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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "dtds/xhtml1-strict.dtd"> |
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<?xml-stylesheet href="W3C-PR.css" type="text/css"?> |
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"> |
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<head> |
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<title>XHTML 1.0: The Extensible HyperText Markup |
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Language</title> |
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<body> |
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<div class="navbar"> |
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<a href="#toc">table of contents</a> |
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<hr /> |
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</div> |
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<div class="head"><p><a href="http://www.w3.org/"><img class="head" |
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src="w3c_home.gif" alt="W3C" /></a></p> |
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<h1 class="head"><a name="title" id="title">XHTML</a><sup>™</sup> 1.0: |
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The Extensible HyperText Markup Language</h1> |
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<h2>A Reformulation of HTML 4.0 in XML 1.0</h2> |
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<h3>W3C Proposed Recommendation 10 December 1999</h3> |
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<dl> |
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<dt>This version:</dt> |
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<dd><a href= |
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"http://www.w3.org/TR/1999/PR-xhtml1-19991210"> |
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http://www.w3.org/TR/1999/PR-xhtml1-19991210</a> <br /> |
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(<a href="xhtml1.ps">Postscript version</a>, |
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<a href="xhtml1.pdf">PDF version</a>, |
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<a href="xhtml1.zip">ZIP archive</a>, or |
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<a href="xhtml1.tgz">Gzip'd TAR archive</a>) |
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</dd> |
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<dt>Latest version:</dt> |
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<dd><a href="http://www.w3.org/TR/xhtml1"> |
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http://www.w3.org/TR/xhtml1</a></dd> |
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<dt>Previous versions:</dt> |
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<dd><a href= |
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"http://www.w3.org/TR/1999/WD-xhtml1-19991124"> |
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http://www.w3.org/TR/1999/WD-xhtml1-19991124</a></dd> |
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<dd><a href= |
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"http://www.w3.org/TR/1999/PR-xhtml1-19990824"> |
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http://www.w3.org/TR/1999/PR-xhtml1-19990824</a></dd> |
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<dt>Authors:</dt> |
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<dd>See <a href="#acks">acknowledgements</a>.</dd> |
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</dl> |
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<p class="copyright"><a href= |
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"http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"> |
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Copyright</a> © 1999 <a href="http://www.w3.org/">W3C</a><sup>®</sup> |
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(<a href="http://www.lcs.mit.edu/">MIT</a>, <a href= |
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"http://www.inria.fr/">INRIA</a>, <a href= |
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"http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. <abbr |
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title="World Wide Web Consortium">W3C</abbr> <a |
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href= |
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"http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer"> |
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liability</a>, <a href= |
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"http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks"> |
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trademark</a>, <a href= |
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"http://www.w3.org/Consortium/Legal/copyright-documents">document |
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use</a> and <a href= |
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"http://www.w3.org/Consortium/Legal/copyright-software">software |
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licensing</a> rules apply.</p> |
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<hr /> |
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</div> |
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<h2 class="notoc">Abstract</h2> |
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<p>This specification defines <abbr title="Extensible Hypertext Markup |
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Language">XHTML</abbr> 1.0, a reformulation of HTML |
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4.0 as an XML 1.0 application, and three <abbr title="Document Type |
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Definition">DTDs</abbr> corresponding to |
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the ones defined by HTML 4.0. The semantics of the elements and |
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their attributes are defined in the W3C Recommendation for HTML |
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4.0. These semantics provide the foundation for future |
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extensibility of XHTML. Compatibility with existing HTML user |
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agents is possible by following a small set of guidelines.</p> |
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<h2>Status of this document</h2> |
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<p><em>This section describes the status of this document at the time |
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of its publication. Other documents may supersede this document. The |
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latest status of this document series is maintained at the W3C.</em></p> |
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<p>This specification is a Proposed Recommendation of the HTML Working Group. It is |
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a revision of the Proposed Recommendation dated <a |
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href= "http://www.w3.org/TR/1999/PR-xhtml1-19990824/">24 August |
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1999</a> incorporating changes as a result of comments from the Proposed |
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Recommendation review, and |
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comments and further deliberations of the W3C HTML Working Group. A |
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<a href="xhtml1-diff-19991210.html">diff-marked version</a> from the previous |
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proposed recommendation is available for comparison purposes.</p> |
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<p>On 10 December 1999, this document enters a |
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<a href="http://www.w3.org/Consortium/Process/#RecsPR"> |
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Proposed Recommendation</a> review period. From that date until 8 January |
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2000, |
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W3C Advisory Committee representatives are encouraged |
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to review this specification and return comments in their completed |
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ballots to [email protected]. Please send any comments of a |
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confidential nature in separate email to [email protected], which is |
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visible to the Team only.</p> |
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<p>No sooner than 14 days after the end of the review period, the |
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Director will announce the document's disposition: it may become a W3C |
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Recommendation (possibly with minor changes), it may revert to Working |
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Draft status, or it may be dropped as a W3C work item.</p> |
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<p>Publication as a Proposed Recommendation does not imply endorsement |
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by the W3C membership. This is still a draft document and may be |
