1 <?xml version="1.0" encoding="ISO-8859-1" standalone="no"?>
2 <!DOCTYPE spec SYSTEM "dtds/spec.dtd" [
3 <!-- LAST TOUCHED BY: Tim Bray, 8 February 1997 --><!-- The words 'FINAL EDIT' in comments mark places where changes
4 need to be made after approval of the document by the ERB, before
5 publication. --><!ENTITY XML.version "1.0">
6 <!ENTITY doc.date "10 February 1998">
7 <!ENTITY iso6.doc.date "19980210">
8 <!ENTITY w3c.doc.date "02-Feb-1998">
9 <!ENTITY draft.day "10">
10 <!ENTITY draft.month "February">
11 <!ENTITY draft.year "1998">
12 <!ENTITY WebSGML "WebSGML Adaptations Annex to ISO 8879">
15 <!ENTITY xmlpio "'<?xml'">
18 <!ENTITY cellback "#c0d9c0">
20 <!-- —, but nsgmls doesn't grok hex --><!ENTITY com "--">
23 <!ENTITY hcro "&#x">
24 <!-- <!ENTITY nbsp " "> --><!ENTITY nbsp " ">
25 <!ENTITY magicents "<code>amp</code>,
30 <!-- audience and distribution status: for use at publication time --><!ENTITY doc.audience "public review and discussion">
31 <!ENTITY doc.distribution "may be distributed freely, as long as
32 all text and legal notices remain intact">
34 <!-- for Panorama *-->
38 <title>Extensible Markup Language (XML) 1.0</title>
40 <w3c-designation>REC-xml-&iso6.doc.date;</w3c-designation>
41 <w3c-doctype>W3C Recommendation</w3c-doctype>
42 <pubdate><day>&draft.day;</day><month>&draft.month;</month><year>&draft.year;</year></pubdate>
45 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;">
46 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;</loc>
47 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.xml">
48 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.xml</loc>
49 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.html">
50 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.html</loc>
51 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.pdf">
52 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.pdf</loc>
53 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.ps">
54 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.ps</loc>
57 <loc href="http://www.w3.org/TR/REC-xml">
58 http://www.w3.org/TR/REC-xml</loc>
61 <loc href="http://www.w3.org/TR/PR-xml-971208">
62 http://www.w3.org/TR/PR-xml-971208</loc>
64 <loc href='http://www.w3.org/TR/WD-xml-961114'>
65 http://www.w3.org/TR/WD-xml-961114</loc>
66 <loc href='http://www.w3.org/TR/WD-xml-lang-970331'>
67 http://www.w3.org/TR/WD-xml-lang-970331</loc>
68 <loc href='http://www.w3.org/TR/WD-xml-lang-970630'>
69 http://www.w3.org/TR/WD-xml-lang-970630</loc>
70 <loc href='http://www.w3.org/TR/WD-xml-970807'>
71 http://www.w3.org/TR/WD-xml-970807</loc>
72 <loc href='http://www.w3.org/TR/WD-xml-971117'>
73 http://www.w3.org/TR/WD-xml-971117</loc>-->
76 <author><name>Tim Bray</name>
77 <affiliation>Textuality and Netscape</affiliation>
78 <email href="mailto:tbray@textuality.com">tbray@textuality.com</email></author>
79 <author><name>Jean Paoli</name>
80 <affiliation>Microsoft</affiliation>
81 <email href="mailto:jeanpa@microsoft.com">jeanpa@microsoft.com</email></author>
82 <author><name>C. M. Sperberg-McQueen</name>
83 <affiliation>University of Illinois at Chicago</affiliation>
84 <email href="mailto:cmsmcq@uic.edu">cmsmcq@uic.edu</email></author>
87 <p>The Extensible Markup Language (XML) is a subset of
88 SGML that is completely described in this document. Its goal is to
89 enable generic SGML to be served, received, and processed on the Web
90 in the way that is now possible with HTML. XML has been designed for
91 ease of implementation and for interoperability with both SGML and
95 <p>This document has been reviewed by W3C Members and
96 other interested parties and has been endorsed by the
97 Director as a W3C Recommendation. It is a stable
98 document and may be used as reference material or cited
99 as a normative reference from another document. W3C's
100 role in making the Recommendation is to draw attention
101 to the specification and to promote its widespread
102 deployment. This enhances the functionality and
103 interoperability of the Web.</p>
105 This document specifies a syntax created by subsetting an existing,
106 widely used international text processing standard (Standard
107 Generalized Markup Language, ISO 8879:1986(E) as amended and
108 corrected) for use on the World Wide Web. It is a product of the W3C
109 XML Activity, details of which can be found at <loc href="http://www.w3.org/XML">http://www.w3.org/XML</loc>. A list of
110 current W3C Recommendations and other technical documents can be found
111 at <loc href="http://www.w3.org/TR">http://www.w3.org/TR</loc>.
113 <p>This specification uses the term URI, which is defined by <bibref ref="Berners-Lee"/>, a work in progress expected to update <bibref ref="RFC1738"/> and <bibref ref="RFC1808"/>.
115 <p>The list of known errors in this specification is
117 <loc href="http://www.w3.org/XML/xml-19980210-errata">http://www.w3.org/XML/xml-19980210-errata</loc>.</p>
118 <p>Please report errors in this document to
119 <loc href="mailto:xml-editor@w3.org">xml-editor@w3.org</loc>.
125 <p>Chicago, Vancouver, Mountain View, et al.:
126 World-Wide Web Consortium, XML Working Group, 1996, 1997.</p>
129 <p>Created in electronic form.</p>
132 <language id="EN">English</language>
133 <language id="ebnf">Extended Backus-Naur Form (formal grammar)</language>
137 <sitem>1997-12-03 : CMSMcQ : yet further changes</sitem>
138 <sitem>1997-12-02 : TB : further changes (see TB to XML WG,
139 2 December 1997)</sitem>
140 <sitem>1997-12-02 : CMSMcQ : deal with as many corrections and
141 comments from the proofreaders as possible:
142 entify hard-coded document date in pubdate element,
143 change expansion of entity WebSGML,
144 update status description as per Dan Connolly (am not sure
145 about refernece to Berners-Lee et al.),
146 add 'The' to abstract as per WG decision,
147 move Relationship to Existing Standards to back matter and
148 combine with References,
149 re-order back matter so normative appendices come first,
150 re-tag back matter so informative appendices are tagged informdiv1,
151 remove XXX XXX from list of 'normative' specs in prose,
152 move some references from Other References to Normative References,
153 add RFC 1738, 1808, and 2141 to Other References (they are not
154 normative since we do not require the processor to enforce any
155 rules based on them),
156 add reference to 'Fielding draft' (Berners-Lee et al.),
157 move notation section to end of body,
158 drop URIchar non-terminal and use SkipLit instead,
159 lose stray reference to defunct nonterminal 'markupdecls',
160 move reference to Aho et al. into appendix (Tim's right),
161 add prose note saying that hash marks and fragment identifiers are
162 NOT part of the URI formally speaking, and are NOT legal in
163 system identifiers (processor 'may' signal an error).
165 Tim Bray reacting to James Clark,
170 change binary / text to unparsed / parsed.
171 handle James's suggestion about < in attriubte values
172 uppercase hex characters,
175 <sitem>1997-12-01 : JB : add some column-width parameters</sitem>
176 <sitem>1997-12-01 : CMSMcQ : begin round of changes to incorporate
177 recent WG decisions and other corrections:
178 binding sources of character encoding info (27 Aug / 3 Sept),
179 correct wording of Faust quotation (restore dropped line),
180 drop SDD from EncodingDecl,
181 change text at version number 1.0,
182 drop misleading (wrong!) sentence about ignorables and extenders,
183 modify definition of PCData to make bar on msc grammatical,
184 change grammar's handling of internal subset (drop non-terminal markupdecls),
185 change definition of includeSect to allow conditional sections,
186 add integral-declaration constraint on internal subset,
187 drop misleading / dangerous sentence about relationship of
188 entities with system storage objects,
189 change table body tag to htbody as per EM change to DTD,
190 add rule about space normalization in public identifiers,
191 add description of how to generate our name-space rules from
192 Unicode character database (needs further work!).
194 <sitem>1997-10-08 : TB : Removed %-constructs again, new rules
195 for PE appearance.</sitem>
196 <sitem>1997-10-01 : TB : Case-sensitive markup; cleaned up
197 element-type defs, lotsa little edits for style</sitem>
198 <sitem>1997-09-25 : TB : Change to elm's new DTD, with
199 substantial detail cleanup as a side-effect</sitem>
200 <sitem>1997-07-24 : CMSMcQ : correct error (lost *) in definition
201 of ignoreSectContents (thanks to Makoto Murata)</sitem>
202 <sitem>Allow all empty elements to have end-tags, consistent with
203 SGML TC (as per JJC).</sitem>
204 <sitem>1997-07-23 : CMSMcQ : pre-emptive strike on pending corrections:
205 introduce the term 'empty-element tag', note that all empty elements
206 may use it, and elements declared EMPTY must use it.
207 Add WFC requiring encoding decl to come first in an entity.
208 Redefine notations to point to PIs as well as binary entities.
209 Change autodetection table by removing bytes 3 and 4 from
210 examples with Byte Order Mark.
211 Add content model as a term and clarify that it applies to both
212 mixed and element content.
214 <sitem>1997-06-30 : CMSMcQ : change date, some cosmetic changes,
215 changes to productions for choice, seq, Mixed, NotationType,
216 Enumeration. Follow James Clark's suggestion and prohibit
217 conditional sections in internal subset. TO DO: simplify
218 production for ignored sections as a result, since we don't
219 need to worry about parsers which don't expand PErefs finding
220 a conditional section.</sitem>
221 <sitem>1997-06-29 : TB : various edits</sitem>
222 <sitem>1997-06-29 : CMSMcQ : further changes:
223 Suppress old FINAL EDIT comments and some dead material.
224 Revise occurrences of % in grammar to exploit Henry Thompson's pun,
225 especially markupdecl and attdef.
226 Remove RMD requirement relating to element content (?).
228 <sitem>1997-06-28 : CMSMcQ : Various changes for 1 July draft:
229 Add text for draconian error handling (introduce
230 the term Fatal Error).
231 RE deleta est (changing wording from
232 original announcement to restrict the requirement to validating
234 Tag definition of validating processor and link to it.
235 Add colon as name character.
236 Change def of %operator.
237 Change standard definitions of lt, gt, amp.
238 Strip leading zeros from #x00nn forms.</sitem>
239 <sitem>1997-04-02 : CMSMcQ : final corrections of editorial errors
240 found in last night's proofreading. Reverse course once more on
241 well-formed: Webster's Second hyphenates it, and that's enough
243 <sitem>1997-04-01 : CMSMcQ : corrections from JJC, EM, HT, and self</sitem>
244 <sitem>1997-03-31 : Tim Bray : many changes</sitem>
245 <sitem>1997-03-29 : CMSMcQ : some Henry Thompson (on entity handling),
246 some Charles Goldfarb, some ERB decisions (PE handling in miscellaneous
247 declarations. Changed Ident element to accept def attribute.
248 Allow normalization of Unicode characters. move def of systemliteral
249 into section on literals.</sitem>
250 <sitem>1997-03-28 : CMSMcQ : make as many corrections as possible, from
251 Terry Allen, Norbert Mikula, James Clark, Jon Bosak, Henry Thompson,
252 Paul Grosso, and self. Among other things: give in on "well formed"
253 (Terry is right), tentatively rename QuotedCData as AttValue
254 and Literal as EntityValue to be more informative, since attribute
255 values are the <emph>only</emph> place QuotedCData was used, and
256 vice versa for entity text and Literal. (I'd call it Entity Text,
257 but 8879 uses that name for both internal and external entities.)</sitem>
258 <sitem>1997-03-26 : CMSMcQ : resynch the two forks of this draft, reapply
259 my changes dated 03-20 and 03-21. Normalize old 'may not' to 'must not'
260 except in the one case where it meant 'may or may not'.</sitem>
261 <sitem>1997-03-21 : TB : massive changes on plane flight from Chicago
263 <sitem>1997-03-21 : CMSMcQ : correct as many reported errors as possible.
