instructions as
part of the document’s text.
B.3.7 Shorthand markup
Some SGML SHORTTAG constructs save typing but add no expressive capability to
the SGML application. Although these constructs technically introduce no ambiguity,
they reduce the robustness of documents, especially when the language is
enhanced to include new elements. Thus, while SHORTTAG constructs of SGML
related to attributes are widely used and implemented, those related to elements are
not. Documents that use them are conforming SGML documents, but are unlikely to
work with many existing HTML tools.
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Performance, Implementation, and Design Notes
The SHORTTAG constructs in question are the following:
NET tags:
<name/.../
closed Start Tag:
<name1<name2>
Empty Start Tag:
<>
Empty End Tag:
</>
B.4 Notes on helping search engines index your Web
site
This section provides some simple suggestions that will make your documents more
accessible to search engines.
Define the document language
In the global context of the Web it is important to know which human language a
page was written in. This is discussed in the section on language information
[p.79] .
Specify language variants of this document
If you have prepared translations of this document into other languages, you
should use the LINK element to reference these. This allows an indexing engine
to offer users search results in the user’s preferred language, regardless of how
the query was written. For instance, the following links offer French and German
alternatives to a search engine:
<LINK rel="alternate"
type="text/html"
href="mydoc-fr.html" hreflang="fr"
lang="fr" title="La vie souterraine">
<LINK rel="alternate"
type="text/html"
href="mydoc-de.html" hreflang="de"
lang="de" title="Das Leben im Untergrund">
Provide keywords and descriptions
Some indexing engines look for META elements that define a comma-separated
list of keywords/phrases, or that give a short description. Search engines may
present these keywords as the result of a search. The value of the name
attribute sought by a search engine is not defined by this specification. Consider
these examples,
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<META name="keywords" content="vacation,Greece,sunshine">
<META name="description" content="Idyllic European vacations">
Indicate the beginning of a collection
Collections of word processing documents or presentations are frequently
translated into collections of HTML documents. It is helpful for search results to
reference the beginning of the collection in addition to the page hit by the
search. You may help search engines by using the LINK element with
rel="start" along with the title attribute, as in:
<LINK rel="start"
type="text/html"
href="page1.html"
title="General Theory of Relativity">
Provide robots with indexing instructions
People may be surprised to find that their site has been indexed by an indexing
robot and that the robot should not have been permitted to visit a sensitive part
of the site. Many Web robots offer facilities for Web site administrators and
content providers to limit what the robot does. This is achieved through two
mechanisms: a "robots.txt" file and the META element in HTML documents,
described below.
B.4.1 Search robots
The robots.txt file
When a Robot visits a Web site, say http://www.foobar.com/, it firsts checks for
http://www.foobar.com/robots.txt. If it can find this document, it will analyze its
contents to see if it is allowed to retrieve the document. You can customize the
robots.txt file to apply only to specific robots, and to disallow access to specific
directories or files.
Here is a sample robots.txt file that prevents all robots from visiting the entire site
User-agent: *
Disallow: /
# applies to all robots
# disallow indexing of all pages
The Robot will simply look for a "/robots.txt" URI on your site, where a site is
defined as a HTTP server running on a particular host and port number. Here are
some sample locations for robots.txt:
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Performance, Implementation, and Design Notes
Site URI
URI for robots.txt
http://www.w3.org/
http://www.w3.org/robots.txt
http://www.w3.org:80/
http://www.w3.org:80/robots.txt
http://www.w3.org:1234/
http://www.w3.org:1234/robots.txt
http://w3.org/
http://w3.org/robots.txt
There can only be a single "/robots.txt" on a site. Specifically, you should not put
"robots.txt" files in user directories, because a robot will never look at them. If you
want your users to be able to create their own "robots.txt", you will need to merge
them all into a single "/robots.txt". If you don’t want to do this your users might want
to use the Robots META Tag instead.
Some tips: URI’s are case-sensitive, and "/robots.txt" string must be all
lower-case. Blank lines are not permitted within a single record in the "robots.txt" file.
There must be exactly one "User-agent" field per record. The robot should be
liberal in interpreting this field. A case-insensitive substring match of the name
without version information is recommended.
If the value is "*", the record describes the default access policy for any robot that
has not matched any of the other records. It is not allowed to have multiple such
records in the "/robots.txt" file.
The "Disallow" field specifies a partial URI that is not to be visited. This can be a
full path, or a partial path; any URI that starts with this value will not be retrieved. For
example,
Disallow: /help disallows both /help.html and /help/index.html, whereas
Disallow: /help/ would disallow /help/index.html but allow /help.html.
An empty value for "Disallow", indicates that all URIs can be retrieved. At least
one "Disallow" field must be present in the robots.txt file.
Robots and the META element
The META element allows HTML authors to tell visiting robots whether a document
may be indexed, or used to harvest more links. No server administrator action is
required.
In the following example a robot should neither index this document, nor analyze it
for links.
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<META name="ROBOTS" content="NOINDEX, NOFOLLOW">
The list of terms in the content is ALL, INDEX, NOFOLLOW, NOINDEX.
Note. In early 1997 only a few robots implement this, but this is expected to
change as more public attention is given to controlling indexing robots.
B.5 Notes on tables
B.5.1 Design rationale
The HTML table model has evolved from studies of existing SGML tables models,
the treatment of tables in common word processing packages, and a wide range of
tabular layout techniques in magazines, books and other paper-based documents.
The model was chosen to allow simple tables to be expressed simply with extra
complexity available when needed. This makes it practical to create the markup for
HTML tables with everyday text editors and reduces the learning curve for getting
started. This feature has been very important to the success of HTML to date.
Increasingly, people are creating tables by converting from other document
formats or by creating them directly with WYSIWYG editors. It is important that the
HTML table model fit well with these authoring tools. This affects how the cells that
span multiple rows or columns are represented, and how alignment and other
presentation properties are associated with groups of cells.
Dynamic reformatting
A major consideration for the HTML table model is that the author does not control
how a user will size a table, what fonts he or she will use, etc. This makes it risky to
rely on column widths specified in terms of absolute pixel units. Instead, tables must
be able to change sizes dynamically to match the current window size and fonts.
Authors can provide guidance as to the relative widths of columns, but user agents
should ensure that columns are wide enough to render the width of the largest
element of the cell’s content. If the author’s specification must be overridden, relative
widths of individual columns should not be changed drastically.
Incremental display
For large tables or slow network connections, incremental table display is important
to user satisfaction. User agents should be able to begin displaying a table before all
of the data has been received. The default window width for most user agents shows
about 80 characters, and the graphics for many HTML pages are designed with
these defaults in mind. By specifying the number of columns, and including provision
for control of table width and the widths of different columns, authors can give hints
to user agents that allow the incremental display of table contents.
For incremental display, the browser needs the number of columns and their
widths. The default width of the table is the current window size (width="100%").
This can be altered by setting the width attribute of the TABLE element. By default,
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Performance, Implementation, and Design Notes
all columns have the same width, but you can specify column widths with one or
more COL elements before the table data starts.
The remaining issue is the number of columns. Some people have suggested
waiting until the first row of the table has been received, but this could take a long
time if the cells have a lot of content. On the whole it makes more sense, when
incremental display is desired, to get authors to explicitly specify the number of
columns in the TABLE element.
Authors still need a way of telling user agents whether to use incremental display
or to size the table automatically to fit the cell contents. In the two pass auto-sizing
mode, the number of columns is determined by the first pass. In the incremental
mode, the number of columns must be stated up front (with COL or COLGROUP
elements).
Structure and presentation
HTML distinguishes structural markup such as paragraphs and quotations from
rendering idioms such as margins, fonts, colors, etc. How does this distinction affect
tables? From the purist’s point of view, the alignment of text within table cells and the
borders between cells is a rendering issue, not one of structure. In practice, though,
it is useful to group these with the structural information, as these features are highly
portable from one application to the next. The HTML table model leaves most
rendering information to associated style sheets. The model presented in this
specification is designed to take advantage of such style sheets but not to require
them.
Current desktop publishing packages provide very rich control over the rendering
of tables, and it would be impractical to reproduce this in HTML, without making
HTML into a bulky rich text format like RTF or MIF. This specification does, however,
offer authors the ability to choose from a set of commonly used classes of border
styles. The frame attribute controls the appearance of the border frame around the
table while the rules attribute determines the choice of rulings within the table. A
finer level of control will be supported via rendering annotations. The style attribute
can be used for specifying rendering information for individual elements. Further
rendering information can be given with the STYLE element in the document head or
via linked style sheets.
During the development of this specification, a number of avenues were
investigated for specifying the ruling patterns for tables. One issue concerns the
kinds of statements that can be made. Including support for edge subtraction as well
as edge addition leads to relatively complex algorithms. For instance, work on
allowing the full set of table elements to include the frame and rules attributes led
to an algorithm involving some 24 steps to determine whether a particular edge of a
cell should be ruled or not. Even this additional complexity doesn’t provide enough
rendering control to meet the full range of needs for tables. The current specification
deliberately sticks to a simple intuitive model, sufficient for most purposes. Further
experimental work is needed before a more complex approach is standardized.
