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55: <div class="navbar">
56: <a href="#toc">table of contents</a>
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59: <div class="head"><p><a href="http://www.w3.org/"><img class="head" src="w3c_home.gif" alt="W3C" /></a></p>
60:
61: <h1 class="head"><a name="title" id="title">XHTML</a><sup>™</sup> 1.0:
62: The Extensible HyperText Markup Language</h1>
63:
64: <h2>A Reformulation of HTML 4.0 in XML 1.0</h2>
65:
66: <h3>W3C Proposed Recommendation 10 December 1999</h3>
67:
68: <dl>
69: <dt>This version:</dt>
70:
71: <dd><a href="http://www.w3.org/TR/1999/PR-xhtml1-19991210">
72: http://www.w3.org/TR/1999/PR-xhtml1-19991210</a> <br />
73: (<a href="xhtml1.ps">Postscript version</a>,
74: <a href="xhtml1.pdf">PDF version</a>,
75: <a href="xhtml1.zip">ZIP archive</a>, or
76: <a href="xhtml1.tgz">Gzip'd TAR archive</a>)
77: </dd>
78:
79: <dt>Latest version:</dt>
80:
81: <dd><a href="http://www.w3.org/TR/xhtml1">
82: http://www.w3.org/TR/xhtml1</a></dd>
83:
84: <dt>Previous versions:</dt>
85:
86: <dd><a href="http://www.w3.org/TR/1999/WD-xhtml1-19991124">
87: http://www.w3.org/TR/1999/WD-xhtml1-19991124</a></dd>
88: <dd><a href="http://www.w3.org/TR/1999/PR-xhtml1-19990824">
89: http://www.w3.org/TR/1999/PR-xhtml1-19990824</a></dd>
90:
91: <dt>Authors:</dt>
92:
93: <dd>See <a href="#acks">acknowledgements</a>.</dd>
94: </dl>
95:
96: <p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">
97: Copyright</a> © 1999 <a href="http://www.w3.org/">W3C</a><sup>®</sup>
98: (<a href="http://www.lcs.mit.edu/">MIT</a>, <a href="http://www.inria.fr/">INRIA</a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. <abbr title="World Wide Web Consortium">W3C</abbr> <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">
99: liability</a>, <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">
100: trademark</a>, <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document
101: use</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-software">software
102: licensing</a> rules apply.</p>
103: <hr />
104: </div>
105:
106: <h2 class="notoc">Abstract</h2>
107:
108: <p>This specification defines <abbr title="Extensible Hypertext Markup Language">XHTML</abbr> 1.0, a reformulation of HTML
109: 4.0 as an XML 1.0 application, and three <abbr title="Document Type Definition">DTDs</abbr> corresponding to
110: the ones defined by HTML 4.0. The semantics of the elements and
111: their attributes are defined in the W3C Recommendation for HTML
112: 4.0. These semantics provide the foundation for future
113: extensibility of XHTML. Compatibility with existing HTML user
114: agents is possible by following a small set of guidelines.</p>
115:
116: <h2>Status of this document</h2>
117:
118: <p><em>This section describes the status of this document at the time
119: of its publication. Other documents may supersede this document. The
120: latest status of this document series is maintained at the W3C.</em></p>
121:
122: <p>This specification is a Proposed Recommendation of the HTML Working Group. It is
123: a revision of the Proposed Recommendation dated <a href="http://www.w3.org/TR/1999/PR-xhtml1-19990824/">24 August
124: 1999</a> incorporating changes as a result of comments from the Proposed
125: Recommendation review, and
126: comments and further deliberations of the W3C HTML Working Group. A
127: <a href="xhtml1-diff-19991210.html">diff-marked version</a> from the previous
128: proposed recommendation is available for comparison purposes.</p>
129:
130: <p>On 10 December 1999, this document enters a
131: <a href="http://www.w3.org/Consortium/Process/#RecsPR">
132: Proposed Recommendation</a> review period. From that date until 8 January
133: 2000,
134: W3C Advisory Committee representatives are encouraged
135: to review this specification and return comments in their completed
136: ballots to w3c-html-review@w3.org. Please send any comments of a
137: confidential nature in separate email to w3t-html@w3.org, which is
138: visible to the Team only.</p>
139:
140: <p>No sooner than 14 days after the end of the review period, the
141: Director will announce the document's disposition: it may become a W3C
142: Recommendation (possibly with minor changes), it may revert to Working
143: Draft status, or it may be dropped as a W3C work item.</p>
144:
145: <p>Publication as a Proposed Recommendation does not imply endorsement
146: by the W3C membership. This is still a draft document and may be
147: updated, replaced or obsoleted by other documents at any time. It is
148: inappropriate to cite W3C Proposed Recommendation as other than "work
149: in progress."</p>
150:
151: <p>This document has been produced as part of the <a href="http://www.w3.org/MarkUp/">W3C HTML Activity</a>. The goals of
152: the <a href="http://www.w3.org/MarkUp/Group/">HTML Working
153: Group</a> <i>(<a href="http://cgi.w3.org/MemberAccess/">members
154: only</a>)</i> are discussed in the <a href="http://www.w3.org/MarkUp/Group/HTMLcharter">HTML Working Group
155: charter</a> <i>(<a href="http://cgi.w3.org/MemberAccess/">members
156: only</a>)</i>.</p>
157:
158: <p>A list of current W3C Recommendations and other technical documents
159: can be found at <a href="http://www.w3.org/TR">http://www.w3.org/TR</a>.</p>
160:
161: <p>Public discussion on <abbr title="HyperText Markup Language">HTML</abbr> features takes place on the mailing list <a href="mailto:www-html@w3.org"> www-html@w3.org</a> (<a href="http://lists.w3.org/Archives/Public/www-html/">archive</a>). The W3C
162: staff contact for work on HTML is <a href="mailto:dsr@w3.org">Dave
163: Raggett</a>.</p>
164:
165: <p>Please report errors in this document to <a href="mailto:www-html-editor@w3.org">www-html-editor@w3.org</a>.</p>
166:
167: <p>The list of known errors in this specification is available at <a href="http://www.w3.org/1999/12/PR-xhtml1-19991210-errata">http://www.w3.org/1999/12/PR-xhtml1-19991210-errata</a>.</p>
168:
169: <h2 class="notoc"><a id="toc" name="toc">Contents</a></h2>
170:
171: <div class="contents">
172: <ul class="toc">
173: <li class="tocline">1. <a href="#xhtml">What is XHTML?</a>
174:
175: <ul class="toc">
176: <li class="tocline">1.1 <a href="#html4">What is HTML 4.0?</a></li>
177:
178: <li class="tocline">1.2 <a href="#xml">What is XML?</a></li>
179:
180: <li class="tocline">1.3 <a href="#why">Why the need for XHTML?</a></li>
181: </ul>
182: </li>
183:
184: <li class="tocline">2. <a href="#defs">Definitions</a>
185:
186: <ul class="toc">
187: <li class="tocline">2.1 <a href="#terms">Terminology</a></li>
188:
189: <li class="tocline">2.2 <a href="#general">General Terms</a></li>
190: </ul>
191: </li>
192:
193: <li class="tocline">3. <a href="#normative">Normative Definition of XHTML 1.0</a>
194:
195:
196: <ul class="toc">
197: <li class="tocline">3.1 <a href="#docconf">Document Conformance</a></li>
198:
199: <li class="tocline">3.2 <a href="#uaconf">User Agent Conformance</a></li>
200: </ul>
201: </li>
202:
203: <li class="tocline">4. <a href="#diffs">Differences with HTML 4.0</a>
204:
205: </li>
206:
207: <li class="tocline">5. <a href="#issues">Compatibility Issues</a>
208:
209: <ul class="toc">
210: <li class="tocline">5.1 <a href="#media">Internet Media Types</a></li>
211: </ul>
212: </li>
213:
214: <li class="tocline">6. <a href="#future">Future Directions</a>
215:
216: <ul class="toc">
217: <li class="tocline">6.1 <a href="#mods">Modularizing HTML</a></li>
218:
219: <li class="tocline">6.2 <a href="#extensions">Subsets and Extensibility</a></li>
220:
221: <li class="tocline">6.3 <a href="#profiles">Document Profiles</a></li>
222: </ul>
223: </li>
224:
225: <li class="tocline"><a href="#dtds">Appendix A. DTDs</a></li>
226:
227: <li class="tocline"><a href="#prohibitions">Appendix B. Element
228: Prohibitions</a></li>
229:
230: <li class="tocline"><a href="#guidelines">Appendix C. HTML Compatibility Guidelines</a></li>
231:
232: <li class="tocline"><a href="#acks">Appendix D. Acknowledgements</a></li>
233:
234: <li class="tocline"><a href="#refs">Appendix E. References</a></li>
235: </ul>
236: </div>
237:
238: <!--OddPage-->
239: <h1><a name="xhtml" id="xhtml">1. What is XHTML?</a></h1>
240:
241: <p>XHTML is a family of current and future document types and modules that
242: 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,
243: and ultimately are designed to work in conjunction with XML-based user agents.