265 <sitem>1997-03-20 : CMSMcQ : correct typos listed in CMSMcQ hand copy of spec.</sitem>
266 <sitem>1997-03-20 : CMSMcQ : cosmetic changes preparatory to revision for
267 WWW conference April 1997: restore some of the internal entity
268 references (e.g. to docdate, etc.), change character xA0 to &nbsp;
269 and define nbsp as &#160;, and refill a lot of paragraphs for
271 <sitem>1996-11-12 : CMSMcQ : revise using Tim's edits:
272 Add list type of NUMBERED and change most lists either to
273 BULLETS or to NUMBERED.
274 Suppress QuotedNames, Names (not used).
275 Correct trivial-grammar doc type decl.
276 Rename 'marked section' as 'CDATA section' passim.
277 Also edits from James Clark:
278 Define the set of characters from which [^abc] subtracts.
279 Charref should use just [0-9] not Digit.
280 Location info needs cleaner treatment: remove? (ERB
282 One example of a PI has wrong pic.
283 Clarify discussion of encoding names.
284 Encoding failure should lead to unspecified results; don't
285 prescribe error recovery.
286 Don't require exposure of entity boundaries.
287 Ignore white space in element content.
288 Reserve entity names of the form u-NNNN.
289 Clarify relative URLs.
291 Correct productions for content model: model cannot
292 consist of a name, so "elements ::= cp" is no good.
294 <sitem>1996-11-11 : CMSMcQ : revise for style.
295 Add new rhs to entity declaration, for parameter entities.</sitem>
296 <sitem>1996-11-10 : CMSMcQ : revise for style.
297 Fix / complete section on names, characters.
298 Add sections on parameter entities, conditional sections.
299 Still to do: Add compatibility note on deterministic content models.
300 Finish stylistic revision.</sitem>
301 <sitem>1996-10-31 : TB : Add Entity Handling section</sitem>
302 <sitem>1996-10-30 : TB : Clean up term & termdef. Slip in
303 ERB decision re EMPTY.</sitem>
304 <sitem>1996-10-28 : TB : Change DTD. Implement some of Michael's
305 suggestions. Change comments back to //. Introduce language for
306 XML namespace reservation. Add section on white-space handling.
307 Lots more cleanup.</sitem>
308 <sitem>1996-10-24 : CMSMcQ : quick tweaks, implement some ERB
309 decisions. Characters are not integers. Comments are /* */ not //.
310 Add bibliographic refs to 10646, HyTime, Unicode.
311 Rename old Cdata as MsData since it's <emph>only</emph> seen
312 in marked sections. Call them attribute-value pairs not
313 name-value pairs, except once. Internal subset is optional, needs
314 '?'. Implied attributes should be signaled to the app, not
315 have values supplied by processor.</sitem>
316 <sitem>1996-10-16 : TB : track down & excise all DSD references;
317 introduce some EBNF for entity declarations.</sitem>
318 <sitem>1996-10-?? : TB : consistency check, fix up scraps so
319 they all parse, get formatter working, correct a few productions.</sitem>
320 <sitem>1996-10-10/11 : CMSMcQ : various maintenance, stylistic, and
321 organizational changes:
322 Replace a few literals with xmlpio and
323 pic entities, to make them consistent and ensure we can change pic
324 reliably when the ERB votes.
325 Drop paragraph on recognizers from notation section.
326 Add match, exact match to terminology.
327 Move old 2.2 XML Processors and Apps into intro.
328 Mention comments, PIs, and marked sections in discussion of
330 Streamline discussion of doctype decl syntax.
331 Drop old section of 'PI syntax' for doctype decl, and add
332 section on partial-DTD summary PIs to end of Logical Structures
334 Revise DSD syntax section to use Tim's subset-in-a-PI
336 <sitem>1996-10-10 : TB : eliminate name recognizers (and more?)</sitem>
337 <sitem>1996-10-09 : CMSMcQ : revise for style, consistency through 2.3
339 <sitem>1996-10-09 : CMSMcQ : re-unite everything for convenience,
340 at least temporarily, and revise quickly</sitem>
341 <sitem>1996-10-08 : TB : first major homogenization pass</sitem>
342 <sitem>1996-10-08 : TB : turn "current" attribute on div type into
344 <sitem>1996-10-02 : TB : remould into skeleton + entities</sitem>
345 <sitem>1996-09-30 : CMSMcQ : add a few more sections prior to exchange
347 <sitem>1996-09-20 : CMSMcQ : finish transcribing notes.</sitem>
348 <sitem>1996-09-19 : CMSMcQ : begin transcribing notes for draft.</sitem>
349 <sitem>1996-09-13 : CMSMcQ : made outline from notes of 09-06,
350 do some housekeeping</sitem>
355 <div1 id="sec-intro">
356 <head>Introduction</head>
357 <p>Extensible Markup Language, abbreviated XML, describes a class of
358 data objects called <termref def="dt-xml-doc">XML documents</termref> and
359 partially describes the behavior of
360 computer programs which process them. XML is an application profile or
361 restricted form of SGML, the Standard Generalized Markup
362 Language <bibref ref="ISO8879"/>.
363 By construction, XML documents
364 are conforming SGML documents.
366 <p>XML documents are made up of storage units called <termref def="dt-entity">entities</termref>, which contain either parsed
368 Parsed data is made up of <termref def="dt-character">characters</termref>,
370 of which form <termref def="dt-chardata">character data</termref>,
371 and some of which form <termref def="dt-markup">markup</termref>.
372 Markup encodes a description of the document's storage layout and
373 logical structure. XML provides a mechanism to impose constraints on
374 the storage layout and logical structure.</p>
375 <p><termdef id="dt-xml-proc" term="XML Processor">A software module
376 called an <term>XML processor</term> is used to read XML documents
377 and provide access to their content and structure.</termdef> <termdef id="dt-app" term="Application">It is assumed that an XML processor is
378 doing its work on behalf of another module, called the
379 <term>application</term>.</termdef> This specification describes the
380 required behavior of an XML processor in terms of how it must read XML
381 data and the information it must provide to the application.</p>
383 <div2 id="sec-origin-goals">
384 <head>Origin and Goals</head>
385 <p>XML was developed by an XML Working Group (originally known as the
386 SGML Editorial Review Board) formed under the auspices of the World
387 Wide Web Consortium (W3C) in 1996.
388 It was chaired by Jon Bosak of Sun
389 Microsystems with the active participation of an XML Special
390 Interest Group (previously known as the SGML Working Group) also
391 organized by the W3C. The membership of the XML Working Group is given
392 in an appendix. Dan Connolly served as the WG's contact with the W3C.
394 <p>The design goals for XML are:<olist>
395 <item><p>XML shall be straightforwardly usable over the
397 <item><p>XML shall support a wide variety of applications.</p></item>
398 <item><p>XML shall be compatible with SGML.</p></item>
399 <item><p>It shall be easy to write programs which process XML
400 documents.</p></item>
401 <item><p>The number of optional features in XML is to be kept to the
402 absolute minimum, ideally zero.</p></item>
403 <item><p>XML documents should be human-legible and reasonably
405 <item><p>The XML design should be prepared quickly.</p></item>
406 <item><p>The design of XML shall be formal and concise.</p></item>
407 <item><p>XML documents shall be easy to create.</p></item>
408 <item><p>Terseness in XML markup is of minimal importance.</p></item></olist>
410 <p>This specification,
411 together with associated standards
412 (Unicode and ISO/IEC 10646 for characters,
413 Internet RFC 1766 for language identification tags,
414 ISO 639 for language name codes, and
415 ISO 3166 for country name codes),
416 provides all the information necessary to understand
417 XML Version &XML.version;
418 and construct computer programs to process it.</p>
419 <p>This version of the XML specification
420 <!-- is for &doc.audience;.-->
421 &doc.distribution;.</p>
428 <div2 id="sec-terminology">
429 <head>Terminology</head>
431 <p>The terminology used to describe XML documents is defined in the body of
433 The terms defined in the following list are used in building those
434 definitions and in describing the actions of an XML processor:
438 <def><p><termdef id="dt-may" term="May">Conforming documents and XML
439 processors are permitted to but need not behave as
440 described.</termdef></p></def>
444 <def><p>Conforming documents and XML processors
445 are required to behave as described; otherwise they are in error.
446 <!-- do NOT change this! this is what defines a violation of
447 a 'must' clause as 'an error'. -MSM -->
452 <def><p><termdef id="dt-error" term="Error">A violation of the rules of this
453 specification; results are
454 undefined. Conforming software may detect and report an error and may
455 recover from it.</termdef></p></def>
458 <label>fatal error</label>
459 <def><p><termdef id="dt-fatal" term="Fatal Error">An error
460 which a conforming <termref def="dt-xml-proc">XML processor</termref>
461 must detect and report to the application.
462 After encountering a fatal error, the
463 processor may continue
464 processing the data to search for further errors and may report such
465 errors to the application. In order to support correction of errors,
466 the processor may make unprocessed data from the document (with
467 intermingled character data and markup) available to the application.
468 Once a fatal error is detected, however, the processor must not
469 continue normal processing (i.e., it must not
470 continue to pass character data and information about the document's
471 logical structure to the application in the normal way).
475 <label>at user option</label>
476 <def><p>Conforming software may or must (depending on the modal verb in the
477 sentence) behave as described; if it does, it must
478 provide users a means to enable or disable the behavior
482 <label>validity constraint</label>
483 <def><p>A rule which applies to all
484 <termref def="dt-valid">valid</termref> XML documents.
485 Violations of validity constraints are errors; they must, at user option,
487 <termref def="dt-validating">validating XML processors</termref>.</p></def>
490 <label>well-formedness constraint</label>
491 <def><p>A rule which applies to all <termref def="dt-wellformed">well-formed</termref> XML documents.
492 Violations of well-formedness constraints are
493 <termref def="dt-fatal">fatal errors</termref>.</p></def>
498 <def><p><termdef id="dt-match" term="match">(Of strings or names:)
499 Two strings or names being compared must be identical.
500 Characters with multiple possible representations in ISO/IEC 10646 (e.g.
502 both precomposed and base+diacritic forms) match only if they have the
503 same representation in both strings.
504 At user option, processors may normalize such characters to
506 No case folding is performed.
507 (Of strings and rules in the grammar:)
508 A string matches a grammatical production if it belongs to the
509 language generated by that production.
510 (Of content and content models:)
511 An element matches its declaration when it conforms
512 in the fashion described in the constraint
513 <specref ref="elementvalid"/>.
518 <label>for compatibility</label>
519 <def><p><termdef id="dt-compat" term="For Compatibility">A feature of
520 XML included solely to ensure that XML remains compatible with SGML.
524 <label>for interoperability</label>
525 <def><p><termdef id="dt-interop" term="For interoperability">A
526 non-binding recommendation included to increase the chances that XML
527 documents can be processed by the existing installed base of SGML
528 processors which predate the
529 &WebSGML;.</termdef></p></def>
539 <div1 id="sec-documents">
540 <head>Documents</head>
542 <p><termdef id="dt-xml-doc" term="XML Document">
544 <term>XML document</term> if it is
545 <termref def="dt-wellformed">well-formed</termref>, as
546 defined in this specification.
547 A well-formed XML document may in addition be
548 <termref def="dt-valid">valid</termref> if it meets certain further
549 constraints.</termdef></p>
551 <p>Each XML document has both a logical and a physical structure.
552 Physically, the document is composed of units called <termref def="dt-entity">entities</termref>. An entity may <termref def="dt-entref">refer</termref> to other entities to cause their
553 inclusion in the document. A document begins in a "root" or <termref def="dt-docent">document entity</termref>.
554 Logically, the document is composed of declarations, elements,
556 character references, and
558 instructions, all of which are indicated in the document by explicit
560 The logical and physical structures must nest properly, as described
561 in <specref ref="wf-entities"/>.