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updated, replaced or obsoleted by other documents at any time. It is |
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inappropriate to cite W3C Proposed Recommendation as other than "work |
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in progress."</p> |
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<p>This document has been produced as part of the <a href= |
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"http://www.w3.org/MarkUp/">W3C HTML Activity</a>. The goals of |
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the <a href="http://www.w3.org/MarkUp/Group/">HTML Working |
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Group</a> <i>(<a href="http://cgi.w3.org/MemberAccess/">members |
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only</a>)</i> are discussed in the <a href= |
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"http://www.w3.org/MarkUp/Group/HTMLcharter">HTML Working Group |
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charter</a> <i>(<a href="http://cgi.w3.org/MemberAccess/">members |
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only</a>)</i>.</p> |
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<p>A list of current W3C Recommendations and other technical documents |
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|
can be found at <a |
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href="http://www.w3.org/TR">http://www.w3.org/TR</a>.</p> |
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<p>Public discussion on <abbr title="HyperText Markup |
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Language">HTML</abbr> features takes place on the mailing list <a |
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href="mailto:[email protected]"> [email protected]</a> (<a href= |
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"http://lists.w3.org/Archives/Public/www-html/">archive</a>). The W3C |
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staff contact for work on HTML is <a href= "mailto:[email protected]">Dave |
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Raggett</a>.</p> |
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<p>Please report errors in this document to <a |
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href="mailto:[email protected]">[email protected]</a>.</p> |
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<p>The list of known errors in this specification is available at <a |
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href="http://www.w3.org/1999/12/PR-xhtml1-19991210-errata">http://www.w3.org/1999/12/PR-xhtml1-19991210-errata</a>.</p> |
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<h2 class="notoc"><a id="toc" name="toc">Contents</a></h2> |
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<div class="contents"> |
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<ul class="toc"> |
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<li class="tocline">1. <a href="#xhtml">What is XHTML?</a> |
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<ul class="toc"> |
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<li class="tocline">1.1 <a href="#html4">What is HTML 4.0?</a></li> |
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<li class="tocline">1.2 <a href="#xml">What is XML?</a></li> |
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<li class="tocline">1.3 <a href="#why">Why the need for XHTML?</a></li> |
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</ul> |
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</li> |
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<li class="tocline">2. <a href="#defs">Definitions</a> |
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<ul class="toc"> |
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<li class="tocline">2.1 <a href="#terms">Terminology</a></li> |
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<li class="tocline">2.2 <a href="#general">General Terms</a></li> |
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</ul> |
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</li> |
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<li class="tocline">3. <a href="#normative">Normative Definition of XHTML 1.0</a> |
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<ul class="toc"> |
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<li class="tocline">3.1 <a href="#docconf">Document Conformance</a></li> |
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<li class="tocline">3.2 <a href="#uaconf">User Agent Conformance</a></li> |
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</ul> |
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</li> |
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<li class="tocline">4. <a href="#diffs">Differences with HTML 4.0</a> |
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</li> |
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<li class="tocline">5. <a href="#issues">Compatibility Issues</a> |
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<ul class="toc"> |
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<li class="tocline">5.1 <a href="#media">Internet Media Types</a></li> |
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</ul> |
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</li> |
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<li class="tocline">6. <a href="#future">Future Directions</a> |
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<ul class="toc"> |
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<li class="tocline">6.1 <a href="#mods">Modularizing HTML</a></li> |
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<li class="tocline">6.2 <a href="#extensions">Subsets and Extensibility</a></li> |
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<li class="tocline">6.3 <a href="#profiles">Document Profiles</a></li> |
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</ul> |
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</li> |
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<li class="tocline"><a href="#dtds">Appendix A. DTDs</a></li> |
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<li class="tocline"><a href="#prohibitions">Appendix B. Element |
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Prohibitions</a></li> |
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<li class="tocline"><a href="#guidelines">Appendix C. HTML Compatibility Guidelines</a></li> |
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<li class="tocline"><a href="#acks">Appendix D. Acknowledgements</a></li> |
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<li class="tocline"><a href="#refs">Appendix E. References</a></li> |
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</ul> |
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</div> |
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<h1><a name="xhtml" id="xhtml">1. What is XHTML?</a></h1> |
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<p>XHTML is a family of current and future document types and modules that |
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reproduce, subset, and extend HTML 4.0 <a href="#ref-html4">[HTML]</a>. XHTML family document types are <abbr title="Extensible Markup Language">XML</abbr> based, |
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and ultimately are designed to work in conjunction with XML-based user agents. |
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The details of this family and its evolution are |
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discussed in more detail in the section on <a href="#future">Future |
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Directions</a>. </p> |
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<p>XHTML 1.0 (this specification) is the first document type in the XHTML |
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family. It is a reformulation of the three HTML 4.0 document types as |
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applications of XML 1.0 <a href="#ref-xml"> [XML]</a>. It is intended |
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to be used as a language for content that is both XML-conforming and, if some |
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simple <a href="#guidelines">guidelines</a> are followed, |
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operates in HTML 4.0 conforming user agents. Developers who migrate |
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their content to XHTML 1.0 will realize the following benefits:</p> |
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<ul> |
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<li>XHTML documents are XML conforming. As such, they are readily viewed, |
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edited, and validated with standard XML tools.</li> |
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<li>XHTML documents can be written to |
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to operate as well or better than they did before in existing |
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HTML 4.0-conforming user agents as well as in new, XHTML 1.0 conforming user |
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agents.</li> |
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<li>XHTML documents can utilize applications (e.g. scripts and applets) that rely |
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upon either the HTML Document Object Model or the XML Document Object Model <a |