244: The details of this family and its evolution are
245: discussed in more detail in the section on <a href="#future">Future
246: Directions</a>. </p>
247:
248: <p>XHTML 1.0 (this specification) is the first document type in the XHTML
249: family. It is a reformulation of the three HTML 4.0 document types as
250: applications of XML 1.0 <a href="#ref-xml"> [XML]</a>. It is intended
251: to be used as a language for content that is both XML-conforming and, if some
252: simple <a href="#guidelines">guidelines</a> are followed,
253: operates in HTML 4.0 conforming user agents. Developers who migrate
254: their content to XHTML 1.0 will realize the following benefits:</p>
255:
256: <ul>
257: <li>XHTML documents are XML conforming. As such, they are readily viewed,
258: edited, and validated with standard XML tools.</li>
259: <li>XHTML documents can be written to
260: to operate as well or better than they did before in existing
261: HTML 4.0-conforming user agents as well as in new, XHTML 1.0 conforming user
262: agents.</li>
263: <li>XHTML documents can utilize applications (e.g. scripts and applets) that rely
264: upon either the HTML Document Object Model or the XML Document Object Model <a href="#ref-dom">[DOM]</a>.</li>
265: <li>As the XHTML family evolves, documents conforming to XHTML 1.0 will be more
266: likely to interoperate within and among various XHTML environments.</li>
267: </ul>
268:
269: <p>The XHTML family is the next step in the evolution of the Internet. By
270: migrating to XHTML today, content developers can enter the XML world with all
271: of its attendant benefits, while still remaining confident in their
272: content's backward and future compatibility.</p>
273:
274: <h2><a name="html4" id="html4">1.1 What is HTML 4.0?</a></h2>
275:
276: <p>HTML 4.0 <a href="#ref-html4">[HTML]</a> is an <abbr title="Standard Generalized Markup Language">SGML</abbr> (Standard
277: Generalized Markup Language) application conforming to
278: International Standard <abbr title="Organization for International Standardization">ISO</abbr> 8879, and is widely regarded as the
279: standard publishing language of the World Wide Web.</p>
280:
281: <p>SGML is a language for describing markup languages,
282: particularly those used in electronic document exchange, document
283: management, and document publishing. HTML is an example of a
284: language defined in SGML.</p>
285:
286: <p>SGML has been around since the middle 1980's and has remained
287: quite stable. Much of this stability stems from the fact that the
288: language is both feature-rich and flexible. This flexibility,
289: however, comes at a price, and that price is a level of
290: complexity that has inhibited its adoption in a diversity of
291: environments, including the World Wide Web.</p>
292:
293: <p>HTML, as originally conceived, was to be a language for the
294: exchange of scientific and other technical documents, suitable
295: for use by non-document specialists. HTML addressed the problem
296: of SGML complexity by specifying a small set of structural and
297: semantic tags suitable for authoring relatively simple documents.
298: In addition to simplifying the document structure, HTML added
299: support for hypertext. Multimedia capabilities were added
300: later.</p>
301:
302: <p>In a remarkably short space of time, HTML became wildly
303: popular and rapidly outgrew its original purpose. Since HTML's
304: inception, there has been rapid invention of new elements for use
305: within HTML (as a standard) and for adapting HTML to vertical,
306: highly specialized, markets. This plethora of new elements has
307: led to compatibility problems for documents across different
308: platforms.</p>
309:
310: <p>As the heterogeneity of both software and platforms rapidly
311: proliferate, it is clear that the suitability of 'classic' HTML
312: 4.0 for use on these platforms is somewhat limited.</p>
313:
314: <h2><a name="xml" id="xml">1.2 What is XML?</a></h2>
315:
316: <p>XML<sup>™</sup> is the shorthand for Extensible Markup
317: Language, and is an acronym of Extensible Markup Language <a href="#ref-xml">[XML]</a>.</p>
318:
319: <p>XML was conceived as a means of regaining the power and
320: flexibility of SGML without most of its complexity. Although a
321: restricted form of SGML, XML nonetheless preserves most of SGML's
322: power and richness, and yet still retains all of SGML's commonly
323: used features.</p>
324:
325: <p>While retaining these beneficial features, XML removes many of
326: the more complex features of SGML that make the authoring and
327: design of suitable software both difficult and costly.</p>
328:
329: <h2><a name="why" id="why">1.3 Why the need for XHTML?</a></h2>
330:
331: <p>The benefits of migrating to XHTML 1.0 are described above. Some of the
332: benefits of migrating to XHTML in general are:</p>
333:
334: <ul>
335: <li>Document developers and user agent designers are constantly
336: discovering new ways to express their ideas through new markup. In XML, it is
337: relatively easy to introduce new elements or additional element
338: attributes. The XHTML family is designed to accommodate these extensions
339: through XHTML modules and techniques for developing new XHTML-conforming
340: modules (described in the forthcoming XHTML Modularization specification).