564 <div2 id="sec-well-formed">
565 <head>Well-Formed XML Documents</head>
567 <p><termdef id="dt-wellformed" term="Well-Formed">
569 a well-formed XML document if:</termdef>
571 <item><p>Taken as a whole, it
572 matches the production labeled <nt def="NT-document">document</nt>.</p></item>
574 meets all the well-formedness constraints given in this specification.</p>
576 <item><p>Each of the <termref def="dt-parsedent">parsed entities</termref>
577 which is referenced directly or indirectly within the document is
578 <titleref href="wf-entities">well-formed</titleref>.</p></item>
581 <scrap lang="ebnf" id="document">
582 <head>Document</head>
583 <prod id="NT-document"><lhs>document</lhs>
584 <rhs><nt def="NT-prolog">prolog</nt>
585 <nt def="NT-element">element</nt>
586 <nt def="NT-Misc">Misc</nt>*</rhs></prod>
589 <p>Matching the <nt def="NT-document">document</nt> production
592 <item><p>It contains one or more
593 <termref def="dt-element">elements</termref>.</p>
595 <!--* N.B. some readers (notably JC) find the following
596 paragraph awkward and redundant. I agree it's logically redundant:
597 it *says* it is summarizing the logical implications of
598 matching the grammar, and that means by definition it's
599 logically redundant. I don't think it's rhetorically
600 redundant or unnecessary, though, so I'm keeping it. It
601 could however use some recasting when the editors are feeling
603 <item><p><termdef id="dt-root" term="Root Element">There is exactly
604 one element, called the <term>root</term>, or document element, no
605 part of which appears in the <termref def="dt-content">content</termref> of any other element.</termdef>
606 For all other elements, if the start-tag is in the content of another
607 element, the end-tag is in the content of the same element. More
608 simply stated, the elements, delimited by start- and end-tags, nest
609 properly within each other.
613 <p><termdef id="dt-parentchild" term="Parent/Child">As a consequence
615 for each non-root element
616 <code>C</code> in the document, there is one other element <code>P</code>
617 in the document such that
618 <code>C</code> is in the content of <code>P</code>, but is not in
619 the content of any other element that is in the content of
621 <code>P</code> is referred to as the
622 <term>parent</term> of <code>C</code>, and <code>C</code> as a
623 <term>child</term> of <code>P</code>.</termdef></p></div2>
626 <head>Characters</head>
628 <p><termdef id="dt-text" term="Text">A parsed entity contains
629 <term>text</term>, a sequence of
630 <termref def="dt-character">characters</termref>,
631 which may represent markup or character data.</termdef>
632 <termdef id="dt-character" term="Character">A <term>character</term>
633 is an atomic unit of text as specified by
634 ISO/IEC 10646 <bibref ref="ISO10646"/>.
635 Legal characters are tab, carriage return, line feed, and the legal
636 graphic characters of Unicode and ISO/IEC 10646.
637 The use of "compatibility characters", as defined in section 6.8
638 of <bibref ref="Unicode"/>, is discouraged.
640 <scrap lang="ebnf" id="char32">
641 <head>Character Range</head>
642 <prodgroup pcw2="4" pcw4="17.5" pcw5="11">
643 <prod id="NT-Char"><lhs>Char</lhs>
644 <rhs>#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD]
645 | [#x10000-#x10FFFF]</rhs>
646 <com>any Unicode character, excluding the
647 surrogate blocks, FFFE, and FFFF.</com> </prod>
652 <p>The mechanism for encoding character code points into bit patterns may
653 vary from entity to entity. All XML processors must accept the UTF-8
654 and UTF-16 encodings of 10646; the mechanisms for signaling which of
655 the two is in use, or for bringing other encodings into play, are
656 discussed later, in <specref ref="charencoding"/>.
659 <p>Regardless of the specific encoding used, any character in the ISO/IEC
660 10646 character set may be referred to by the decimal or hexadecimal
666 <div2 id="sec-common-syn">
667 <head>Common Syntactic Constructs</head>
669 <p>This section defines some symbols used widely in the grammar.</p>
670 <p><nt def="NT-S">S</nt> (white space) consists of one or more space (#x20)
671 characters, carriage returns, line feeds, or tabs.
673 <scrap lang="ebnf" id="white">
674 <head>White Space</head>
675 <prodgroup pcw2="4" pcw4="17.5" pcw5="11">
676 <prod id="NT-S"><lhs>S</lhs>
677 <rhs>(#x20 | #x9 | #xD | #xA)+</rhs>
681 <p>Characters are classified for convenience as letters, digits, or other
682 characters. Letters consist of an alphabetic or syllabic
683 base character possibly
684 followed by one or more combining characters, or of an ideographic
686 Full definitions of the specific characters in each class
687 are given in <specref ref="CharClasses"/>.</p>
688 <p><termdef id="dt-name" term="Name">A <term>Name</term> is a token
689 beginning with a letter or one of a few punctuation characters, and continuing
690 with letters, digits, hyphens, underscores, colons, or full stops, together
691 known as name characters.</termdef>
692 Names beginning with the string "<code>xml</code>", or any string
693 which would match <code>(('X'|'x') ('M'|'m') ('L'|'l'))</code>, are
694 reserved for standardization in this or future versions of this
698 <p>The colon character within XML names is reserved for experimentation with
700 Its meaning is expected to be
701 standardized at some future point, at which point those documents
702 using the colon for experimental purposes may need to be updated.
703 (There is no guarantee that any name-space mechanism
704 adopted for XML will in fact use the colon as a name-space delimiter.)
705 In practice, this means that authors should not use the colon in XML
706 names except as part of name-space experiments, but that XML processors
707 should accept the colon as a name character.</p>
710 <nt def="NT-Nmtoken">Nmtoken</nt> (name token) is any mixture of
713 <head>Names and Tokens</head>
714 <prod id="NT-NameChar"><lhs>NameChar</lhs>
715 <rhs><nt def="NT-Letter">Letter</nt>
716 | <nt def="NT-Digit">Digit</nt>
717 | '.' | '-' | '_' | ':'
718 | <nt def="NT-CombiningChar">CombiningChar</nt>
719 | <nt def="NT-Extender">Extender</nt></rhs>
721 <prod id="NT-Name"><lhs>Name</lhs>
722 <rhs>(<nt def="NT-Letter">Letter</nt> | '_' | ':')
723 (<nt def="NT-NameChar">NameChar</nt>)*</rhs></prod>
724 <prod id="NT-Names"><lhs>Names</lhs>
725 <rhs><nt def="NT-Name">Name</nt>
726 (<nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt>)*</rhs></prod>
727 <prod id="NT-Nmtoken"><lhs>Nmtoken</lhs>
728 <rhs>(<nt def="NT-NameChar">NameChar</nt>)+</rhs></prod>
729 <prod id="NT-Nmtokens"><lhs>Nmtokens</lhs>
730 <rhs><nt def="NT-Nmtoken">Nmtoken</nt> (<nt def="NT-S">S</nt> <nt def="NT-Nmtoken">Nmtoken</nt>)*</rhs></prod>
733 <p>Literal data is any quoted string not containing
734 the quotation mark used as a delimiter for that string.
736 for specifying the content of internal entities
737 (<nt def="NT-EntityValue">EntityValue</nt>),
738 the values of attributes (<nt def="NT-AttValue">AttValue</nt>),
739 and external identifiers
740 (<nt def="NT-SystemLiteral">SystemLiteral</nt>).
741 Note that a <nt def="NT-SystemLiteral">SystemLiteral</nt>
742 can be parsed without scanning for markup.
744 <head>Literals</head>
745 <prod id="NT-EntityValue"><lhs>EntityValue</lhs>
748 | <nt def="NT-PEReference">PEReference</nt>
749 | <nt def="NT-Reference">Reference</nt>)*
755 | <nt def="NT-PEReference">PEReference</nt>
756 | <nt def="NT-Reference">Reference</nt>)*
759 <prod id="NT-AttValue"><lhs>AttValue</lhs>
762 | <nt def="NT-Reference">Reference</nt>)*
768 | <nt def="NT-Reference">Reference</nt>)*
771 <prod id="NT-SystemLiteral"><lhs>SystemLiteral</lhs>
772 <rhs>('"' [^"]* '"') | ("'" [^']* "'")
775 <prod id="NT-PubidLiteral"><lhs>PubidLiteral</lhs>
776 <rhs>'"' <nt def="NT-PubidChar">PubidChar</nt>*
778 | "'" (<nt def="NT-PubidChar">PubidChar</nt> - "'")* "'"</rhs>
780 <prod id="NT-PubidChar"><lhs>PubidChar</lhs>
781 <rhs>#x20 | #xD | #xA
783 | [-'()+,./:=?;!*#@$_%]</rhs>
791 <head>Character Data and Markup</head>
793 <p><termref def="dt-text">Text</termref> consists of intermingled
794 <termref def="dt-chardata">character
795 data</termref> and markup.
796 <termdef id="dt-markup" term="Markup"><term>Markup</term> takes the form of
797 <termref def="dt-stag">start-tags</termref>,
798 <termref def="dt-etag">end-tags</termref>,
799 <termref def="dt-empty">empty-element tags</termref>,
800 <termref def="dt-entref">entity references</termref>,
801 <termref def="dt-charref">character references</termref>,
802 <termref def="dt-comment">comments</termref>,
803 <termref def="dt-cdsection">CDATA section</termref> delimiters,
804 <termref def="dt-doctype">document type declarations</termref>, and
805 <termref def="dt-pi">processing instructions</termref>.
808 <p><termdef id="dt-chardata" term="Character Data">All text that is not markup
809 constitutes the <term>character data</term> of
810 the document.</termdef></p>
811 <p>The ampersand character (&) and the left angle bracket (<)
812 may appear in their literal form <emph>only</emph> when used as markup
813 delimiters, or within a <termref def="dt-comment">comment</termref>, a
814 <termref def="dt-pi">processing instruction</termref>,
815 or a <termref def="dt-cdsection">CDATA section</termref>.
817 They are also legal within the <termref def="dt-litentval">literal entity
818 value</termref> of an internal entity declaration; see
819 <specref ref="wf-entities"/>.
820 <!-- FINAL EDIT: restore internal entity decl or leave it out. -->
821 If they are needed elsewhere,
822 they must be <termref def="dt-escape">escaped</termref>
823 using either <termref def="dt-charref">numeric character references</termref>
825 "<code>&amp;</code>" and "<code>&lt;</code>" respectively.
827 bracket (>) may be represented using the string
828 "<code>&gt;</code>", and must, <termref def="dt-compat">for
829 compatibility</termref>,
831 "<code>&gt;</code>" or a character reference
832 when it appears in the string
833 "<code>]]></code>"
835 when that string is not marking the end of
836 a <termref def="dt-cdsection">CDATA section</termref>.
839 In the content of elements, character data
840 is any string of characters which does
841 not contain the start-delimiter of any markup.
842 In a CDATA section, character data
843 is any string of characters not including the CDATA-section-close
844 delimiter, "<code>]]></code>".</p>
846 To allow attribute values to contain both single and double quotes, the
847 apostrophe or single-quote character (') may be represented as
848 "<code>&apos;</code>", and the double-quote character (") as
849 "<code>&quot;</code>".
851 <head>Character Data</head>
852 <prod id="NT-CharData">
854 <rhs>[^<&]* - ([^<&]* ']]>' [^<&]*)</rhs>
860 <div2 id="sec-comments">
861 <head>Comments</head>
863 <p><termdef id="dt-comment" term="Comment"><term>Comments</term> may
864 appear anywhere in a document outside other
865 <termref def="dt-markup">markup</termref>; in addition,
866 they may appear within the document type declaration
867 at places allowed by the grammar.
868 They are not part of the document's <termref def="dt-chardata">character
869 data</termref>; an XML
870 processor may, but need not, make it possible for an application to
871 retrieve the text of comments.