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Row and column groups
This specification provides a superset of the simpler model presented in earlier work
on HTML+. Tables are considered as being formed from an optional caption together
with a sequence of rows, which in turn consist of a sequence of table cells. The
model further differentiates header and data cells, and allows cells to span multiple
rows and columns.
Following the CALS table model (see [CALS] [p.355] ), this specification allows
table rows to be grouped into head and body and foot sections. This simplifies the
representation of rendering information and can be used to repeat table head and
foot rows when breaking tables across page boundaries, or to provide fixed headers
above a scrollable body panel. In the markup, the foot section is placed before the
body sections. This is an optimization shared with CALS for dealing with very long
tables. It allows the foot to be rendered without having to wait for the entire table to
be processed.
Accessibility
For the visually impaired, HTML offers the hope of setting to rights the damage
caused by the adoption of windows based graphical user interfaces. The HTML table
model includes attributes for labeling each cell, to support high quality text to speech
conversion. The same attributes can also be used to support automated import and
export of table data to databases or spreadsheets.
B.5.2 Recommended Layout Algorithms
If COL or COLGROUP elements are present, they specify the number of columns and
the table may be rendered using a fixed layout. Otherwise the autolayout algorithm
described below should be used.
If the width attribute is not specified, visual user agents should assume a default
value of 100% for formatting.
It is recommended that user agents increase table widths beyond the value
specified by width in cases when cell contents would otherwise overflow. User
agents that override the specified width should do so within reason. User agents
may elect to split words across lines to avoid the need for excessive horizontal
scrolling or when such scrolling is impractical or undesired.
For the purposes of layout, user agents should consider that table captions
(specified by the CAPTION element) behave like cells. Each caption is a cell that
spans all of the table’s columns if at the top or bottom of the table, and rows if at the
left or right side of the table.
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Fixed Layout Algorithm
For this algorithm, it is assumed that the number of columns is known. The column
widths by default should be set to the same size. Authors may override this by
specifying relative or absolute column widths, using the COLGROUP or COL elements.
The default table width is the space between the current left and right margins, but
may be overridden by the width attribute on the TABLE element, or determined
from absolute column widths. To deal with mixtures of absolute and relative column
widths, the first step is to allocate space from the table width to columns with
absolute widths. After this, the space remaining is divided up between the columns
with relative widths.
The table syntax alone is insufficient to guarantee the consistency of attribute
values. For instance, the number of COL and COLGROUP elements may be
inconsistent with the number of columns implied by the table cells. A further problem
occurs when the columns are too narrow to avoid overflow of cell contents. The
width of the table as specified by the TABLE element or COL elements may result in
overflow of cell contents. It is recommended that user agents attempt to recover
gracefully from these situations, e.g., by hyphenating words [p.96] and resorting to
splitting words if hyphenation points are unknown.
In the event that an indivisible element causes cell overflow, the user agent may
consider adjusting column widths and re-rendering the table. In the worst case,
clipping may be considered if column width adjustments and/or scrollable cell
content are not feasible. In any case, if cell content is split or clipped this should be
indicated to the user in an appropriate manner.
Autolayout Algorithm
If the number of columns is not specified with COL and COLGROUP elements, then
the user agent should use the following autolayout algorithm. It uses two passes
through the table data and scales linearly with the size of the table.
In the first pass, line wrapping is disabled, and the user agent keeps track of the
minimum and maximum width of each cell. The maximum width is given by the
widest line. Since line wrap has been disabled, paragraphs are treated as long lines
unless broken by BR elements. The minimum width is given by the widest text
element (word, image, etc.) taking into account leading indents and list bullets, etc.
In other words, it is necessary to determine the minimum width a cell would require
in a window of its own before the cell begins to overflow. Allowing user agents to
split words will minimize the need for horizontal scrolling or in the worst case,
clipping the cell contents.
This process also applies to any nested tables occurring in cell content. The
minimum and maximum widths for cells in nested tables are used to determine the
minimum and maximum widths for these tables and hence for the parent table cell
itself. The algorithm is linear with aggregate cell content, and broadly speaking,
independent of the depth of nesting.
345
24 Dec 1999 18:26
Performance, Implementation, and Design Notes
To cope with character alignment of cell contents, the algorithm keeps three
running min/max totals for each column: Left of align char, right of align char and
unaligned. The minimum width for a column is then: max(min_left +
min_right, min_non-aligned).
The minimum and maximum cell widths are then used to determine the
corresponding minimum and maximum widths for the columns. These in turn, are
used to find the minimum and maximum width for the table. Note that cells can
contain nested tables, but this doesn’t complicate the code significantly. The next
step is to assign column widths according to the available space (i.e., the space
between the current left and right margins).
For cells that span multiple columns, a simple approach consists of apportioning
the min/max widths evenly to each of the constituent columns. A slightly more
complex approach is to use the min/max widths of unspanned cells to weight how
spanned widths are apportioned. Experiments suggest that a blend of the two
approaches gives good results for a wide range of tables.
The table borders and intercell margins need to be included in assigning column
widths. There are three cases:
1. The minimum table width is equal to or wider than the available space. In
this case, assign the minimum widths and allow the user to scroll horizontally.
For conversion to braille, it will be necessary to replace the cells by references
to notes containing their full content. By convention these appear before the
table.
2. The maximum table width fits within the available space. In this case, set
the columns to their maximum widths.
3. The maximum width of the table is greater than the available space, but
the minimum table width is smaller. In this case, find the difference between
the available space and the minimum table width, lets call it W. Lets also call D
the difference between maximum and minimum width of the table.
For each column, let d be the difference between maximum and minimum
width of that column. Now set the column’s width to the minimum width plus d
times W over D. This makes columns with large differences between minimum
and maximum widths wider than columns with smaller differences.
This assignment step is then repeated for nested tables using the minimum and
maximum widths derived for all such tables in the first pass. In this case, the width of
the parent table cell plays the role of the current window size in the above
description. This process is repeated recursively for all nested tables. The topmost
table is then rendered using the assigned widths. Nested tables are subsequently
rendered as part of the parent table’s cell contents.
If the table width is specified with the width attribute, the user agent attempts to
set column widths to match. The width attribute is not binding if this results in
columns having less than their minimum (i.e., indivisible) widths.
24 Dec 1999 18:26
346
Performance, Implementation, and Design Notes
If relative widths are specified with the COL element, the algorithm is modified to
increase column widths over the minimum width to meet the relative width
constraints. The COL elements should be taken as hints only, so columns shouldn’t
be set to less than their minimum width. Similarly, columns shouldn’t be made so
wide that the table stretches well beyond the extent of the window. If a COL element
specifies a relative width of zero, the column should always be set to its minimum
width.
When using the two pass layout algorithm, the default alignment position in the
absence of an explicit or inherited charoff attribute can be determined by choosing
the position that would center lines for which the widths before and after the
alignment character are at the maximum values for any of the lines in the column for
which align="char". For incremental table layout the suggested default is
charoff="50%". If several cells in different rows for the same column use
character alignment, then by default, all such cells should line up, regardless of
which character is used for alignment. Rules for handling objects too large for a
column apply when the explicit or implied alignment results in a situation where the
data exceeds the assigned width of the column.
Choice of attribute names. It would have been preferable to choose values for
the frame attribute consistent with the rules attribute and the values used for
alignment. For instance: none, top, bottom, topbot, left, right,
leftright, all. Unfortunately, SGML requires enumerated attribute values to be
unique for each element, independent of the attribute name. This causes immediate
problems for "none", "left", "right" and "all". The values for the frame attribute have
been chosen to avoid clashes with the rules, align, and valign attributes. This
provides a measure of future proofing, as it is anticipated that the frame and rules
attributes will be added to other table elements in future revisions to this
specification. An alternative would be to make frame a CDATA attribute. The
consensus of the W3C HTML Working Group was that the benefits of being able to
use SGML validation tools to check attributes based on enumerated values
outweighs the need for consistent names.
B.6 Notes on forms
B.6.1 Incremental display
The incremental display of documents being received from the network gives rise to
certain problems with respect to forms. User agents should prevent forms from being
submitted until all of the form’s elements have been received.
The incremental display of documents raises some issues with respect to tabbing
navigation. The heuristic of giving focus to the lowest valued tabindex in the
document seems reasonable enough at first glance. However this implies having to
wait until all of the document’s text is received, since until then, the lowest valued
tabindex may still change. If the user hits the tab key before then, it is reasonable
for user agents to move the focus to the lowest currently available tabindex.
347
24 Dec 1999 18:26
Performance, Implementation, and Design Notes
If forms are associated with client-side scripts, there is further potential for
problems. For instance, a script handler for a given field may refer to a field that
doesn’t yet exist.
B.6.2 Future projects
This specification defines a set of elements and attributes powerful enough to fulfill
the general need for producing forms. However there is still room for many possible
improvements. For instance the following problems could be addressed in the future:
The range of form field types is too limited in comparison with modern user
interfaces. For instance there is no provision for tabular data entry, sliders or
multiple page layouts.
Servers cannot update the fields in a submitted form and instead have to send a
complete HTML document causing screen flicker.