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href="#ref-dom">[DOM]</a>.</li> |
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<li>As the XHTML family evolves, documents conforming to XHTML 1.0 will be more |
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likely to interoperate within and among various XHTML environments.</li> |
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</ul> |
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<p>The XHTML family is the next step in the evolution of the Internet. By |
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migrating to XHTML today, content developers can enter the XML world with all |
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of its attendant benefits, while still remaining confident in their |
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content's backward and future compatibility.</p> |
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<h2><a name="html4" id="html4">1.1 What is HTML 4.0?</a></h2> |
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<p>HTML 4.0 <a href="#ref-html4">[HTML]</a> is an <abbr title="Standard |
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Generalized Markup Language">SGML</abbr> (Standard |
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Generalized Markup Language) application conforming to |
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International Standard <abbr title="Organization for International |
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Standardization">ISO</abbr> 8879, and is widely regarded as the |
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standard publishing language of the World Wide Web.</p> |
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<p>SGML is a language for describing markup languages, |
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particularly those used in electronic document exchange, document |
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management, and document publishing. HTML is an example of a |
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language defined in SGML.</p> |
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<p>SGML has been around since the middle 1980's and has remained |
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quite stable. Much of this stability stems from the fact that the |
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language is both feature-rich and flexible. This flexibility, |
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however, comes at a price, and that price is a level of |
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complexity that has inhibited its adoption in a diversity of |
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environments, including the World Wide Web.</p> |
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<p>HTML, as originally conceived, was to be a language for the |
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exchange of scientific and other technical documents, suitable |
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for use by non-document specialists. HTML addressed the problem |
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of SGML complexity by specifying a small set of structural and |
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semantic tags suitable for authoring relatively simple documents. |
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In addition to simplifying the document structure, HTML added |
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support for hypertext. Multimedia capabilities were added |
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later.</p> |
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<p>In a remarkably short space of time, HTML became wildly |
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popular and rapidly outgrew its original purpose. Since HTML's |
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inception, there has been rapid invention of new elements for use |
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within HTML (as a standard) and for adapting HTML to vertical, |
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highly specialized, markets. This plethora of new elements has |
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led to compatibility problems for documents across different |
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platforms.</p> |
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<p>As the heterogeneity of both software and platforms rapidly |
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proliferate, it is clear that the suitability of 'classic' HTML |
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4.0 for use on these platforms is somewhat limited.</p> |
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<h2><a name="xml" id="xml">1.2 What is XML?</a></h2> |
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<p>XML<sup>™</sup> is the shorthand for Extensible Markup |
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Language, and is an acronym of Extensible Markup Language <a |
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href="#ref-xml">[XML]</a>.</p> |
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<p>XML was conceived as a means of regaining the power and |
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flexibility of SGML without most of its complexity. Although a |
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restricted form of SGML, XML nonetheless preserves most of SGML's |
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power and richness, and yet still retains all of SGML's commonly |
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used features.</p> |
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<p>While retaining these beneficial features, XML removes many of |
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the more complex features of SGML that make the authoring and |
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design of suitable software both difficult and costly.</p> |
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<h2><a name="why" id="why">1.3 Why the need for XHTML?</a></h2> |
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<p>The benefits of migrating to XHTML 1.0 are described above. Some of the |
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benefits of migrating to XHTML in general are:</p> |
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<ul> |
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<li>Document developers and user agent designers are constantly |
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discovering new ways to express their ideas through new markup. In XML, it is |
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relatively easy to introduce new elements or additional element |
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attributes. The XHTML family is designed to accommodate these extensions |
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through XHTML modules and techniques for developing new XHTML-conforming |
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modules (described in the forthcoming XHTML Modularization specification). |
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These modules will permit the combination of existing and |
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new feature sets when developing content and when designing new user |
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agents.</li> |
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<li>Alternate ways of accessing the Internet are constantly being |
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introduced. Some estimates indicate that by the year 2002, 75% of |
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Internet document viewing will be carried out on these alternate |
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platforms. The XHTML family is designed with general user agent |
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interoperability in mind. Through a new user agent and document profiling |
|
|
mechanism, servers, proxies, and user agents will be able to perform |
|
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best effort content transformation. Ultimately, it will be possible to |
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develop XHTML-conforming content that is usable by any XHTML-conforming |
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user agent.</li> |
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</ul> |
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<h1><a name="defs" id="defs">2. Definitions</a></h1> |
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<h2><a name="terms" id="terms">2.1 Terminology</a></h2> |
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<p>The following terms are used in this specification. These |
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terms extend the definitions in <a href="#ref-rfc2119"> |
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|
[RFC2119]</a> in ways based upon similar definitions in ISO/<abbr |
|
|
title="International Electro-technical Commission">IEC</abbr> |
|
|
9945-1:1990 <a href="#ref-posix">[POSIX.1]</a>:</p> |
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<dl> |
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<dt>Implementation-defined</dt> |