872 <termref def="dt-compat">For compatibility</termref>, the string
873 "<code>--</code>" (double-hyphen) must not occur within
876 <head>Comments</head>
877 <prod id="NT-Comment"><lhs>Comment</lhs>
879 ((<nt def="NT-Char">Char</nt> - '-')
880 | ('-' (<nt def="NT-Char">Char</nt> - '-')))*
885 <p>An example of a comment:
886 <eg><!&como; declarations for <head> & <body> &comc;></eg>
891 <head>Processing Instructions</head>
893 <p><termdef id="dt-pi" term="Processing instruction"><term>Processing
894 instructions</term> (PIs) allow documents to contain instructions
898 <head>Processing Instructions</head>
899 <prod id="NT-PI"><lhs>PI</lhs>
900 <rhs>'<?' <nt def="NT-PITarget">PITarget</nt>
901 (<nt def="NT-S">S</nt>
902 (<nt def="NT-Char">Char</nt>* -
903 (<nt def="NT-Char">Char</nt>* &pic; <nt def="NT-Char">Char</nt>*)))?
905 <prod id="NT-PITarget"><lhs>PITarget</lhs>
906 <rhs><nt def="NT-Name">Name</nt> -
907 (('X' | 'x') ('M' | 'm') ('L' | 'l'))</rhs>
910 PIs are not part of the document's <termref def="dt-chardata">character
911 data</termref>, but must be passed through to the application. The
912 PI begins with a target (<nt def="NT-PITarget">PITarget</nt>) used
913 to identify the application to which the instruction is directed.
914 The target names "<code>XML</code>", "<code>xml</code>", and so on are
915 reserved for standardization in this or future versions of this
918 XML <termref def="dt-notation">Notation</termref> mechanism
920 formal declaration of PI targets.
924 <div2 id="sec-cdata-sect">
925 <head>CDATA Sections</head>
927 <p><termdef id="dt-cdsection" term="CDATA Section"><term>CDATA sections</term>
929 anywhere character data may occur; they are
930 used to escape blocks of text containing characters which would
931 otherwise be recognized as markup. CDATA sections begin with the
932 string "<code><![CDATA[</code>" and end with the string
933 "<code>]]></code>":
935 <head>CDATA Sections</head>
936 <prod id="NT-CDSect"><lhs>CDSect</lhs>
937 <rhs><nt def="NT-CDStart">CDStart</nt>
938 <nt def="NT-CData">CData</nt>
939 <nt def="NT-CDEnd">CDEnd</nt></rhs></prod>
940 <prod id="NT-CDStart"><lhs>CDStart</lhs>
941 <rhs>'<![CDATA['</rhs>
943 <prod id="NT-CData"><lhs>CData</lhs>
944 <rhs>(<nt def="NT-Char">Char</nt>* -
945 (<nt def="NT-Char">Char</nt>* ']]>' <nt def="NT-Char">Char</nt>*))
948 <prod id="NT-CDEnd"><lhs>CDEnd</lhs>
953 Within a CDATA section, only the <nt def="NT-CDEnd">CDEnd</nt> string is
954 recognized as markup, so that left angle brackets and ampersands may occur in
955 their literal form; they need not (and cannot) be escaped using
956 "<code>&lt;</code>" and "<code>&amp;</code>". CDATA sections
957 cannot nest.</termdef>
960 <p>An example of a CDATA section, in which "<code><greeting></code>" and
961 "<code></greeting></code>"
962 are recognized as <termref def="dt-chardata">character data</termref>, not
963 <termref def="dt-markup">markup</termref>:
964 <eg><![CDATA[<greeting>Hello, world!</greeting>]]></eg>
968 <div2 id="sec-prolog-dtd">
969 <head>Prolog and Document Type Declaration</head>
971 <p><termdef id="dt-xmldecl" term="XML Declaration">XML documents
973 begin with an <term>XML declaration</term> which specifies
975 XML being used.</termdef>
976 For example, the following is a complete XML document, <termref def="dt-wellformed">well-formed</termref> but not
977 <termref def="dt-valid">valid</termref>:
978 <eg><![CDATA[<?xml version="1.0"?>
979 <greeting>Hello, world!</greeting>
982 <eg><![CDATA[<greeting>Hello, world!</greeting>
986 <p>The version number "<code>1.0</code>" should be used to indicate
987 conformance to this version of this specification; it is an error
988 for a document to use the value "<code>1.0</code>"
989 if it does not conform to this version of this specification.
991 of the XML working group to give later versions of this specification
992 numbers other than "<code>1.0</code>", but this intent does not
994 commitment to produce any future versions of XML, nor if any are produced, to
995 use any particular numbering scheme.
996 Since future versions are not ruled out, this construct is provided
997 as a means to allow the possibility of automatic version recognition, should
999 Processors may signal an error if they receive documents labeled with
1000 versions they do not support.
1002 <p>The function of the markup in an XML document is to describe its
1003 storage and logical structure and to associate attribute-value pairs
1004 with its logical structures. XML provides a mechanism, the <termref def="dt-doctype">document type declaration</termref>, to define
1005 constraints on the logical structure and to support the use of
1006 predefined storage units.
1008 <termdef id="dt-valid" term="Validity">An XML document is
1009 <term>valid</term> if it has an associated document type
1010 declaration and if the document
1011 complies with the constraints expressed in it.</termdef></p>
1012 <p>The document type declaration must appear before
1013 the first <termref def="dt-element">element</termref> in the document.
1014 <scrap lang="ebnf" id="xmldoc">
1016 <prodgroup pcw2="6" pcw4="17.5" pcw5="9">
1017 <prod id="NT-prolog"><lhs>prolog</lhs>
1018 <rhs><nt def="NT-XMLDecl">XMLDecl</nt>?
1019 <nt def="NT-Misc">Misc</nt>*
1020 (<nt def="NT-doctypedecl">doctypedecl</nt>
1021 <nt def="NT-Misc">Misc</nt>*)?</rhs></prod>
1022 <prod id="NT-XMLDecl"><lhs>XMLDecl</lhs>
1024 <nt def="NT-VersionInfo">VersionInfo</nt>
1025 <nt def="NT-EncodingDecl">EncodingDecl</nt>?
1026 <nt def="NT-SDDecl">SDDecl</nt>?
1027 <nt def="NT-S">S</nt>?
1030 <prod id="NT-VersionInfo"><lhs>VersionInfo</lhs>
1031 <rhs><nt def="NT-S">S</nt> 'version' <nt def="NT-Eq">Eq</nt>
1032 (' <nt def="NT-VersionNum">VersionNum</nt> '
1033 | " <nt def="NT-VersionNum">VersionNum</nt> ")</rhs>
1035 <prod id="NT-Eq"><lhs>Eq</lhs>
1036 <rhs><nt def="NT-S">S</nt>? '=' <nt def="NT-S">S</nt>?</rhs></prod>
1037 <prod id="NT-VersionNum">
1038 <lhs>VersionNum</lhs>
1039 <rhs>([a-zA-Z0-9_.:] | '-')+</rhs>
1041 <prod id="NT-Misc"><lhs>Misc</lhs>
1042 <rhs><nt def="NT-Comment">Comment</nt> | <nt def="NT-PI">PI</nt> |
1043 <nt def="NT-S">S</nt></rhs></prod>
1047 <p><termdef id="dt-doctype" term="Document Type Declaration">The XML
1048 <term>document type declaration</term>
1049 contains or points to
1050 <termref def="dt-markupdecl">markup declarations</termref>
1051 that provide a grammar for a
1053 This grammar is known as a document type definition,
1054 or <term>DTD</term>.
1055 The document type declaration can point to an external subset (a
1057 <termref def="dt-extent">external entity</termref>) containing markup
1058 declarations, or can
1059 contain the markup declarations directly in an internal subset, or can do
1061 The DTD for a document consists of both subsets taken
1064 <p><termdef id="dt-markupdecl" term="markup declaration">
1065 A <term>markup declaration</term> is
1066 an <termref def="dt-eldecl">element type declaration</termref>,
1067 an <termref def="dt-attdecl">attribute-list declaration</termref>,
1068 an <termref def="dt-entdecl">entity declaration</termref>, or
1069 a <termref def="dt-notdecl">notation declaration</termref>.
1071 These declarations may be contained in whole or in part
1072 within <termref def="dt-PE">parameter entities</termref>,
1073 as described in the well-formedness and validity constraints below.
1074 For fuller information, see
1075 <specref ref="sec-physical-struct"/>.</p>
1076 <scrap lang="ebnf" id="dtd">
1077 <head>Document Type Definition</head>
1078 <prodgroup pcw2="6" pcw4="17.5" pcw5="9">
1079 <prod id="NT-doctypedecl"><lhs>doctypedecl</lhs>
1080 <rhs>'<!DOCTYPE' <nt def="NT-S">S</nt>
1081 <nt def="NT-Name">Name</nt> (<nt def="NT-S">S</nt>
1082 <nt def="NT-ExternalID">ExternalID</nt>)?
1083 <nt def="NT-S">S</nt>? ('['
1084 (<nt def="NT-markupdecl">markupdecl</nt>
1085 | <nt def="NT-PEReference">PEReference</nt>
1086 | <nt def="NT-S">S</nt>)*
1088 <nt def="NT-S">S</nt>?)? '>'</rhs>
1089 <vc def="vc-roottype"/>
1091 <prod id="NT-markupdecl"><lhs>markupdecl</lhs>
1092 <rhs><nt def="NT-elementdecl">elementdecl</nt>
1093 | <nt def="NT-AttlistDecl">AttlistDecl</nt>
1094 | <nt def="NT-EntityDecl">EntityDecl</nt>
1095 | <nt def="NT-NotationDecl">NotationDecl</nt>
1096 | <nt def="NT-PI">PI</nt>
1097 | <nt def="NT-Comment">Comment</nt>
1099 <vc def="vc-PEinMarkupDecl"/>
1100 <wfc def="wfc-PEinInternalSubset"/>
1106 <p>The markup declarations may be made up in whole or in part of
1107 the <termref def="dt-repltext">replacement text</termref> of
1108 <termref def="dt-PE">parameter entities</termref>.
1109 The productions later in this specification for
1110 individual nonterminals (<nt def="NT-elementdecl">elementdecl</nt>,
1111 <nt def="NT-AttlistDecl">AttlistDecl</nt>, and so on) describe
1112 the declarations <emph>after</emph> all the parameter entities have been
1113 <termref def="dt-include">included</termref>.</p>
1115 <vcnote id="vc-roottype">
1116 <head>Root Element Type</head>
1118 The <nt def="NT-Name">Name</nt> in the document type declaration must
1119 match the element type of the <termref def="dt-root">root element</termref>.
1123 <vcnote id="vc-PEinMarkupDecl">
1124 <head>Proper Declaration/PE Nesting</head>
1126 <termref def="dt-repltext">replacement text</termref> must be properly nested
1127 with markup declarations.
1128 That is to say, if either the first character
1129 or the last character of a markup
1130 declaration (<nt def="NT-markupdecl">markupdecl</nt> above)
1131 is contained in the replacement text for a
1132 <termref def="dt-PERef">parameter-entity reference</termref>,
1133 both must be contained in the same replacement text.</p>
1135 <wfcnote id="wfc-PEinInternalSubset">
1136 <head>PEs in Internal Subset</head>
1137 <p>In the internal DTD subset,
1138 <termref def="dt-PERef">parameter-entity references</termref>
1139 can occur only where markup declarations can occur, not
1140 within markup declarations. (This does not apply to
1141 references that occur in
1142 external parameter entities or to the external subset.)
1146 Like the internal subset, the external subset and
1147 any external parameter entities referred to in the DTD
1148 must consist of a series of complete markup declarations of the types
1149 allowed by the non-terminal symbol
1150 <nt def="NT-markupdecl">markupdecl</nt>, interspersed with white space
1151 or <termref def="dt-PERef">parameter-entity references</termref>.
1152 However, portions of the contents
1154 external subset or of external parameter entities may conditionally be ignored
1156 the <termref def="dt-cond-section">conditional section</termref>
1157 construct; this is not allowed in the internal subset.