These also cause problems for speech based browsers, making it difficult for
the visually impaired to interact with HTML forms.
Another possible extension would be to add the usemap attribute to INPUT for use
as client-side image map when "type=image". The AREA element corresponding to
the location clicked would contribute the value to be passed to the server. To avoid
the need to modify server scripts, it may be appropriate to extend AREA to provide x
and y values for use with the INPUT element.
B.7 Notes on scripting
B.7.1 Reserved syntax for future script macros
This specification reserves syntax for the future support of script macros in HTML
CDATA attributes. The intention is to allow attributes to be set depending on the
properties of objects that appear earlier on the page. The syntax is:
attribute = "... &{ macro body }; ... "
Current Practice for Script Macros
The macro body is made up of one or more statements in the default scripting
language (as per intrinsic event attributes). The semicolon following the right brace is
always needed, as otherwise the right brace character "}" is treated as being part of
the macro body. Its also worth noting that quote marks are always needed for
attributes containing script macros.
The processing of CDATA attributes proceeds as follows:
1. The SGML parser evaluates any SGML entities (e.g., "&gt;").
2. Next the script macros are evaluated by the script engine.
3. Finally the resultant character string is passed to the application for subsequent
processing.
24 Dec 1999 18:26
348
Performance, Implementation, and Design Notes
Macro processing takes place when the document is loaded (or reloaded) but
does not take place again when the document is resized, repainted, etc.
DEPRECATED EXAMPLE:
Here are some examples using JavaScript. The first one randomizes the document
background color:
<BODY bgcolor=’&{randomrgb};’>
Perhaps you want to dim the background for evening viewing:
<BODY bgcolor=’&{if(Date.getHours > 18)...};’>
The next example uses JavaScript to set the coordinates for a client-side image
map:
<MAP NAME=foo>
<AREA shape="rect" coords="&{myrect(imageuri)};" href="&{myuri};" alt="">
</MAP>
This example sets the size of an image based upon document properties:
<IMG src="bar.gif" width=’&{document.banner.width/2};’ height=’50%’ alt="banner">
You can set the URI for a link or image by script:
<SCRIPT type="text/javascript">
function manufacturer(widget) {
...
}
function location(manufacturer) {
...
}
function logo(manufacturer) {
...
}
</SCRIPT>
<A href=’&{location(manufacturer("widget"))};’>widget</A>
<IMG src=’&{logo(manufacturer("widget"))};’ alt="logo">
This last example shows how SGML CDATA attributes can be quoted using single
or double quote marks. If you use single quotes around the attribute string then you
can include double quote marks as part of the attribute string. Another approach is
use &quot; for double quote marks:
<IMG src="&{logo(manufacturer(&quot;widget&quot;))};" alt="logo">
349
24 Dec 1999 18:26
Performance, Implementation, and Design Notes
B.8 Notes on frames
Since there is no guarantee that a frame target name is unique, it is appropriate to
describe the current practice in finding a frame given a target name:
1. If the target name is a reserved word as described in the normative text, apply it
as described.
2. Otherwise, perform a depth-first search of the frame hierarchy in the window
that contained the link. Use the first frame whose name is an exact match.
3. If no such frame was found in (2), apply step 2 to each window, in a
front-to-back ordering. Stop as soon as you encounter a frame with exactly the
same name.
4. If no such frame was found in (3), create a new window and assign it the target
name.
B.9 Notes on accessibility
The W3C Web Accessibility Initiative ([WAI] [p.357] ) is producing a series of
guidelines to improve Web accessibility for people with disabilities. There are three
sets of guidelines:
Web Content Accessibility Guidelines ([WCGL] [p.357] ), for authors and site
managers. Please consult the Web Content Accessibility Guidelines for
information about supplying alternative text for images, applets, scripts, etc.
User Agent Accessibility Guidelines ([UAGL] [p.357] ), for user agent developers
(browsers, multimedia players, assistive technologies). Please consult these
guidelines for guidance on handling alternate text.
Authoring Tool Accessibility Guidelines ([ATGL] [p.355] ), for authoring tool
developers.
B.10 Notes on security
Anchors, embedded images, and all other elements that contain URIs [p.51] as
parameters may cause the URI to be dereferenced in response to user input. In this
case, the security issues of [RFC1738] [p.354] , section 6, should be considered.
The widely deployed methods for submitting form requests -- HTTP and SMTP -provide little assurance of confidentiality. Information providers who request sensitive
information via forms -- especially with the INPUT element, type="password" -should be aware and make their users aware of the lack of confidentiality.
B.10.1 Security issues for forms
A user agent should not send any file that the user has not explicitly asked to be
sent. Thus, HTML user agents are expected to confirm any default file names that
might be suggested by the value attribute of the INPUT element. Hidden controls
must not specify files.
24 Dec 1999 18:26
350
Performance, Implementation, and Design Notes
This specification does not contain a mechanism for encryption of the data; this
should be handled by whatever other mechanisms are in place for secure
transmission of data.
Once a file is uploaded, the processing agent should process and store it
appropriately.
351
24 Dec 1999 18:26
Performance, Implementation, and Design Notes
24 Dec 1999 18:26
352
HTML 4 Specification References
References
Contents
1. Normative references
2. Informative references
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. 353
.
. 355
.
Normative references
[CSS1]
"Cascading Style Sheets, level 1", H. W. Lie and B. Bos, 17 December 1996.
Revised 11 January 1999. This document is
http://www.w3.org/TR/1999/REC-CSS1-19990111
[DATETIME]
"Date and Time Formats", W3C Note, M. Wolf and C. Wicksteed, 15 September
1997. Revised 27 August 1998. This document is
http://www.w3.org/TR/1998/NOTE-datetime-19980827
[HTML40]
"HTML 4.0 Specification", D. Raggett, A. Le Hors, I. Jacobs. The 24 April 1998
version is http://www.w3.org/TR/1998/REC-html40-19980424. The 24 April
version included editorial changes from the original 18 December 1997
Revision.
[IANA]
"Assigned Numbers", STD 2, RFC 1700, USC/ISI, J. Reynolds and J. Postel,
October 1994.
[ISO639]
"Codes for the representation of names of languages", ISO 639:1988. For more
information, consult http://www.iso.ch/cate/d4766.html. Refer also to
http://www.oasis-open.org/cover/iso639a.html.
[ISO3166]
"Codes for the representation of names of countries", ISO 3166:1993.
[ISO8601]
"Data elements and interchange formats -- Information interchange -Representation of dates and times", ISO 8601:1988.
[ISO8879]
"Information Processing -- Text and Office Systems -- Standard Generalized
Markup Language (SGML)", ISO 8879:1986. Please consult
http://www.iso.ch/cate/d16387.html for information about the standard.
[ISO10646]
"Information Technology -- Universal Multiple-Octet Coded Character Set (UCS)
-- Part 1: Architecture and Basic Multilingual Plane", ISO/IEC 10646-1:1993.
This reference refers to a set of codepoints that may evolve as new characters
are assigned to them. This reference therefore includes future amendments as
long as they do not change character assignments up to and including the first
five amendments to ISO/IEC 10646-1:1993. Also, this reference assumes that
the character sets defined by ISO 10646 and Unicode remain
353
24 Dec 1999 18:26
HTML 4 Specification References
character-by-character equivalent. This reference also includes future
publications of other parts of 10646 (i.e., other than Part 1) that define
characters in planes 1-16.
[ISO88591]
"Information Processing -- 8-bit single-byte coded graphic character sets -- Part
1: Latin alphabet No. 1", ISO 8859-1:1987.
[MIMETYPES]
List of registered content types (MIME types). Download a list of registered
content types from ftp://ftp.isi.edu/in-notes/iana/assignments/media-types/.
[RFC1555]
"Hebrew Character Encoding for Internet Messages", H. Nussbacher and Y.
Bourvine, December 1993.
[RFC1556]
"Handling of Bi-directional Texts in MIME", H. Nussbacher, December 1993.
[RFC1738]
"Uniform Resource Locators", T. Berners-Lee, L. Masinter, and M. McCahill,
December 1994.
[RFC1766]
"Tags for the Identification of Languages", H. Alvestrand, March 1995. RFC1766
is expected to be updated by
http://www.ietf.org/internet-drafts/draft-alvestrand-lang-tags-v2-00.txt, currently a
work in progress.
[RFC1808]
"Relative Uniform Resource Locators", R. Fielding, June 1995.
[RFC2045]
"Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", N. Freed and N. Borenstein, November 1996. Note that this
RFC obsoletes RFC1521, RFC1522, and RFC1590.
[RFC2046]
"Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", N.
Freed and N. Borenstein, November 1996. Note that this RFC obsoletes
RFC1521, RFC1522, and RFC1590.
[RFC2119]
"Key words for use in RFCs to Indicate Requirement Levels", S. Bradner, March
1997.
[RFC2141]
"URN Syntax", R. Moats, May 1997.
[RFC2279]
"UTF-8, a transformation format of ISO 10646", F. Yergeau, January 1998. This
RFC obsoletes RFC 2044.
[RFC2616]
"Hypertext Transfer Protocol -- HTTP/1.1", R. Fielding, J. Gettys, J. Mogul, H.
