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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"
60: src="w3c_home.gif" alt="W3C" /></a></p>
61:
62: <h1 class="head"><a name="title" id="title">XHTML</a><sup>™</sup> 1.0:
63: The Extensible HyperText Markup Language</h1>
64:
65: <h2>A Reformulation of HTML 4.0 in XML 1.0</h2>
66:
67: <h3>W3C Proposed Recommendation 10 December 1999</h3>
68:
69: <dl>
70: <dt>This version:</dt>
71:
72: <dd><a href=
73: "http://www.w3.org/TR/1999/PR-xhtml1-19991210">
74: http://www.w3.org/TR/1999/PR-xhtml1-19991210</a> <br />
75: (<a href="xhtml1.ps">Postscript version</a>,
76: <a href="xhtml1.pdf">PDF version</a>,
77: <a href="xhtml1.zip">ZIP archive</a>, or
78: <a href="xhtml1.tgz">Gzip'd TAR archive</a>)
79: </dd>
80:
81: <dt>Latest version:</dt>
82:
83: <dd><a href="http://www.w3.org/TR/xhtml1">
84: http://www.w3.org/TR/xhtml1</a></dd>
85:
86: <dt>Previous versions:</dt>
87:
88: <dd><a href=
89: "http://www.w3.org/TR/1999/WD-xhtml1-19991124">
90: http://www.w3.org/TR/1999/WD-xhtml1-19991124</a></dd>
91: <dd><a href=
92: "http://www.w3.org/TR/1999/PR-xhtml1-19990824">
93: http://www.w3.org/TR/1999/PR-xhtml1-19990824</a></dd>
94:
95: <dt>Authors:</dt>
96:
97: <dd>See <a href="#acks">acknowledgements</a>.</dd>
98: </dl>
99:
100: <p class="copyright"><a href=
101: "http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">
102: Copyright</a> © 1999 <a href="http://www.w3.org/">W3C</a><sup>®</sup>
103: (<a href="http://www.lcs.mit.edu/">MIT</a>, <a href=
104: "http://www.inria.fr/">INRIA</a>, <a href=
105: "http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. <abbr
106: title="World Wide Web Consortium">W3C</abbr> <a
107: href=
108: "http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">
109: liability</a>, <a href=
110: "http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">
111: trademark</a>, <a href=
112: "http://www.w3.org/Consortium/Legal/copyright-documents">document
113: use</a> and <a href=
114: "http://www.w3.org/Consortium/Legal/copyright-software">software
115: licensing</a> rules apply.</p>
116: <hr />
117: </div>
118:
119: <h2 class="notoc">Abstract</h2>
120:
121: <p>This specification defines <abbr title="Extensible Hypertext Markup
122: Language">XHTML</abbr> 1.0, a reformulation of HTML
123: 4.0 as an XML 1.0 application, and three <abbr title="Document Type
124: Definition">DTDs</abbr> corresponding to
125: the ones defined by HTML 4.0. The semantics of the elements and
126: their attributes are defined in the W3C Recommendation for HTML
127: 4.0. These semantics provide the foundation for future
128: extensibility of XHTML. Compatibility with existing HTML user
129: agents is possible by following a small set of guidelines.</p>
130:
131: <h2>Status of this document</h2>
132:
133: <p><em>This section describes the status of this document at the time
134: of its publication. Other documents may supersede this document. The
135: latest status of this document series is maintained at the W3C.</em></p>
136:
137: <p>This specification is a Proposed Recommendation of the HTML Working Group. It is
138: a revision of the Proposed Recommendation dated <a
139: href= "http://www.w3.org/TR/1999/PR-xhtml1-19990824/">24 August
140: 1999</a> incorporating changes as a result of comments from the Proposed
141: Recommendation review, and
142: comments and further deliberations of the W3C HTML Working Group. A
143: <a href="xhtml1-diff-19991210.html">diff-marked version</a> from the previous
144: proposed recommendation is available for comparison purposes.</p>
145:
146: <p>On 10 December 1999, this document enters a
147: <a href="http://www.w3.org/Consortium/Process/#RecsPR">
148: Proposed Recommendation</a> review period. From that date until 8 January
149: 2000,
150: W3C Advisory Committee representatives are encouraged
151: to review this specification and return comments in their completed
152: ballots to w3c-html-review@w3.org. Please send any comments of a
153: confidential nature in separate email to w3t-html@w3.org, which is
154: visible to the Team only.</p>
155:
156: <p>No sooner than 14 days after the end of the review period, the
157: Director will announce the document's disposition: it may become a W3C
158: Recommendation (possibly with minor changes), it may revert to Working
159: Draft status, or it may be dropped as a W3C work item.</p>
160:
161: <p>Publication as a Proposed Recommendation does not imply endorsement
162: by the W3C membership. This is still a draft document and may be
163: updated, replaced or obsoleted by other documents at any time. It is
164: inappropriate to cite W3C Proposed Recommendation as other than "work
165: in progress."</p>
166:
167: <p>This document has been produced as part of the <a href=
168: "http://www.w3.org/MarkUp/">W3C HTML Activity</a>. The goals of
169: the <a href="http://www.w3.org/MarkUp/Group/">HTML Working
170: Group</a> <i>(<a href="http://cgi.w3.org/MemberAccess/">members
171: only</a>)</i> are discussed in the <a href=
172: "http://www.w3.org/MarkUp/Group/HTMLcharter">HTML Working Group
173: charter</a> <i>(<a href="http://cgi.w3.org/MemberAccess/">members
174: only</a>)</i>.</p>
175:
176: <p>A list of current W3C Recommendations and other technical documents
177: can be found at <a
178: href="http://www.w3.org/TR">http://www.w3.org/TR</a>.</p>
179:
180: <p>Public discussion on <abbr title="HyperText Markup
181: Language">HTML</abbr> features takes place on the mailing list <a
182: href="mailto:www-html@w3.org"> www-html@w3.org</a> (<a href=
183: "http://lists.w3.org/Archives/Public/www-html/">archive</a>). The W3C
184: staff contact for work on HTML is <a href= "mailto:dsr@w3.org">Dave
185: Raggett</a>.</p>
186:
187: <p>Please report errors in this document to <a
188: href="mailto:www-html-editor@w3.org">www-html-editor@w3.org</a>.</p>
189:
190: <p>The list of known errors in this specification is available at <a
191: href="http://www.w3.org/1999/12/PR-xhtml1-19991210-errata">http://www.w3.org/1999/12/PR-xhtml1-19991210-errata</a>.</p>
192:
193: <h2 class="notoc"><a id="toc" name="toc">Contents</a></h2>
194:
195: <div class="contents">
196: <ul class="toc">
197: <li class="tocline">1. <a href="#xhtml">What is XHTML?</a>
198:
199: <ul class="toc">
200: <li class="tocline">1.1 <a href="#html4">What is HTML 4.0?</a></li>
201:
202: <li class="tocline">1.2 <a href="#xml">What is XML?</a></li>
203:
204: <li class="tocline">1.3 <a href="#why">Why the need for XHTML?</a></li>
205: </ul>
206: </li>
207:
208: <li class="tocline">2. <a href="#defs">Definitions</a>
209:
210: <ul class="toc">
211: <li class="tocline">2.1 <a href="#terms">Terminology</a></li>
212:
213: <li class="tocline">2.2 <a href="#general">General Terms</a></li>
214: </ul>
215: </li>
216:
217: <li class="tocline">3. <a href="#normative">Normative Definition of XHTML 1.0</a>
218:
219:
220: <ul class="toc">
221: <li class="tocline">3.1 <a href="#docconf">Document Conformance</a></li>
222:
223: <li class="tocline">3.2 <a href="#uaconf">User Agent Conformance</a></li>
224: </ul>
225: </li>
226:
227: <li class="tocline">4. <a href="#diffs">Differences with HTML 4.0</a>
228:
229: </li>
230:
231: <li class="tocline">5. <a href="#issues">Compatibility Issues</a>
232:
233: <ul class="toc">
234: <li class="tocline">5.1 <a href="#media">Internet Media Types</a></li>
235: </ul>
236: </li>
237:
238: <li class="tocline">6. <a href="#future">Future Directions</a>
239:
240: <ul class="toc">
241: <li class="tocline">6.1 <a href="#mods">Modularizing HTML</a></li>
242:
243: <li class="tocline">6.2 <a href="#extensions">Subsets and Extensibility</a></li>
244:
245: <li class="tocline">6.3 <a href="#profiles">Document Profiles</a></li>
246: </ul>
247: </li>
248:
249: <li class="tocline"><a href="#dtds">Appendix A. DTDs</a></li>
250:
251: <li class="tocline"><a href="#prohibitions">Appendix B. Element
252: Prohibitions</a></li>
253:
254: <li class="tocline"><a href="#guidelines">Appendix C. HTML Compatibility Guidelines</a></li>
255:
256: <li class="tocline"><a href="#acks">Appendix D. Acknowledgements</a></li>
257:
258: <li class="tocline"><a href="#refs">Appendix E. References</a></li>
259: </ul>
260: </div>
261:
262: <!--OddPage-->
263: <h1><a name="xhtml" id="xhtml">1. What is XHTML?</a></h1>
264:
265: <p>XHTML is a family of current and future document types and modules that
266: 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,
267: and ultimately are designed to work in conjunction with XML-based user agents.