341: These modules will permit the combination of existing and
342: new feature sets when developing content and when designing new user
343: agents.</li>
344:
345: <li>Alternate ways of accessing the Internet are constantly being
346: introduced. Some estimates indicate that by the year 2002, 75% of
347: Internet document viewing will be carried out on these alternate
348: platforms. The XHTML family is designed with general user agent
349: interoperability in mind. Through a new user agent and document profiling
350: mechanism, servers, proxies, and user agents will be able to perform
351: best effort content transformation. Ultimately, it will be possible to
352: develop XHTML-conforming content that is usable by any XHTML-conforming
353: user agent.</li>
354:
355: </ul>
356: <!--OddPage-->
357: <h1><a name="defs" id="defs">2. Definitions</a></h1>
358:
359: <h2><a name="terms" id="terms">2.1 Terminology</a></h2>
360:
361: <p>The following terms are used in this specification. These
362: terms extend the definitions in <a href="#ref-rfc2119">
363: [RFC2119]</a> in ways based upon similar definitions in ISO/<abbr title="International Electro-technical Commission">IEC</abbr>
364: 9945-1:1990 <a href="#ref-posix">[POSIX.1]</a>:</p>
365:
366: <dl>
367: <dt>Implementation-defined</dt>
368:
369: <dd>A value or behavior is implementation-defined when it is left
370: to the implementation to define [and document] the corresponding
371: requirements for correct document construction.</dd>
372:
373: <dt>May</dt>
374:
375: <dd>With respect to implementations, the word "may" is to be
376: interpreted as an optional feature that is not required in this
377: specification but can be provided. With respect to <a href="#docconf">Document Conformance</a>, the word "may" means that
378: the optional feature must not be used. The term "optional" has
379: the same definition as "may".</dd>
380:
381: <dt>Must</dt>
382:
383: <dd>In this specification, the word "must" is to be interpreted
384: as a mandatory requirement on the implementation or on Strictly
385: Conforming XHTML Documents, depending upon the context. The term
386: "shall" has the same definition as "must".</dd>
387:
388: <dt>Reserved</dt>
389:
390: <dd>A value or behavior is unspecified, but it is not allowed to
391: be used by Conforming Documents nor to be supported by a
392: Conforming User Agents.</dd>
393:
394: <dt>Should</dt>
395:
396: <dd>With respect to implementations, the word "should" is to be
397: interpreted as an implementation recommendation, but not a
398: requirement. With respect to documents, the word "should" is to
399: be interpreted as recommended programming practice for documents
400: and a requirement for Strictly Conforming XHTML Documents.</dd>
401:
402: <dt>Supported</dt>
403:
404: <dd>Certain facilities in this specification are optional. If a
405: facility is supported, it behaves as specified by this
406: specification.</dd>
407:
408: <dt>Unspecified</dt>
409:
410: <dd>When a value or behavior is unspecified, the specification
411: defines no portability requirements for a facility on an
412: implementation even when faced with a document that uses the
413: facility. A document that requires specific behavior in such an
414: instance, rather than tolerating any behavior when using that
415: facility, is not a Strictly Conforming XHTML Document.</dd>
416: </dl>
417:
418: <h2><a name="general" id="general">2.2 General Terms</a></h2>
419:
420: <dl>
421: <dt>Attribute</dt>
422:
423: <dd>An attribute is a parameter to an element declared in the
424: DTD. An attribute's type and value range, including a possible
425: default value, are defined in the DTD.</dd>
426:
427: <dt>DTD</dt>
428:
429: <dd>A DTD, or document type definition, is a collection of XML
430: declarations that, as a collection, defines the legal structure,
431: <span class="term">elements</span>, and <span class="term">
432: attributes</span> that are available for use in a document that
433: complies to the DTD.</dd>
434:
435: <dt>Document</dt>
436:
437: <dd>A document is a stream of data that, after being combined
438: with any other streams it references, is structured such that it
439: holds information contained within <span class="term">
440: elements</span> that are organized as defined in the associated
441: <span class="term">DTD</span>. See <a href="#docconf">Document
442: Conformance</a> for more information.</dd>
443:
444: <dt>Element</dt>
445:
446: <dd>An element is a document structuring unit declared in the
447: <span class="term">DTD</span>. The element's content model is
448: defined in the <span class="term">DTD</span>, and additional
449: semantics may be defined in the prose description of the
450: element.</dd>
451:
452: <dt><a name="facilities" id="facilities">Facilities</a></dt>
453:
454: <dd>Functionality includes <span class="term">elements</span>,
455: <span class="term">attributes</span>, and the semantics
456: associated with those <span class="term">elements</span> and
457: <span class="term">attributes</span>. An implementation
458: supporting that functionality is said to provide the necessary
459: facilities.</dd>
460:
461: <dt>Implementation</dt>
462:
463: <dd>An implementation is a system that provides collection of
464: <span class="term">facilities</span> and services that supports
465: this specification. See <a href="#uaconf">User Agent
466: Conformance</a> for more information.</dd>
467:
468: <dt>Parsing</dt>
469:
470: <dd>Parsing is the act whereby a <span class="term">
471: document</span> is scanned, and the information contained within
472: the <span class="term">document</span> is filtered into the
473: context of the <span class="term">elements</span> in which the
474: information is structured.</dd>
475:
476: <dt>Rendering</dt>
477:
478: <dd>Rendering is the act whereby the information in a <span class="term">document</span> is presented. This presentation is
479: done in the form most appropriate to the environment (e.g.
480: aurally, visually, in print).</dd>
481:
482: <dt>User Agent</dt>
483:
484: <dd>A user agent is an <span class="term">implementation</span>
485: that retrieves and processes XHTML documents. See <a href="#uaconf">User Agent Conformance</a> for more information.</dd>
486:
487: <dt>Validation</dt>
488:
489: <dd>Validation is a process whereby <span class="term">
490: 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">
491: attributes</span> are consistent with the definitions in the
492: <span class="term">DTD</span>.</dd>
493:
494: <dt><a name="wellformed" id="wellformed">Well-formed</a></dt>
495:
496: <dd>A <span class="term">document</span> is well-formed when it
497: 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
498: the XML 1.0 Recommendation <a href="#ref-xml">[XML]</a>.
499: Basically, this definition states that elements, delimited by
500: their start and end tags, are nested properly within one
501: another.</dd>
502: </dl>
503:
504: <!--OddPage-->
505: <h1><a name="normative" id="normative">3. Normative Definition of
506: XHTML 1.0</a></h1>
507:
508: <h2><a name="docconf" id="docconf">3.1 Document
509: Conformance</a></h2>
510:
511: <p>This version of XHTML provides a definition of strictly
512: conforming XHTML documents, which are restricted to tags and
513: attributes from the XHTML namespace. See <a href="#well-formed">Section 3.1.2</a> for information on using XHTML
514: with other namespaces, for instance, to include metadata
515: expressed in <abbr title="Resource Description Format">RDF</abbr> within XHTML documents.</p>
516:
517: <h3><a name="strict" id="strict">3.1.1 Strictly Conforming
518: Documents</a></h3>
519:
520: <p>A Strictly Conforming XHTML Document is a document that
521: requires only the facilities described as mandatory in this
522: specification. Such a document must meet all of the following
523: criteria:</p>
524:
525: <ol>
526: <li>
527: <p>It must validate against one of the three DTDs found in <a href="#dtds">Appendix A</a>.</p>
528: </li>
529:
530: <li>
531: <p>The root element of the document must be <code>
532: <html></code>.</p>
533: </li>
534:
535: <li>
536: <p>The root element of the document must designate the XHTML
537: namespace using the <code>xmlns</code> attribute <a href="#ref-xmlns">[XMLNAMES]</a>. The namespace for XHTML is
538: defined to be
539: <code>http://www.w3.org/1999/xhtml</code>.</p>
540: </li>
541:
542: <li>
543: <p>There must be a DOCTYPE declaration in the document prior to
544: the root element. The public identifier included in
545: the DOCTYPE declaration must reference one of the three DTDs
546: found in <a href="#dtds">Appendix A</a> using the respective
547: Formal Public Identifier. The system identifier may be changed to reflect
548: local system conventions.</p>
549:
550: <pre>
551: <!DOCTYPE html
552: PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
553: "http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-strict.dtd>
554:
555: <!DOCTYPE html
556: PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
557: "http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-transitional.dtd>
558:
559: <!DOCTYPE html
560: PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
561: "http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-frameset.dtd>
562: </pre>
563: </li>
564: </ol>
565:
566: <p>Here is an example of a minimal XHTML document.</p>
567:
568: <div class="good">
569: <pre>
570: <?xml version="1.0" encoding="UTF-8"?>
571: <!DOCTYPE html
572: PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
573: "http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-strict.dtd">
574: <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
575: <head>
576: <title>Virtual Library</title>
577: </head>
578: <body>
579: <p>Moved to <a href="http://vlib.org/">vlib.org</a>.</p>
580: </body>
581: </html></pre>
582: </div>
583:
584: <p>Note that in this example, the XML declaration is included. An XML
585: declaration like the one above is
586: 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
587: when the character encoding of the document is other than the default UTF-8 or
588: UTF-16.</p>
589:
590: <h3><a name="well-formed" id="well-formed">3.1.2 Using XHTML with
591: other namespaces</a></h3>
592:
593: <p>The XHTML namespace may be used with other XML namespaces
594: as per <a href="#ref-xmlns">[XMLNAMES]</a>, although such
595: documents are not strictly conforming XHTML 1.0 documents as
596: defined above. Future work by W3C will address ways to specify
597: conformance for documents involving multiple namespaces.</p>
598:
599: <p>The following example shows the way in which XHTML 1.0 could
600: be used in conjunction with the MathML Recommendation:</p>
601:
602: <div class="good">
603: <pre>
604: <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
605: <head>
606: <title>A Math Example</title>
607: </head>
608: <body>
609: <p>The following is MathML markup:</p>
610: <math xmlns="http://www.w3.org/1998/Math/MathML">
611: <apply> <log/>
612: <logbase>
613: <cn> 3 </cn>
614: </logbase>
615: <ci> x </ci>
616: </apply>
617: </math>
618: </body>
619: </html>
620: </pre>
621: </div>
622:
623: <p>The following example shows the way in which XHTML 1.0 markup
624: could be incorporated into another XML namespace:</p>
625:
626: <div class="good">
627: <pre>
628: <?xml version="1.0" encoding="UTF-8"?>
629: <!-- initially, the default namespace is "books" -->
630: <book xmlns='urn:loc.gov:books'
631: xmlns:isbn='urn:ISBN:0-395-36341-6' xml:lang="en" lang="en">
632: <title>Cheaper by the Dozen</title>
633: <isbn:number>1568491379</isbn:number>
634: <notes>
635: <!-- make HTML the default namespace for a hypertext commentary -->
636: <p xmlns='http://www.w3.org/1999/xhtml'>
637: This is also available <a href="http://www.w3.org/">online</a>.