1159 <scrap id="ext-Subset">
1160 <head>External Subset</head>
1161 <prodgroup pcw2="6" pcw4="17.5" pcw5="9">
1162 <prod id="NT-extSubset"><lhs>extSubset</lhs>
1163 <rhs><nt def="NT-TextDecl">TextDecl</nt>?
1164 <nt def="NT-extSubsetDecl">extSubsetDecl</nt></rhs></prod>
1165 <prod id="NT-extSubsetDecl"><lhs>extSubsetDecl</lhs>
1167 <nt def="NT-markupdecl">markupdecl</nt>
1168 | <nt def="NT-conditionalSect">conditionalSect</nt>
1169 | <nt def="NT-PEReference">PEReference</nt>
1170 | <nt def="NT-S">S</nt>
1175 <p>The external subset and external parameter entities also differ
1176 from the internal subset in that in them,
1177 <termref def="dt-PERef">parameter-entity references</termref>
1178 are permitted <emph>within</emph> markup declarations,
1179 not only <emph>between</emph> markup declarations.</p>
1180 <p>An example of an XML document with a document type declaration:
1181 <eg><![CDATA[<?xml version="1.0"?>
1182 <!DOCTYPE greeting SYSTEM "hello.dtd">
1183 <greeting>Hello, world!</greeting>
1185 The <termref def="dt-sysid">system identifier</termref>
1186 "<code>hello.dtd</code>" gives the URI of a DTD for the document.</p>
1187 <p>The declarations can also be given locally, as in this
1189 <eg><![CDATA[<?xml version="1.0" encoding="UTF-8" ?>
1190 <!DOCTYPE greeting [
1191 <!ELEMENT greeting (#PCDATA)>
1193 <greeting>Hello, world!</greeting>
1195 If both the external and internal subsets are used, the
1196 internal subset is considered to occur before the external subset.
1197 <!-- 'is considered to'? boo. whazzat mean? -->
1198 This has the effect that entity and attribute-list declarations in the
1199 internal subset take precedence over those in the external subset.
1204 <head>Standalone Document Declaration</head>
1205 <p>Markup declarations can affect the content of the document,
1206 as passed from an <termref def="dt-xml-proc">XML processor</termref>
1207 to an application; examples are attribute defaults and entity
1209 The standalone document declaration,
1210 which may appear as a component of the XML declaration, signals
1211 whether or not there are such declarations which appear external to
1212 the <termref def="dt-docent">document entity</termref>.
1213 <scrap lang="ebnf" id="fulldtd">
1214 <head>Standalone Document Declaration</head>
1215 <prodgroup pcw2="4" pcw4="19.5" pcw5="9">
1216 <prod id="NT-SDDecl"><lhs>SDDecl</lhs>
1218 <nt def="NT-S">S</nt>
1219 'standalone' <nt def="NT-Eq">Eq</nt>
1220 (("'" ('yes' | 'no') "'") | ('"' ('yes' | 'no') '"'))
1222 <vc def="vc-check-rmd"/></prod>
1226 In a standalone document declaration, the value "<code>yes</code>" indicates
1228 are no markup declarations external to the <termref def="dt-docent">document
1229 entity</termref> (either in the DTD external subset, or in an
1230 external parameter entity referenced from the internal subset)
1231 which affect the information passed from the XML processor to
1233 The value "<code>no</code>" indicates that there are or may be such
1234 external markup declarations.
1235 Note that the standalone document declaration only
1236 denotes the presence of external <emph>declarations</emph>; the presence, in a
1238 references to external <emph>entities</emph>, when those entities are
1239 internally declared,
1240 does not change its standalone status.</p>
1241 <p>If there are no external markup declarations, the standalone document
1242 declaration has no meaning.
1243 If there are external markup declarations but there is no standalone
1244 document declaration, the value "<code>no</code>" is assumed.</p>
1245 <p>Any XML document for which <code>standalone="no"</code> holds can
1246 be converted algorithmically to a standalone document,
1247 which may be desirable for some network delivery applications.</p>
1248 <vcnote id="vc-check-rmd">
1249 <head>Standalone Document Declaration</head>
1250 <p>The standalone document declaration must have
1251 the value "<code>no</code>" if any external markup declarations
1252 contain declarations of:</p><ulist>
1253 <item><p>attributes with <termref def="dt-default">default</termref> values, if
1255 these attributes apply appear in the document without
1256 specifications of values for these attributes, or</p></item>
1257 <item><p>entities (other than &magicents;),
1258 if <termref def="dt-entref">references</termref> to those
1259 entities appear in the document, or</p>
1261 <item><p>attributes with values subject to
1262 <titleref href="AVNormalize">normalization</titleref>, where the
1263 attribute appears in the document with a value which will
1264 change as a result of normalization, or</p>
1267 <p>element types with <termref def="dt-elemcontent">element content</termref>,
1268 if white space occurs
1269 directly within any instance of those types.
1274 <p>An example XML declaration with a standalone document declaration:<eg><?xml version="&XML.version;" standalone='yes'?></eg></p>
1276 <div2 id="sec-white-space">
1277 <head>White Space Handling</head>
1279 <p>In editing XML documents, it is often convenient to use "white space"
1280 (spaces, tabs, and blank lines, denoted by the nonterminal
1281 <nt def="NT-S">S</nt> in this specification) to
1282 set apart the markup for greater readability. Such white space is typically
1283 not intended for inclusion in the delivered version of the document.
1284 On the other hand, "significant" white space that should be preserved in the
1285 delivered version is common, for example in poetry and
1287 <p>An <termref def="dt-xml-proc">XML processor</termref>
1288 must always pass all characters in a document that are not
1289 markup through to the application. A <termref def="dt-validating">
1290 validating XML processor</termref> must also inform the application
1291 which of these characters constitute white space appearing
1292 in <termref def="dt-elemcontent">element content</termref>.
1294 <p>A special <termref def="dt-attr">attribute</termref>
1295 named <kw>xml:space</kw> may be attached to an element
1296 to signal an intention that in that element,
1297 white space should be preserved by applications.
1298 In valid documents, this attribute, like any other, must be
1299 <termref def="dt-attdecl">declared</termref> if it is used.
1300 When declared, it must be given as an
1301 <termref def="dt-enumerated">enumerated type</termref> whose only
1302 possible values are "<code>default</code>" and "<code>preserve</code>".
1303 For example:<eg><![CDATA[ <!ATTLIST poem xml:space (default|preserve) 'preserve'>]]></eg></p>
1304 <p>The value "<code>default</code>" signals that applications'
1305 default white-space processing modes are acceptable for this element; the
1306 value "<code>preserve</code>" indicates the intent that applications preserve
1307 all the white space.
1308 This declared intent is considered to apply to all elements within the content
1309 of the element where it is specified, unless overriden with another instance
1310 of the <kw>xml:space</kw> attribute.
1312 <p>The <termref def="dt-root">root element</termref> of any document
1313 is considered to have signaled no intentions as regards application space
1314 handling, unless it provides a value for
1315 this attribute or the attribute is declared with a default value.
1319 <div2 id="sec-line-ends">
1320 <head>End-of-Line Handling</head>
1321 <p>XML <termref def="dt-parsedent">parsed entities</termref> are often stored in
1322 computer files which, for editing convenience, are organized into lines.
1323 These lines are typically separated by some combination of the characters
1324 carriage-return (#xD) and line-feed (#xA).</p>
1325 <p>To simplify the tasks of <termref def="dt-app">applications</termref>,
1326 wherever an external parsed entity or the literal entity value
1327 of an internal parsed entity contains either the literal
1328 two-character sequence "#xD#xA" or a standalone literal
1329 #xD, an <termref def="dt-xml-proc">XML processor</termref> must
1330 pass to the application the single character #xA.
1332 conveniently be produced by normalizing all
1333 line breaks to #xA on input, before parsing.)
1336 <div2 id="sec-lang-tag">
1337 <head>Language Identification</head>
1338 <p>In document processing, it is often useful to
1339 identify the natural or formal language
1340 in which the content is
1342 A special <termref def="dt-attr">attribute</termref> named
1343 <kw>xml:lang</kw> may be inserted in
1344 documents to specify the
1345 language used in the contents and attribute values
1346 of any element in an XML document.
1347 In valid documents, this attribute, like any other, must be
1348 <termref def="dt-attdecl">declared</termref> if it is used.
1349 The values of the attribute are language identifiers as defined
1350 by <bibref ref="RFC1766"/>, "Tags for the Identification of Languages":
1352 <head>Language Identification</head>
1353 <prod id="NT-LanguageID"><lhs>LanguageID</lhs>
1354 <rhs><nt def="NT-Langcode">Langcode</nt>
1355 ('-' <nt def="NT-Subcode">Subcode</nt>)*</rhs></prod>
1356 <prod id="NT-Langcode"><lhs>Langcode</lhs>
1357 <rhs><nt def="NT-ISO639Code">ISO639Code</nt> |
1358 <nt def="NT-IanaCode">IanaCode</nt> |
1359 <nt def="NT-UserCode">UserCode</nt></rhs>
1361 <prod id="NT-ISO639Code"><lhs>ISO639Code</lhs>
1362 <rhs>([a-z] | [A-Z]) ([a-z] | [A-Z])</rhs></prod>
1363 <prod id="NT-IanaCode"><lhs>IanaCode</lhs>
1364 <rhs>('i' | 'I') '-' ([a-z] | [A-Z])+</rhs></prod>
1365 <prod id="NT-UserCode"><lhs>UserCode</lhs>
1366 <rhs>('x' | 'X') '-' ([a-z] | [A-Z])+</rhs></prod>
1367 <prod id="NT-Subcode"><lhs>Subcode</lhs>
1368 <rhs>([a-z] | [A-Z])+</rhs></prod>
1370 The <nt def="NT-Langcode">Langcode</nt> may be any of the following:
1372 <item><p>a two-letter language code as defined by
1373 <bibref ref="ISO639"/>, "Codes
1374 for the representation of names of languages"</p></item>
1375 <item><p>a language identifier registered with the Internet
1376 Assigned Numbers Authority <bibref ref="IANA"/>; these begin with the
1377 prefix "<code>i-</code>" (or "<code>I-</code>")</p></item>
1378 <item><p>a language identifier assigned by the user, or agreed on
1379 between parties in private use; these must begin with the
1380 prefix "<code>x-</code>" or "<code>X-</code>" in order to ensure that they do not conflict
1381 with names later standardized or registered with IANA</p></item>
1383 <p>There may be any number of <nt def="NT-Subcode">Subcode</nt> segments; if
1385 subcode segment exists and the Subcode consists of two
1386 letters, then it must be a country code from
1387 <bibref ref="ISO3166"/>, "Codes
1388 for the representation of names of countries."
1390 subcode consists of more than two letters, it must be
1391 a subcode for the language in question registered with IANA,
1392 unless the <nt def="NT-Langcode">Langcode</nt> begins with the prefix
1393 "<code>x-</code>" or
1394 "<code>X-</code>". </p>
1395 <p>It is customary to give the language code in lower case, and
1396 the country code (if any) in upper case.
1397 Note that these values, unlike other names in XML documents,
1398 are case insensitive.</p>
1400 <eg><![CDATA[<p xml:lang="en">The quick brown fox jumps over the lazy dog.</p>
1401 <p xml:lang="en-GB">What colour is it?</p>
1402 <p xml:lang="en-US">What color is it?</p>
1403 <sp who="Faust" desc='leise' xml:lang="de">
1404 <l>Habe nun, ach! Philosophie,</l>
1405 <l>Juristerei, und Medizin</l>
1406 <l>und leider auch Theologie</l>
1407 <l>durchaus studiert mit heißem Bemüh'n.</l>
1409 <!--<p>The xml:lang value is considered to apply both to the contents of an
1411 (unless otherwise via attribute default values) to the
1412 values of all of its attributes with free-text (CDATA) values. -->
1413 <p>The intent declared with <kw>xml:lang</kw> is considered to apply to
1414 all attributes and content of the element where it is specified,
1415 unless overridden with an instance of <kw>xml:lang</kw>
1416 on another element within that content.</p>
1419 value is specified for xml:lang on an element, and no default value is
1420 defined for it in the DTD, then the xml:lang attribute of any element
1421 takes the same value it has in the parent element, if any. The two
1422 technical terms in the following example both have the same effective
1425 <p xml:lang="en">Here the keywords are
1426 <term xml:lang="en">shift</term> and
1427 <term>reduce</term>. ...</p>
1429 The application, not the XML processor, is responsible for this '
1430 inheritance' of attribute values.