268: The details of this family and its evolution are
269: discussed in more detail in the section on <a href="#future">Future
270: Directions</a>. </p>
271:
272: <p>XHTML 1.0 (this specification) is the first document type in the XHTML
273: family. It is a reformulation of the three HTML 4.0 document types as
274: applications of XML 1.0 <a href="#ref-xml"> [XML]</a>. It is intended
275: to be used as a language for content that is both XML-conforming and, if some
276: simple <a href="#guidelines">guidelines</a> are followed,
277: operates in HTML 4.0 conforming user agents. Developers who migrate
278: their content to XHTML 1.0 will realize the following benefits:</p>
279:
280: <ul>
281: <li>XHTML documents are XML conforming. As such, they are readily viewed,
282: edited, and validated with standard XML tools.</li>
283: <li>XHTML documents can be written to
284: to operate as well or better than they did before in existing
285: HTML 4.0-conforming user agents as well as in new, XHTML 1.0 conforming user
286: agents.</li>
287: <li>XHTML documents can utilize applications (e.g. scripts and applets) that rely
288: upon either the HTML Document Object Model or the XML Document Object Model <a
289: href="#ref-dom">[DOM]</a>.</li>
290: <li>As the XHTML family evolves, documents conforming to XHTML 1.0 will be more
291: likely to interoperate within and among various XHTML environments.</li>
292: </ul>
293:
294: <p>The XHTML family is the next step in the evolution of the Internet. By
295: migrating to XHTML today, content developers can enter the XML world with all
296: of its attendant benefits, while still remaining confident in their
297: content's backward and future compatibility.</p>
298:
299: <h2><a name="html4" id="html4">1.1 What is HTML 4.0?</a></h2>
300:
301: <p>HTML 4.0 <a href="#ref-html4">[HTML]</a> is an <abbr title="Standard
302: Generalized Markup Language">SGML</abbr> (Standard
303: Generalized Markup Language) application conforming to
304: International Standard <abbr title="Organization for International
305: Standardization">ISO</abbr> 8879, and is widely regarded as the
306: standard publishing language of the World Wide Web.</p>
307:
308: <p>SGML is a language for describing markup languages,
309: particularly those used in electronic document exchange, document
310: management, and document publishing. HTML is an example of a
311: language defined in SGML.</p>
312:
313: <p>SGML has been around since the middle 1980's and has remained
314: quite stable. Much of this stability stems from the fact that the
315: language is both feature-rich and flexible. This flexibility,
316: however, comes at a price, and that price is a level of
317: complexity that has inhibited its adoption in a diversity of
318: environments, including the World Wide Web.</p>
319:
320: <p>HTML, as originally conceived, was to be a language for the
321: exchange of scientific and other technical documents, suitable
322: for use by non-document specialists. HTML addressed the problem
323: of SGML complexity by specifying a small set of structural and
324: semantic tags suitable for authoring relatively simple documents.
325: In addition to simplifying the document structure, HTML added
326: support for hypertext. Multimedia capabilities were added
327: later.</p>
328:
329: <p>In a remarkably short space of time, HTML became wildly
330: popular and rapidly outgrew its original purpose. Since HTML's
331: inception, there has been rapid invention of new elements for use
332: within HTML (as a standard) and for adapting HTML to vertical,
333: highly specialized, markets. This plethora of new elements has
334: led to compatibility problems for documents across different
335: platforms.</p>
336:
337: <p>As the heterogeneity of both software and platforms rapidly
338: proliferate, it is clear that the suitability of 'classic' HTML
339: 4.0 for use on these platforms is somewhat limited.</p>
340:
341: <h2><a name="xml" id="xml">1.2 What is XML?</a></h2>
342:
343: <p>XML<sup>™</sup> is the shorthand for Extensible Markup
344: Language, and is an acronym of Extensible Markup Language <a
345: href="#ref-xml">[XML]</a>.</p>
346:
347: <p>XML was conceived as a means of regaining the power and
348: flexibility of SGML without most of its complexity. Although a
349: restricted form of SGML, XML nonetheless preserves most of SGML's
350: power and richness, and yet still retains all of SGML's commonly
351: used features.</p>
352:
353: <p>While retaining these beneficial features, XML removes many of
354: the more complex features of SGML that make the authoring and
355: design of suitable software both difficult and costly.</p>
356:
357: <h2><a name="why" id="why">1.3 Why the need for XHTML?</a></h2>
358:
359: <p>The benefits of migrating to XHTML 1.0 are described above. Some of the
360: benefits of migrating to XHTML in general are:</p>
361:
362: <ul>
363: <li>Document developers and user agent designers are constantly
364: discovering new ways to express their ideas through new markup. In XML, it is
365: relatively easy to introduce new elements or additional element
366: attributes. The XHTML family is designed to accommodate these extensions
367: through XHTML modules and techniques for developing new XHTML-conforming
368: modules (described in the forthcoming XHTML Modularization specification).