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<dd>A value or behavior is implementation-defined when it is left |
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to the implementation to define [and document] the corresponding |
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requirements for correct document construction.</dd> |
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<dt>May</dt> |
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<dd>With respect to implementations, the word "may" is to be |
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interpreted as an optional feature that is not required in this |
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specification but can be provided. With respect to <a href= |
|
|
"#docconf">Document Conformance</a>, the word "may" means that |
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|
the optional feature must not be used. The term "optional" has |
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|
the same definition as "may".</dd> |
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<dt>Must</dt> |
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|
|
<dd>In this specification, the word "must" is to be interpreted |
|
|
as a mandatory requirement on the implementation or on Strictly |
|
|
Conforming XHTML Documents, depending upon the context. The term |
|
|
"shall" has the same definition as "must".</dd> |
|
|
|
|
|
<dt>Reserved</dt> |
|
|
|
|
|
<dd>A value or behavior is unspecified, but it is not allowed to |
|
|
be used by Conforming Documents nor to be supported by a |
|
|
Conforming User Agents.</dd> |
|
|
|
|
|
<dt>Should</dt> |
|
|
|
|
|
<dd>With respect to implementations, the word "should" is to be |
|
|
interpreted as an implementation recommendation, but not a |
|
|
requirement. With respect to documents, the word "should" is to |
|
|
be interpreted as recommended programming practice for documents |
|
|
and a requirement for Strictly Conforming XHTML Documents.</dd> |
|
|
|
|
|
<dt>Supported</dt> |
|
|
|
|
|
<dd>Certain facilities in this specification are optional. If a |
|
|
facility is supported, it behaves as specified by this |
|
|
specification.</dd> |
|
|
|
|
|
<dt>Unspecified</dt> |
|
|
|
|
|
<dd>When a value or behavior is unspecified, the specification |
|
|
defines no portability requirements for a facility on an |
|
|
implementation even when faced with a document that uses the |
|
|
facility. A document that requires specific behavior in such an |
|
|
instance, rather than tolerating any behavior when using that |
|
|
facility, is not a Strictly Conforming XHTML Document.</dd> |
|
|
</dl> |
|
|
|
|
|
<h2><a name="general" id="general">2.2 General Terms</a></h2> |
|
|
|
|
|
<dl> |
|
|
<dt>Attribute</dt> |
|
|
|
|
|
<dd>An attribute is a parameter to an element declared in the |
|
|
DTD. An attribute's type and value range, including a possible |
|
|
default value, are defined in the DTD.</dd> |
|
|
|
|
|
<dt>DTD</dt> |
|
|
|
|
|
<dd>A DTD, or document type definition, is a collection of XML |
|
|
declarations that, as a collection, defines the legal structure, |
|
|
<span class="term">elements</span>, and <span class="term"> |
|
|
attributes</span> that are available for use in a document that |
|
|
complies to the DTD.</dd> |
|
|
|
|
|
<dt>Document</dt> |
|
|
|
|
|
<dd>A document is a stream of data that, after being combined |
|
|
with any other streams it references, is structured such that it |
|
|
holds information contained within <span class="term"> |
|
|
elements</span> that are organized as defined in the associated |
|
|
<span class="term">DTD</span>. See <a href="#docconf">Document |
|
|
Conformance</a> for more information.</dd> |
|
|
|
|
|
<dt>Element</dt> |
|
|
|
|
|
<dd>An element is a document structuring unit declared in the |
|
|
<span class="term">DTD</span>. The element's content model is |
|
|
defined in the <span class="term">DTD</span>, and additional |
|
|
semantics may be defined in the prose description of the |
|
|
element.</dd> |
|
|
|
|
|
<dt><a name="facilities" id="facilities">Facilities</a></dt> |
|
|
|
|
|
<dd>Functionality includes <span class="term">elements</span>, |
|
|
<span class="term">attributes</span>, and the semantics |
|
|
associated with those <span class="term">elements</span> and |
|
|
<span class="term">attributes</span>. An implementation |
|
|
supporting that functionality is said to provide the necessary |
|
|
facilities.</dd> |
|
|
|
|
|
<dt>Implementation</dt> |
|
|
|
|
|
<dd>An implementation is a system that provides collection of |
|
|
<span class="term">facilities</span> and services that supports |
|
|
this specification. See <a href="#uaconf">User Agent |
|
|
Conformance</a> for more information.</dd> |
|
|
|
|
|
<dt>Parsing</dt> |
|
|
|
|
|
<dd>Parsing is the act whereby a <span class="term"> |
|
|
document</span> is scanned, and the information contained within |
|
|
the <span class="term">document</span> is filtered into the |
|
|
context of the <span class="term">elements</span> in which the |
|
|
information is structured.</dd> |
|
|
|
|
|
<dt>Rendering</dt> |
|
|
|
|
|
<dd>Rendering is the act whereby the information in a <span |
|
|
class="term">document</span> is presented. This presentation is |
|
|
done in the form most appropriate to the environment (e.g. |
|
|
aurally, visually, in print).</dd> |
|
|
|
|
|
<dt>User Agent</dt> |
|
|
|
|
|
<dd>A user agent is an <span class="term">implementation</span> |
|
|
that retrieves and processes XHTML documents. See <a href= |
|
|
"#uaconf">User Agent Conformance</a> for more information.</dd> |
|
|
|
|
|
<dt>Validation</dt> |
|
|
|
|
|
<dd>Validation is a process whereby <span class="term"> |
|
|
documents</span> are verified against the associated <span class= |
|
|
"term">DTD</span>, ensuring that the structure, use of <span |
|
|
class="term">elements</span>, and use of <span class="term"> |
|
|
attributes</span> are consistent with the definitions in the |
|
|
<span class="term">DTD</span>.</dd> |
|
|
|
|
|
<dt><a name="wellformed" id="wellformed">Well-formed</a></dt> |
|
|
|
|
|
<dd>A <span class="term">document</span> is well-formed when it |
|
|
is structured according to the rules defined in <a href= |
|
|
"http://www.w3.org/TR/REC-xml#sec-well-formed">Section 2.1</a> of |
|
|
the XML 1.0 Recommendation <a href="#ref-xml">[XML]</a>. |
|
|
Basically, this definition states that elements, delimited by |
|
|
their start and end tags, are nested properly within one |
|
|
another.</dd> |
|
|
</dl> |
|
|
|
|
|
|
|
|
<h1><a name="normative" id="normative">3. Normative Definition of |
|
|
XHTML 1.0</a></h1> |
|
|
|
|
|
<h2><a name="docconf" id="docconf">3.1 Document |
|
|
Conformance</a></h2> |
|
|
|
|
|
<p>This version of XHTML provides a definition of strictly |
|
|
conforming XHTML documents, which are restricted to tags and |
|
|
attributes from the XHTML namespace. See <a href= |
|
|
"#well-formed">Section 3.1.2</a> for information on using XHTML |
|
|
with other namespaces, for instance, to include metadata |
|
|
expressed in <abbr title="Resource Description Format">RDF</abbr> within XHTML documents.</p> |
|
|
|
|
|
<h3><a name="strict" id="strict">3.1.1 Strictly Conforming |
|
|
Documents</a></h3> |
|
|
|
|
|
<p>A Strictly Conforming XHTML Document is a document that |
|
|
requires only the facilities described as mandatory in this |
|
|
specification. Such a document must meet all of the following |
|
|
criteria:</p> |
|
|
|
|
|
<ol> |
|
|
<li> |
|
|
<p>It must validate against one of the three DTDs found in <a |
|
|
href="#dtds">Appendix A</a>.</p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p>The root element of the document must be <code> |
|
|
<html></code>.</p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p>The root element of the document must designate the XHTML |
|
|
namespace using the <code>xmlns</code> attribute <a href= |
|
|
"#ref-xmlns">[XMLNAMES]</a>. The namespace for XHTML is |
|
|
defined to be |
|
|
<code>http://www.w3.org/1999/xhtml</code>.</p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p>There must be a DOCTYPE declaration in the document prior to |
|
|
the root element. The public identifier included in |
|
|
the DOCTYPE declaration must reference one of the three DTDs |
|
|
found in <a href="#dtds">Appendix A</a> using the respective |
|
|
Formal Public Identifier. The system identifier may be changed to reflect |
|
|
local system conventions.</p> |
|
|
|
|
|
<pre> |
|
|
<!DOCTYPE html |
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" |
|
|
"http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-strict.dtd> |
|
|
|
|
|
<!DOCTYPE html |
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" |
|
|
"http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-transitional.dtd> |
|
|
|
|
|
<!DOCTYPE html |
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" |
|
|
"http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-frameset.dtd> |
|
|
</pre> |
|
|
</li> |
|
|
</ol> |
|
|
|
|
|
<p>Here is an example of a minimal XHTML document.</p> |
|
|
|
|
|
<div class="good"> |
|
|
<pre> |
|
|
<?xml version="1.0" encoding="UTF-8"?> |
|
|
<!DOCTYPE html |
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" |
|
|
"http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-strict.dtd"> |
|
|
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> |
|
|
<head> |
|
|
<title>Virtual Library</title> |
|
|
</head> |
|
|
<body> |
|
|
<p>Moved to <a href="http://vlib.org/">vlib.org</a>.</p> |
|
|
</body> |
|
|
</html></pre> |
|
|
</div> |
|
|
|
|
|