1432 <p>A simple declaration for <kw>xml:lang</kw> might take
1434 <eg>xml:lang NMTOKEN #IMPLIED</eg>
1435 but specific default values may also be given, if appropriate. In a
1436 collection of French poems for English students, with glosses and
1437 notes in English, the xml:lang attribute might be declared this way:
1438 <eg><![CDATA[ <!ATTLIST poem xml:lang NMTOKEN 'fr'>
1439 <!ATTLIST gloss xml:lang NMTOKEN 'en'>
1440 <!ATTLIST note xml:lang NMTOKEN 'en'>]]></eg>
1447 <div1 id="sec-logical-struct">
1448 <head>Logical Structures</head>
1450 <p><termdef id="dt-element" term="Element">Each <termref def="dt-xml-doc">XML document</termref> contains one or more
1451 <term>elements</term>, the boundaries of which are
1452 either delimited by <termref def="dt-stag">start-tags</termref>
1453 and <termref def="dt-etag">end-tags</termref>, or, for <termref def="dt-empty">empty</termref> elements, by an <termref def="dt-eetag">empty-element tag</termref>. Each element has a type,
1454 identified by name, sometimes called its "generic
1455 identifier" (GI), and may have a set of
1456 attribute specifications.</termdef> Each attribute specification
1457 has a <termref def="dt-attrname">name</termref> and a <termref def="dt-attrval">value</termref>.
1459 <scrap lang="ebnf"><head>Element</head>
1460 <prod id="NT-element"><lhs>element</lhs>
1461 <rhs><nt def="NT-EmptyElemTag">EmptyElemTag</nt></rhs>
1462 <rhs>| <nt def="NT-STag">STag</nt> <nt def="NT-content">content</nt>
1463 <nt def="NT-ETag">ETag</nt></rhs>
1464 <wfc def="GIMatch"/>
1465 <vc def="elementvalid"/>
1468 <p>This specification does not constrain the semantics, use, or (beyond
1469 syntax) names of the element types and attributes, except that names
1470 beginning with a match to <code>(('X'|'x')('M'|'m')('L'|'l'))</code>
1471 are reserved for standardization in this or future versions of this
1474 <wfcnote id="GIMatch">
1475 <head>Element Type Match</head>
1477 The <nt def="NT-Name">Name</nt> in an element's end-tag must match
1482 <vcnote id="elementvalid">
1483 <head>Element Valid</head>
1486 there is a declaration matching
1487 <nt def="NT-elementdecl">elementdecl</nt> where the
1488 <nt def="NT-Name">Name</nt> matches the element type, and
1489 one of the following holds:</p>
1491 <item><p>The declaration matches <kw>EMPTY</kw> and the element has no
1492 <termref def="dt-content">content</termref>.</p></item>
1493 <item><p>The declaration matches <nt def="NT-children">children</nt> and
1495 <termref def="dt-parentchild">child elements</termref>
1496 belongs to the language generated by the regular expression in
1497 the content model, with optional white space (characters
1498 matching the nonterminal <nt def="NT-S">S</nt>) between each pair
1499 of child elements.</p></item>
1500 <item><p>The declaration matches <nt def="NT-Mixed">Mixed</nt> and
1501 the content consists of <termref def="dt-chardata">character
1502 data</termref> and <termref def="dt-parentchild">child elements</termref>
1503 whose types match names in the content model.</p></item>
1504 <item><p>The declaration matches <kw>ANY</kw>, and the types
1505 of any <termref def="dt-parentchild">child elements</termref> have
1506 been declared.</p></item>
1510 <div2 id="sec-starttags">
1511 <head>Start-Tags, End-Tags, and Empty-Element Tags</head>
1513 <p><termdef id="dt-stag" term="Start-Tag">The beginning of every
1514 non-empty XML element is marked by a <term>start-tag</term>.
1516 <head>Start-tag</head>
1517 <prodgroup pcw2="6" pcw4="15" pcw5="11.5">
1518 <prod id="NT-STag"><lhs>STag</lhs>
1519 <rhs>'<' <nt def="NT-Name">Name</nt>
1520 (<nt def="NT-S">S</nt> <nt def="NT-Attribute">Attribute</nt>)*
1521 <nt def="NT-S">S</nt>? '>'</rhs>
1522 <wfc def="uniqattspec"/>
1524 <prod id="NT-Attribute"><lhs>Attribute</lhs>
1525 <rhs><nt def="NT-Name">Name</nt> <nt def="NT-Eq">Eq</nt>
1526 <nt def="NT-AttValue">AttValue</nt></rhs>
1527 <vc def="ValueType"/>
1528 <wfc def="NoExternalRefs"/>
1529 <wfc def="CleanAttrVals"/></prod>
1532 The <nt def="NT-Name">Name</nt> in
1533 the start- and end-tags gives the
1534 element's <term>type</term>.</termdef>
1535 <termdef id="dt-attr" term="Attribute">
1536 The <nt def="NT-Name">Name</nt>-<nt def="NT-AttValue">AttValue</nt> pairs are
1538 the <term>attribute specifications</term> of the element</termdef>,
1539 <termdef id="dt-attrname" term="Attribute Name">with the
1540 <nt def="NT-Name">Name</nt> in each pair
1541 referred to as the <term>attribute name</term></termdef> and
1542 <termdef id="dt-attrval" term="Attribute Value">the content of the
1543 <nt def="NT-AttValue">AttValue</nt> (the text between the
1544 <code>'</code> or <code>"</code> delimiters)
1545 as the <term>attribute value</term>.</termdef>
1547 <wfcnote id="uniqattspec">
1548 <head>Unique Att Spec</head>
1550 No attribute name may appear more than once in the same start-tag
1551 or empty-element tag.
1554 <vcnote id="ValueType">
1555 <head>Attribute Value Type</head>
1557 The attribute must have been declared; the value must be of the type
1559 (For attribute types, see <specref ref="attdecls"/>.)
1562 <wfcnote id="NoExternalRefs">
1563 <head>No External Entity References</head>
1565 Attribute values cannot contain direct or indirect entity references
1566 to external entities.
1569 <wfcnote id="CleanAttrVals">
1570 <head>No <code><</code> in Attribute Values</head>
1571 <p>The <termref def="dt-repltext">replacement text</termref> of any entity
1572 referred to directly or indirectly in an attribute
1573 value (other than "<code>&lt;</code>") must not contain
1574 a <code><</code>.
1576 <p>An example of a start-tag:
1577 <eg><termdef id="dt-dog" term="dog"></eg></p>
1578 <p><termdef id="dt-etag" term="End Tag">The end of every element
1579 that begins with a start-tag must
1580 be marked by an <term>end-tag</term>
1581 containing a name that echoes the element's type as given in the
1584 <head>End-tag</head>
1585 <prodgroup pcw2="6" pcw4="15" pcw5="11.5">
1586 <prod id="NT-ETag"><lhs>ETag</lhs>
1587 <rhs>'</' <nt def="NT-Name">Name</nt>
1588 <nt def="NT-S">S</nt>? '>'</rhs></prod>
1592 <p>An example of an end-tag:<eg></termdef></eg></p>
1593 <p><termdef id="dt-content" term="Content">The
1594 <termref def="dt-text">text</termref> between the start-tag and
1595 end-tag is called the element's
1596 <term>content</term>:
1598 <head>Content of Elements</head>
1599 <prodgroup pcw2="6" pcw4="15" pcw5="11.5">
1600 <prod id="NT-content"><lhs>content</lhs>
1601 <rhs>(<nt def="NT-element">element</nt> | <nt def="NT-CharData">CharData</nt>
1602 | <nt def="NT-Reference">Reference</nt> | <nt def="NT-CDSect">CDSect</nt>
1603 | <nt def="NT-PI">PI</nt> | <nt def="NT-Comment">Comment</nt>)*</rhs>
1608 <p><termdef id="dt-empty" term="Empty">If an element is <term>empty</term>,
1609 it must be represented either by a start-tag immediately followed
1610 by an end-tag or by an empty-element tag.</termdef>
1611 <termdef id="dt-eetag" term="empty-element tag">An
1612 <term>empty-element tag</term> takes a special form:
1614 <head>Tags for Empty Elements</head>
1615 <prodgroup pcw2="6" pcw4="15" pcw5="11.5">
1616 <prod id="NT-EmptyElemTag"><lhs>EmptyElemTag</lhs>
1617 <rhs>'<' <nt def="NT-Name">Name</nt> (<nt def="NT-S">S</nt>
1618 <nt def="NT-Attribute">Attribute</nt>)* <nt def="NT-S">S</nt>?
1620 <wfc def="uniqattspec"/>
1625 <p>Empty-element tags may be used for any element which has no
1626 content, whether or not it is declared using the keyword
1628 <termref def="dt-interop">For interoperability</termref>, the empty-element
1629 tag must be used, and can only be used, for elements which are
1630 <termref def="dt-eldecl">declared</termref> <kw>EMPTY</kw>.</p>
1631 <p>Examples of empty elements:
1632 <eg><IMG align="left"
1633 src="http://www.w3.org/Icons/WWW/w3c_home" />
1634 <br></br>
1635 <br/></eg></p>
1638 <div2 id="elemdecls">
1639 <head>Element Type Declarations</head>
1641 <p>The <termref def="dt-element">element</termref> structure of an
1642 <termref def="dt-xml-doc">XML document</termref> may, for
1643 <termref def="dt-valid">validation</termref> purposes,
1645 using element type and attribute-list declarations.
1646 An element type declaration constrains the element's
1647 <termref def="dt-content">content</termref>.
1650 <p>Element type declarations often constrain which element types can
1651 appear as <termref def="dt-parentchild">children</termref> of the element.
1652 At user option, an XML processor may issue a warning
1653 when a declaration mentions an element type for which no declaration
1654 is provided, but this is not an error.</p>
1655 <p><termdef id="dt-eldecl" term="Element Type declaration">An <term>element
1656 type declaration</term> takes the form:
1658 <head>Element Type Declaration</head>
1659 <prodgroup pcw2="5.5" pcw4="18" pcw5="9">
1660 <prod id="NT-elementdecl"><lhs>elementdecl</lhs>
1661 <rhs>'<!ELEMENT' <nt def="NT-S">S</nt>
1662 <nt def="NT-Name">Name</nt>
1663 <nt def="NT-S">S</nt>
1664 <nt def="NT-contentspec">contentspec</nt>
1665 <nt def="NT-S">S</nt>? '>'</rhs>
1666 <vc def="EDUnique"/></prod>
1667 <prod id="NT-contentspec"><lhs>contentspec</lhs>
1670 | <nt def="NT-Mixed">Mixed</nt>
1671 | <nt def="NT-children">children</nt>
1676 where the <nt def="NT-Name">Name</nt> gives the element type
1677 being declared.</termdef>
1680 <vcnote id="EDUnique">
1681 <head>Unique Element Type Declaration</head>
1683 No element type may be declared more than once.
1687 <p>Examples of element type declarations:
1688 <eg><!ELEMENT br EMPTY>
1689 <!ELEMENT p (#PCDATA|emph)* >
1690 <!ELEMENT %name.para; %content.para; >
1691 <!ELEMENT container ANY></eg></p>
1693 <div3 id="sec-element-content">
1694 <head>Element Content</head>
1696 <p><termdef id="dt-elemcontent" term="Element content">An element <termref def="dt-stag">type</termref> has
1697 <term>element content</term> when elements of that
1698 type must contain only <termref def="dt-parentchild">child</termref>
1699 elements (no character data), optionally separated by
1700 white space (characters matching the nonterminal
1701 <nt def="NT-S">S</nt>).