Frystyk Nielsen, L. Masinter, P. Leach and T. Berners-Lee, June 1999. This
RFC obsoletes RFC 2068.
[SRGB]
"A Standard Default color Space for the Internet", version 1.10, M. Stokes, M.
24 Dec 1999 18:26
354
HTML 4 Specification References
Anderson, S. Chandrasekar, and R. Motta, 5 November 1996. This document is
http://www.w3.org/Graphics/Color/sRGB
[UNICODE]
The Unicode Consortium. "The Unicode Standard, Version 3.0", Reading, MA,
Addison-Wesley Developers Press, 2000. ISBN 0-201-61633-5. Refer also to
http://www.unicode.org/unicode/standard/versions/.
[URI]
"Uniform Resource Identifiers (URI): Generic Syntax", T. Berners-Lee, R.
Fielding, L. Masinter, August 1998. Note that RFC 2396 updates [RFC1738]
[p.354] and [RFC1808] [p.354] .
[WEBSGML]
"Final text of revised TC2 to ISO 8879:1986", C. F. Goldfarb, ed., 6 December
1998.
Informative references
[ATGL]
"Authoring Tool Accessibility Guidelines", J. Treviranus, J. Richards, I. Jacobs,
C. McCathieNevile, eds. The latest Working Draft of these guidelines for
designing accessible authoring tools is available at
http://www.w3.org/TR/WAI-AUTOOLS/
[BRYAN88]
"SGML: An Author’s Guide to the Standard Generalized Markup Language", M.
Bryan, Addison-Wesley Publishing Co., 1988.
[CALS]
Continuous Acquisition and Life-Cycle Support (CALS). CALS is a Department
of Defense strategy for achieving effective creation, exchange, and use of digital
data for weapon systems and equipment. More information can be found on the
CALS home page.
[CHARSETS]
Registered charset values. Download a list of registered charset values from
ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets.
[CSS2]
"Cascading Style Sheets, level 2", B. Bos, H. W. Lie, C. Lilley, and I. Jacobs, 12
May 1998. This document is http://www.w3.org/TR/1998/REC-CSS2-19980512
[DCORE]
The Dublin Core. For more information refer to http://purl.org/dc
[ETHNO]
"Ethnologue, Languages of the World", 12th Edition, Barbara F. Grimes editor,
Summer Institute of Linguistics, October 1992.
[GOLD90]
"The SGML Handbook", C. F. Goldfarb, Clarendon Press, 1991.
[HTML30]
"HyperText Markup Language Specification Version 3.0", D. Raggett,
September 1995. This document is http://www.w3.org/MarkUp/html3/CoverPage
355
24 Dec 1999 18:26
HTML 4 Specification References
[HTML32]
"HTML 3.2 Reference Specification", D. Raggett, 14 January 1997. This
document is http://www.w3.org/TR/REC-html32
[HTML3STYLE]
"HTML and Style Sheets", B. Bos, D. Raggett, and H. Lie, 24 March 1997. This
document is http://www.w3.org/TR/WD-style-970324
[LEXHTML]
"A Lexical Analyzer for HTML and Basic SGML", D. Connolly, 15 June 1996.
This document is http://www.w3.org/TR/WD-sgml-lex-960615
[OASISOPEN]
The Organization for the Advancement of Structured Information Standards
(OASIS): http://www.oasis-open.org/.
[PICS]
Platform for Internet Content (PICS). For more information refer to
http://www.w3.org/PICS/
[RDF10]
"Resource Description Framework (RDF) Model and Syntax Specification", O.
Lassila, R. Swick, eds., 22 February 1999. This document is
http://www.w3.org/TR/1999/REC-rdf-syntax-19990222
[RFC822]
"Standard for the Format of ARPA Internet Text Messages", Revised by David
H. Crocker, August 1982.
[RFC850]
"Standard for Interchange of USENET Messages", M. Horton, June 1983.
[RFC1468]
"Japanese Character Encoding for Internet Messages", J. Murai, M. Crispin, and
E. van der Poel, June 1993.
[RFC1630]
"Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression
of Names and Addresses of Objects on the Network as used in the World-Wide
Web", T. Berners-Lee, June 1994.
[RFC1866]
"HyperText Markup Language 2.0", T. Berners-Lee and D. Connolly, November
1995.
[RFC1942]
"HTML Tables", Dave Raggett, May 1996.
[RFC2048]
"Multipurpose Internet Mail Extensions (MIME) Part Four: Registration
Procedures", N. Freed, J. Klensin, and J. Postel, November 1996. Note that this
RFC obsoletes RFC1521, RFC1522, and RFC1590.
[RFC2070]
"Internationalization of the HyperText Markup Language", F. Yergeau, G. Nicol,
G. Adams, and M. Dürst, January 1997.
[RFC2388]
"Returning Values from Forms: multipart/form-data", L. Masinter, August 1998.
Refer also to RFC 1867, "Form-based File Upload in HTML", E. Nebel and L.
24 Dec 1999 18:26
356
HTML 4 Specification References
Masinter, November 1995.
[SP]
SP is a public domain SGML parser. Further information is available at
http://www.jclark.com/sp/index.htm.
[SQ91]
"The SGML Primer", 3rd Edition, SoftQuad Inc., 1991.
[TAKADA]
"Multilingual Information Exchange through the World-Wide Web", Toshihiro
Takada, Computer Networks and ISDN Systems, Vol. 27, No. 2, pp. 235-241,
November 1994.
[UAGL]
"User Agent Accessibility Guidelines", J. Gunderson and I. Jacobs, eds. The
latest Working Draft of these guidelines for designing accessible user agents is
available at http://www.w3.org/TR/WAI-USERAGENT.
[WAI]
Guidelines for designing accessible HTML documents are available at the Web
Accessibility Initiative (WAI) Web site: http://www.w3.org/WAI/.
[WCGL]
"Web Content Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden, and
I. Jacobs, eds., 5 May 1999. This document is
http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505.
[VANH90]
"Practical SGML", E. van Herwijnen, Kluwer Academic Publishers Group,
Norwell and Dordrecht, 1990.
[XHTML]
"XHTML[tm] 1.0: The Extensible HyperText Markup Language", S. Pemberton
et al. The latest version of this specification is available at
http://www.w3.org/TR/xhtml1. As of the publication of the current document,
XHTML 1.0 is a W3C Proposed Recommendation.
357
24 Dec 1999 18:26
HTML 4 Specification References
24 Dec 1999 18:26
358
Index of the HTML 4 Elements
Index of Elements
Legend: Optional, Forbidden, Empty, Deprecated, Loose DTD, Frameset DTD
Name
Start
Tag
End
Empty Depr. DTD
Tag
A [p.149]
Description
anchor
abbreviated form (e.g.,
WWW, HTTP, etc.)
ABBR [p.90]
ACRONYM
[p.90]
ADDRESS
[p.76]
information on author
APPLET [p.171]
D
AREA [p.174]
F
L
E
Java applet
client-side image map area
B [p.199]
bold text style
BASE [p.157]
F
E
BASEFONT
[p.200]
F
E
document base URI
D
L
base font size
BDO [p.85]
I18N BiDi over-ride
BIG [p.199]
large text style
BLOCKQUOTE
[p.92]
long quotation
BODY [p.69]
BR [p.96]
O
O
F
document body
E
forced line break
BUTTON [p.228]
push button
CAPTION
[p.115]
table caption
CENTER [p.197]
CITE [p.90]
CODE [p.90]
359
D
L
shorthand for DIV
align=center
citation
computer code fragment
24 Dec 1999 18:26
Index of the HTML 4 Elements
COL [p.120]
F
E
table column
COLGROUP
[p.118]
O
table column group
DD [p.106]
O
definition description
DEL [p.99]
deleted text
DFN [p.90]
instance definition
DIR [p.109]
D
L
directory list
DIV [p.73]
generic language/style
container
DL [p.106]
definition list
DT [p.106]
O
definition term
EM [p.90]
emphasis
FIELDSET
[p.239]
form control group
FONT [p.200]
D
L
FORM [p.222]
local change to font
interactive form
FRAME [p.209]
F
E
FRAMESET
[p.206]
F
subwindow
F
window subdivision
H1 [p.75]
heading
H2 [p.75]
heading
H3 [p.75]
heading
H4 [p.75]
heading
H5 [p.75]
heading
H6 [p.75]
heading
HEAD [p.62]
O
HR [p.202]
HTML [p.61]
O
F
O
document head
E
horizontal rule
O
document root element
I [p.199]
IFRAME [p.217]
24 Dec 1999 18:26
italic text style
L
inline subwindow
360
Index of the HTML 4 Elements
IMG [p.160]
F
E
Embedded image
INPUT [p.224]
F
E
form control
INS [p.99]
ISINDEX [p.236]
inserted text
F
E
D
L
text to be entered by the
user
KBD [p.90]
LABEL [p.237]
form field label text
fieldset legend
LEGEND [p.239]
LI [p.105]
O
LINK [p.154]
F
list item
E
a media-independent link
MAP [p.174]
client-side image map
MENU [p.109]
META [p.65]
single line prompt
D
F
L
E
menu list
generic metainformation
NOFRAMES
[p.214]
F
alternate content container
for non frame-based
rendering
alternate content container
for non script-based
rendering
NOSCRIPT
[p.258]
generic embedded object
OBJECT [p.162]
OL [p.104]
ordered list
OPTGROUP
[p.230]
option group
OPTION [p.230]
O
selectable choice
P [p.95]
O
paragraph
PARAM [p.167]
F
E
named property value
PRE [p.97]
preformatted text
Q [p.92]
S [p.199]
SAMP [p.90]
361
short inline quotation
D
L
strike-through text style
sample program output,
scripts, etc.