369: These modules will permit the combination of existing and
370: new feature sets when developing content and when designing new user
371: agents.</li>
372:
373: <li>Alternate ways of accessing the Internet are constantly being
374: introduced. Some estimates indicate that by the year 2002, 75% of
375: Internet document viewing will be carried out on these alternate
376: platforms. The XHTML family is designed with general user agent
377: interoperability in mind. Through a new user agent and document profiling
378: mechanism, servers, proxies, and user agents will be able to perform
379: best effort content transformation. Ultimately, it will be possible to
380: develop XHTML-conforming content that is usable by any XHTML-conforming
381: user agent.</li>
382:
383: </ul>
384: <!--OddPage-->
385: <h1><a name="defs" id="defs">2. Definitions</a></h1>
386:
387: <h2><a name="terms" id="terms">2.1 Terminology</a></h2>
388:
389: <p>The following terms are used in this specification. These
390: terms extend the definitions in <a href="#ref-rfc2119">
391: [RFC2119]</a> in ways based upon similar definitions in ISO/<abbr
392: title="International Electro-technical Commission">IEC</abbr>
393: 9945-1:1990 <a href="#ref-posix">[POSIX.1]</a>:</p>
394:
395: <dl>
396: <dt>Implementation-defined</dt>
397:
398: <dd>A value or behavior is implementation-defined when it is left
399: to the implementation to define [and document] the corresponding
400: requirements for correct document construction.</dd>
401:
402: <dt>May</dt>
403:
404: <dd>With respect to implementations, the word "may" is to be
405: interpreted as an optional feature that is not required in this
406: specification but can be provided. With respect to <a href=
407: "#docconf">Document Conformance</a>, the word "may" means that
408: the optional feature must not be used. The term "optional" has
409: the same definition as "may".</dd>
410:
411: <dt>Must</dt>
412:
413: <dd>In this specification, the word "must" is to be interpreted
414: as a mandatory requirement on the implementation or on Strictly
415: Conforming XHTML Documents, depending upon the context. The term
416: "shall" has the same definition as "must".</dd>
417:
418: <dt>Reserved</dt>
419:
420: <dd>A value or behavior is unspecified, but it is not allowed to
421: be used by Conforming Documents nor to be supported by a
422: Conforming User Agents.</dd>
423:
424: <dt>Should</dt>
425:
426: <dd>With respect to implementations, the word "should" is to be
427: interpreted as an implementation recommendation, but not a
428: requirement. With respect to documents, the word "should" is to
429: be interpreted as recommended programming practice for documents
430: and a requirement for Strictly Conforming XHTML Documents.</dd>
431:
432: <dt>Supported</dt>
433:
434: <dd>Certain facilities in this specification are optional. If a
435: facility is supported, it behaves as specified by this
436: specification.</dd>
437:
438: <dt>Unspecified</dt>
439:
440: <dd>When a value or behavior is unspecified, the specification
441: defines no portability requirements for a facility on an
442: implementation even when faced with a document that uses the
443: facility. A document that requires specific behavior in such an
444: instance, rather than tolerating any behavior when using that
445: facility, is not a Strictly Conforming XHTML Document.</dd>
446: </dl>
447:
448: <h2><a name="general" id="general">2.2 General Terms</a></h2>
449:
450: <dl>
451: <dt>Attribute</dt>
452:
453: <dd>An attribute is a parameter to an element declared in the
454: DTD. An attribute's type and value range, including a possible
455: default value, are defined in the DTD.</dd>
456:
457: <dt>DTD</dt>
458:
459: <dd>A DTD, or document type definition, is a collection of XML
460: declarations that, as a collection, defines the legal structure,
461: <span class="term">elements</span>, and <span class="term">
462: attributes</span> that are available for use in a document that
463: complies to the DTD.</dd>
464:
465: <dt>Document</dt>
466:
467: <dd>A document is a stream of data that, after being combined
468: with any other streams it references, is structured such that it
469: holds information contained within <span class="term">
470: elements</span> that are organized as defined in the associated
471: <span class="term">DTD</span>. See <a href="#docconf">Document
472: Conformance</a> for more information.</dd>
473:
474: <dt>Element</dt>
475:
476: <dd>An element is a document structuring unit declared in the
477: <span class="term">DTD</span>. The element's content model is
478: defined in the <span class="term">DTD</span>, and additional
479: semantics may be defined in the prose description of the
480: element.</dd>
481:
482: <dt><a name="facilities" id="facilities">Facilities</a></dt>
483:
484: <dd>Functionality includes <span class="term">elements</span>,
485: <span class="term">attributes</span>, and the semantics
486: associated with those <span class="term">elements</span> and
487: <span class="term">attributes</span>. An implementation
488: supporting that functionality is said to provide the necessary
489: facilities.</dd>
490:
491: <dt>Implementation</dt>
492:
493: <dd>An implementation is a system that provides collection of
494: <span class="term">facilities</span> and services that supports
495: this specification. See <a href="#uaconf">User Agent
496: Conformance</a> for more information.</dd>
497:
498: <dt>Parsing</dt>
499:
500: <dd>Parsing is the act whereby a <span class="term">
501: document</span> is scanned, and the information contained within
502: the <span class="term">document</span> is filtered into the
503: context of the <span class="term">elements</span> in which the
504: information is structured.</dd>
505:
506: <dt>Rendering</dt>
507:
508: <dd>Rendering is the act whereby the information in a <span
509: class="term">document</span> is presented. This presentation is
510: done in the form most appropriate to the environment (e.g.
511: aurally, visually, in print).</dd>
512:
513: <dt>User Agent</dt>
514:
515: <dd>A user agent is an <span class="term">implementation</span>
516: that retrieves and processes XHTML documents. See <a href=
517: "#uaconf">User Agent Conformance</a> for more information.</dd>
518:
519: <dt>Validation</dt>
520:
521: <dd>Validation is a process whereby <span class="term">
522: documents</span> are verified against the associated <span class=
523: "term">DTD</span>, ensuring that the structure, use of <span
524: class="term">elements</span>, and use of <span class="term">
525: attributes</span> are consistent with the definitions in the
526: <span class="term">DTD</span>.</dd>
527:
528: <dt><a name="wellformed" id="wellformed">Well-formed</a></dt>
529:
530: <dd>A <span class="term">document</span> is well-formed when it
531: is structured according to the rules defined in <a href=
532: "http://www.w3.org/TR/REC-xml#sec-well-formed">Section 2.1</a> of
533: the XML 1.0 Recommendation <a href="#ref-xml">[XML]</a>.
534: Basically, this definition states that elements, delimited by
535: their start and end tags, are nested properly within one
536: another.</dd>
537: </dl>
538:
539: <!--OddPage-->
540: <h1><a name="normative" id="normative">3. Normative Definition of
541: XHTML 1.0</a></h1>
542:
543: <h2><a name="docconf" id="docconf">3.1 Document
544: Conformance</a></h2>
545:
546: <p>This version of XHTML provides a definition of strictly
547: conforming XHTML documents, which are restricted to tags and
548: attributes from the XHTML namespace. See <a href=
549: "#well-formed">Section 3.1.2</a> for information on using XHTML
550: with other namespaces, for instance, to include metadata
551: expressed in <abbr title="Resource Description Format">RDF</abbr> within XHTML documents.</p>
552:
553: <h3><a name="strict" id="strict">3.1.1 Strictly Conforming
554: Documents</a></h3>
555:
556: <p>A Strictly Conforming XHTML Document is a document that
557: requires only the facilities described as mandatory in this
558: specification. Such a document must meet all of the following
559: criteria:</p>
560:
561: <ol>
562: <li>
563: <p>It must validate against one of the three DTDs found in <a
564: href="#dtds">Appendix A</a>.</p>
565: </li>
566:
567: <li>
568: <p>The root element of the document must be <code>
569: <html></code>.</p>
570: </li>
571:
572: <li>
573: <p>The root element of the document must designate the XHTML
574: namespace using the <code>xmlns</code> attribute <a href=
575: "#ref-xmlns">[XMLNAMES]</a>. The namespace for XHTML is
576: defined to be
577: <code>http://www.w3.org/1999/xhtml</code>.</p>
578: </li>
579:
580: <li>
581: <p>There must be a DOCTYPE declaration in the document prior to
582: the root element. The public identifier included in
583: the DOCTYPE declaration must reference one of the three DTDs
584: found in <a href="#dtds">Appendix A</a> using the respective
585: Formal Public Identifier. The system identifier may be changed to reflect
586: local system conventions.</p>
587:
588: <pre>
589: <!DOCTYPE html
590: PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
591: "http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-strict.dtd>
592:
593: <!DOCTYPE html
594: PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
595: "http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-transitional.dtd>
596:
597: <!DOCTYPE html
598: PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
599: "http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-frameset.dtd>
600: </pre>
601: </li>
602: </ol>
603:
604: <p>Here is an example of a minimal XHTML document.</p>
605:
606: <div class="good">
607: <pre>
608: <?xml version="1.0" encoding="UTF-8"?>
609: <!DOCTYPE html
610: PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
611: "http://www.w3.org/TR/1999/PR-xhtml1-19991210/DTD/xhtml1-strict.dtd">
612: <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
613: <head>
614: <title>Virtual Library</title>
615: </head>
616: <body>
617: <p>Moved to <a href="http://vlib.org/">vlib.org</a>.</p>
618: </body>
619: </html></pre>
620: </div>
621:
622: <p>Note that in this example, the XML declaration is included. An XML
623: declaration like the one above is
624: 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
625: when the character encoding of the document is other than the default UTF-8 or
626: UTF-16.</p>
627:
628: <h3><a name="well-formed" id="well-formed">3.1.2 Using XHTML with
629: other namespaces</a></h3>
630:
631: <p>The XHTML namespace may be used with other XML namespaces
632: as per <a href="#ref-xmlns">[XMLNAMES]</a>, although such
633: documents are not strictly conforming XHTML 1.0 documents as
634: defined above. Future work by W3C will address ways to specify
635: conformance for documents involving multiple namespaces.</p>
636:
637: <p>The following example shows the way in which XHTML 1.0 could
638: be used in conjunction with the MathML Recommendation:</p>
639:
640: <div class="good">
641: <pre>
642: <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
643: <head>
644: <title>A Math Example</title>
645: </head>
646: <body>
647: <p>The following is MathML markup:</p>
648: <math xmlns="http://www.w3.org/1998/Math/MathML">
649: <apply> <log/>
650: <logbase>
651: <cn> 3 </cn>
652: </logbase>
653: <ci> x </ci>
654: </apply>
655: </math>
656: </body>
657: </html>
658: </pre>
659: </div>
660:
661: <p>The following example shows the way in which XHTML 1.0 markup
662: could be incorporated into another XML namespace:</p>
663:
664: <div class="good">
665: <pre>
666: <?xml version="1.0" encoding="UTF-8"?>
667: <!-- initially, the default namespace is "books" -->
668: <book xmlns='urn:loc.gov:books'
669: xmlns:isbn='urn:ISBN:0-395-36341-6' xml:lang="en" lang="en">
670: <title>Cheaper by the Dozen</title>
671: <isbn:number>1568491379</isbn:number>
672: <notes>
673: <!-- make HTML the default namespace for a hypertext commentary -->
674: <p xmlns='http://www.w3.org/1999/xhtml'>
675: This is also available <a href="http://www.w3.org/">online</a>.