638: </p>
639: </notes>
640: </book>
641: </pre>
642: </div>
643:
644: <h2><a name="uaconf" id="uaconf">3.2 User Agent
645: Conformance</a></h2>
646:
647: <p>A conforming user agent must meet all of the following
648: criteria:</p>
649:
650: <ol>
651: <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
652: an XHTML document for well-formedness. If the user agent claims
653: to be a validating user agent, it must also validate documents
654: against their referenced DTDs according to <a href="#ref-xml">
655: [XML]</a>.</li>
656:
657: <li>When the user agent claims to support <a href="#facilities">
658: facilities</a> defined within this specification or required by
659: this specification through normative reference, it must do so in
660: ways consistent with the facilities' definition.</li>
661:
662: <li>When a user agent processes an XHTML document as generic XML,
663: it shall only recognize attributes of type
664: <code>ID</code> (e.g. the <code>id</code> attribute on most XHTML elements)
665: as fragment identifiers.</li>
666:
667: <li>If a user agent encounters an element it does not recognize,
668: it must render the element's content.</li>
669:
670: <li>If a user agent encounters an attribute it does not
671: recognize, it must ignore the entire attribute specification
672: (i.e., the attribute and its value).</li>
673:
674: <li>If a user agent encounters an attribute value it doesn't
675: recognize, it must use the default attribute value.</li>
676:
677: <li>If it encounters an entity reference (other than one
678: of the predefined entities) for which the User Agent has
679: processed no declaration (which could happen if the declaration
680: is in the external subset which the User Agent hasn't read), the entity
681: reference should be rendered as the characters (starting
682: with the ampersand and ending with the semi-colon) that
683: make up the entity reference.</li>
684:
685: <li>When rendering content, User Agents that encounter
686: 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>
687:
688: <li>
689: The following characters are defined in [XML] as whitespace characters:
690:
691: <ul>
692: <li>Space (&#x0020;)</li>
693: <li>Tab (&#x0009;)</li>
694: <li>Carriage return (&#x000D;)</li>
695: <li>Line feed (&#x000A;)</li>
696: </ul>
697:
698: <p>
699: The XML processor normalizes different system's line end codes into one
700: single line-feed character, that is passed up to the application. The XHTML
701: user agent in addition, must treat the following characters as whitespace:
702: </p>
703:
704: <ul>
705: <li>Form feed (&#x000C;)</li>
706: <li>Zero-width space (&#x200B;)</li>
707: </ul>
708:
709: <p>
710: In elements where the 'xml:space' attribute is set to 'preserve', the user
711: agent must leave all whitespace characters intact (with the exception of
712: leading and trailing whitespace characters, which should be removed).
713: Otherwise, whitespace
714: is handled according to the following rules:
715: </p>
716:
717: <ul>
718: <li>
719: All whitespace surrounding block elements should be removed.
720: </li>
721: <li>
722: Comments are removed entirely and do not affect whitespace handling. One
723: whitespace character on either side of a comment is treated as two white
724: space characters.
725: </li>
726: <li>
727: Leading and trailing whitespace inside a block element must be removed.
728: </li>
729: <li>Line feed characters within a block element must be converted into a
730: space (except when the 'xml:space' attribute is set to 'preserve').
731: </li>
732: <li>
733: A sequence of white space characters must be reduced to a single space
734: character (except when the 'xml:space' attribute is set to 'preserve').
735: </li>
736: <li>
737: With regard to rendition,
738: the User Agent should render the content in a
739: manner appropriate to the language in which the content is written.
740: In languages whose primary script is Latinate, the ASCII space
741: character is typically used to encode both grammatical word boundaries and
742: typographic whitespace; in languages whose script is related to Nagari
743: (e.g., Sanskrit, Thai, etc.), grammatical boundaries may be encoded using
744: the ZW 'space' character, but will not typically be represented by
745: typographic whitespace in rendered output; languages using Arabiform scripts
746: may encode typographic whitespace using a space character, but may also use
747: the ZW space character to delimit 'internal' grammatical boundaries (what
748: look like words in Arabic to an English eye frequently encode several words,
749: e.g. 'kitAbuhum' = 'kitAbu-hum' = 'book them' == their book); and languages
750: in the Chinese script tradition typically neither encode such delimiters nor
751: use typographic whitespace in this way.
752: </li>
753: </ul>
754:
755: <p>Whitespace in attribute values is processed according to <a href="#ref-xml">[XML]</a>.</p>
756: </li>
757: </ol>
758:
759: <!--OddPage-->
760: <h1><a name="diffs" id="diffs">4. Differences with HTML
761: 4.0</a></h1>
762:
763: <p>Due to the fact that XHTML is an XML application, certain
764: practices that were perfectly legal in SGML-based HTML 4.0 <a href="#ref-html4">[HTML]</a> must be changed.</p>
765:
766: <h2><a name="h-4.1" id="h-4.1">4.1 Documents must be
767: well-formed</a></h2>
768:
769: <p><a href="#wellformed">Well-formedness</a> is a new concept
770: introduced by <a href="#ref-xml">[XML]</a>. Essentially this
771: means that all elements must either have closing tags or be
772: written in a special form (as described below), and that all the
773: elements must nest.</p>
774:
775: <p>Although overlapping is illegal in SGML, it was widely
776: tolerated in existing browsers.</p>
777:
778: <div class="good">
779: <p><strong><em>CORRECT: nested elements.</em></strong></p>
780:
781: <p><p>here is an emphasized
782: <em>paragraph</em>.</p></p>
783: </div>
784:
785: <div class="bad">
786: <p><strong><em>INCORRECT: overlapping elements</em></strong></p>
787:
788: <p><p>here is an emphasized
789: <em>paragraph.</p></em></p>
790: </div>
791:
792: <h2><a name="h-4.2" id="h-4.2">4.2 Element and attribute
793: names must be in lower case</a></h2>
794:
795: <p>XHTML documents must use lower case for all HTML element and
796: attribute names. This difference is necessary because XML is
797: case-sensitive e.g. <li> and <LI> are different
798: tags.</p>
799:
800: <h2><a name="h-4.3" id="h-4.3">4.3 For non-empty elements,
801: end tags are required</a></h2>
802:
803: <p>In SGML-based HTML 4.0 certain elements were permitted to omit
804: the end tag; with the elements that followed implying closure.