24 Dec 1999 18:26
Index of the HTML 4 Elements
SCRIPT [p.252]
script statements
SELECT [p.230]
option selector
SMALL [p.199]
small text style
generic language/style
container
SPAN [p.73]
STRIKE [p.199]
D
L
strike-through text
STRONG [p.90]
strong emphasis
STYLE [p.187]
style info
SUB [p.94]
subscript
SUP [p.94]
superscript
TABLE [p.113]
TBODY [p.116]
TD [p.125]
O
O
table body
O
table data cell
TEXTAREA
[p.234]
multi-line text field
TFOOT [p.116]
O
table footer
TH [p.125]
O
table header cell
THEAD [p.116]
O
table header
TITLE [p.62]
TR [p.124]
document title
O
table row
teletype or monospaced
text style
TT [p.199]
U [p.199]
D
L
underlined text style
UL [p.104]
unordered list
VAR [p.90]
instance of a variable or
program argument
24 Dec 1999 18:26
362
Index of the HTML 4 Attributes
Index of Attributes
Legend: Deprecated, Loose DTD, Frameset DTD
Related
Elements
Type
Default
abbr [p.126]
TD, TH
%Text; [p.266]
#IMPLIED
abbreviation for
header cell
accept-charset
[p.223]
FORM
%Charsets;
[p.266]
#IMPLIED
list of supported
charsets
accept [p.223]
FORM, INPUT
%ContentTypes;
[p.266]
#IMPLIED
list of MIME types
for file upload
accesskey
[p.242]
A, AREA,
BUTTON,
INPUT, LABEL,
LEGEND,
TEXTAREA
%Character;
[p.266]
#IMPLIED
accessibility key
character
action [p.223]
FORM
%URI; [p.266]
#REQUIRED
server-side form
handler
align [p.115]
CAPTION
%CAlign; [p.292]
#IMPLIED
D
L
relative to table
align [p.180]
APPLET,
IFRAME, IMG,
INPUT,
OBJECT
%IAlign; [p.285]
#IMPLIED
D
L
vertical or
horizontal
alignment
align [p.239]
LEGEND
%LAlign; [p.290]
#IMPLIED
D
L
relative to fieldset
align [p.113]
TABLE
%TAlign; [p.291]
#IMPLIED
D
L
table position
relative to window
align [p.202]
HR
(left | center |
right)
#IMPLIED
D
L
align [p.196]
DIV, H1, H2,
H3, H4, H5, H6,
P
(left | center |
right | justify)
#IMPLIED
D
L
align, text
alignment
align [p.132]
COL,
COLGROUP,
TBODY, TD,
TFOOT, TH,
THEAD, TR
(left | center |
right | justify |
char)
#IMPLIED
alink [p.69]
BODY
%Color; [p.281]
#IMPLIED
D
L
color of selected
links
alt [p.181]
APPLET
%Text; [p.281]
#IMPLIED
D
L
short description
alt [p.181]
AREA, IMG
%Text; [p.266]
#REQUIRED
short description
alt [p.181]
INPUT
CDATA [p.50]
#IMPLIED
short description
archive [p.171]
APPLET
CDATA [p.50]
#IMPLIED
archive [p.163]
OBJECT
CDATA [p.50]
#IMPLIED
Name
363
Depr. DTD
D
L
Comment
comma-separated
archive list
space-separated
list of URIs
24 Dec 1999 18:26
Index of the HTML 4 Attributes
comma-separated
list of related
headers
axis [p.126]
TD, TH
CDATA [p.50]
#IMPLIED
background
[p.69]
BODY
%URI; [p.280]
#IMPLIED
D
L
texture tile for
document
background
bgcolor
[p.195]
TABLE
%Color; [p.281]
#IMPLIED
D
L
background color
for cells
bgcolor
[p.195]
TR
%Color; [p.281]
#IMPLIED
D
L
background color
for row
bgcolor
[p.195]
TD, TH
%Color; [p.281]
#IMPLIED
D
L
cell background
color
bgcolor
[p.195]
BODY
%Color; [p.281]
#IMPLIED
D
L
document
background color
border [p.130]
TABLE
%Pixels; [p.270]
#IMPLIED
border [p.180]
IMG, OBJECT
%Pixels; [p.285]
#IMPLIED
cellpadding
[p.135]
TABLE
%Length; [p.270]
#IMPLIED
spacing within
cells
cellspacing
[p.134]
TABLE
%Length; [p.270]
#IMPLIED
spacing between
cells
char [p.132]
COL,
COLGROUP,
TBODY, TD,
TFOOT, TH,
THEAD, TR
%Character;
[p.266]
#IMPLIED
alignment char,
e.g. char=’:’
charoff [p.133]
COL,
COLGROUP,
TBODY, TD,
TFOOT, TH,
THEAD, TR
%Length; [p.270]
#IMPLIED
offset for
alignment char
charset
[p.150]
A, LINK,
SCRIPT
%Charset; [p.266]
#IMPLIED
char encoding of
linked resource
checked
[p.225]
INPUT
(checked)
#IMPLIED
for radio buttons
and check boxes
cite [p.93]
BLOCKQUOTE,
Q
%URI; [p.266]
#IMPLIED
URI for source
document or msg
cite [p.100]
DEL, INS
%URI; [p.266]
#IMPLIED
info on reason for
change
class [p.71]
All elements but
BASE,
BASEFONT,
HEAD, HTML,
META, PARAM,
SCRIPT,
STYLE, TITLE
CDATA [p.50]
#IMPLIED
space-separated
list of classes
24 Dec 1999 18:26
controls frame
width around
table
D
L
link border width
364
Index of the HTML 4 Attributes
identifies an
implementation
OBJECT
%URI; [p.266]
#IMPLIED
clear [p.198]
BR
(left | all | right |
none)
none
D
L
control of text flow
code [p.171]
APPLET
CDATA [p.50]
#IMPLIED
D
L
applet class file
codebase
[p.163]
OBJECT
%URI; [p.266]
#IMPLIED
codebase
[p.171]
APPLET
%URI; [p.280]
#IMPLIED
codetype
[p.163]
OBJECT
%ContentType;
[p.266]
#IMPLIED
color [p.201]
BASEFONT,
FONT
%Color; [p.281]
#IMPLIED
cols [p.207]
FRAMESET
%MultiLengths;
[p.270]
#IMPLIED
cols [p.235]
TEXTAREA
NUMBER [p.50]
#REQUIRED
colspan
[p.126]
TD, TH
NUMBER [p.50]
1
compact
[p.105]
DIR, DL,
MENU, OL, UL
(compact)
#IMPLIED
content [p.65]
META
CDATA [p.50]
#REQUIRED
associated
information
coords [p.175]
AREA
%Coords; [p.269]
#IMPLIED
comma-separated
list of lengths
coords [p.175]
A
%Coords; [p.269]
#IMPLIED
for use with
client-side image
maps
data [p.163]
OBJECT
%URI; [p.266]
#IMPLIED
reference to
object’s data
datetime
[p.100]
DEL, INS
%Datetime;
[p.266]
#IMPLIED
date and time of
change
declare
[p.164]
OBJECT
(declare)
#IMPLIED
declare but don’t
instantiate flag
defer [p.252]
SCRIPT
(defer)
#IMPLIED
UA may defer
execution of script
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FRAME,
FRAMESET,
IFRAME,
PARAM,
SCRIPT
(ltr | rtl)
#IMPLIED
direction for
weak/neutral text
classid [p.163]
dir [p.82]
365
base URI for
classid, data,
archive
D
L
optional base URI
for applet
content type for
code
D
L
text color
F
list of lengths,
default: 100% (1
col)
number of cols
spanned by cell
D
L
reduced interitem
spacing
24 Dec 1999 18:26
Index of the HTML 4 Attributes
dir [p.85]
BDO
(ltr | rtl)
#REQUIRED
directionality
disabled
[p.244]
BUTTON,
INPUT,
OPTGROUP,
OPTION,
SELECT,
TEXTAREA
(disabled)
#IMPLIED
unavailable in this
context
enctype
[p.223]
FORM
%ContentType;
[p.266]
"application/x-wwwform-urlencoded"
BASEFONT,
FONT
CDATA [p.50]
#IMPLIED
for [p.237]
LABEL
IDREF [p.50]
#IMPLIED
matches field ID
value
frame [p.130]
TABLE
%TFrame; [p.275]
#IMPLIED
which parts of
frame to render
frameborder
[p.210]
FRAME,
IFRAME
(1 | 0)
1
headers
[p.125]
TD, TH
IDREFS [p.50]
#IMPLIED
height [p.217]
IFRAME
%Length; [p.285]
#IMPLIED
height [p.126]
TD, TH
%Length; [p.285]
#IMPLIED
height [p.179]
IMG, OBJECT
%Length; [p.270]
#IMPLIED
height [p.172]
APPLET
%Length; [p.285]
#REQUIRED
href [p.149]
A, AREA, LINK
%URI; [p.266]
#IMPLIED
URI for linked
resource
href [p.157]
BASE
%URI; [p.266]
#IMPLIED
URI that acts as
base URI
A, LINK
%LanguageCode;
[p.266]
#IMPLIED
language code
APPLET, IMG,
OBJECT
%Pixels; [p.285]
#IMPLIED
META
NAME [p.50]
#IMPLIED
HTTP response
header name
All elements but
BASE, HEAD,
HTML, META,
SCRIPT,
STYLE, TITLE
ID [p.50]
#IMPLIED
document-wide
unique id
ismap [p.179]
IMG, INPUT
(ismap)
#IMPLIED
use server-side
image map
label [p.232]
OPTION
%Text; [p.266]
#IMPLIED
for use in
hierarchical
menus
label [p.232]
OPTGROUP
%Text; [p.266]
#REQUIRED
for use in
hierarchical
menus
face [p.201]
hreflang
[p.149]
hspace [p.180]
http-equiv
[p.65]
id [p.71]
24 Dec 1999 18:26
D
L
F
comma-separated
list of font names
request frame
borders?