676: </p>
677: </notes>
678: </book>
679: </pre>
680: </div>
681:
682: <h2><a name="uaconf" id="uaconf">3.2 User Agent
683: Conformance</a></h2>
684:
685: <p>A conforming user agent must meet all of the following
686: criteria:</p>
687:
688: <ol>
689: <li>In order to be consistent with the XML 1.0 Recommendation <a
690: href="#ref-xml">[XML]</a>, the user agent must parse and evaluate
691: an XHTML document for well-formedness. If the user agent claims
692: to be a validating user agent, it must also validate documents
693: against their referenced DTDs according to <a href="#ref-xml">
694: [XML]</a>.</li>
695:
696: <li>When the user agent claims to support <a href="#facilities">
697: facilities</a> defined within this specification or required by
698: this specification through normative reference, it must do so in
699: ways consistent with the facilities' definition.</li>
700:
701: <li>When a user agent processes an XHTML document as generic XML,
702: it shall only recognize attributes of type
703: <code>ID</code> (e.g. the <code>id</code> attribute on most XHTML elements)
704: as fragment identifiers.</li>
705:
706: <li>If a user agent encounters an element it does not recognize,
707: it must render the element's content.</li>
708:
709: <li>If a user agent encounters an attribute it does not
710: recognize, it must ignore the entire attribute specification
711: (i.e., the attribute and its value).</li>
712:
713: <li>If a user agent encounters an attribute value it doesn't
714: recognize, it must use the default attribute value.</li>
715:
716: <li>If it encounters an entity reference (other than one
717: of the predefined entities) for which the User Agent has
718: processed no declaration (which could happen if the declaration
719: is in the external subset which the User Agent hasn't read), the entity
720: reference should be rendered as the characters (starting
721: with the ampersand and ending with the semi-colon) that
722: make up the entity reference.</li>
723:
724: <li>When rendering content, User Agents that encounter
725: 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>
726:
727: <li>
728: The following characters are defined in [XML] as whitespace characters:
729:
730: <ul>
731: <li>Space (&#x0020;)</li>
732: <li>Tab (&#x0009;)</li>
733: <li>Carriage return (&#x000D;)</li>
734: <li>Line feed (&#x000A;)</li>
735: </ul>
736:
737: <p>
738: The XML processor normalizes different system's line end codes into one
739: single line-feed character, that is passed up to the application. The XHTML
740: user agent in addition, must treat the following characters as whitespace:
741: </p>
742:
743: <ul>
744: <li>Form feed (&#x000C;)</li>
745: <li>Zero-width space (&#x200B;)</li>
746: </ul>
747:
748: <p>
749: In elements where the 'xml:space' attribute is set to 'preserve', the user
750: agent must leave all whitespace characters intact (with the exception of
751: leading and trailing whitespace characters, which should be removed).
752: Otherwise, whitespace
753: is handled according to the following rules:
754: </p>
755:
756: <ul>
757: <li>
758: All whitespace surrounding block elements should be removed.
759: </li>
760: <li>
761: Comments are removed entirely and do not affect whitespace handling. One
762: whitespace character on either side of a comment is treated as two white
763: space characters.
764: </li>
765: <li>
766: Leading and trailing whitespace inside a block element must be removed.
767: </li>
768: <li>Line feed characters within a block element must be converted into a
769: space (except when the 'xml:space' attribute is set to 'preserve').
770: </li>
771: <li>
772: A sequence of white space characters must be reduced to a single space
773: character (except when the 'xml:space' attribute is set to 'preserve').
774: </li>
775: <li>
776: With regard to rendition,
777: the User Agent should render the content in a
778: manner appropriate to the language in which the content is written.
779: In languages whose primary script is Latinate, the ASCII space
780: character is typically used to encode both grammatical word boundaries and
781: typographic whitespace; in languages whose script is related to Nagari
782: (e.g., Sanskrit, Thai, etc.), grammatical boundaries may be encoded using
783: the ZW 'space' character, but will not typically be represented by
784: typographic whitespace in rendered output; languages using Arabiform scripts
785: may encode typographic whitespace using a space character, but may also use
786: the ZW space character to delimit 'internal' grammatical boundaries (what
787: look like words in Arabic to an English eye frequently encode several words,
788: e.g. 'kitAbuhum' = 'kitAbu-hum' = 'book them' == their book); and languages
789: in the Chinese script tradition typically neither encode such delimiters nor
790: use typographic whitespace in this way.
791: </li>
792: </ul>
793:
794: <p>Whitespace in attribute values is processed according to <a
795: href="#ref-xml">[XML]</a>.</p>
796: </li>
797: </ol>
798:
799: <!--OddPage-->
800: <h1><a name="diffs" id="diffs">4. Differences with HTML
801: 4.0</a></h1>
802:
803: <p>Due to the fact that XHTML is an XML application, certain
804: practices that were perfectly legal in SGML-based HTML 4.0 <a
805: href="#ref-html4">[HTML]</a> must be changed.</p>
806:
807: <h2><a name="h-4.1" id="h-4.1">4.1 Documents must be
808: well-formed</a></h2>
809:
810: <p><a href="#wellformed">Well-formedness</a> is a new concept
811: introduced by <a href="#ref-xml">[XML]</a>. Essentially this
812: means that all elements must either have closing tags or be
813: written in a special form (as described below), and that all the
814: elements must nest.</p>
815:
816: <p>Although overlapping is illegal in SGML, it was widely
817: tolerated in existing browsers.</p>
818:
819: <div class="good">
820: <p><strong><em>CORRECT: nested elements.</em></strong></p>
821:
822: <p><p>here is an emphasized
823: <em>paragraph</em>.</p></p>
824: </div>
825:
826: <div class="bad">
827: <p><strong><em>INCORRECT: overlapping elements</em></strong></p>
828:
829: <p><p>here is an emphasized
830: <em>paragraph.</p></em></p>
831: </div>
832:
833: <h2><a name="h-4.2" id="h-4.2">4.2 Element and attribute
834: names must be in lower case</a></h2>
835:
836: <p>XHTML documents must use lower case for all HTML element and
837: attribute names. This difference is necessary because XML is
838: case-sensitive e.g. <li> and <LI> are different
839: tags.</p>
840:
841: <h2><a name="h-4.3" id="h-4.3">4.3 For non-empty elements,
842: end tags are required</a></h2>
843:
844: <p>In SGML-based HTML 4.0 certain elements were permitted to omit
845: the end tag; with the elements that followed implying closure.