805: This omission is not permitted in XML-based XHTML. All elements
806: other than those declared in the DTD as <code>EMPTY</code> must
807: have an end tag.</p>
808:
809: <div class="good">
810: <p><strong><em>CORRECT: terminated elements</em></strong></p>
811:
812: <p><p>here is a paragraph.</p><p>here is
813: another paragraph.</p></p>
814: </div>
815:
816: <div class="bad">
817: <p><strong><em>INCORRECT: unterminated elements</em></strong></p>
818:
819: <p><p>here is a paragraph.<p>here is another
820: paragraph.</p>
821: </div>
822:
823: <h2><a name="h-4.4" id="h-4.4">4.4 Attribute values must
824: always be quoted</a></h2>
825:
826: <p>All attribute values must be quoted, even those which appear
827: to be numeric.</p>
828:
829: <div class="good">
830: <p><strong><em>CORRECT: quoted attribute values</em></strong></p>
831:
832: <p><table rows="3"></p>
833: </div>
834:
835: <div class="bad">
836: <p><strong><em>INCORRECT: unquoted attribute values</em></strong></p>
837:
838: <p><table rows=3></p>
839: </div>
840:
841: <h2><a name="h-4.5" id="h-4.5">4.5 Attribute
842: Minimization</a></h2>
843:
844: <p>XML does not support attribute minimization. Attribute-value
845: pairs must be written in full. Attribute names such as <code>
846: compact</code> and <code>checked</code> cannot occur in elements
847: without their value being specified.</p>
848:
849: <div class="good">
850: <p><strong><em>CORRECT: unminimized attributes</em></strong></p>
851:
852: <p><dl compact="compact"></p>
853: </div>
854:
855: <div class="bad">
856: <p><strong><em>INCORRECT: minimized attributes</em></strong></p>
857:
858: <p><dl compact></p>
859: </div>
860:
861: <h2><a name="h-4.6" id="h-4.6">4.6 Empty Elements</a></h2>
862:
863: <p>Empty elements must either have an end tag or the start tag must end with <code>/></code>. For instance,
864: <code><br/></code> or <code><hr></hr></code>. See <a href="#guidelines">HTML Compatibility Guidelines</a> for information on ways to
865: ensure this is backward compatible with HTML 4.0 user agents.</p>
866:
867: <div class="good">
868: <p><strong><em>CORRECT: terminated empty tags</em></strong></p>
869:
870: <p><br/><hr/></p>
871: </div>
872:
873: <div class="bad">
874: <p><strong><em>INCORRECT: unterminated empty tags</em></strong></p>
875:
876: <p><br><hr></p>
877: </div>
878:
879: <h2><a name="h-4.7" id="h-4.7">4.7 Whitespace handling in
880: attribute values</a></h2>
881:
882: <p>In attribute values, user agents will strip leading and
883: trailing whitespace from attribute values and map sequences
884: of one or more whitespace characters (including line breaks) to
885: a single inter-word space (an ASCII space character for western
886: scripts). See <a href="http://www.w3.org/TR/REC-xml#AVNormalize">
887: Section 3.3.3</a> of <a href="#ref-xml">[XML]</a>.</p>
888:
889: <h2><a name="h-4.8" id="h-4.8">4.8 Script and Style
890: elements</a></h2>
891:
892: <p>In XHTML, the script and style elements are declared as having
893: <code>#PCDATA</code> content. As a result, <code><</code> and
894: <code>&</code> will be treated as the start of markup, and
895: entities such as <code>&lt;</code> and <code>&amp;</code>
896: will be recognized as entity references by the XML processor to
897: <code><</code> and <code>&</code> respectively. Wrapping
898: the content of the script or style element within a <code>
899: CDATA</code> marked section avoids the expansion of these
900: entities.</p>
901:
902: <div class="good">
903: <pre>
904: <script>
905: <![CDATA[
906: ... unescaped script content ...
907: ]]>
908: </script>
909: </pre>
910: </div>
911:
912: <p><code>CDATA</code> sections are recognized by the XML
913: processor and appear as nodes in the Document Object Model, see
914: <a href="http://www.w3.org/TR/REC-DOM-Level-1/level-one-core.html#ID-E067D597">
915: Section 1.3</a> of the DOM Level 1 Recommendation <a href="#ref-dom">[DOM]</a>.</p>
916:
917: <p>An alternative is to use external script and style
918: documents.</p>
919:
920: <h2><a name="h-4.9" id="h-4.9">4.9 SGML exclusions</a></h2>
921:
922: <p>SGML gives the writer of a DTD the ability to exclude specific
923: elements from being contained within an element. Such
924: prohibitions (called "exclusions") are not possible in XML.</p>
925:
926: <p>For example, the HTML 4.0 Strict DTD forbids the nesting of an
927: '<code>a</code>' element within another '<code>a</code>' element
928: to any descendant depth. It is not possible to spell out such
929: prohibitions in XML. Even though these prohibitions cannot be
930: defined in the DTD, certain elements should not be nested. A
931: summary of such elements and the elements that should not be
932: nested in them is found in the normative <a href="#prohibitions">
933: Appendix B</a>.</p>
934:
935: <h2><a name="h-4.10" id="h-4.10">4.10 The elements with 'id' and 'name'
936: attributes</a></h2>
937:
938: <p>HTML 4.0 defined the <code>name</code> attribute for the elements
939: <code>a</code>,
940: <code>applet</code>, <code>frame</code>,
941: <code>iframe</code>, <code>img</code>, and <code>map</code>.
942: HTML 4.0 also introduced
943: the <code>id</code> attribute. Both of these attributes are designed to be
944: used as fragment identifiers.</p>
945: <p>In XML, fragment identifiers are of type <code>ID</code>, and
946: there can only be a single attribute of type <code>ID</code> per element.
947: Therefore, in XHTML 1.0 the <code>id</code>
948: attribute is defined to be of type <code>ID</code>. In order to
949: ensure that XHTML 1.0 documents are well-structured XML documents, XHTML 1.0
950: documents MUST use the <code>id</code> attribute when defining fragment
951: identifiers, even on elements that historically have also had a
952: <code>name</code> attribute.
953: See the <a href="#guidelines">HTML Compatibility
954: Guidelines</a> for information on ensuring such anchors are backwards
955: compatible when serving XHTML documents as media type <code>text/html</code>.