list of id’s for
header cells
D
L
frame height
L
height for cell
override height
D
D
L
L
initial height
horizontal gutter
366
Index of the HTML 4 Attributes
lang [p.79]
All elements but
APPLET,
BASE,
BASEFONT,
%LanguageCode;
BR, FRAME,
[p.266]
FRAMESET,
IFRAME,
PARAM,
SCRIPT
#IMPLIED
language code
language
[p.252]
SCRIPT
CDATA [p.50]
#IMPLIED
D
L
predefined script
language name
link [p.69]
BODY
%Color; [p.281]
#IMPLIED
D
L
color of links
longdesc
[p.161]
IMG
%URI; [p.266]
#IMPLIED
longdesc
[p.209]
FRAME,
IFRAME
%URI; [p.266]
#IMPLIED
F
link to long
description
(complements
title)
marginheight
[p.210]
FRAME,
IFRAME
%Pixels; [p.270]
#IMPLIED
F
margin height in
pixels
marginwidth
[p.210]
FRAME,
IFRAME
%Pixels; [p.270]
#IMPLIED
F
margin widths in
pixels
maxlength
[p.225]
INPUT
NUMBER [p.50]
#IMPLIED
max chars for text
fields
media [p.187]
STYLE
%MediaDesc;
[p.266]
#IMPLIED
designed for use
with these media
media [p.187]
LINK
%MediaDesc;
[p.266]
#IMPLIED
for rendering on
these media
method
[p.223]
FORM
(GET | POST)
GET
HTTP method
used to submit
the form
multiple
[p.230]
SELECT
(multiple)
#IMPLIED
default is single
selection
name [p.229]
BUTTON,
TEXTAREA
CDATA [p.50]
#IMPLIED
name [p.171]
APPLET
CDATA [p.50]
#IMPLIED
name [p.230]
SELECT
CDATA [p.50]
#IMPLIED
field name
name [p.223]
FORM
CDATA [p.50]
#IMPLIED
name of form for
scripting
name [p.209]
FRAME,
IFRAME
CDATA [p.50]
#IMPLIED
name [p.161]
IMG
CDATA [p.50]
#IMPLIED
name of image for
scripting
name [p.149]
A
CDATA [p.50]
#IMPLIED
named link end
367
link to long
description
(complements alt)
D
L
F
allows applets to
find each other
name of frame for
targetting
24 Dec 1999 18:26
Index of the HTML 4 Attributes
name [p.225]
INPUT,
OBJECT
CDATA [p.50]
#IMPLIED
submit as part of
form
name [p.174]
MAP
CDATA [p.50]
#REQUIRED
for reference by
usemap
name [p.167]
PARAM
CDATA [p.50]
#REQUIRED
property name
name [p.65]
META
NAME [p.50]
#IMPLIED
metainformation
name
nohref [p.175]
AREA
(nohref)
#IMPLIED
this region has no
action
noresize
[p.210]
FRAME
(noresize)
#IMPLIED
noshade
[p.202]
HR
(noshade)
#IMPLIED
D
L
nowrap
[p.126]
TD, TH
(nowrap)
#IMPLIED
D
L
suppress word
wrap
object [p.171]
APPLET
CDATA [p.50]
#IMPLIED
D
L
serialized applet
file
onblur [p.255]
A, AREA,
BUTTON,
INPUT, LABEL,
SELECT,
TEXTAREA
%Script; [p.266]
#IMPLIED
the element lost
the focus
INPUT,
SELECT,
TEXTAREA
%Script; [p.266]
#IMPLIED
the element value
was changed
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
FRAMESET,
onclick [p.255]
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a pointer button
was clicked
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
FRAMESET,
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a pointer button
was double
clicked
onchange
[p.256]
ondblclick
[p.255]
24 Dec 1999 18:26
F
allow users to
resize frames?
368
Index of the HTML 4 Attributes
onfocus
[p.255]
A, AREA,
BUTTON,
INPUT, LABEL,
SELECT,
TEXTAREA
%Script; [p.266]
#IMPLIED
the element got
the focus
onkeydown
[p.255]
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
FRAMESET,
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a key was
pressed down
onkeypress
[p.255]
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
FRAMESET,
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a key was
pressed and
released
onkeyup
[p.255]
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
FRAMESET,
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a key was
released
onload [p.254]
FRAMESET
%Script; [p.266]
#IMPLIED
onload [p.254]
BODY
%Script; [p.266]
#IMPLIED
369
F
all the frames
have been loaded
the document has
been loaded
24 Dec 1999 18:26
Index of the HTML 4 Attributes
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
onmousedown
FRAMESET,
[p.255]
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a pointer button
was pressed
down
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
onmousemove
FRAMESET,
[p.255]
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a pointer was
moved within
onmouseout
[p.255]
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
FRAMESET,
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a pointer was
moved away
onmouseover
[p.255]
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
FRAMESET,
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a pointer was
moved onto
24 Dec 1999 18:26
370
Index of the HTML 4 Attributes
All elements but
APPLET,
BASE,
BASEFONT,
BDO, BR,
FONT, FRAME,
FRAMESET,
HEAD, HTML,
IFRAME,
ISINDEX,
META, PARAM,
SCRIPT,
STYLE, TITLE
%Script; [p.266]
#IMPLIED
a pointer button
was released
onreset
[p.256]
FORM
%Script; [p.266]
#IMPLIED
the form was
reset
onselect
[p.256]
INPUT,
TEXTAREA
%Script; [p.266]
#IMPLIED
some text was
selected
onsubmit
[p.255]
FORM
%Script; [p.266]
#IMPLIED
the form was
submitted
onunload
[p.255]
FRAMESET
%Script; [p.266]
#IMPLIED
onunload
[p.255]
BODY
%Script; [p.266]
#IMPLIED
the document has
been removed
profile [p.62]
HEAD
%URI; [p.266]
#IMPLIED
named dictionary
of meta info
ISINDEX
%Text; [p.281]
#IMPLIED
readonly
[p.244]
TEXTAREA
(readonly)
#IMPLIED
readonly
[p.244]
INPUT
(readonly)
#IMPLIED
for text and
passwd
rel [p.149]
A, LINK
%LinkTypes;
[p.266]
#IMPLIED
forward link types
rev [p.150]
A, LINK
%LinkTypes;
[p.266]
#IMPLIED
reverse link types
rows [p.207]
FRAMESET
%MultiLengths;
[p.270]
#IMPLIED
rows [p.235]
TEXTAREA
NUMBER [p.50]
#REQUIRED
rowspan
[p.126]
TD, TH
NUMBER [p.50]
1
number of rows
spanned by cell
rules [p.130]
TABLE
%TRules; [p.275]
#IMPLIED
rulings between
rows and cols
scheme [p.65]
META
CDATA [p.50]
#IMPLIED
select form of
content
scope [p.125]
TD, TH
%Scope; [p.277]
#IMPLIED
scope covered by
header cells
onmouseup
[p.255]
prompt [p.236]
371
F
D
L
F
all the frames
have been
removed
prompt message
list of lengths,
default: 100% (1
row)
24 Dec 1999 18:26
Index of the HTML 4 Attributes
scrolling
[p.210]
FRAME,
IFRAME
(yes | no | auto)
auto
selected
[p.232]
OPTION
(selected)
#IMPLIED
shape [p.174]
AREA
%Shape; [p.269]
rect
controls
interpretation of
coords
shape [p.174]
A
%Shape; [p.269]
rect
for use with
client-side image
maps
size [p.202]
HR
%Pixels; [p.285]
#IMPLIED
D
L
size [p.201]
FONT
CDATA [p.50]
#IMPLIED
D
L
size [p.225]
INPUT
CDATA [p.50]
#IMPLIED
size [p.201]
BASEFONT
CDATA [p.50]
#REQUIRED
size [p.230]
SELECT
NUMBER [p.50]
#IMPLIED
rows visible
span [p.121]
COL
NUMBER [p.50]
1
COL attributes
affect N columns
span [p.119]
COLGROUP
NUMBER [p.50]
1
default number of
columns in group
src [p.252]
SCRIPT
%URI; [p.266]
#IMPLIED
URI for an
external script
src [p.225]
INPUT
%URI; [p.266]
#IMPLIED
for fields with
images
src [p.210]
FRAME,
IFRAME
%URI; [p.266]
#IMPLIED
src [p.161]
IMG
%URI; [p.266]
#REQUIRED
URI of image to
embed
OBJECT
%Text; [p.266]
#IMPLIED
message to show
while loading
start [p.105]
OL
NUMBER [p.50]
#IMPLIED
style [p.186]
All elements but
BASE,
BASEFONT,
HEAD, HTML,
META, PARAM,
SCRIPT,
STYLE, TITLE
%StyleSheet;
[p.266]
#IMPLIED
associated style
info
TABLE
%Text; [p.266]
#IMPLIED
purpose/structure
for speech output
standby
[p.164]
summary
[p.113]
24 Dec 1999 18:26
F
scrollbar or none
[+|-]nn e.g.