846: This omission is not permitted in XML-based XHTML. All elements
847: other than those declared in the DTD as <code>EMPTY</code> must
848: have an end tag.</p>
849:
850: <div class="good">
851: <p><strong><em>CORRECT: terminated elements</em></strong></p>
852:
853: <p><p>here is a paragraph.</p><p>here is
854: another paragraph.</p></p>
855: </div>
856:
857: <div class="bad">
858: <p><strong><em>INCORRECT: unterminated elements</em></strong></p>
859:
860: <p><p>here is a paragraph.<p>here is another
861: paragraph.</p>
862: </div>
863:
864: <h2><a name="h-4.4" id="h-4.4">4.4 Attribute values must
865: always be quoted</a></h2>
866:
867: <p>All attribute values must be quoted, even those which appear
868: to be numeric.</p>
869:
870: <div class="good">
871: <p><strong><em>CORRECT: quoted attribute values</em></strong></p>
872:
873: <p><table rows="3"></p>
874: </div>
875:
876: <div class="bad">
877: <p><strong><em>INCORRECT: unquoted attribute values</em></strong></p>
878:
879: <p><table rows=3></p>
880: </div>
881:
882: <h2><a name="h-4.5" id="h-4.5">4.5 Attribute
883: Minimization</a></h2>
884:
885: <p>XML does not support attribute minimization. Attribute-value
886: pairs must be written in full. Attribute names such as <code>
887: compact</code> and <code>checked</code> cannot occur in elements
888: without their value being specified.</p>
889:
890: <div class="good">
891: <p><strong><em>CORRECT: unminimized attributes</em></strong></p>
892:
893: <p><dl compact="compact"></p>
894: </div>
895:
896: <div class="bad">
897: <p><strong><em>INCORRECT: minimized attributes</em></strong></p>
898:
899: <p><dl compact></p>
900: </div>
901:
902: <h2><a name="h-4.6" id="h-4.6">4.6 Empty Elements</a></h2>
903:
904: <p>Empty elements must either have an end tag or the start tag must end with <code>/></code>. For instance,
905: <code><br/></code> or <code><hr></hr></code>. See <a
906: href="#guidelines">HTML Compatibility Guidelines</a> for information on ways to
907: ensure this is backward compatible with HTML 4.0 user agents.</p>
908:
909: <div class="good">
910: <p><strong><em>CORRECT: terminated empty tags</em></strong></p>
911:
912: <p><br/><hr/></p>
913: </div>
914:
915: <div class="bad">
916: <p><strong><em>INCORRECT: unterminated empty tags</em></strong></p>
917:
918: <p><br><hr></p>
919: </div>
920:
921: <h2><a name="h-4.7" id="h-4.7">4.7 Whitespace handling in
922: attribute values</a></h2>
923:
924: <p>In attribute values, user agents will strip leading and
925: trailing whitespace from attribute values and map sequences
926: of one or more whitespace characters (including line breaks) to
927: a single inter-word space (an ASCII space character for western
928: scripts). See <a href="http://www.w3.org/TR/REC-xml#AVNormalize">
929: Section 3.3.3</a> of <a href="#ref-xml">[XML]</a>.</p>
930:
931: <h2><a name="h-4.8" id="h-4.8">4.8 Script and Style
932: elements</a></h2>
933:
934: <p>In XHTML, the script and style elements are declared as having
935: <code>#PCDATA</code> content. As a result, <code><</code> and
936: <code>&</code> will be treated as the start of markup, and
937: entities such as <code>&lt;</code> and <code>&amp;</code>
938: will be recognized as entity references by the XML processor to
939: <code><</code> and <code>&</code> respectively. Wrapping
940: the content of the script or style element within a <code>
941: CDATA</code> marked section avoids the expansion of these
942: entities.</p>
943:
944: <div class="good">
945: <pre>
946: <script>
947: <![CDATA[
948: ... unescaped script content ...
949: ]]>
950: </script>
951: </pre>
952: </div>
953:
954: <p><code>CDATA</code> sections are recognized by the XML
955: processor and appear as nodes in the Document Object Model, see
956: <a href=
957: "http://www.w3.org/TR/REC-DOM-Level-1/level-one-core.html#ID-E067D597">
958: Section 1.3</a> of the DOM Level 1 Recommendation <a href=
959: "#ref-dom">[DOM]</a>.</p>
960:
961: <p>An alternative is to use external script and style
962: documents.</p>
963:
964: <h2><a name="h-4.9" id="h-4.9">4.9 SGML exclusions</a></h2>
965:
966: <p>SGML gives the writer of a DTD the ability to exclude specific
967: elements from being contained within an element. Such
968: prohibitions (called "exclusions") are not possible in XML.</p>
969:
970: <p>For example, the HTML 4.0 Strict DTD forbids the nesting of an
971: '<code>a</code>' element within another '<code>a</code>' element
972: to any descendant depth. It is not possible to spell out such
973: prohibitions in XML. Even though these prohibitions cannot be
974: defined in the DTD, certain elements should not be nested. A
975: summary of such elements and the elements that should not be
976: nested in them is found in the normative <a href="#prohibitions">
977: Appendix B</a>.</p>
978:
979: <h2><a name="h-4.10" id="h-4.10">4.10 The elements with 'id' and 'name'
980: attributes</a></h2>
981:
982: <p>HTML 4.0 defined the <code>name</code> attribute for the elements
983: <code>a</code>,
984: <code>applet</code>, <code>frame</code>,
985: <code>iframe</code>, <code>img</code>, and <code>map</code>.
986: HTML 4.0 also introduced
987: the <code>id</code> attribute. Both of these attributes are designed to be
988: used as fragment identifiers.</p>
989: <p>In XML, fragment identifiers are of type <code>ID</code>, and
990: there can only be a single attribute of type <code>ID</code> per element.
991: Therefore, in XHTML 1.0 the <code>id</code>
992: attribute is defined to be of type <code>ID</code>. In order to
993: ensure that XHTML 1.0 documents are well-structured XML documents, XHTML 1.0
994: documents MUST use the <code>id</code> attribute when defining fragment
995: identifiers, even on elements that historically have also had a
996: <code>name</code> attribute.
997: See the <a href="#guidelines">HTML Compatibility
998: Guidelines</a> for information on ensuring such anchors are backwards
999: compatible when serving XHTML documents as media type <code>text/html</code>.