<p>Note that in this example, the XML declaration is included. An XML |
|
|
declaration like the one above is |
|
|
not required in all XML documents. XHTML document authors are strongly encouraged to use XML declarations in all their documents. Such a declaration is required |
|
|
when the character encoding of the document is other than the default UTF-8 or |
|
|
UTF-16.</p> |
|
|
|
|
|
<h3><a name="well-formed" id="well-formed">3.1.2 Using XHTML with |
|
|
other namespaces</a></h3> |
|
|
|
|
|
<p>The XHTML namespace may be used with other XML namespaces |
|
|
as per <a href="#ref-xmlns">[XMLNAMES]</a>, although such |
|
|
documents are not strictly conforming XHTML 1.0 documents as |
|
|
defined above. Future work by W3C will address ways to specify |
|
|
conformance for documents involving multiple namespaces.</p> |
|
|
|
|
|
<p>The following example shows the way in which XHTML 1.0 could |
|
|
be used in conjunction with the MathML Recommendation:</p> |
|
|
|
|
|
<div class="good"> |
|
|
<pre> |
|
|
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> |
|
|
<head> |
|
|
<title>A Math Example</title> |
|
|
</head> |
|
|
<body> |
|
|
<p>The following is MathML markup:</p> |
|
|
<math xmlns="http://www.w3.org/1998/Math/MathML"> |
|
|
<apply> <log/> |
|
|
<logbase> |
|
|
<cn> 3 </cn> |
|
|
</logbase> |
|
|
<ci> x </ci> |
|
|
</apply> |
|
|
</math> |
|
|
</body> |
|
|
</html> |
|
|
</pre> |
|
|
</div> |
|
|
|
|
|
<p>The following example shows the way in which XHTML 1.0 markup |
|
|
could be incorporated into another XML namespace:</p> |
|
|
|
|
|
<div class="good"> |
|
|
<pre> |
|
|
<?xml version="1.0" encoding="UTF-8"?> |
|
|
<!-- initially, the default namespace is "books" --> |
|
|
<book xmlns='urn:loc.gov:books' |
|
|
xmlns:isbn='urn:ISBN:0-395-36341-6' xml:lang="en" lang="en"> |
|
|
<title>Cheaper by the Dozen</title> |
|
|
<isbn:number>1568491379</isbn:number> |
|
|
<notes> |
|
|
<!-- make HTML the default namespace for a hypertext commentary --> |
|
|
<p xmlns='http://www.w3.org/1999/xhtml'> |
|
|
This is also available <a href="http://www.w3.org/">online</a>. |
|
|
</p> |
|
|
</notes> |
|
|
</book> |
|
|
</pre> |
|
|
</div> |
|
|
|
|
|
<h2><a name="uaconf" id="uaconf">3.2 User Agent |
|
|
Conformance</a></h2> |
|
|
|
|
|
<p>A conforming user agent must meet all of the following |
|
|
criteria:</p> |
|
|
|
|
|
<ol> |
|
|
<li>In order to be consistent with the XML 1.0 Recommendation <a |
|
|
href="#ref-xml">[XML]</a>, the user agent must parse and evaluate |
|
|
an XHTML document for well-formedness. If the user agent claims |
|
|
to be a validating user agent, it must also validate documents |
|
|
against their referenced DTDs according to <a href="#ref-xml"> |
|
|
[XML]</a>.</li> |
|
|
|
|
|
<li>When the user agent claims to support <a href="#facilities"> |
|
|
facilities</a> defined within this specification or required by |
|
|
this specification through normative reference, it must do so in |
|
|
ways consistent with the facilities' definition.</li> |
|
|
|
|
|
<li>When a user agent processes an XHTML document as generic XML, |
|
|
it shall only recognize attributes of type |
|
|
<code>ID</code> (e.g. the <code>id</code> attribute on most XHTML elements) |
|
|
as fragment identifiers.</li> |
|
|
|
|
|
<li>If a user agent encounters an element it does not recognize, |
|
|
it must render the element's content.</li> |
|
|
|
|
|
<li>If a user agent encounters an attribute it does not |
|
|
recognize, it must ignore the entire attribute specification |
|
|
(i.e., the attribute and its value).</li> |
|
|
|
|
|
<li>If a user agent encounters an attribute value it doesn't |
|
|
recognize, it must use the default attribute value.</li> |
|
|
|
|
|
<li>If it encounters an entity reference (other than one |
|
|
of the predefined entities) for which the User Agent has |
|
|
processed no declaration (which could happen if the declaration |
|
|
is in the external subset which the User Agent hasn't read), the entity |
|
|
reference should be rendered as the characters (starting |
|
|
with the ampersand and ending with the semi-colon) that |
|
|
make up the entity reference.</li> |
|
|
|
|
|
<li>When rendering content, User Agents that encounter |
|
|
characters or character entity references that are recognized but not renderable should display the document in such a way that it is obvious to the user that normal rendering has not taken place.</li> |
|
|
|
|
|
<li> |
|
|
The following characters are defined in [XML] as whitespace characters: |
|
|
|
|
|
<ul> |
|
|
<li>Space (&#x0020;)</li> |
|
|
<li>Tab (&#x0009;)</li> |
|
|
<li>Carriage return (&#x000D;)</li> |
|
|
<li>Line feed (&#x000A;)</li> |
|
|
</ul> |
|
|
|
|
|
<p> |
|
|
The XML processor normalizes different system's line end codes into one |
|
|
single line-feed character, that is passed up to the application. The XHTML |
|
|
user agent in addition, must treat the following characters as whitespace: |
|
|
</p> |
|
|
|
|
|
<ul> |
|
|
<li>Form feed (&#x000C;)</li> |
|
|
<li>Zero-width space (&#x200B;)</li> |
|
|
</ul> |
|
|
|
|
|
<p> |
|
|
In elements where the 'xml:space' attribute is set to 'preserve', the user |
|
|
agent must leave all whitespace characters intact (with the exception of |
|
|
leading and trailing whitespace characters, which should be removed). |
|
|
Otherwise, whitespace |
|
|
is handled according to the following rules: |
|
|
</p> |
|
|
|
|
|
<ul> |
|
|
<li> |
|
|
All whitespace surrounding block elements should be removed. |
|
|
</li> |
|
|
<li> |
|
|
Comments are removed entirely and do not affect whitespace handling. One |
|
|
whitespace character on either side of a comment is treated as two white |
|
|
space characters. |
|
|
</li> |
|
|
<li> |
|
|
Leading and trailing whitespace inside a block element must be removed. |
|
|
</li> |
|
|
<li>Line feed characters within a block element must be converted into a |
|
|
space (except when the 'xml:space' attribute is set to 'preserve'). |
|
|
</li> |
|
|
<li> |
|
|
A sequence of white space characters must be reduced to a single space |
|
|
character (except when the 'xml:space' attribute is set to 'preserve'). |
|
|
</li> |
|
|
<li> |
|
|
With regard to rendition, |
|
|
the User Agent should render the content in a |
|
|
manner appropriate to the language in which the content is written. |
|
|
In languages whose primary script is Latinate, the ASCII space |
|
|
character is typically used to encode both grammatical word boundaries and |
|
|
typographic whitespace; in languages whose script is related to Nagari |
|
|
(e.g., Sanskrit, Thai, etc.), grammatical boundaries may be encoded using |
|
|
the ZW 'space' character, but will not typically be represented by |
|
|
typographic whitespace in rendered output; languages using Arabiform scripts |
|
|
may encode typographic whitespace using a space character, but may also use |
|
|
the ZW space character to delimit 'internal' grammatical boundaries (what |
|
|
look like words in Arabic to an English eye frequently encode several words, |
|
|
e.g. 'kitAbuhum' = 'kitAbu-hum' = 'book them' == their book); and languages |
|
|
in the Chinese script tradition typically neither encode such delimiters nor |
|
|
use typographic whitespace in this way. |
|
|
</li> |
|
|
</ul> |
|
|
|
|
|
<p>Whitespace in attribute values is processed according to <a |
|
|
href="#ref-xml">[XML]</a>.</p> |
|
|
</li> |
|
|
</ol> |
|
|
|
|
|
|
|
|
<h1><a name="diffs" id="diffs">4. Differences with HTML |
|
|
4.0</a></h1> |
|
|
|
|
|
<p>Due to the fact that XHTML is an XML application, certain |
|
|
practices that were perfectly legal in SGML-based HTML 4.0 <a |
|
|
href="#ref-html4">[HTML]</a> must be changed.</p> |
|
|
|
|
|
<h2><a name="h-4.1" id="h-4.1">4.1 Documents must be |
|
|
well-formed</a></h2> |
|
|
|
|
|
<p><a href="#wellformed">Well-formedness</a> is a new concept |
|
|
introduced by <a href="#ref-xml">[XML]</a>. Essentially this |
|
|
means that all elements must either have closing tags or be |
|
|
written in a special form (as described below), and that all the |
|
|
elements must nest.</p> |
|
|
|
|
|
<p>Although overlapping is illegal in SGML, it was widely |
|
|
tolerated in existing browsers.</p> |
|
|
|
|
|
<div class="good"> |
|
|
<p><strong><em>CORRECT: nested elements.</em></strong></p> |
|
|
|
|
|
<p><p>here is an emphasized |
|
|
<em>paragraph</em>.</p></p> |
|
|
</div> |
|
|
|
|
|
<div class="bad"> |
|
|
<p><strong><em>INCORRECT: overlapping elements</em></strong></p> |
|
|
|
|
|
<p><p>here is an emphasized |
|
|
<em>paragraph.</p></em></p> |
|
|
</div> |
|
|
|
|
|
<h2><a name="h-4.2" id="h-4.2">4.2 Element and attribute |
|
|
names must be in lower case</a></h2> |
|
|
|
|
|
<p>XHTML documents must use lower case for all HTML element and |
|
|
attribute names. This difference is necessary because XML is |
|
|
case-sensitive e.g. <li> and <LI> are different |
|
|
tags.</p> |
|
|
|
|
|
<h2><a name="h-4.3" id="h-4.3">4.3 For non-empty elements, |
|
|
end tags are required</a></h2> |
|
|
|
|
|
<p>In SGML-based HTML 4.0 certain elements were permitted to omit |
|
|
the end tag; with the elements that followed implying closure. |
|
|
This omission is not permitted in XML-based XHTML. All elements |
|
|
other than those declared in the DTD as <code>EMPTY</code> must |
|
|
have an end tag.</p> |
|
|
|
|
|
<div class="good"> |
|
|
<p><strong><em>CORRECT: terminated elements</em></strong></p> |
|
|
|
|
|
<p><p>here is a paragraph.</p><p>here is |
|
|
another paragraph.</p></p> |
|
|
</div> |
|
|
|
|
|
<div class="bad"> |
|
|
<p><strong><em>INCORRECT: unterminated elements</em></strong></p> |