size="+1",
size="4"
specific to each
type of field
D
L
F
D
L
base font size for
FONT elements
source of frame
content
starting sequence
number
372
Index of the HTML 4 Attributes
A, AREA,
BUTTON,
INPUT,
OBJECT,
SELECT,
TEXTAREA
NUMBER [p.50]
#IMPLIED
A, AREA,
BASE, FORM,
LINK
%FrameTarget;
[p.281]
#IMPLIED
text [p.69]
BODY
%Color; [p.281]
#IMPLIED
title [p.63]
All elements but
BASE,
BASEFONT,
HEAD, HTML,
META, PARAM,
SCRIPT, TITLE
%Text; [p.266]
#IMPLIED
advisory title
type [p.149]
A, LINK
%ContentType;
[p.266]
#IMPLIED
advisory content
type
type [p.163]
OBJECT
%ContentType;
[p.266]
#IMPLIED
content type for
data
type [p.167]
PARAM
%ContentType;
[p.266]
#IMPLIED
content type for
value when
valuetype=ref
type [p.252]
SCRIPT
%ContentType;
[p.266]
#REQUIRED
content type of
script language
type [p.187]
STYLE
%ContentType;
[p.266]
#REQUIRED
content type of
style language
type [p.225]
INPUT
%InputType;
[p.273]
TEXT
what kind of
widget is needed
type [p.105]
LI
%LIStyle; [p.289]
#IMPLIED
D
L
list item style
type [p.105]
OL
%OLStyle;
[p.288]
#IMPLIED
D
L
numbering style
type [p.105]
UL
%ULStyle; [p.288]
#IMPLIED
D
L
bullet style
type [p.229]
BUTTON
(button | submit |
reset)
submit
for use as form
button
usemap
[p.175]
IMG, INPUT,
OBJECT
%URI; [p.266]
#IMPLIED
use client-side
image map
valign [p.132]
COL,
COLGROUP,
TBODY, TD,
TFOOT, TH,
THEAD, TR
(top | middle |
bottom | baseline)
#IMPLIED
vertical alignment
in cells
value [p.225]
INPUT
CDATA [p.50]
#IMPLIED
Specify for radio
buttons and
checkboxes
value [p.232]
OPTION
CDATA [p.50]
#IMPLIED
defaults to
element content
tabindex
[p.241]
target [p.212]
373
position in tabbing
order
D
L
render in this
frame
L
document text
color
24 Dec 1999 18:26
Index of the HTML 4 Attributes
value [p.167]
PARAM
CDATA [p.50]
#IMPLIED
property value
value [p.229]
BUTTON
CDATA [p.50]
#IMPLIED
sent to server
when submitted
value [p.105]
LI
NUMBER [p.50]
#IMPLIED
PARAM
(DATA | REF |
OBJECT)
DATA
version [p.61]
HTML
CDATA [p.50]
%HTML.Version;
[p.279]
D
L
Constant
vlink [p.69]
BODY
%Color; [p.281]
#IMPLIED
D
L
color of visited
links
APPLET, IMG,
OBJECT
%Pixels; [p.285]
#IMPLIED
D
L
vertical gutter
width [p.202]
HR
%Length; [p.285]
#IMPLIED
D
L
width [p.217]
IFRAME
%Length; [p.285]
#IMPLIED
width [p.179]
IMG, OBJECT
%Length; [p.270]
#IMPLIED
override width
width [p.113]
TABLE
%Length; [p.270]
#IMPLIED
table width
width [p.126]
TD, TH
%Length; [p.285]
#IMPLIED
D
L
width for cell
width [p.171]
APPLET
%Length; [p.285]
#REQUIRED
D
L
initial width
width [p.121]
COL
%MultiLength;
[p.270]
#IMPLIED
column width
specification
width [p.119]
COLGROUP
%MultiLength;
[p.270]
#IMPLIED
default width for
enclosed COLs
width [p.97]
PRE
NUMBER [p.50]
#IMPLIED
valuetype
[p.167]
vspace [p.180]
24 Dec 1999 18:26
D
L
reset sequence
number
How to interpret
value
L
D
frame width
L
374
Index
Index
abbreviations and acronyms 92
access key 242
accessibility
access keys 242
alternate object content 166
alternate text 181
and alternate frame content 214
and long frame descriptions 215
and style sheets 184
features in HTML 4 22
long image description 162
of image maps 174, 176
alignment
floating text 198
floats 197
of block-level elements 195
of images 180
of objects 180
of table contents 132
alternate style sheets 190
alternate text
specifying 181
anchor 145
ASCII characters in name 152
case of name 152
character references in name 153
creation of with A 150
creation with id attribute 152
name space of 153
non-ASCII characters in name 335
set by script 150
syntax of name 152
uniqueness of name 152
with A vs. id 153
applet
ways to include 160
application/x-www-form-urlencoded 247, 223
attribute 29
#FIXED value of 34
#IMPLIED value of 34
#REQUIRED value of 34
boolean 36
case of values 34
case-insensitive 30
375
24 Dec 1999 18:26
Index
declaration of in DTD 34
minimized boolean 36
quotation marks around value 30
%attrs; 35
author 37
authoring tool 37, 90
and default style sheet language 186
background color 195
base URI 157
bidirection
Unicode algorithm 82
and character encoding 86
and style sheets 88
override of 85
block-level
and bidirection 83, 73
element 73
%block; 32
BODY
none in frameset 71
boolean attribute 337, 36
minimized 36
border
around a frame 210
around a table 130
around image 180
around object 180
cascading style sheets 192
case
of URIs 51
of anchor name 152
of attribute names 30
of attribute values 30, 34, 49
of character encodings 53
of character entity reference 46
of color names 51
of content types 53
of element names 29
of language codes 53
of length values 52
of link types 54
of media descriptors 57
of numeric character references 45
of script data 57
of style data 57
24 Dec 1999 18:26
376
Index
catalog for HTML 262
CDATA 34, 50
script and style data 50
CERN 21
character encoding 42, 40
UTF-1 43
UTF-16 43
and bidirection 86
choice of 42
common examples 43
default 44
for form submission 223
names of 53
of links 148
specification of 43
user agent’s determination of 44
character entity references 46
character reference 45, 30
for directionality 87
character repertoire 41
%Character; 53
characters
abstract 41
access key 242
best effort to render 80
handling undisplayable 47
rendering undisplayable 47
%Charset; 53
checkbox 221
class attribute
roles of 71
client-side image map 174
creation of 176
clipping
table text 116
code position 41
color
background 195
names of 51
%Color; 51
column
number of in a table 121
width of in a table 122
column group 118
comments
character references in 45
377
24 Dec 1999 18:26
Index
in DTD 31
in HTML 30
informative only 39
not rendered 39
used to hide script data 259
used to hide style sheet data 193
conformance 38
content model 32
excluded elements in 34
syntax of in DTD 33
content type
application/x-www-form-urlencoded 247
multipart/form-data 248
text/html 39
content types
for encoding form data 247
Content-Language header 90
Content-Script-Type header 253
Content-Style-Type header 186
Content-Type header 43
%ContentType; 53
control 220
access key for 242
control name 220
control value 220
disabled 244
events for 256
giving focus to 241
initial value 220
read only 244
successful 245
tabbing navigation 241
types of 221
coordinates
of form submit click 226
of server-side image map 179
data cell
in table 127
data type
CDATA 50
ID 50
IDREF 50
IDREFS 50
NAME 50
NUMBER 50
24 Dec 1999 18:26
378
Index
date
format of 54
of inserted and deleted text 100
%Datetime; 54
default
character encoding 44
scripting language 253
style sheet language 186
target frame 213
deprecated 38
elements 327
direction
inheritance of for nested elements 83
of table information 115
of text 82
disabled controls 244
not successful 245
document
SGML validation 261
dynamic modification with script 258
ways to embed 173
ways to include 217, 160
document character set 41
ISO10646 41, 261
equivalence of ISO10646 and UNICODE 42
document type declaration 60
for frameset DTD 60
for strict DTD 60
for transitional DTD 60
document type definition 28
DTD fragments conform to 39
comments in 31
examples conform to 39
frameset 297
how to read 31
strict 265
transitional 279
Dublin Core 69
element
block-level 73
case-insensitive 29
content model of 32
empty 29, 32
end tag 28
inline 73
list of deprecated 327
379
24 Dec 1999 18:26
Index
list of obsolete 328
omitted end tag 28
omitted start tag 28
references from scripts 254
start tag 28
support for deprecated 38
support for obsolete 38
type declaration 28, 32
types 28
unique identifier for 71
empty element 32
end tag 28
declared as optional 32
omitted 28
entity sets
URIs for HTML 4.01 60
error
handling by user agents 334, 38
image map with IMG in BUTTON 230
rendering style rules in STYLE 187
unavailable resource 154
events 254
file select control 222
submission of 246
#FIXED attribute value 34
floating objects 197
floating text 198
focus 241
and access key 243
label gives to control 239
font
style with HTML 199
form
adding labels to 237
content types for encoding 247
control types 221
controls in 220
display notes 347
encoding data of 246