956: </p>
957: <p>Note that in XHTML 1.0, the <code>name</code> attribute of these
958: elements is formally deprecated, and will be removed in a
959: subsequent version of XHTML.</p>
960:
961: <!--OddPage-->
962: <h1><a name="issues" id="issues">5. Compatibility Issues</a></h1>
963:
964: <p>Although there is no requirement for XHTML 1.0 documents to be
965: compatible with existing user agents, in practice this is easy to
966: accomplish. Guidelines for creating compatible documents can be
967: found in <a href="#guidelines">Appendix C</a>.</p>
968:
969: <h2><a name="media" id="media">5.1 Internet Media Type</a></h2>
970: <p>As of the publication of this recommendation, the general
971: recommended MIME labeling for XML-based applications
972: has yet to be resolved.</p>
973:
974: <p>However, XHTML Documents which follow the guidelines set forth
975: in <a href="#guidelines">Appendix C</a>, "HTML Compatibility Guidelines" may be
976: labeled with the Internet Media Type "text/html", as they
977: are compatible with most HTML browsers. This document
978: makes no recommendation about MIME labeling of other
979: XHTML documents.</p>
980:
981: <!--OddPage-->
982: <h1><a name="future" id="future">6. Future Directions</a></h1>
983:
984: <p>XHTML 1.0 provides the basis for a family of document types
985: that will extend and subset XHTML, in order to support a wide
986: range of new devices and applications, by defining modules and
987: specifying a mechanism for combining these modules. This
988: mechanism will enable the extension and sub-setting of XHTML 1.0
989: in a uniform way through the definition of new modules.</p>
990:
991: <h2><a name="mods" id="mods">6.1 Modularizing HTML</a></h2>
992:
993: <p>As the use of XHTML moves from the traditional desktop user
994: agents to other platforms, it is clear that not all of the XHTML
995: elements will be required on all platforms. For example a hand
996: held device or a cell-phone may only support a subset of XHTML
997: elements.</p>
998:
999: <p>The process of modularization breaks XHTML up into a series of
1000: smaller element sets. These elements can then be recombined to
1001: meet the needs of different communities.</p>
1002:
1003: <p>These modules will be defined in a later W3C document.</p>
1004:
1005: <h2><a name="extensions" id="extensions">6.2 Subsets and
1006: Extensibility</a></h2>
1007:
1008: <p>Modularization brings with it several advantages:</p>
1009:
1010: <ul>
1011: <li>
1012: <p>It provides a formal mechanism for sub-setting XHTML.</p>
1013: </li>
1014:
1015: <li>
1016: <p>It provides a formal mechanism for extending XHTML.</p>
1017: </li>
1018:
1019: <li>
1020: <p>It simplifies the transformation between document types.</p>
1021: </li>
1022:
1023: <li>
1024: <p>It promotes the reuse of modules in new document types.</p>
1025: </li>
1026: </ul>
1027:
1028: <h2><a name="profiles" id="profiles">6.3 Document
1029: Profiles</a></h2>
1030:
1031: <p>A document profile specifies the syntax and semantics of a set
1032: of documents. Conformance to a document profile provides a basis
1033: for interoperability guarantees. The document profile specifies
1034: the facilities required to process documents of that type, e.g.
1035: which image formats can be used, levels of scripting, style sheet
1036: support, and so on.</p>
1037:
1038: <p>For product designers this enables various groups to define
1039: their own standard profile.</p>
1040:
1041: <p>For authors this will obviate the need to write several
1042: different versions of documents for different clients.</p>
1043:
1044: <p>For special groups such as chemists, medical doctors, or
1045: mathematicians this allows a special profile to be built using
1046: standard HTML elements plus a group of elements geared to the
1047: specialist's needs.</p>
1048:
1049: <!--OddPage-->
1050: <h1><a name="appendices" id="appendices"></a>
1051: <a name="dtds" id="dtds">Appendix A. DTDs</a></h1>
1052:
1053: <p><b>This appendix is normative.</b></p>
1054:
1055: <p>These DTDs and entity sets form a normative part of this
1056: specification. The complete set of DTD files together with an XML
1057: declaration and SGML Open Catalog is included in the <a href="xhtml1.zip">zip file</a> for this specification.</p>
1058:
1059: <h2><a name="h-A1" id="h-A1">A.1 Document Type
1060: Definitions</a></h2>
1061:
1062: <p>These DTDs approximate the HTML 4.0 DTDs. It is likely that
1063: when the DTDs are modularized, a method of DTD construction will
1064: be employed that corresponds more closely to HTML 4.0.</p>
1065:
1066: <ul>
1067: <li>
1068: <p><a href="DTD/xhtml1-strict.dtd" type="text/plain">
1069: XHTML-1.0-Strict</a></p>
1070: </li>
1071:
1072: <li>
1073: <p><a href="DTD/xhtml1-transitional.dtd" type="text/plain">
1074: XHTML-1.0-Transitional</a></p>
1075: </li>
1076:
1077: <li>
1078: <p><a href="DTD/xhtml1-frameset.dtd" type="text/plain">
1079: XHTML-1.0-Frameset</a></p>
1080: </li>
1081: </ul>
1082:
1083: <h2><a name="h-A2" id="h-A2">A.2 Entity Sets</a></h2>
1084:
1085: <p>The XHTML entity sets are the same as for HTML 4.0, but have
1086: been modified to be valid XML 1.0 entity declarations. Note the
1087: entity for the Euro currency sign (<code>&euro;</code> or
1088: <code>&#8364;</code> or <code>&#x20AC;</code>) is defined
1089: as part of the special characters.</p>
1090:
1091: <ul>
1092: <li>
1093: <p><a href="DTD/xhtml-lat1.ent">Latin-1 characters</a></p>
1094: </li>
1095:
1096: <li>
1097: <p><a href="DTD/xhtml-special.ent">Special characters</a></p>
1098: </li>
1099:
1100: <li>
1101: <p><a href="DTD/xhtml-symbol.ent">Symbols</a></p>
1102: </li>
1103: </ul>
1104:
1105: <!--OddPage-->
1106: <h1><a name="prohibitions" id="prohibitions">Appendix B. Element
1107: Prohibitions</a></h1>
1108:
1109: <p><b>This appendix is normative.</b></p>
1110:
1111: <p>The following elements have prohibitions on which elements
1112: they can contain (see <a href="#h-4.9">Section 4.9</a>). This
1113: prohibition applies to all depths of nesting, i.e. it contains
1114: all the descendant elements.</p>
1115:
1116: <dl><dt><code class="tag">a</code></dt>
1117: <dd>
1118: cannot contain other <code>a</code> elements.</dd>
1119: <dt><code class="tag">pre</code></dt>
1120: <dd>cannot contain the <code>img</code>, <code>object</code>,
1121: <code>big</code>, <code>small</code>, <code>sub</code>, or <code>
1122: sup</code> elements.</dd>
1123:
1124: <dt><code class="tag">button</code></dt>
1125: <dd>cannot contain the <code>input</code>, <code>select</code>,
1126: <code>textarea</code>, <code>label</code>, <code>button</code>,
1127: <code>form</code>, <code>fieldset</code>, <code>iframe</code> or
1128: <code>isindex</code> elements.</dd>
1129: <dt><code class="tag">label</code></dt>
1130: <dd>cannot contain other <code class="tag">label</code> elements.</dd>
1131: <dt><code class="tag">form</code></dt>
1132: <dd>cannot contain other <code>form</code> elements.</dd>
1133: </dl>
1134:
1135: <!--OddPage-->
1136: <h1><a name="guidelines" id="guidelines">Appendix C.