|
|
|
|
|
<p><p>here is a paragraph.<p>here is another |
|
|
paragraph.</p> |
|
|
</div> |
|
|
|
|
|
<h2><a name="h-4.4" id="h-4.4">4.4 Attribute values must |
|
|
always be quoted</a></h2> |
|
|
|
|
|
<p>All attribute values must be quoted, even those which appear |
|
|
to be numeric.</p> |
|
|
|
|
|
<div class="good"> |
|
|
<p><strong><em>CORRECT: quoted attribute values</em></strong></p> |
|
|
|
|
|
<p><table rows="3"></p> |
|
|
</div> |
|
|
|
|
|
<div class="bad"> |
|
|
<p><strong><em>INCORRECT: unquoted attribute values</em></strong></p> |
|
|
|
|
|
<p><table rows=3></p> |
|
|
</div> |
|
|
|
|
|
<h2><a name="h-4.5" id="h-4.5">4.5 Attribute |
|
|
Minimization</a></h2> |
|
|
|
|
|
<p>XML does not support attribute minimization. Attribute-value |
|
|
pairs must be written in full. Attribute names such as <code> |
|
|
compact</code> and <code>checked</code> cannot occur in elements |
|
|
without their value being specified.</p> |
|
|
|
|
|
<div class="good"> |
|
|
<p><strong><em>CORRECT: unminimized attributes</em></strong></p> |
|
|
|
|
|
<p><dl compact="compact"></p> |
|
|
</div> |
|
|
|
|
|
<div class="bad"> |
|
|
<p><strong><em>INCORRECT: minimized attributes</em></strong></p> |
|
|
|
|
|
<p><dl compact></p> |
|
|
</div> |
|
|
|
|
|
<h2><a name="h-4.6" id="h-4.6">4.6 Empty Elements</a></h2> |
|
|
|
|
|
<p>Empty elements must either have an end tag or the start tag must end with <code>/></code>. For instance, |
|
|
<code><br/></code> or <code><hr></hr></code>. See <a |
|
|
href="#guidelines">HTML Compatibility Guidelines</a> for information on ways to |
|
|
ensure this is backward compatible with HTML 4.0 user agents.</p> |
|
|
|
|
|
<div class="good"> |
|
|
<p><strong><em>CORRECT: terminated empty tags</em></strong></p> |
|
|
|
|
|
<p><br/><hr/></p> |
|
|
</div> |
|
|
|
|
|
<div class="bad"> |
|
|
<p><strong><em>INCORRECT: unterminated empty tags</em></strong></p> |
|
|
|
|
|
<p><br><hr></p> |
|
|
</div> |
|
|
|
|
|
<h2><a name="h-4.7" id="h-4.7">4.7 Whitespace handling in |
|
|
attribute values</a></h2> |
|
|
|
|
|
<p>In attribute values, user agents will strip leading and |
|
|
trailing whitespace from attribute values and map sequences |
|
|
of one or more whitespace characters (including line breaks) to |
|
|
a single inter-word space (an ASCII space character for western |
|
|
scripts). See <a href="http://www.w3.org/TR/REC-xml#AVNormalize"> |
|
|
Section 3.3.3</a> of <a href="#ref-xml">[XML]</a>.</p> |
|
|
|
|
|
<h2><a name="h-4.8" id="h-4.8">4.8 Script and Style |
|
|
elements</a></h2> |
|
|
|
|
|
<p>In XHTML, the script and style elements are declared as having |
|
|
<code>#PCDATA</code> content. As a result, <code><</code> and |
|
|
<code>&</code> will be treated as the start of markup, and |
|
|
entities such as <code>&lt;</code> and <code>&amp;</code> |
|
|
will be recognized as entity references by the XML processor to |
|
|
<code><</code> and <code>&</code> respectively. Wrapping |
|
|
the content of the script or style element within a <code> |
|
|
CDATA</code> marked section avoids the expansion of these |
|
|
entities.</p> |
|
|
|
|
|
<div class="good"> |
|
|
<pre> |
|
|
<script> |
|
|
<![CDATA[ |
|
|
... unescaped script content ... |
|
|
]]> |
|
|
</script> |
|
|
</pre> |
|
|
</div> |
|
|
|
|
|
<p><code>CDATA</code> sections are recognized by the XML |
|
|
processor and appear as nodes in the Document Object Model, see |
|
|
<a href= |
|
|
"http://www.w3.org/TR/REC-DOM-Level-1/level-one-core.html#ID-E067D597"> |
|
|
Section 1.3</a> of the DOM Level 1 Recommendation <a href= |
|
|
"#ref-dom">[DOM]</a>.</p> |
|
|
|
|
|
<p>An alternative is to use external script and style |
|
|
documents.</p> |
|
|
|
|
|
<h2><a name="h-4.9" id="h-4.9">4.9 SGML exclusions</a></h2> |
|
|
|
|
|
<p>SGML gives the writer of a DTD the ability to exclude specific |
|
|
elements from being contained within an element. Such |
|
|
prohibitions (called "exclusions") are not possible in XML.</p> |
|
|
|
|
|
<p>For example, the HTML 4.0 Strict DTD forbids the nesting of an |
|
|
'<code>a</code>' element within another '<code>a</code>' element |
|
|
to any descendant depth. It is not possible to spell out such |
|
|
prohibitions in XML. Even though these prohibitions cannot be |
|
|
defined in the DTD, certain elements should not be nested. A |
|
|
summary of such elements and the elements that should not be |
|
|
nested in them is found in the normative <a href="#prohibitions"> |
|
|
Appendix B</a>.</p> |
|
|
|
|
|
<h2><a name="h-4.10" id="h-4.10">4.10 The elements with 'id' and 'name' |
|
|
attributes</a></h2> |
|
|
|
|
|
<p>HTML 4.0 defined the <code>name</code> attribute for the elements |
|
|
<code>a</code>, |
|
|
<code>applet</code>, <code>frame</code>, |
|
|
<code>iframe</code>, <code>img</code>, and <code>map</code>. |
|
|
HTML 4.0 also introduced |
|
|
the <code>id</code> attribute. Both of these attributes are designed to be |
|
|
used as fragment identifiers.</p> |
|
|
<p>In XML, fragment identifiers are of type <code>ID</code>, and |
|
|
there can only be a single attribute of type <code>ID</code> per element. |
|
|
Therefore, in XHTML 1.0 the <code>id</code> |
|
|
attribute is defined to be of type <code>ID</code>. In order to |
|
|
ensure that XHTML 1.0 documents are well-structured XML documents, XHTML 1.0 |
|
|
documents MUST use the <code>id</code> attribute when defining fragment |
|
|
identifiers, even on elements that historically have also had a |
|
|
<code>name</code> attribute. |
|
|
See the <a href="#guidelines">HTML Compatibility |
|
|
Guidelines</a> for information on ensuring such anchors are backwards |
|
|
compatible when serving XHTML documents as media type <code>text/html</code>. |
|
|
</p> |
|
|
<p>Note that in XHTML 1.0, the <code>name</code> attribute of these |
|
|
elements is formally deprecated, and will be removed in a |
|
|
subsequent version of XHTML.</p> |
|
|
|
|
|
|
|
|
<h1><a name="issues" id="issues">5. Compatibility Issues</a></h1> |
|
|
|
|
|
<p>Although there is no requirement for XHTML 1.0 documents to be |
|
|
compatible with existing user agents, in practice this is easy to |
|
|
accomplish. Guidelines for creating compatible documents can be |
|
|
found in <a href="#guidelines">Appendix C</a>.</p> |
|
|
|
|
|
<h2><a name="media" id="media">5.1 Internet Media Type</a></h2> |
|
|
<p>As of the publication of this recommendation, the general |
|
|
recommended MIME labeling for XML-based applications |
|
|
has yet to be resolved.</p> |
|
|
|
|
|
<p>However, XHTML Documents which follow the guidelines set forth |
|
|
in <a href="#guidelines">Appendix C</a>, "HTML Compatibility Guidelines" may be |
|
|
labeled with the Internet Media Type "text/html", as they |
|
|
are compatible with most HTML browsers. This document |
|
|
makes no recommendation about MIME labeling of other |
|
|
XHTML documents.</p> |
|
|
|
|
|
|
|
|
<h1><a name="future" id="future">6. Future Directions</a></h1> |
|
|
|
|
|
<p>XHTML 1.0 provides the basis for a family of document types |
|
|
that will extend and subset XHTML, in order to support a wide |
|
|
range of new devices and applications, by defining modules and |
|
|
specifying a mechanism for combining these modules. This |
|
|
mechanism will enable the extension and sub-setting of XHTML 1.0 |
|
|
in a uniform way through the definition of new modules.</p> |
|
|
|
|
|
<h2><a name="mods" id="mods">6.1 Modularizing HTML</a></h2> |
|
|
|
|
|
<p>As the use of XHTML moves from the traditional desktop user |
|
|
agents to other platforms, it is clear that not all of the XHTML |
|
|
elements will be required on all platforms. For example a hand |
|
|
held device or a cell-phone may only support a subset of XHTML |
|
|
elements.</p> |
|
|
|
|
|
<p>The process of modularization breaks XHTML up into a series of |
|
|
smaller element sets. These elements can then be recombined to |
|
|
meet the needs of different communities.</p> |
|
|
|
|
|
<p>These modules will be defined in a later W3C document.</p> |
|
|
|
|
|
<h2><a name="extensions" id="extensions">6.2 Subsets and |
|
|
Extensibility</a></h2> |
|
|
|
|
|
<p>Modularization brings with it several advantages:</p> |
|
|
|
|
|
<ul> |
|
|
<li> |
|
|
<p>It provides a formal mechanism for sub-setting XHTML.</p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p>It provides a formal mechanism for extending XHTML.</p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p>It simplifies the transformation between document types.</p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p>It promotes the reuse of modules in new document types.</p> |
|
|
</li> |
|
|
</ul> |
|
|
|
|
|
<h2><a name="profiles" id="profiles">6.3 Document |
|
|
Profiles</a></h2> |
|
|
|
|
|
<p>A document profile specifies the syntax and semantics of a set |
|
|
of documents. Conformance to a document profile provides a basis |
|
|
for interoperability guarantees. The document profile specifies |
|
|
the facilities required to process documents of that type, e.g. |
|
|
which image formats can be used, levels of scripting, style sheet |
|
|
support, and so on.</p> |
|
|
|
|
|
<p>For product designers this enables various groups to define |
|
|
their own standard profile.</p> |
|
|
|
|
|
<p>For authors this will obviate the need to write several |
|
|
different versions of documents for different clients.</p> |
|
|
|
|
|
<p>For special groups such as chemists, medical doctors, or |
|
|
mathematicians this allows a special profile to be built using |
|
|
standard HTML elements plus a group of elements geared to the |