methods and actions 247
navigating through controls 241
processing controls of 246
reset of 220
structuring controls in 240
submission method of 245
submission of 245
24 Dec 1999 18:26
380
Index
tabbing order of controls 241
values submitted 245
form data set 246
encoding 246
fragment identifier 20, 146
frame
URI problems with 213
border of 210
initial contents of 210
inline 217
introduction to 205
list of reserved target names 58
long description of 215
target algorithm 350
target of document 212
white space around 210
frameset
DTD, declaration of 60
DTD, definition of 297
alternate content for 214
navigation problems with 213
nested 208
sharing data among 208
specifying layout of 207
use of NOFRAMES in 215
frameset document 206
%FrameTarget; 57
GET
and form submission 245
header cell
abbreviation 136
in table 127
scope of 136
headings
properly nested 76
hidden control 222, 246
HTML
as SGML application 39
authoring tips 24
comments in 30
development of 21
specifying data external to 336
version 2.0 21
version 3.0 21
version 3.2 21
381
24 Dec 1999 18:26
Index
version HTML+ 21
HTML document 37
HTML Working Group
members of 17
HTTP
Content-Language header 90
Content-Script-Type header 253
Content-Style-Type header 186
Content-Type header 43
Default-Style header 191
GET and POST with forms 245
used to link external style sheets 194
hyphenation 96
ID 50
id attribute
roles of 71
same name space as name attribute 153
IDREF 50
IDREFS 50
image
alignment of 180
border around 180
long description of 162
not directly in frame 215
visual rendering of 179
ways to include 160
white space around 180
width and height of 179
image map 173, 179
accessibility of 176
client-side 174
illegal for IMG in BUTTON 230
overlapping regions of 176
server side 179
server-side 174
with OBJECT 176
#IMPLIED attribute value 34
including an object 164
inline
element 73
%inline; 32
inter-word space 90
Internet Engineering Task Force (IETF) 21
intrinsic events 254
24 Dec 1999 18:26
382
Index
label
and focus 239
explicit association with control 237
implicit association with control 238
lang attribute
not for direction 82
when applicable 79
language
codes to specify 80
of linked resource 148
of script 253
of text 79
%LanguageCode; 53
%Length; 52
line break 95
and bidirectional text 96
and floating text 198
forcing 96
prohibiting 96
link
and character encoding 148
and external style sheets 191, 155
and media-dependent style sheets 192
default target for 213
definition of 145
forward and reverse 155
nesting illegal 152
rendering of 150
semantics with target frame 214
title of 148
type of 54
used to define relationship 147
used to retrieve resource 145
link type
case of 54
list of recognized 54
profiles for new 56
list
definition list 106
nesting of 106
numbering of 106
ordered 104
style sheets and 108
unordered 104
visual rendering of 108
383
24 Dec 1999 18:26
Index
long image description
relation to alt text 162
markup 27
markup language 27
media
and external style sheets 192
used with style sheets 189
media descriptor
case of 57
list of recognized 56
parsing of 56
%MediaDesc; 56
menu 222
grouping of choices 231
preselected options 231
rendering of choices 233
visual rendering of grouped options 234
message entity 39
meta data 64
LINK vs META 66
profiles for 68
scheme for 68
%MultiLength; 52
multipart/form-data 248, 223
NAME 50
notes about minimized 337
NUMBER 50
numbered headings
numbered 76
numeric character reference 45
object
alignment of 180
border around 180
fallback rendering of 165
generic inclusion 164
in HEAD 208, 165, 165
in form 222
initialization 167
locating implementation and data 165
naming schemes for 169
rules for embedded 165
statically declared 169
visual rendering of 179
white space around 180
24 Dec 1999 18:26
384
Index
width and height of 179
object control 222, 246
obsolete 38
elements 328
paragraph
visual rendering of 98
parameter entity
%Character; 53
%Charset; 53
%Color; 51
%ContentType; 53
%Datetime; 54
%FrameTarget; 57
%LanguageCode; 53
%Length; 52
%MediaDesc; 56
%MultiLength; 52
%Pixels; 52
%Script; 57
%Text; 50
%URI; 51
%attrs; 35
%block; 32
%inline; 32
parameter entity definition 31
password input control 226
persistent style sheets 190
pixel 52
%Pixels; 52
Platform for Internet Content Selection (PICS) 67
POST
and form submission 245
for non-ASCII form data 245
preferred style sheets 190
profile 68
push button 221
quoted text 93
rendering of 93
radio button 221
read only controls 244
relative length 52
relative URI 20
resolution of 20
385
24 Dec 1999 18:26
Index
#REQUIRED attribute value 34
reset button 221
resetting a form 220
resolution of relative URI 158
Resource Description Framework (RDF) 24, 64
row
number of in table 114
row group 117
rule
between block-level elements 202
between table cells 130
scheme 68
scope
of table header cell 136
script
comments to hide 259
data 57
executed on event 251
executed when document loaded 251
implementation notes 348
introduction to 251
references to elements 254
reserved syntax for 348
used to modify document 258
used to set anchor 150
uses of 251
when unsupported 258
%Script; 57
scripting language
default 253
local declaration 254
specification of 253
search engine
and links 155
helping 339, 66
search robot
helping 340
security
notes on 350
of password control 226
server-side image map 174, 179
click coordinates 179
SGML
application 28
catalog for HTML 262
declaration 28
24 Dec 1999 18:26
386
Index
declaration of HTML 4 263
document character set 41
document type definition (DTD) 28
document validation 261
element type declaration 28
features with limited support 337, 337
implementation notes 335
introduction to 27
treatment of line breaks 335
soft hyphen 96
start tag 28
omitted 28
strict DTD
declaration of 60
definition of 265
style sheet
alternate 190
and bidirection 88
cascading 192
comments to hide 193
data 57
external 190
external through links 155
inline rules 186
introduction to 183
persistent 190
preferred 190
rules in HEAD 187
specification of external 191
specification of preferred 191
target media for 189
used with DIV and SPAN 188
style sheet language
default 186
submit button 221
successful control 245
summary
of table contents 116
tabbing navigation 241
tabbing order 241
table
algorithm to find heading 142
alignment of contents 132
borders and rules of 130
caption for 116
categorization of cells 139
387
24 Dec 1999 18:26
Index
cell margins 134
cells that span several rows/columns 128
column group in 118
data cells 127
directionality of 115
header cells 127
incremental display notes 342
incremental rendering of 114
layout algorithms for 344
non-visual rendering of 136
not for formatting pages 23
number of columns 121
number of rows 114
row group in 117
speaking cell data 142
summary of contents 116
visual rendering of 130
width of columns 122
target frame
algorithm 350
default 213
reserved names 58
semantics of 214
specification of 212
text
direction of 82
floating 198
markup for inserted and deleted 100
preformatted 97
quoted 93
wrapping in paragraph 99
text input control 222
multi-line 235
single-line 226
text/html 39
%Text; 50
time
format of 54
title
available to user 63
of a document 63
used to annotate elements 63
transitional DTD
declaration of 60
definition of 279
24 Dec 1999 18:26
388
Index
Unicode bidirectional algorithm 82
universal character set 41
Universal Resource Identifier (see URI) 19
URI
case of 51
non-ASCII characters in attribute values 334
relative 20
resolution of relative 20, 158
specifying base 157
uses of in HTML 21
%URI; 51
URL
relationship to URI 20
user 37
user agent 37
and error conditions 334, 38
and script data 259
and style data 193
conforming 38
handling image maps 176
processing script and style data 50
UTF-1 43
UTF-16 43
white space 89
around frame 210
around images and objects 180
around table contents 134
character 89
collapsed 90
preserved in PRE 97
World Wide Web (Web) 19
wrapping text 99
389
24 Dec 1999 18:26
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