1137: HTML Compatibility Guidelines</a></h1>
1138:
1139: <p><b>This appendix is informative.</b></p>
1140:
1141: <p>This appendix summarizes design guidelines for authors who
1142: wish their XHTML documents to render on existing HTML user
1143: agents.</p>
1144:
1145: <h2>C.1 Processing Instructions</h2>
1146: <p>Be aware that processing instructions are rendered on some
1147: user agents. However, also note that when the XML declaration is not included
1148: in a document, the document can only use the default character encodings UTF-8
1149: or UTF-16.</p>
1150:
1151: <h2>C.2 Empty Elements</h2>
1152: <p>Include a space before the trailing <code>/</code> and <code>
1153: ></code> of empty elements, e.g. <code class="greenmono">
1154: <br /></code>, <code class="greenmono">
1155: <hr /></code> and <code class="greenmono"><img
1156: src="karen.jpg" alt="Karen" /></code>. Also, use the
1157: 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
1158: gives uncertain results in many existing user agents.</p>
1159:
1160: <h2>C.3 Element Minimization and Empty Element Content</h2>
1161: <p>Given an empty instance of an element whose content model is
1162: not <code>EMPTY</code> (for example, an empty title or paragraph)
1163: do not use the minimized form (e.g. use <code class="greenmono">
1164: <p> </p></code> and not <code class="greenmono">
1165: <p /></code>).</p>
1166:
1167: <h2>C.4 Embedded Style Sheets and Scripts</h2>
1168: <p>Use external style sheets if your style sheet uses <code>
1169: <</code> or <code>&</code> or <code>]]></code> or <code>--</code>. Use
1170: external scripts if your script uses <code><</code> or <code>
1171: &</code> or <code>]]></code> or <code>--</code>. Note that XML parsers
1172: are permitted to silently remove the contents of comments. Therefore, the historical
1173: practice of "hiding" scripts and style sheets within comments to make the
1174: documents backward compatible is likely to not work as expected in XML-based
1175: implementations.</p>
1176:
1177: <h2>C.5 Line Breaks within Attribute Values</h2>
1178: <p>Avoid line breaks and multiple whitespace characters within
1179: attribute values. These are handled inconsistently by user
1180: agents.</p>
1181:
1182: <h2>C.6 Isindex</h2>
1183: <p>Don't include more than one <code>isindex</code> element in
1184: the document <code>head</code>. The <code>isindex</code> element
1185: is deprecated in favor of the <code>input</code> element.</p>
1186:
1187: <h2>C.7 The <code>lang</code> and <code>xml:lang</code> Attributes</h2>
1188: <p>Use both the <code>lang</code> and <code>xml:lang</code>
1189: attributes when specifying the language of an element. The value
1190: of the <code>xml:lang</code> attribute takes precedence.</p>
1191:
1192: <h2>C.8 Fragment Identifiers</h2>
1193: <p>In XML, <abbr title="Uniform Resource Identifiers">URIs</abbr> [<a href="#ref-rfc2396">RFC2396</a>] that end with fragment identifiers of the form
1194: <code>"#foo"</code> do not refer to elements with an attribute
1195: <code>name="foo"</code>; rather, they refer to elements with an
1196: attribute defined to be of type <code>ID</code>, e.g., the <code>
1197: id</code> attribute in HTML 4.0. Many existing HTML clients don't
1198: support the use of <code>ID</code>-type attributes in this way,
1199: so identical values may be supplied for both of these attributes to ensure
1200: maximum forward and backward compatibility (e.g., <code class="greenmono"><a id="foo" name="foo">...</a></code>).</p>
1201:
1202: <p>Further, since the set of
1203: legal values for attributes of type <code>ID</code> is much smaller than
1204: for those of type <code>CDATA</code>, the type of the <code>name</code>
1205: attribute has been changed to <code>NMTOKEN</code>. This attribute is
1206: constrained such that it can only have the same values as type
1207: <code>ID</code>, or as the <code>Name</code> production in XML 1.0 Section
1208: 2.5, production 5. Unfortunately, this constraint cannot be expressed in the
1209: XHTML 1.0 DTDs. Because of this change, care must be taken when
1210: converting existing HTML documents. The values of these attributes
1211: must be unique within the document, valid, and any references to these
1212: fragment identifiers (both
1213: internal and external) must be updated should the values be changed during
1214: conversion.</p>
1215: <p>Finally, note that XHTML 1.0 has deprecated the
1216: <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>
1217: elements, and it will be
1218: removed from XHTML in subsequent versions.</p>
1219:
1220: <h2>C.9 Character Encoding</h2>
1221: <p>To specify a character encoding in the document, use both the
1222: encoding attribute specification on the xml declaration (e.g.
1223: <code class="greenmono"><?xml version="1.0"
1224: encoding="EUC-JP"?></code>) and a meta http-equiv statement
1225: (e.g. <code class="greenmono"><meta http-equiv="Content-type"
1226: content='text/html; charset="EUC-JP"' /></code>). The
1227: value of the encoding attribute of the xml processing instruction
1228: takes precedence.</p>
1229:
1230: <h2>C.10 Boolean Attributes</h2>
1231: <p>Some HTML user agents are unable to interpret boolean
1232: attributes when these appear in their full (non-minimized) form,
1233: as required by XML 1.0. Note this problem doesn't effect user
1234: agents compliant with HTML 4.0. The following attributes are
1235: involved: <code>compact</code>, <code>nowrap</code>, <code>
1236: ismap</code>, <code>declare</code>, <code>noshade</code>, <code>
1237: checked</code>, <code>disabled</code>, <code>readonly</code>,
1238: <code>multiple</code>, <code>selected</code>, <code>
1239: noresize</code>, <code>defer</code>.</p>
1240:
1241: <h2>C.11 Document Object Model and XHTML</h2>
1242: <p>
1243: The Document Object Model level 1 Recommendation [<a href="#ref-dom">DOM</a>]
1244: defines document object model interfaces for XML and HTML 4.0. The HTML 4.0
1245: document object model specifies that HTML element and attribute names are
1246: returned in upper-case. The XML document object model specifies that
1247: element and attribute names are returned in the case they are specified. In
1248: XHTML 1.0, elements and attributes are specified in lower-case. This apparent difference can be
1249: addressed in two ways:
1250: </p>
1251: <ol>
1252: <li>Applications that access XHTML documents served as Internet media type
1253: <code>text/html</code>
1254: via the <abbr title="Document Object Model">DOM</abbr> can use the HTML DOM,
1255: and can rely upon element and attribute names being returned in
1256: upper-case from those interfaces.</li>
1257: <li>Applications that access XHTML documents served as Internet media types
1258: <code>text/xml</code> or <code>application/xml</code>
1259: can also use the XML DOM. Elements and attributes will be returned in lower-case.
1260: Also, some XHTML elements may or may
1261: not appear
1262: in the object tree because they are optional in the content model
1263: (e.g. the <code>tbody</code> element within
1264: <code>table</code>). This occurs because in HTML 4.0 some elements were
1265: permitted to be minimized such that their start and end tags are both omitted
1266: (an SGML feature).
1267: This is not possible in XML. Rather than require document authors to insert
1268: extraneous elements, XHTML has made the elements optional.
1269: Applications need to adapt to this
1270: accordingly.</li>
1271: </ol>
1272:
1273: <h2>C.12 Using Ampersands in Attribute Values</h2>
1274: <p>
1275: When an attribute value contains an ampersand, it must be expressed as a character
1276: entity reference
1277: (e.g. "<code>&amp;</code>"). For example, when the
1278: <code>href</code> attribute
1279: of the <code>a</code> element refers to a
1280: CGI script that takes parameters, it must be expressed as
1281: <code>http://my.site.dom/cgi-bin/myscript.pl?class=guest&amp;name=user</code>
1282: rather than as
1283: <code>http://my.site.dom/cgi-bin/myscript.pl?class=guest&name=user</code>.
1284: </p>
1285:
1286: <h2>C.13 Cascading Style Sheets (CSS) and XHTML</h2>
1287:
1288: <p>The Cascading Style Sheets level 2 Recommendation [<a href="#ref-css2">CSS2</a>] defines style
1289: properties which are applied to the parse tree of the HTML or XML
1290: document. Differences in parsing will produce different visual or
1291: aural results, depending on the selectors used. The following hints
1292: will reduce this effect for documents which are served without
1293: modification as both media types:</p>
1294:
1295: <ol>
1296: <li>
1297: CSS style sheets for XHTML should use lower case element and
1298: attribute names.</li>
1299:
1300:
1301: <li>In tables, the tbody element will be inferred by the parser of an
1302: HTML user agent, but not by the parser of an XML user agent. Therefore
1303: you should always explicitely add a tbody element if it is referred to
1304: in a CSS selector.</li>
1305:
1306: <li>Within the XHTML name space, user agents are expected to
1307: recognize the "id" attribute as an attribute of type ID.
1308: Therefore, style sheets should be able to continue using the
1309: shorthand "#" selector syntax even if the user agent does not read
1310: the DTD.</li>
1311:
1312: <li>Within the XHTML name space, user agents are expected to
1313: recognize the "class" attribute. Therefore, style sheets should be
1314: able to continue using the shorthand "." selector syntax.</li>
1315:
1316: <li>
1317: CSS defines different conformance rules for HTML and XML documents;
1318: be aware that the HTML rules apply to XHTML documents delivered as
1319: HTML and the XML rules apply to XHTML documents delivered as XML.</li>
1320: </ol>
1321: <!--OddPage-->
1322: <h1><a name="acks" id="acks">Appendix D.