1000: </p>
1001: <p>Note that in XHTML 1.0, the <code>name</code> attribute of these
1002: elements is formally deprecated, and will be removed in a
1003: subsequent version of XHTML.</p>
1004:
1005: <!--OddPage-->
1006: <h1><a name="issues" id="issues">5. Compatibility Issues</a></h1>
1007:
1008: <p>Although there is no requirement for XHTML 1.0 documents to be
1009: compatible with existing user agents, in practice this is easy to
1010: accomplish. Guidelines for creating compatible documents can be
1011: found in <a href="#guidelines">Appendix C</a>.</p>
1012:
1013: <h2><a name="media" id="media">5.1 Internet Media Type</a></h2>
1014: <p>As of the publication of this recommendation, the general
1015: recommended MIME labeling for XML-based applications
1016: has yet to be resolved.</p>
1017:
1018: <p>However, XHTML Documents which follow the guidelines set forth
1019: in <a href="#guidelines">Appendix C</a>, "HTML Compatibility Guidelines" may be
1020: labeled with the Internet Media Type "text/html", as they
1021: are compatible with most HTML browsers. This document
1022: makes no recommendation about MIME labeling of other
1023: XHTML documents.</p>
1024:
1025: <!--OddPage-->
1026: <h1><a name="future" id="future">6. Future Directions</a></h1>
1027:
1028: <p>XHTML 1.0 provides the basis for a family of document types
1029: that will extend and subset XHTML, in order to support a wide
1030: range of new devices and applications, by defining modules and
1031: specifying a mechanism for combining these modules. This
1032: mechanism will enable the extension and sub-setting of XHTML 1.0
1033: in a uniform way through the definition of new modules.</p>
1034:
1035: <h2><a name="mods" id="mods">6.1 Modularizing HTML</a></h2>
1036:
1037: <p>As the use of XHTML moves from the traditional desktop user
1038: agents to other platforms, it is clear that not all of the XHTML
1039: elements will be required on all platforms. For example a hand
1040: held device or a cell-phone may only support a subset of XHTML
1041: elements.</p>
1042:
1043: <p>The process of modularization breaks XHTML up into a series of
1044: smaller element sets. These elements can then be recombined to
1045: meet the needs of different communities.</p>
1046:
1047: <p>These modules will be defined in a later W3C document.</p>
1048:
1049: <h2><a name="extensions" id="extensions">6.2 Subsets and
1050: Extensibility</a></h2>
1051:
1052: <p>Modularization brings with it several advantages:</p>
1053:
1054: <ul>
1055: <li>
1056: <p>It provides a formal mechanism for sub-setting XHTML.</p>
1057: </li>
1058:
1059: <li>
1060: <p>It provides a formal mechanism for extending XHTML.</p>
1061: </li>
1062:
1063: <li>
1064: <p>It simplifies the transformation between document types.</p>
1065: </li>
1066:
1067: <li>
1068: <p>It promotes the reuse of modules in new document types.</p>
1069: </li>
1070: </ul>
1071:
1072: <h2><a name="profiles" id="profiles">6.3 Document
1073: Profiles</a></h2>
1074:
1075: <p>A document profile specifies the syntax and semantics of a set
1076: of documents. Conformance to a document profile provides a basis
1077: for interoperability guarantees. The document profile specifies
1078: the facilities required to process documents of that type, e.g.
1079: which image formats can be used, levels of scripting, style sheet
1080: support, and so on.</p>
1081:
1082: <p>For product designers this enables various groups to define
1083: their own standard profile.</p>
1084:
1085: <p>For authors this will obviate the need to write several
1086: different versions of documents for different clients.</p>
1087:
1088: <p>For special groups such as chemists, medical doctors, or
1089: mathematicians this allows a special profile to be built using
1090: standard HTML elements plus a group of elements geared to the
1091: specialist's needs.</p>
1092:
1093: <!--OddPage-->
1094: <h1><a name="appendices" id="appendices"></a>
1095: <a name="dtds" id="dtds">Appendix A. DTDs</a></h1>
1096:
1097: <p><b>This appendix is normative.</b></p>
1098:
1099: <p>These DTDs and entity sets form a normative part of this
1100: specification. The complete set of DTD files together with an XML
1101: declaration and SGML Open Catalog is included in the <a href=
1102: "xhtml1.zip">zip file</a> for this specification.</p>
1103:
1104: <h2><a name="h-A1" id="h-A1">A.1 Document Type
1105: Definitions</a></h2>
1106:
1107: <p>These DTDs approximate the HTML 4.0 DTDs. It is likely that
1108: when the DTDs are modularized, a method of DTD construction will
1109: be employed that corresponds more closely to HTML 4.0.</p>
1110:
1111: <ul>
1112: <li>
1113: <p><a href="DTD/xhtml1-strict.dtd" type="text/plain">
1114: XHTML-1.0-Strict</a></p>
1115: </li>
1116:
1117: <li>
1118: <p><a href="DTD/xhtml1-transitional.dtd" type="text/plain">
1119: XHTML-1.0-Transitional</a></p>
1120: </li>
1121:
1122: <li>
1123: <p><a href="DTD/xhtml1-frameset.dtd" type="text/plain">
1124: XHTML-1.0-Frameset</a></p>
1125: </li>
1126: </ul>
1127:
1128: <h2><a name="h-A2" id="h-A2">A.2 Entity Sets</a></h2>
1129:
1130: <p>The XHTML entity sets are the same as for HTML 4.0, but have
1131: been modified to be valid XML 1.0 entity declarations. Note the
1132: entity for the Euro currency sign (<code>&euro;</code> or
1133: <code>&#8364;</code> or <code>&#x20AC;</code>) is defined
1134: as part of the special characters.</p>
1135:
1136: <ul>
1137: <li>
1138: <p><a href="DTD/xhtml-lat1.ent">Latin-1 characters</a></p>
1139: </li>
1140:
1141: <li>
1142: <p><a href="DTD/xhtml-special.ent">Special characters</a></p>
1143: </li>
1144:
1145: <li>
1146: <p><a href="DTD/xhtml-symbol.ent">Symbols</a></p>
1147: </li>
1148: </ul>
1149:
1150: <!--OddPage-->
1151: <h1><a name="prohibitions" id="prohibitions">Appendix B. Element
1152: Prohibitions</a></h1>
1153:
1154: <p><b>This appendix is normative.</b></p>
1155:
1156: <p>The following elements have prohibitions on which elements
1157: they can contain (see <a href="#h-4.9">Section 4.9</a>). This
1158: prohibition applies to all depths of nesting, i.e. it contains
1159: all the descendant elements.</p>
1160:
1161: <dl><dt><code class="tag">a</code></dt>
1162: <dd>
1163: cannot contain other <code>a</code> elements.</dd>
1164: <dt><code class="tag">pre</code></dt>
1165: <dd>cannot contain the <code>img</code>, <code>object</code>,
1166: <code>big</code>, <code>small</code>, <code>sub</code>, or <code>
1167: sup</code> elements.</dd>
1168:
1169: <dt><code class="tag">button</code></dt>
1170: <dd>cannot contain the <code>input</code>, <code>select</code>,
1171: <code>textarea</code>, <code>label</code>, <code>button</code>,
1172: <code>form</code>, <code>fieldset</code>, <code>iframe</code> or
1173: <code>isindex</code> elements.</dd>
1174: <dt><code class="tag">label</code></dt>
1175: <dd>cannot contain other <code class="tag">label</code> elements.</dd>
1176: <dt><code class="tag">form</code></dt>
1177: <dd>cannot contain other <code>form</code> elements.</dd>
1178: </dl>
1179:
1180: <!--OddPage-->
1181: <h1><a name="guidelines" id="guidelines">Appendix C.