1704 constraint includes a content model, a simple grammar governing
1705 the allowed types of the child
1706 elements and the order in which they are allowed to appear.
1707 The grammar is built on
1708 content particles (<nt def="NT-cp">cp</nt>s), which consist of names,
1709 choice lists of content particles, or
1710 sequence lists of content particles:
1712 <head>Element-content Models</head>
1713 <prodgroup pcw2="5.5" pcw4="16" pcw5="11">
1714 <prod id="NT-children"><lhs>children</lhs>
1715 <rhs>(<nt def="NT-choice">choice</nt>
1716 | <nt def="NT-seq">seq</nt>)
1717 ('?' | '*' | '+')?</rhs></prod>
1718 <prod id="NT-cp"><lhs>cp</lhs>
1719 <rhs>(<nt def="NT-Name">Name</nt>
1720 | <nt def="NT-choice">choice</nt>
1721 | <nt def="NT-seq">seq</nt>)
1722 ('?' | '*' | '+')?</rhs></prod>
1723 <prod id="NT-choice"><lhs>choice</lhs>
1724 <rhs>'(' <nt def="NT-S">S</nt>? cp
1725 ( <nt def="NT-S">S</nt>? '|' <nt def="NT-S">S</nt>? <nt def="NT-cp">cp</nt> )*
1726 <nt def="NT-S">S</nt>? ')'</rhs>
1727 <vc def="vc-PEinGroup"/></prod>
1728 <prod id="NT-seq"><lhs>seq</lhs>
1729 <rhs>'(' <nt def="NT-S">S</nt>? cp
1730 ( <nt def="NT-S">S</nt>? ',' <nt def="NT-S">S</nt>? <nt def="NT-cp">cp</nt> )*
1731 <nt def="NT-S">S</nt>? ')'</rhs>
1732 <vc def="vc-PEinGroup"/></prod>
1736 where each <nt def="NT-Name">Name</nt> is the type of an element which may
1737 appear as a <termref def="dt-parentchild">child</termref>.
1739 particle in a choice list may appear in the <termref def="dt-elemcontent">element content</termref> at the location where
1740 the choice list appears in the grammar;
1741 content particles occurring in a sequence list must each
1742 appear in the <termref def="dt-elemcontent">element content</termref> in the
1743 order given in the list.
1744 The optional character following a name or list governs
1745 whether the element or the content particles in the list may occur one
1746 or more (<code>+</code>), zero or more (<code>*</code>), or zero or
1747 one times (<code>?</code>).
1748 The absence of such an operator means that the element or content particle
1749 must appear exactly once.
1751 and meaning are identical to those used in the productions in this
1754 The content of an element matches a content model if and only if it is
1755 possible to trace out a path through the content model, obeying the
1756 sequence, choice, and repetition operators and matching each element in
1757 the content against an element type in the content model. <termref def="dt-compat">For compatibility</termref>, it is an error
1758 if an element in the document can
1759 match more than one occurrence of an element type in the content model.
1760 For more information, see <specref ref="determinism"/>.
1761 <!-- appendix <specref ref="determinism"/>. -->
1762 <!-- appendix on deterministic content models. -->
1764 <vcnote id="vc-PEinGroup">
1765 <head>Proper Group/PE Nesting</head>
1767 <termref def="dt-repltext">replacement text</termref> must be properly nested
1768 with parenthetized groups.
1769 That is to say, if either of the opening or closing parentheses
1770 in a <nt def="NT-choice">choice</nt>, <nt def="NT-seq">seq</nt>, or
1771 <nt def="NT-Mixed">Mixed</nt> construct
1772 is contained in the replacement text for a
1773 <termref def="dt-PERef">parameter entity</termref>,
1774 both must be contained in the same replacement text.</p>
1775 <p><termref def="dt-interop">For interoperability</termref>,
1776 if a parameter-entity reference appears in a
1777 <nt def="NT-choice">choice</nt>, <nt def="NT-seq">seq</nt>, or
1778 <nt def="NT-Mixed">Mixed</nt> construct, its replacement text
1779 should not be empty, and
1780 neither the first nor last non-blank
1781 character of the replacement text should be a connector
1782 (<code>|</code> or <code>,</code>).
1785 <p>Examples of element-content models:
1786 <eg><!ELEMENT spec (front, body, back?)>
1787 <!ELEMENT div1 (head, (p | list | note)*, div2*)>
1788 <!ELEMENT dictionary-body (%div.mix; | %dict.mix;)*></eg></p>
1791 <div3 id="sec-mixed-content">
1792 <head>Mixed Content</head>
1794 <p><termdef id="dt-mixed" term="Mixed Content">An element
1795 <termref def="dt-stag">type</termref> has
1796 <term>mixed content</term> when elements of that type may contain
1797 character data, optionally interspersed with
1798 <termref def="dt-parentchild">child</termref> elements.</termdef>
1799 In this case, the types of the child elements
1800 may be constrained, but not their order or their number of occurrences:
1802 <head>Mixed-content Declaration</head>
1803 <prodgroup pcw2="5.5" pcw4="16" pcw5="11">
1804 <prod id="NT-Mixed"><lhs>Mixed</lhs>
1805 <rhs>'(' <nt def="NT-S">S</nt>?
1807 (<nt def="NT-S">S</nt>?
1809 <nt def="NT-S">S</nt>?
1810 <nt def="NT-Name">Name</nt>)*
1811 <nt def="NT-S">S</nt>?
1813 <rhs>| '(' <nt def="NT-S">S</nt>? '#PCDATA' <nt def="NT-S">S</nt>? ')'
1814 </rhs><vc def="vc-PEinGroup"/>
1815 <vc def="vc-MixedChildrenUnique"/>
1820 where the <nt def="NT-Name">Name</nt>s give the types of elements
1821 that may appear as children.
1823 <vcnote id="vc-MixedChildrenUnique">
1824 <head>No Duplicate Types</head>
1825 <p>The same name must not appear more than once in a single mixed-content
1828 <p>Examples of mixed content declarations:
1829 <eg><!ELEMENT p (#PCDATA|a|ul|b|i|em)*>
1830 <!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* >
1831 <!ELEMENT b (#PCDATA)></eg></p>
1835 <div2 id="attdecls">
1836 <head>Attribute-List Declarations</head>
1838 <p><termref def="dt-attr">Attributes</termref> are used to associate
1839 name-value pairs with <termref def="dt-element">elements</termref>.
1840 Attribute specifications may appear only within <termref def="dt-stag">start-tags</termref>
1841 and <termref def="dt-eetag">empty-element tags</termref>;
1842 thus, the productions used to
1843 recognize them appear in <specref ref="sec-starttags"/>.
1845 declarations may be used:
1847 <item><p>To define the set of attributes pertaining to a given
1848 element type.</p></item>
1849 <item><p>To establish type constraints for these
1850 attributes.</p></item>
1851 <item><p>To provide <termref def="dt-default">default values</termref>
1852 for attributes.</p></item>
1855 <p><termdef id="dt-attdecl" term="Attribute-List Declaration">
1856 <term>Attribute-list declarations</term> specify the name, data type, and default
1857 value (if any) of each attribute associated with a given element type:
1859 <head>Attribute-list Declaration</head>
1860 <prod id="NT-AttlistDecl"><lhs>AttlistDecl</lhs>
1861 <rhs>'<!ATTLIST' <nt def="NT-S">S</nt>
1862 <nt def="NT-Name">Name</nt>
1863 <nt def="NT-AttDef">AttDef</nt>*
1864 <nt def="NT-S">S</nt>? '>'</rhs>
1866 <prod id="NT-AttDef"><lhs>AttDef</lhs>
1867 <rhs><nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt>
1868 <nt def="NT-S">S</nt> <nt def="NT-AttType">AttType</nt>
1869 <nt def="NT-S">S</nt> <nt def="NT-DefaultDecl">DefaultDecl</nt></rhs>
1872 The <nt def="NT-Name">Name</nt> in the
1873 <nt def="NT-AttlistDecl">AttlistDecl</nt> rule is the type of an element. At
1874 user option, an XML processor may issue a warning if attributes are
1875 declared for an element type not itself declared, but this is not an
1876 error. The <nt def="NT-Name">Name</nt> in the
1877 <nt def="NT-AttDef">AttDef</nt> rule is
1878 the name of the attribute.</termdef></p>
1880 When more than one <nt def="NT-AttlistDecl">AttlistDecl</nt> is provided for a
1881 given element type, the contents of all those provided are merged. When
1882 more than one definition is provided for the same attribute of a
1883 given element type, the first declaration is binding and later
1884 declarations are ignored.
1885 <termref def="dt-interop">For interoperability,</termref> writers of DTDs
1886 may choose to provide at most one attribute-list declaration
1887 for a given element type, at most one attribute definition
1888 for a given attribute name, and at least one attribute definition
1889 in each attribute-list declaration.
1890 For interoperability, an XML processor may at user option
1891 issue a warning when more than one attribute-list declaration is
1892 provided for a given element type, or more than one attribute definition
1894 for a given attribute, but this is not an error.
1897 <div3 id="sec-attribute-types">
1898 <head>Attribute Types</head>
1900 <p>XML attribute types are of three kinds: a string type, a
1901 set of tokenized types, and enumerated types. The string type may take
1902 any literal string as a value; the tokenized types have varying lexical
1903 and semantic constraints, as noted:
1905 <head>Attribute Types</head>
1906 <prodgroup pcw4="14" pcw5="11.5">
1907 <prod id="NT-AttType"><lhs>AttType</lhs>
1908 <rhs><nt def="NT-StringType">StringType</nt>
1909 | <nt def="NT-TokenizedType">TokenizedType</nt>
1910 | <nt def="NT-EnumeratedType">EnumeratedType</nt>
1913 <prod id="NT-StringType"><lhs>StringType</lhs>
1916 <prod id="NT-TokenizedType"><lhs>TokenizedType</lhs>
1919 <vc def="one-id-per-el"/>
1920 <vc def="id-default"/>
1921 <rhs>| 'IDREF'</rhs>
1923 <rhs>| 'IDREFS'</rhs>
1925 <rhs>| 'ENTITY'</rhs>
1927 <rhs>| 'ENTITIES'</rhs>
1929 <rhs>| 'NMTOKEN'</rhs>
1931 <rhs>| 'NMTOKENS'</rhs>
1932 <vc def="nmtok"/></prod>
1939 Values of type <kw>ID</kw> must match the
1940 <nt def="NT-Name">Name</nt> production.
1941 A name must not appear more than once in
1942 an XML document as a value of this type; i.e., ID values must uniquely
1943 identify the elements which bear them.
1946 <vcnote id="one-id-per-el">
1947 <head>One ID per Element Type</head>
1948 <p>No element type may have more than one ID attribute specified.</p>
1950 <vcnote id="id-default">
1951 <head>ID Attribute Default</head>
1952 <p>An ID attribute must have a declared default of <kw>#IMPLIED</kw> or
1953 <kw>#REQUIRED</kw>.</p>
1958 Values of type <kw>IDREF</kw> must match
1959 the <nt def="NT-Name">Name</nt> production, and
1960 values of type <kw>IDREFS</kw> must match
1961 <nt def="NT-Names">Names</nt>;
1962 each <nt def="NT-Name">Name</nt> must match the value of an ID attribute on
1963 some element in the XML document; i.e. <kw>IDREF</kw> values must
1964 match the value of some ID attribute.
1967 <vcnote id="entname">
1968 <head>Entity Name</head>
1970 Values of type <kw>ENTITY</kw>
1971 must match the <nt def="NT-Name">Name</nt> production,
1972 values of type <kw>ENTITIES</kw> must match
1973 <nt def="NT-Names">Names</nt>;
1974 each <nt def="NT-Name">Name</nt> must
1976 name of an <termref def="dt-unparsed">unparsed entity</termref> declared in the
1977 <termref def="dt-doctype">DTD</termref>.