|
|
specialist's needs.</p> |
|
|
|
|
|
|
|
|
<h1><a name="appendices" id="appendices"></a> |
|
|
<a name="dtds" id="dtds">Appendix A. DTDs</a></h1> |
|
|
|
|
|
<p><b>This appendix is normative.</b></p> |
|
|
|
|
|
<p>These DTDs and entity sets form a normative part of this |
|
|
specification. The complete set of DTD files together with an XML |
|
|
declaration and SGML Open Catalog is included in the <a href= |
|
|
"xhtml1.zip">zip file</a> for this specification.</p> |
|
|
|
|
|
<h2><a name="h-A1" id="h-A1">A.1 Document Type |
|
|
Definitions</a></h2> |
|
|
|
|
|
<p>These DTDs approximate the HTML 4.0 DTDs. It is likely that |
|
|
when the DTDs are modularized, a method of DTD construction will |
|
|
be employed that corresponds more closely to HTML 4.0.</p> |
|
|
|
|
|
<ul> |
|
|
<li> |
|
|
<p><a href="DTD/xhtml1-strict.dtd" type="text/plain"> |
|
|
XHTML-1.0-Strict</a></p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p><a href="DTD/xhtml1-transitional.dtd" type="text/plain"> |
|
|
XHTML-1.0-Transitional</a></p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p><a href="DTD/xhtml1-frameset.dtd" type="text/plain"> |
|
|
XHTML-1.0-Frameset</a></p> |
|
|
</li> |
|
|
</ul> |
|
|
|
|
|
<h2><a name="h-A2" id="h-A2">A.2 Entity Sets</a></h2> |
|
|
|
|
|
<p>The XHTML entity sets are the same as for HTML 4.0, but have |
|
|
been modified to be valid XML 1.0 entity declarations. Note the |
|
|
entity for the Euro currency sign (<code>&euro;</code> or |
|
|
<code>&#8364;</code> or <code>&#x20AC;</code>) is defined |
|
|
as part of the special characters.</p> |
|
|
|
|
|
<ul> |
|
|
<li> |
|
|
<p><a href="DTD/xhtml-lat1.ent">Latin-1 characters</a></p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p><a href="DTD/xhtml-special.ent">Special characters</a></p> |
|
|
</li> |
|
|
|
|
|
<li> |
|
|
<p><a href="DTD/xhtml-symbol.ent">Symbols</a></p> |
|
|
</li> |
|
|
</ul> |
|
|
|
|
|
|
|
|
<h1><a name="prohibitions" id="prohibitions">Appendix B. Element |
|
|
Prohibitions</a></h1> |
|
|
|
|
|
<p><b>This appendix is normative.</b></p> |
|
|
|
|
|
<p>The following elements have prohibitions on which elements |
|
|
they can contain (see <a href="#h-4.9">Section 4.9</a>). This |
|
|
prohibition applies to all depths of nesting, i.e. it contains |
|
|
all the descendant elements.</p> |
|
|
|
|
|
<dl><dt><code class="tag">a</code></dt> |
|
|
<dd> |
|
|
cannot contain other <code>a</code> elements.</dd> |
|
|
<dt><code class="tag">pre</code></dt> |
|
|
<dd>cannot contain the <code>img</code>, <code>object</code>, |
|
|
<code>big</code>, <code>small</code>, <code>sub</code>, or <code> |
|
|
sup</code> elements.</dd> |
|
|
|
|
|
<dt><code class="tag">button</code></dt> |
|
|
<dd>cannot contain the <code>input</code>, <code>select</code>, |
|
|
<code>textarea</code>, <code>label</code>, <code>button</code>, |
|
|
<code>form</code>, <code>fieldset</code>, <code>iframe</code> or |
|
|
<code>isindex</code> elements.</dd> |
|
|
<dt><code class="tag">label</code></dt> |
|
|
<dd>cannot contain other <code class="tag">label</code> elements.</dd> |
|
|
<dt><code class="tag">form</code></dt> |
|
|
<dd>cannot contain other <code>form</code> elements.</dd> |
|
|
</dl> |
|
|
|
|
|
|
|
|
<h1><a name="guidelines" id="guidelines">Appendix C. |
|
|
HTML Compatibility Guidelines</a></h1> |
|
|
|
|
|
<p><b>This appendix is informative.</b></p> |
|
|
|
|
|
<p>This appendix summarizes design guidelines for authors who |
|
|
wish their XHTML documents to render on existing HTML user |
|
|
agents.</p> |
|
|
|
|
|
<h2>C.1 Processing Instructions</h2> |
|
|
<p>Be aware that processing instructions are rendered on some |
|
|
user agents. However, also note that when the XML declaration is not included |
|
|
in a document, the document can only use the default character encodings UTF-8 |
|
|
or UTF-16.</p> |
|
|
|
|
|
<h2>C.2 Empty Elements</h2> |
|
|
<p>Include a space before the trailing <code>/</code> and <code> |
|
|
></code> of empty elements, e.g. <code class="greenmono"> |
|
|
<br /></code>, <code class="greenmono"> |
|
|
<hr /></code> and <code class="greenmono"><img |
|
|
src="karen.jpg" alt="Karen" /></code>. Also, use the |
|
|
minimized tag syntax for empty elements, e.g. <code class= |
|
|
"greenmono"><br /></code>, as the alternative syntax <code |
|
|
class="greenmono"><br></br></code> allowed by XML |
|
|
gives uncertain results in many existing user agents.</p> |
|
|
|
|
|
<h2>C.3 Element Minimization and Empty Element Content</h2> |
|
|
<p>Given an empty instance of an element whose content model is |
|
|
not <code>EMPTY</code> (for example, an empty title or paragraph) |
|
|
do not use the minimized form (e.g. use <code class="greenmono"> |
|
|
<p> </p></code> and not <code class="greenmono"> |
|
|
<p /></code>).</p> |
|
|
|
|
|
<h2>C.4 Embedded Style Sheets and Scripts</h2> |
|
|
<p>Use external style sheets if your style sheet uses <code> |
|
|
<</code> or <code>&</code> or <code>]]></code> or <code>--</code>. Use |
|
|
external scripts if your script uses <code><</code> or <code> |
|
|
&</code> or <code>]]></code> or <code>--</code>. Note that XML parsers |
|
|
are permitted to silently remove the contents of comments. Therefore, the historical |
|
|
practice of "hiding" scripts and style sheets within comments to make the |
|
|
documents backward compatible is likely to not work as expected in XML-based |
|
|
implementations.</p> |
|
|
|
|
|
<h2>C.5 Line Breaks within Attribute Values</h2> |
|
|
<p>Avoid line breaks and multiple whitespace characters within |
|
|
attribute values. These are handled inconsistently by user |
|
|
agents.</p> |
|
|
|
|
|
<h2>C.6 Isindex</h2> |
|
|
<p>Don't include more than one <code>isindex</code> element in |
|
|
the document <code>head</code>. The <code>isindex</code> element |
|
|
is deprecated in favor of the <code>input</code> element.</p> |
|
|
|
|
|
<h2>C.7 The <code>lang</code> and <code>xml:lang</code> Attributes</h2> |
|
|
<p>Use both the <code>lang</code> and <code>xml:lang</code> |
|
|
attributes when specifying the language of an element. The value |
|
|
of the <code>xml:lang</code> attribute takes precedence.</p> |
|
|
|
|
|
<h2>C.8 Fragment Identifiers</h2> |
|
|
<p>In XML, <abbr title="Uniform Resource Identifiers">URIs</abbr> [<a href="#ref-rfc2396">RFC2396</a>] that end with fragment identifiers of the form |
|
|
<code>"#foo"</code> do not refer to elements with an attribute |
|
|
<code>name="foo"</code>; rather, they refer to elements with an |
|
|
attribute defined to be of type <code>ID</code>, e.g., the <code> |
|
|
id</code> attribute in HTML 4.0. Many existing HTML clients don't |
|
|
support the use of <code>ID</code>-type attributes in this way, |
|
|
so identical values may be supplied for both of these attributes to ensure |
|
|
maximum forward and backward compatibility (e.g., <code class= |
|
|
"greenmono"><a id="foo" name="foo">...</a></code>).</p> |
|
|
|
|
|
<p>Further, since the set of |
|
|
legal values for attributes of type <code>ID</code> is much smaller than |
|
|
for those of type <code>CDATA</code>, the type of the <code>name</code> |
|
|
attribute has been changed to <code>NMTOKEN</code>. This attribute is |
|
|
constrained such that it can only have the same values as type |
|
|
<code>ID</code>, or as the <code>Name</code> production in XML 1.0 Section |
|
|
2.5, production 5. Unfortunately, this constraint cannot be expressed in the |
|
|
XHTML 1.0 DTDs. Because of this change, care must be taken when |
|
|
converting existing HTML documents. The values of these attributes |
|
|
must be unique within the document, valid, and any references to these |
|
|
fragment identifiers (both |
|
|
internal and external) must be updated should the values be changed during |
|
|
conversion.</p> |
|
|
<p>Finally, note that XHTML 1.0 has deprecated the |
|
|
<code>name</code> attribute of the <code>a</code>, <code>applet</code>, <code>frame</code>, <code>iframe</code>, <code>img</code>, and <code>map</code> |
|
|
elements, and it will be |
|
|
removed from XHTML in subsequent versions.</p> |
|
|
|
|
|
<h2>C.9 Character Encoding</h2> |
|
|
<p>To specify a character encoding in the document, use both the |
|
|
encoding attribute specification on the xml declaration (e.g. |
|
|
<code class="greenmono"><?xml version="1.0" |
|
|
encoding="EUC-JP"?></code>) and a meta http-equiv statement |
|
|
(e.g. <code class="greenmono"><meta http-equiv="Content-type" |
|
|
content='text/html; charset="EUC-JP"' /></code>). The |
|
|
value of the encoding attribute of the xml processing instruction |
|
|
takes precedence.</p> |
|
|
|
|
|
<h2>C.10 Boolean Attributes</h2> |
|
|
<p>Some HTML user agents are unable to interpret boolean |
|
|
attributes when these appear in their full (non-minimized) form, |
|
|
as required by XML 1.0. Note this problem doesn't effect user |
|
|
agents compliant with HTML 4.0. The following attributes are |
|
|
involved: <code>compact</code>, <code>nowrap</code>, <code> |
|
|
ismap</code>, <code>declare</code>, <code>noshade</code>, <code> |
|
|
checked</code>, <code>disabled</code>, <code>readonly</code>, |
|
|
<code>multiple</code>, <code>selected</code>, <code> |
|
|
noresize</code>, <code>defer</code>.</p> |
|
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|
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|
<h2>C.11 Document Object Model and XHTML</h2> |
|
|
<p> |
|
|
The Document Object Model level 1 Recommendation [<a href="#ref-dom">DOM</a>] |
|
|
defines document object model interfaces for XML and HTML 4.0. The HTML 4.0 |
|
|