1182: HTML Compatibility Guidelines</a></h1>
1183:
1184: <p><b>This appendix is informative.</b></p>
1185:
1186: <p>This appendix summarizes design guidelines for authors who
1187: wish their XHTML documents to render on existing HTML user
1188: agents.</p>
1189:
1190: <h2>C.1 Processing Instructions</h2>
1191: <p>Be aware that processing instructions are rendered on some
1192: user agents. However, also note that when the XML declaration is not included
1193: in a document, the document can only use the default character encodings UTF-8
1194: or UTF-16.</p>
1195:
1196: <h2>C.2 Empty Elements</h2>
1197: <p>Include a space before the trailing <code>/</code> and <code>
1198: ></code> of empty elements, e.g. <code class="greenmono">
1199: <br /></code>, <code class="greenmono">
1200: <hr /></code> and <code class="greenmono"><img
1201: src="karen.jpg" alt="Karen" /></code>. Also, use the
1202: minimized tag syntax for empty elements, e.g. <code class=
1203: "greenmono"><br /></code>, as the alternative syntax <code
1204: class="greenmono"><br></br></code> allowed by XML
1205: gives uncertain results in many existing user agents.</p>
1206:
1207: <h2>C.3 Element Minimization and Empty Element Content</h2>
1208: <p>Given an empty instance of an element whose content model is
1209: not <code>EMPTY</code> (for example, an empty title or paragraph)
1210: do not use the minimized form (e.g. use <code class="greenmono">
1211: <p> </p></code> and not <code class="greenmono">
1212: <p /></code>).</p>
1213:
1214: <h2>C.4 Embedded Style Sheets and Scripts</h2>
1215: <p>Use external style sheets if your style sheet uses <code>
1216: <</code> or <code>&</code> or <code>]]></code> or <code>--</code>. Use
1217: external scripts if your script uses <code><</code> or <code>
1218: &</code> or <code>]]></code> or <code>--</code>. Note that XML parsers
1219: are permitted to silently remove the contents of comments. Therefore, the historical
1220: practice of "hiding" scripts and style sheets within comments to make the
1221: documents backward compatible is likely to not work as expected in XML-based
1222: implementations.</p>
1223:
1224: <h2>C.5 Line Breaks within Attribute Values</h2>
1225: <p>Avoid line breaks and multiple whitespace characters within
1226: attribute values. These are handled inconsistently by user
1227: agents.</p>
1228:
1229: <h2>C.6 Isindex</h2>
1230: <p>Don't include more than one <code>isindex</code> element in
1231: the document <code>head</code>. The <code>isindex</code> element
1232: is deprecated in favor of the <code>input</code> element.</p>
1233:
1234: <h2>C.7 The <code>lang</code> and <code>xml:lang</code> Attributes</h2>
1235: <p>Use both the <code>lang</code> and <code>xml:lang</code>
1236: attributes when specifying the language of an element. The value
1237: of the <code>xml:lang</code> attribute takes precedence.</p>
1238:
1239: <h2>C.8 Fragment Identifiers</h2>
1240: <p>In XML, <abbr title="Uniform Resource Identifiers">URIs</abbr> [<a href="#ref-rfc2396">RFC2396</a>] that end with fragment identifiers of the form
1241: <code>"#foo"</code> do not refer to elements with an attribute
1242: <code>name="foo"</code>; rather, they refer to elements with an
1243: attribute defined to be of type <code>ID</code>, e.g., the <code>
1244: id</code> attribute in HTML 4.0. Many existing HTML clients don't
1245: support the use of <code>ID</code>-type attributes in this way,
1246: so identical values may be supplied for both of these attributes to ensure
1247: maximum forward and backward compatibility (e.g., <code class=
1248: "greenmono"><a id="foo" name="foo">...</a></code>).</p>
1249:
1250: <p>Further, since the set of
1251: legal values for attributes of type <code>ID</code> is much smaller than
1252: for those of type <code>CDATA</code>, the type of the <code>name</code>
1253: attribute has been changed to <code>NMTOKEN</code>. This attribute is
1254: constrained such that it can only have the same values as type
1255: <code>ID</code>, or as the <code>Name</code> production in XML 1.0 Section
1256: 2.5, production 5. Unfortunately, this constraint cannot be expressed in the
1257: XHTML 1.0 DTDs. Because of this change, care must be taken when
1258: converting existing HTML documents. The values of these attributes
1259: must be unique within the document, valid, and any references to these
1260: fragment identifiers (both
1261: internal and external) must be updated should the values be changed during
1262: conversion.</p>
1263: <p>Finally, note that XHTML 1.0 has deprecated the
1264: <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>
1265: elements, and it will be
1266: removed from XHTML in subsequent versions.</p>
1267:
1268: <h2>C.9 Character Encoding</h2>
1269: <p>To specify a character encoding in the document, use both the
1270: encoding attribute specification on the xml declaration (e.g.
1271: <code class="greenmono"><?xml version="1.0"
1272: encoding="EUC-JP"?></code>) and a meta http-equiv statement
1273: (e.g. <code class="greenmono"><meta http-equiv="Content-type"
1274: content='text/html; charset="EUC-JP"' /></code>). The
1275: value of the encoding attribute of the xml processing instruction
1276: takes precedence.</p>
1277:
1278: <h2>C.10 Boolean Attributes</h2>
1279: <p>Some HTML user agents are unable to interpret boolean
1280: attributes when these appear in their full (non-minimized) form,
1281: as required by XML 1.0. Note this problem doesn't effect user
1282: agents compliant with HTML 4.0. The following attributes are
1283: involved: <code>compact</code>, <code>nowrap</code>, <code>
1284: ismap</code>, <code>declare</code>, <code>noshade</code>, <code>
1285: checked</code>, <code>disabled</code>, <code>readonly</code>,
1286: <code>multiple</code>, <code>selected</code>, <code>
1287: noresize</code>, <code>defer</code>.</p>
1288:
1289: <h2>C.11 Document Object Model and XHTML</h2>
1290: <p>
1291: The Document Object Model level 1 Recommendation [<a href="#ref-dom">DOM</a>]
1292: defines document object model interfaces for XML and HTML 4.0. The HTML 4.0
1293: document object model specifies that HTML element and attribute names are
1294: returned in upper-case. The XML document object model specifies that
1295: element and attribute names are returned in the case they are specified. In
1296: XHTML 1.0, elements and attributes are specified in lower-case. This apparent difference can be
1297: addressed in two ways:
1298: </p>
1299: <ol>
1300: <li>Applications that access XHTML documents served as Internet media type
1301: <code>text/html</code>
1302: via the <abbr title="Document Object Model">DOM</abbr> can use the HTML DOM,
1303: and can rely upon element and attribute names being returned in
1304: upper-case from those interfaces.</li>
1305: <li>Applications that access XHTML documents served as Internet media types
1306: <code>text/xml</code> or <code>application/xml</code>
1307: can also use the XML DOM. Elements and attributes will be returned in lower-case.
1308: Also, some XHTML elements may or may
1309: not appear
1310: in the object tree because they are optional in the content model
1311: (e.g. the <code>tbody</code> element within
1312: <code>table</code>). This occurs because in HTML 4.0 some elements were
1313: permitted to be minimized such that their start and end tags are both omitted
1314: (an SGML feature).
1315: This is not possible in XML. Rather than require document authors to insert
1316: extraneous elements, XHTML has made the elements optional.
1317: Applications need to adapt to this
1318: accordingly.</li>
1319: </ol>
1320:
1321: <h2>C.12 Using Ampersands in Attribute Values</h2>
1322: <p>
1323: When an attribute value contains an ampersand, it must be expressed as a character
1324: entity reference
1325: (e.g. "<code>&amp;</code>"). For example, when the
1326: <code>href</code> attribute
1327: of the <code>a</code> element refers to a
1328: CGI script that takes parameters, it must be expressed as
1329: <code>http://my.site.dom/cgi-bin/myscript.pl?class=guest&amp;name=user</code>
1330: rather than as
1331: <code>http://my.site.dom/cgi-bin/myscript.pl?class=guest&name=user</code>.
1332: </p>
1333:
1334: <h2>C.13 Cascading Style Sheets (CSS) and XHTML</h2>
1335:
1336: <p>The Cascading Style Sheets level 2 Recommendation [<a href="#ref-css2">CSS2</a>] defines style
1337: properties which are applied to the parse tree of the HTML or XML
1338: document. Differences in parsing will produce different visual or
1339: aural results, depending on the selectors used. The following hints
1340: will reduce this effect for documents which are served without
1341: modification as both media types:</p>
1342:
1343: <ol>
1344: <li>
1345: CSS style sheets for XHTML should use lower case element and
1346: attribute names.</li>
1347:
1348:
1349: <li>In tables, the tbody element will be inferred by the parser of an
1350: HTML user agent, but not by the parser of an XML user agent. Therefore
1351: you should always explicitely add a tbody element if it is referred to
1352: in a CSS selector.</li>
1353:
1354: <li>Within the XHTML name space, user agents are expected to
1355: recognize the "id" attribute as an attribute of type ID.
1356: Therefore, style sheets should be able to continue using the
1357: shorthand "#" selector syntax even if the user agent does not read
1358: the DTD.</li>
1359:
1360: <li>Within the XHTML name space, user agents are expected to
1361: recognize the "class" attribute. Therefore, style sheets should be
1362: able to continue using the shorthand "." selector syntax.</li>
1363:
1364: <li>
1365: CSS defines different conformance rules for HTML and XML documents;
1366: be aware that the HTML rules apply to XHTML documents delivered as
1367: HTML and the XML rules apply to XHTML documents delivered as XML.</li>
1368: </ol>
1369: <!--OddPage-->
1370: <h1><a name="acks" id="acks">Appendix D.