1323: Acknowledgements</a></h1>
1324:
1325: <p><b>This appendix is informative.</b></p>
1326:
1327: <p>This specification was written with the participation of the
1328: members of the W3C HTML working group:</p>
1329:
1330: <dl>
1331: <dd>Steven Pemberton, CWI (HTML Working Group Chair)<br />
1332: Murray Altheim, Sun Microsystems<br />
1333: Daniel Austin, CNET: The Computer Network<br />
1334: Frank Boumphrey, HTML Writers Guild<br />
1335: John Burger, Mitre<br />
1336: Andrew W. Donoho, IBM<br />
1337: Sam Dooley, IBM<br />
1338: Klaus Hofrichter, GMD<br />
1339: Philipp Hoschka, W3C<br />
1340: Masayasu Ishikawa, W3C<br />
1341: Warner ten Kate, Philips Electronics<br />
1342: Peter King, Phone.com<br />
1343: Paula Klante, JetForm<br />
1344: Shin'ichi Matsui, W3C/Panasonic<br />
1345: Shane McCarron, Applied Testing and Technology (The Open Group through August
1346: 1999)<br />
1347: Ann Navarro, HTML Writers Guild<br />
1348: Zach Nies, Quark<br />
1349: Dave Raggett, W3C/HP (W3C lead for HTML)<br />
1350: Patrick Schmitz, Microsoft<br />
1351: Sebastian Schnitzenbaumer, Stack Overflow<br />
1352: Chris Wilson, Microsoft<br />
1353: Ted Wugofski, Gateway 2000<br />
1354: Dan Zigmond, WebTV Networks</dd>
1355: </dl>
1356:
1357: <!--OddPage-->
1358: <h1><a name="refs" id="refs">Appendix E. References</a></h1>
1359:
1360: <p><b>This appendix is informative.</b></p>
1361:
1362: <dl>
1363:
1364: <dt><a name="ref-css2" id="ref-css2"><b>[CSS2]</b></a></dt>
1365:
1366: <dd><a href="http://www.w3.org/TR/REC-CSS2">"Cascading Style Sheets, level 2 (CSS2) Specification"</a>, B.
1367: Bos, H. W. Lie, C. Lilley, I. Jacobs, 12 May 1998.<br />
1368: Available at: <a href="http://www.w3.org/TR/REC-CSS2">
1369: http://www.w3.org/TR/REC-CSS2</a></dd>
1370:
1371: <dt><a name="ref-dom" id="ref-dom"><b>[DOM]</b></a></dt>
1372:
1373: <dd><a href="http://www.w3.org/TR/REC-DOM-Level-1">"Document Object Model (DOM) Level 1 Specification"</a>, Lauren
1374: Wood <i>et al.</i>, 1 October 1998.<br />
1375: Available at: <a href="http://www.w3.org/TR/REC-DOM-Level-1">
1376: http://www.w3.org/TR/REC-DOM-Level-1</a></dd>
1377:
1378: <dt><a name="ref-html4" id="ref-html4"><b>[HTML]</b></a></dt>
1379:
1380: <dd><a href="http://www.w3.org/TR/1999/PR-html40-19990824">"HTML 4.01 Specification"</a>, D. Raggett, A. Le Hors, I.
1381: Jacobs, 24 August 1999.<br />
1382: Available at: <a href="http://www.w3.org/TR/1999/PR-html40-19990824">
1383: http://www.w3.org/TR/1999/PR-html40-19990824</a></dd>
1384:
1385: <dt><a name="ref-posix" id="ref-posix"><b>[POSIX.1]</b></a></dt>
1386:
1387: <dd>"ISO/IEC 9945-1:1990 Information Technology - Portable
1388: Operating System Interface (POSIX) - Part 1: System Application
1389: Program Interface (API) [C Language]", Institute of Electrical
1390: and Electronics Engineers, Inc, 1990.</dd>
1391:
1392: <dt><a name="ref-rfc2046" id="ref-rfc2046"><b>
1393: [RFC2046]</b></a></dt>
1394:
1395: <dd><a href="http://www.ietf.org/rfc/rfc2046.txt">"RFC2046: Multipurpose Internet Mail Extensions (MIME) Part
1396: Two: Media Types"</a>, N. Freed and N. Borenstein, November
1397: 1996.<br />
1398: Available at <a href="http://www.ietf.org/rfc/rfc2046.txt">
1399: http://www.ietf.org/rfc/rfc2046.txt</a>. Note that this RFC
1400: obsoletes RFC1521, RFC1522, and RFC1590.</dd>
1401:
1402: <dt><a name="ref-rfc2119" id="ref-rfc2119"><b>
1403: [RFC2119]</b></a></dt>
1404:
1405: <dd><a href="http://www.ietf.org/rfc/rfc2119.txt">"RFC2119: Key words for use in RFCs to Indicate Requirement
1406: Levels"</a>, S. Bradner, March 1997.<br />
1407: Available at: <a href="http://www.ietf.org/rfc/rfc2119.txt">
1408: http://www.ietf.org/rfc/rfc2119.txt</a></dd>
1409:
1410: <dt><a name="ref-rfc2376" id="ref-rfc2376"><b>
1411: [RFC2376]</b></a></dt>
1412:
1413: <dd><a href="http://www.ietf.org/rfc/rfc2376.txt">"RFC2376: XML Media Types"</a>, E. Whitehead, M. Murata, July
1414: 1998.<br />
1415: Available at: <a href="http://www.ietf.org/rfc/rfc2376.txt">
1416: http://www.ietf.org/rfc/rfc2376.txt</a></dd>
1417:
1418: <dt><a name="ref-rfc2396" id="ref-rfc2396"><b>
1419: [RFC2396]</b></a></dt>
1420:
1421: <dd><a href="http://www.ietf.org/rfc/rfc2396.txt">"RFC2396: Uniform Resource Identifiers (URI): Generic
1422: Syntax"</a>, T. Berners-Lee, R. Fielding, L. Masinter, August
1423: 1998.<br />
1424: This document updates RFC1738 and RFC1808.<br />
1425: Available at: <a href="http://www.ietf.org/rfc/rfc2396.txt">
1426: http://www.ietf.org/rfc/rfc2396.txt</a></dd>
1427:
1428: <dt><a name="ref-xml" id="ref-xml"><b>[XML]</b></a></dt>
1429:
1430: <dd><a href="http://www.w3.org/TR/REC-xml">"Extensible Markup Language (XML) 1.0 Specification"</a>, T.
1431: Bray, J. Paoli, C. M. Sperberg-McQueen, 10 February 1998.<br />
1432: Available at: <a href="http://www.w3.org/TR/REC-xml">
1433: http://www.w3.org/TR/REC-xml</a></dd>
1434:
1435: <dt><a name="ref-xmlns" id="ref-xmlns"><b>[XMLNAMES]</b></a></dt>
1436:
1437: <dd><a href="http://www.w3.org/TR/REC-xml-names">"Namespaces in XML"</a>, T. Bray, D. Hollander, A. Layman, 14
1438: January 1999.<br />
1439: XML namespaces provide a simple method for qualifying names used
1440: in XML documents by associating them with namespaces identified
1441: by URI.<br />
1442: Available at: <a href="http://www.w3.org/TR/REC-xml-names">
1443: http://www.w3.org/TR/REC-xml-names</a></dd>
1444:
1445: </dl>
1446: <p><a href="http://www.w3.org/WAI/WCAG1AAA-Conformance" title="Explanation of Level Triple-A Conformance">
1447: <img height="32" width="88" src="wcag1AAA.gif" alt="Level Triple-A conformance icon, W3C-WAI Web Content Accessibility Guidelines 1.0" /></a></p>
1448: <div class="navbar">
1449: <hr />
1450: <a href="#toc">table of contents</a>
1451: </div>
1452: </body>
1453: </html>
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