document object model specifies that HTML element and attribute names are |
|
|
returned in upper-case. The XML document object model specifies that |
|
|
element and attribute names are returned in the case they are specified. In |
|
|
XHTML 1.0, elements and attributes are specified in lower-case. This apparent difference can be |
|
|
addressed in two ways: |
|
|
</p> |
|
|
<ol> |
|
|
<li>Applications that access XHTML documents served as Internet media type |
|
|
<code>text/html</code> |
|
|
via the <abbr title="Document Object Model">DOM</abbr> can use the HTML DOM, |
|
|
and can rely upon element and attribute names being returned in |
|
|
upper-case from those interfaces.</li> |
|
|
<li>Applications that access XHTML documents served as Internet media types |
|
|
<code>text/xml</code> or <code>application/xml</code> |
|
|
can also use the XML DOM. Elements and attributes will be returned in lower-case. |
|
|
Also, some XHTML elements may or may |
|
|
not appear |
|
|
in the object tree because they are optional in the content model |
|
|
(e.g. the <code>tbody</code> element within |
|
|
<code>table</code>). This occurs because in HTML 4.0 some elements were |
|
|
permitted to be minimized such that their start and end tags are both omitted |
|
|
(an SGML feature). |
|
|
This is not possible in XML. Rather than require document authors to insert |
|
|
extraneous elements, XHTML has made the elements optional. |
|
|
Applications need to adapt to this |
|
|
accordingly.</li> |
|
|
</ol> |
|
|
|
|
|
<h2>C.12 Using Ampersands in Attribute Values</h2> |
|
|
<p> |
|
|
When an attribute value contains an ampersand, it must be expressed as a character |
|
|
entity reference |
|
|
(e.g. "<code>&amp;</code>"). For example, when the |
|
|
<code>href</code> attribute |
|
|
of the <code>a</code> element refers to a |
|
|
CGI script that takes parameters, it must be expressed as |
|
|
<code>http://my.site.dom/cgi-bin/myscript.pl?class=guest&amp;name=user</code> |
|
|
rather than as |
|
|
<code>http://my.site.dom/cgi-bin/myscript.pl?class=guest&name=user</code>. |
|
|
</p> |
|
|
|
|
|
<h2>C.13 Cascading Style Sheets (CSS) and XHTML</h2> |
|
|
|
|
|
<p>The Cascading Style Sheets level 2 Recommendation [<a href="#ref-css2">CSS2</a>] defines style |
|
|
properties which are applied to the parse tree of the HTML or XML |
|
|
document. Differences in parsing will produce different visual or |
|
|
aural results, depending on the selectors used. The following hints |
|
|
will reduce this effect for documents which are served without |
|
|
modification as both media types:</p> |
|
|
|
|
|
<ol> |
|
|
<li> |
|
|
CSS style sheets for XHTML should use lower case element and |
|
|
attribute names.</li> |
|
|
|
|
|
|
|
|
<li>In tables, the tbody element will be inferred by the parser of an |
|
|
HTML user agent, but not by the parser of an XML user agent. Therefore |
|
|
you should always explicitly add a tbody element if it is referred to |
|
|
in a CSS selector.</li> |
|
|
|
|
|
<li>Within the XHTML name space, user agents are expected to |
|
|
recognize the "id" attribute as an attribute of type ID. |
|
|
Therefore, style sheets should be able to continue using the |
|
|
shorthand "#" selector syntax even if the user agent does not read |
|
|
the DTD.</li> |
|
|
|
|
|
<li>Within the XHTML name space, user agents are expected to |
|
|
recognize the "class" attribute. Therefore, style sheets should be |
|
|
able to continue using the shorthand "." selector syntax.</li> |
|
|
|
|
|
<li> |
|
|
CSS defines different conformance rules for HTML and XML documents; |
|
|
be aware that the HTML rules apply to XHTML documents delivered as |
|
|
HTML and the XML rules apply to XHTML documents delivered as XML.</li> |
|
|
</ol> |
|
|
|
|
|
<h1><a name="acks" id="acks">Appendix D. |
|
|
Acknowledgements</a></h1> |
|
|
|
|
|
<p><b>This appendix is informative.</b></p> |
|
|
|
|
|
<p>This specification was written with the participation of the |
|
|
members of the W3C HTML working group:</p> |
|
|
|
|
|
<dl> |
|
|
<dd>Steven Pemberton, CWI (HTML Working Group Chair)<br /> |
|
|
Murray Altheim, Sun Microsystems<br /> |
|
|
Daniel Austin, CNET: The Computer Network<br /> |
|
|
Frank Boumphrey, HTML Writers Guild<br /> |
|
|
John Burger, Mitre<br /> |
|
|
Andrew W. Donoho, IBM<br /> |
|
|
Sam Dooley, IBM<br /> |
|
|
Klaus Hofrichter, GMD<br /> |
|
|
Philipp Hoschka, W3C<br /> |
|
|
Masayasu Ishikawa, W3C<br /> |
|
|
Warner ten Kate, Philips Electronics<br /> |
|
|
Peter King, Phone.com<br /> |
|
|
Paula Klante, JetForm<br /> |
|
|
Shin'ichi Matsui, W3C/Panasonic<br /> |
|
|
Shane McCarron, Applied Testing and Technology (The Open Group through August |
|
|
1999)<br /> |
|
|
Ann Navarro, HTML Writers Guild<br /> |
|
|
Zach Nies, Quark<br /> |
|
|
Dave Raggett, W3C/HP (W3C lead for HTML)<br /> |
|
|
Patrick Schmitz, Microsoft<br /> |
|
|
Sebastian Schnitzenbaumer, Stack Overflow<br /> |
|
|
Chris Wilson, Microsoft<br /> |
|
|
Ted Wugofski, Gateway 2000<br /> |
|
|
Dan Zigmond, WebTV Networks</dd> |
|
|
</dl> |
|
|
|
|
|
|
|
|
<h1><a name="refs" id="refs">Appendix E. References</a></h1> |
|
|
|
|
|
<p><b>This appendix is informative.</b></p> |
|
|
|
|
|
<dl> |
|
|
|
|
|
<dt><a name="ref-css2" id="ref-css2"><b>[CSS2]</b></a></dt> |
|
|
|
|
|
<dd><a href="http://www.w3.org/TR/REC-CSS2">"Cascading Style Sheets, level 2 (CSS2) Specification"</a>, B. |
|
|
Bos, H. W. Lie, C. Lilley, I. Jacobs, 12 May 1998.<br /> |
|
|
Available at: <a href="http://www.w3.org/TR/REC-CSS2"> |
|
|
http://www.w3.org/TR/REC-CSS2</a></dd> |
|
|
|
|
|
<dt><a name="ref-dom" id="ref-dom"><b>[DOM]</b></a></dt> |
|
|
|
|
|
<dd><a href="http://www.w3.org/TR/REC-DOM-Level-1">"Document Object Model (DOM) Level 1 Specification"</a>, Lauren |
|
|
Wood <i>et al.</i>, 1 October 1998.<br /> |
|
|
Available at: <a href="http://www.w3.org/TR/REC-DOM-Level-1"> |
|
|
http://www.w3.org/TR/REC-DOM-Level-1</a></dd> |
|
|
|
|
|
<dt><a name="ref-html4" id="ref-html4"><b>[HTML]</b></a></dt> |
|
|
|
|
|
<dd><a href="http://www.w3.org/TR/1999/PR-html40-19990824">"HTML 4.01 Specification"</a>, D. Raggett, A. Le Hors, I. |
|
|
Jacobs, 24 August 1999.<br /> |
|
|
Available at: <a href="http://www.w3.org/TR/1999/PR-html40-19990824"> |
|
|
http://www.w3.org/TR/1999/PR-html40-19990824</a></dd> |
|
|
|
|
|
<dt><a name="ref-posix" id="ref-posix"><b>[POSIX.1]</b></a></dt> |
|
|
|
|
|
<dd>"ISO/IEC 9945-1:1990 Information Technology - Portable |
|
|
Operating System Interface (POSIX) - Part 1: System Application |
|
|
Program Interface (API) [C Language]", Institute of Electrical |
|
|
and Electronics Engineers, Inc, 1990.</dd> |
|
|
|
|
|
<dt><a name="ref-rfc2046" id="ref-rfc2046"><b> |
|
|
[RFC2046]</b></a></dt> |
|
|
|
|
|
<dd><a href="http://www.ietf.org/rfc/rfc2046.txt">"RFC2046: Multipurpose Internet Mail Extensions (MIME) Part |
|
|
Two: Media Types"</a>, N. Freed and N. Borenstein, November |
|
|
1996.<br /> |
|
|
Available at <a href="http://www.ietf.org/rfc/rfc2046.txt"> |
|
|
http://www.ietf.org/rfc/rfc2046.txt</a>. Note that this RFC |
|
|
obsoletes RFC1521, RFC1522, and RFC1590.</dd> |
|
|
|
|
|
<dt><a name="ref-rfc2119" id="ref-rfc2119"><b> |
|
|
[RFC2119]</b></a></dt> |
|
|
|
|
|
<dd><a href="http://www.ietf.org/rfc/rfc2119.txt">"RFC2119: Key words for use in RFCs to Indicate Requirement |
|
|
Levels"</a>, S. Bradner, March 1997.<br /> |
|
|
Available at: <a href="http://www.ietf.org/rfc/rfc2119.txt"> |
|
|
http://www.ietf.org/rfc/rfc2119.txt</a></dd> |
|
|
|
|
|
<dt><a name="ref-rfc2376" id="ref-rfc2376"><b> |
|
|
[RFC2376]</b></a></dt> |
|
|
|
|
|
<dd><a href="http://www.ietf.org/rfc/rfc2376.txt">"RFC2376: XML Media Types"</a>, E. Whitehead, M. Murata, July |
|
|
1998.<br /> |
|
|
Available at: <a href="http://www.ietf.org/rfc/rfc2376.txt"> |
|
|
http://www.ietf.org/rfc/rfc2376.txt</a></dd> |
|
|
|
|
|
<dt><a name="ref-rfc2396" id="ref-rfc2396"><b> |
|
|
[RFC2396]</b></a></dt> |
|
|
|
|
|
<dd><a href="http://www.ietf.org/rfc/rfc2396.txt">"RFC2396: Uniform Resource Identifiers (URI): Generic |
|
|
Syntax"</a>, T. Berners-Lee, R. Fielding, L. Masinter, August |
|
|
1998.<br /> |
|
|
This document updates RFC1738 and RFC1808.<br /> |
|
|
Available at: <a href="http://www.ietf.org/rfc/rfc2396.txt"> |
|
|
http://www.ietf.org/rfc/rfc2396.txt</a></dd> |
|
|
|
|
|
<dt><a name="ref-xml" id="ref-xml"><b>[XML]</b></a></dt> |
|
|
|
|
|
<dd><a href="http://www.w3.org/TR/REC-xml">"Extensible Markup Language (XML) 1.0 Specification"</a>, T. |
|
|
Bray, J. Paoli, C. M. Sperberg-McQueen, 10 February 1998.<br /> |
|
|
Available at: <a href="http://www.w3.org/TR/REC-xml"> |
|
|
http://www.w3.org/TR/REC-xml</a></dd> |
|
|
|
|
|
<dt><a name="ref-xmlns" id="ref-xmlns"><b>[XMLNAMES]</b></a></dt> |
|
|
|
|
|
<dd><a href="http://www.w3.org/TR/REC-xml-names">"Namespaces in XML"</a>, T. Bray, D. Hollander, A. Layman, 14 |
|
|
January 1999.<br /> |
|
|
XML namespaces provide a simple method for qualifying names used |
|
|
in XML documents by associating them with namespaces identified |
|
|
by URI.<br /> |
|
|
Available at: <a href="http://www.w3.org/TR/REC-xml-names"> |
|
|
http://www.w3.org/TR/REC-xml-names</a></dd> |
|
|
|
|
|
</dl> |
|
|
<p><a href="http://www.w3.org/WAI/WCAG1AAA-Conformance" |
|
|
title="Explanation of Level Triple-A Conformance"> |
|
|
<img height="32" width="88" |
|
|
src="wcag1AAA.gif" |
|
|
alt="Level Triple-A conformance icon, W3C-WAI Web Content Accessibility Guidelines 1.0" /></a></p> |
|
|
<div class="navbar"> |
|
|
<hr /> |
|
|
<a href="#toc">table of contents</a> |
|
|
</div> |
|
|
</body> |
|
|
</html> |
|
|
|
|
|
|