1371: Acknowledgements</a></h1>
1372:
1373: <p><b>This appendix is informative.</b></p>
1374:
1375: <p>This specification was written with the participation of the
1376: members of the W3C HTML working group:</p>
1377:
1378: <dl>
1379: <dd>Steven Pemberton, CWI (HTML Working Group Chair)<br />
1380: Murray Altheim, Sun Microsystems<br />
1381: Daniel Austin, CNET: The Computer Network<br />
1382: Frank Boumphrey, HTML Writers Guild<br />
1383: John Burger, Mitre<br />
1384: Andrew W. Donoho, IBM<br />
1385: Sam Dooley, IBM<br />
1386: Klaus Hofrichter, GMD<br />
1387: Philipp Hoschka, W3C<br />
1388: Masayasu Ishikawa, W3C<br />
1389: Warner ten Kate, Philips Electronics<br />
1390: Peter King, Phone.com<br />
1391: Paula Klante, JetForm<br />
1392: Shin'ichi Matsui, W3C/Panasonic<br />
1393: Shane McCarron, Applied Testing and Technology (The Open Group through August
1394: 1999)<br />
1395: Ann Navarro, HTML Writers Guild<br />
1396: Zach Nies, Quark<br />
1397: Dave Raggett, W3C/HP (W3C lead for HTML)<br />
1398: Patrick Schmitz, Microsoft<br />
1399: Sebastian Schnitzenbaumer, Stack Overflow<br />
1400: Chris Wilson, Microsoft<br />
1401: Ted Wugofski, Gateway 2000<br />
1402: Dan Zigmond, WebTV Networks</dd>
1403: </dl>
1404:
1405: <!--OddPage-->
1406: <h1><a name="refs" id="refs">Appendix E. References</a></h1>
1407:
1408: <p><b>This appendix is informative.</b></p>
1409:
1410: <dl>
1411:
1412: <dt><a name="ref-css2" id="ref-css2"><b>[CSS2]</b></a></dt>
1413:
1414: <dd><a href="http://www.w3.org/TR/REC-CSS2">"Cascading Style Sheets, level 2 (CSS2) Specification"</a>, B.
1415: Bos, H. W. Lie, C. Lilley, I. Jacobs, 12 May 1998.<br />
1416: Available at: <a href="http://www.w3.org/TR/REC-CSS2">
1417: http://www.w3.org/TR/REC-CSS2</a></dd>
1418:
1419: <dt><a name="ref-dom" id="ref-dom"><b>[DOM]</b></a></dt>
1420:
1421: <dd><a href="http://www.w3.org/TR/REC-DOM-Level-1">"Document Object Model (DOM) Level 1 Specification"</a>, Lauren
1422: Wood <i>et al.</i>, 1 October 1998.<br />
1423: Available at: <a href="http://www.w3.org/TR/REC-DOM-Level-1">
1424: http://www.w3.org/TR/REC-DOM-Level-1</a></dd>
1425:
1426: <dt><a name="ref-html4" id="ref-html4"><b>[HTML]</b></a></dt>
1427:
1428: <dd><a href="http://www.w3.org/TR/1999/PR-html40-19990824">"HTML 4.01 Specification"</a>, D. Raggett, A. Le Hors, I.
1429: Jacobs, 24 August 1999.<br />
1430: Available at: <a href="http://www.w3.org/TR/1999/PR-html40-19990824">
1431: http://www.w3.org/TR/1999/PR-html40-19990824</a></dd>
1432:
1433: <dt><a name="ref-posix" id="ref-posix"><b>[POSIX.1]</b></a></dt>
1434:
1435: <dd>"ISO/IEC 9945-1:1990 Information Technology - Portable
1436: Operating System Interface (POSIX) - Part 1: System Application
1437: Program Interface (API) [C Language]", Institute of Electrical
1438: and Electronics Engineers, Inc, 1990.</dd>
1439:
1440: <dt><a name="ref-rfc2046" id="ref-rfc2046"><b>
1441: [RFC2046]</b></a></dt>
1442:
1443: <dd><a href="http://www.ietf.org/rfc/rfc2046.txt">"RFC2046: Multipurpose Internet Mail Extensions (MIME) Part
1444: Two: Media Types"</a>, N. Freed and N. Borenstein, November
1445: 1996.<br />
1446: Available at <a href="http://www.ietf.org/rfc/rfc2046.txt">
1447: http://www.ietf.org/rfc/rfc2046.txt</a>. Note that this RFC
1448: obsoletes RFC1521, RFC1522, and RFC1590.</dd>
1449:
1450: <dt><a name="ref-rfc2119" id="ref-rfc2119"><b>
1451: [RFC2119]</b></a></dt>
1452:
1453: <dd><a href="http://www.ietf.org/rfc/rfc2119.txt">"RFC2119: Key words for use in RFCs to Indicate Requirement
1454: Levels"</a>, S. Bradner, March 1997.<br />
1455: Available at: <a href="http://www.ietf.org/rfc/rfc2119.txt">
1456: http://www.ietf.org/rfc/rfc2119.txt</a></dd>
1457:
1458: <dt><a name="ref-rfc2376" id="ref-rfc2376"><b>
1459: [RFC2376]</b></a></dt>
1460:
1461: <dd><a href="http://www.ietf.org/rfc/rfc2376.txt">"RFC2376: XML Media Types"</a>, E. Whitehead, M. Murata, July
1462: 1998.<br />
1463: Available at: <a href="http://www.ietf.org/rfc/rfc2376.txt">
1464: http://www.ietf.org/rfc/rfc2376.txt</a></dd>
1465:
1466: <dt><a name="ref-rfc2396" id="ref-rfc2396"><b>
1467: [RFC2396]</b></a></dt>
1468:
1469: <dd><a href="http://www.ietf.org/rfc/rfc2396.txt">"RFC2396: Uniform Resource Identifiers (URI): Generic
1470: Syntax"</a>, T. Berners-Lee, R. Fielding, L. Masinter, August
1471: 1998.<br />
1472: This document updates RFC1738 and RFC1808.<br />
1473: Available at: <a href="http://www.ietf.org/rfc/rfc2396.txt">
1474: http://www.ietf.org/rfc/rfc2396.txt</a></dd>
1475:
1476: <dt><a name="ref-xml" id="ref-xml"><b>[XML]</b></a></dt>
1477:
1478: <dd><a href="http://www.w3.org/TR/REC-xml">"Extensible Markup Language (XML) 1.0 Specification"</a>, T.
1479: Bray, J. Paoli, C. M. Sperberg-McQueen, 10 February 1998.<br />
1480: Available at: <a href="http://www.w3.org/TR/REC-xml">
1481: http://www.w3.org/TR/REC-xml</a></dd>
1482:
1483: <dt><a name="ref-xmlns" id="ref-xmlns"><b>[XMLNAMES]</b></a></dt>
1484:
1485: <dd><a href="http://www.w3.org/TR/REC-xml-names">"Namespaces in XML"</a>, T. Bray, D. Hollander, A. Layman, 14
1486: January 1999.<br />
1487: XML namespaces provide a simple method for qualifying names used
1488: in XML documents by associating them with namespaces identified
1489: by URI.<br />
1490: Available at: <a href="http://www.w3.org/TR/REC-xml-names">
1491: http://www.w3.org/TR/REC-xml-names</a></dd>
1492:
1493: </dl>
1494: <p><a href="http://www.w3.org/WAI/WCAG1AAA-Conformance"
1495: title="Explanation of Level Triple-A Conformance">
1496: <img height="32" width="88"
1497: src="wcag1AAA.gif"
1498: alt="Level Triple-A conformance icon, W3C-WAI Web Content Accessibility Guidelines 1.0" /></a></p>
1499: <div class="navbar">
1500: <hr />
1501: <a href="#toc">table of contents</a>
1502: </div>
1503: </body>
1504: </html>
1505:
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