1981 <head>Name Token</head>
1983 Values of type <kw>NMTOKEN</kw> must match the
1984 <nt def="NT-Nmtoken">Nmtoken</nt> production;
1985 values of type <kw>NMTOKENS</kw> must
1986 match <termref def="NT-Nmtokens">Nmtokens</termref>.
1990 <p>The XML processor must normalize attribute values before
1991 passing them to the application, as described in
1992 <specref ref="AVNormalize"/>.</p>-->
1993 <p><termdef id="dt-enumerated" term="Enumerated Attribute Values"><term>Enumerated attributes</term> can take one
1994 of a list of values provided in the declaration</termdef>. There are two
1995 kinds of enumerated types:
1997 <head>Enumerated Attribute Types</head>
1998 <prod id="NT-EnumeratedType"><lhs>EnumeratedType</lhs>
1999 <rhs><nt def="NT-NotationType">NotationType</nt>
2000 | <nt def="NT-Enumeration">Enumeration</nt>
2002 <prod id="NT-NotationType"><lhs>NotationType</lhs>
2004 <nt def="NT-S">S</nt>
2006 <nt def="NT-S">S</nt>?
2007 <nt def="NT-Name">Name</nt>
2008 (<nt def="NT-S">S</nt>? '|' <nt def="NT-S">S</nt>?
2009 <nt def="NT-Name">Name</nt>)*
2010 <nt def="NT-S">S</nt>? ')'
2012 <vc def="notatn"/></prod>
2013 <prod id="NT-Enumeration"><lhs>Enumeration</lhs>
2014 <rhs>'(' <nt def="NT-S">S</nt>?
2015 <nt def="NT-Nmtoken">Nmtoken</nt>
2016 (<nt def="NT-S">S</nt>? '|'
2017 <nt def="NT-S">S</nt>?
2018 <nt def="NT-Nmtoken">Nmtoken</nt>)*
2019 <nt def="NT-S">S</nt>?
2021 <vc def="enum"/></prod>
2023 A <kw>NOTATION</kw> attribute identifies a
2024 <termref def="dt-notation">notation</termref>, declared in the
2025 DTD with associated system and/or public identifiers, to
2026 be used in interpreting the element to which the attribute
2030 <vcnote id="notatn">
2031 <head>Notation Attributes</head>
2033 Values of this type must match
2034 one of the <titleref href="Notations">notation</titleref> names included in
2035 the declaration; all notation names in the declaration must
2040 <head>Enumeration</head>
2043 must match one of the <nt def="NT-Nmtoken">Nmtoken</nt> tokens in the
2047 <p><termref def="dt-interop">For interoperability,</termref> the same
2048 <nt def="NT-Nmtoken">Nmtoken</nt> should not occur more than once in the
2049 enumerated attribute types of a single element type.
2053 <div3 id="sec-attr-defaults">
2054 <head>Attribute Defaults</head>
2056 <p>An <termref def="dt-attdecl">attribute declaration</termref> provides
2057 information on whether
2058 the attribute's presence is required, and if not, how an XML processor should
2059 react if a declared attribute is absent in a document.
2061 <head>Attribute Defaults</head>
2062 <prodgroup pcw4="14" pcw5="11.5">
2063 <prod id="NT-DefaultDecl"><lhs>DefaultDecl</lhs>
2065 | '#IMPLIED' </rhs>
2066 <rhs>| (('#FIXED' S)? <nt def="NT-AttValue">AttValue</nt>)</rhs>
2067 <vc def="RequiredAttr"/>
2068 <vc def="defattrvalid"/>
2069 <wfc def="CleanAttrVals"/>
2070 <vc def="FixedAttr"/>
2076 <p>In an attribute declaration, <kw>#REQUIRED</kw> means that the
2077 attribute must always be provided, <kw>#IMPLIED</kw> that no default
2080 <kw>#IMPLIED</kw> means that if the attribute is omitted
2081 from an element of this type,
2082 the XML processor must inform the application
2083 that no value was specified; no constraint is placed on the behavior
2084 of the application. -->
2085 <termdef id="dt-default" term="Attribute Default">If the
2087 is neither <kw>#REQUIRED</kw> nor <kw>#IMPLIED</kw>, then the
2088 <nt def="NT-AttValue">AttValue</nt> value contains the declared
2089 <term>default</term> value; the <kw>#FIXED</kw> keyword states that
2090 the attribute must always have the default value.
2092 is declared, when an XML processor encounters an omitted attribute, it
2093 is to behave as though the attribute were present with
2094 the declared default value.</termdef></p>
2095 <vcnote id="RequiredAttr">
2096 <head>Required Attribute</head>
2097 <p>If the default declaration is the keyword <kw>#REQUIRED</kw>, then
2098 the attribute must be specified for
2099 all elements of the type in the attribute-list declaration.
2101 <vcnote id="defattrvalid">
2102 <head>Attribute Default Legal</head>
2105 default value must meet the lexical constraints of the declared attribute type.
2108 <vcnote id="FixedAttr">
2109 <head>Fixed Attribute Default</head>
2110 <p>If an attribute has a default value declared with the
2111 <kw>#FIXED</kw> keyword, instances of that attribute must
2112 match the default value.
2115 <p>Examples of attribute-list declarations:
2116 <eg><!ATTLIST termdef
2118 name CDATA #IMPLIED>
2120 type (bullets|ordered|glossary) "ordered">
2122 method CDATA #FIXED "POST"></eg></p>
2124 <div3 id="AVNormalize">
2125 <head>Attribute-Value Normalization</head>
2126 <p>Before the value of an attribute is passed to the application
2127 or checked for validity, the
2128 XML processor must normalize it as follows:
2130 <item><p>a character reference is processed by appending the referenced
2131 character to the attribute value</p></item>
2132 <item><p>an entity reference is processed by recursively processing the
2133 replacement text of the entity</p></item>
2134 <item><p>a whitespace character (#x20, #xD, #xA, #x9) is processed by
2135 appending #x20 to the normalized value, except that only a single #x20
2136 is appended for a "#xD#xA" sequence that is part of an external
2137 parsed entity or the literal entity value of an internal parsed
2139 <item><p>other characters are processed by appending them to the normalized
2143 <p>If the declared value is not CDATA, then the XML processor must
2144 further process the normalized attribute value by discarding any
2145 leading and trailing space (#x20) characters, and by replacing
2146 sequences of space (#x20) characters by a single space (#x20)
2149 All attributes for which no declaration has been read should be treated
2150 by a non-validating parser as if declared
2155 <div2 id="sec-condition-sect">
2156 <head>Conditional Sections</head>
2157 <p><termdef id="dt-cond-section" term="conditional section">
2158 <term>Conditional sections</term> are portions of the
2159 <termref def="dt-doctype">document type declaration external subset</termref>
2161 included in, or excluded from, the logical structure of the DTD based on
2162 the keyword which governs them.</termdef>
2164 <head>Conditional Section</head>
2165 <prodgroup pcw2="9" pcw4="14.5">
2166 <prod id="NT-conditionalSect"><lhs>conditionalSect</lhs>
2167 <rhs><nt def="NT-includeSect">includeSect</nt>
2168 | <nt def="NT-ignoreSect">ignoreSect</nt>
2171 <prod id="NT-includeSect"><lhs>includeSect</lhs>
2172 <rhs>'<![' S? 'INCLUDE' S? '['
2174 <nt def="NT-extSubsetDecl">extSubsetDecl</nt>
2178 <prod id="NT-ignoreSect"><lhs>ignoreSect</lhs>
2179 <rhs>'<![' S? 'IGNORE' S? '['
2180 <nt def="NT-ignoreSectContents">ignoreSectContents</nt>*
2184 <prod id="NT-ignoreSectContents"><lhs>ignoreSectContents</lhs>
2185 <rhs><nt def="NT-Ignore">Ignore</nt>
2186 ('<![' <nt def="NT-ignoreSectContents">ignoreSectContents</nt> ']]>'
2187 <nt def="NT-Ignore">Ignore</nt>)*</rhs></prod>
2188 <prod id="NT-Ignore"><lhs>Ignore</lhs>
2189 <rhs><nt def="NT-Char">Char</nt>* -
2190 (<nt def="NT-Char">Char</nt>* ('<![' | ']]>')
2191 <nt def="NT-Char">Char</nt>*)
2197 <p>Like the internal and external DTD subsets, a conditional section
2198 may contain one or more complete declarations,
2199 comments, processing instructions,
2200 or nested conditional sections, intermingled with white space.
2202 <p>If the keyword of the
2203 conditional section is <kw>INCLUDE</kw>, then the contents of the conditional
2204 section are part of the DTD.
2205 If the keyword of the conditional
2206 section is <kw>IGNORE</kw>, then the contents of the conditional section are
2207 not logically part of the DTD.
2208 Note that for reliable parsing, the contents of even ignored
2209 conditional sections must be read in order to
2210 detect nested conditional sections and ensure that the end of the
2211 outermost (ignored) conditional section is properly detected.
2212 If a conditional section with a
2213 keyword of <kw>INCLUDE</kw> occurs within a larger conditional
2214 section with a keyword of <kw>IGNORE</kw>, both the outer and the
2215 inner conditional sections are ignored.</p>
2216 <p>If the keyword of the conditional section is a
2217 parameter-entity reference, the parameter entity must be replaced by its
2218 content before the processor decides whether to
2219 include or ignore the conditional section.</p>
2221 <eg><!ENTITY % draft 'INCLUDE' >
2222 <!ENTITY % final 'IGNORE' >
2225 <!ELEMENT book (comments*, title, body, supplements?)>
2228 <!ELEMENT book (title, body, supplements?)>
2236 <div2 id='sec-pass-to-app'>
2237 <head>XML Processor Treatment of Logical Structure</head>
2238 <p>When an XML processor encounters a start-tag, it must make
2239 at least the following information available to the application:
2242 <p>the element type's generic identifier</p>
2245 <p>the names of attributes known to apply to this element type
2246 (validating processors must make available names of all attributes
2247 declared for the element type; non-validating processors must
2248 make available at least the names of the attributes for which
2249 values are specified.
2260 <div1 id="sec-physical-struct">
2261 <head>Physical Structures</head>
2263 <p><termdef id="dt-entity" term="Entity">An XML document may consist
2264 of one or many storage units. These are called
2265 <term>entities</term>; they all have <term>content</term> and are all
2266 (except for the document entity, see below, and
2267 the <termref def="dt-doctype">external DTD subset</termref>)
2268 identified by <term>name</term>.
2270 Each XML document has one entity
2271 called the <termref def="dt-docent">document entity</termref>, which serves
2272 as the starting point for the <termref def="dt-xml-proc">XML
2273 processor</termref> and may contain the whole document.</p>
2274 <p>Entities may be either parsed or unparsed.
2275 <termdef id="dt-parsedent" term="Text Entity">A <term>parsed entity's</term>
2276 contents are referred to as its
2277 <termref def="dt-repltext">replacement text</termref>;
2278 this <termref def="dt-text">text</termref> is considered an
2279 integral part of the document.</termdef></p>
2281 <p><termdef id="dt-unparsed" term="Unparsed Entity">An
2282 <term>unparsed entity</term>
2283 is a resource whose contents may or may not be
2284 <termref def="dt-text">text</termref>, and if text, may not be XML.
2285 Each unparsed entity
2286 has an associated <termref def="dt-notation">notation</termref>, identified by name.
2287 Beyond a requirement
2288 that an XML processor make the identifiers for the entity and
2289 notation available to the application,
2290 XML places no constraints on the contents of unparsed entities.</termdef>
2293 Parsed entities are invoked by name using entity references;
2294 unparsed entities by name, given in the value of <kw>ENTITY</kw>
2295 or <kw>ENTITIES</kw>
2297 <p><termdef id="gen-entity" term="general entity"><term>General entities</term>
2298 are entities for use within the document content.
2299 In this specification, general entities are sometimes referred
2300 to with the unqualified term <emph>entity</emph> when this leads
2301 to no ambiguity.</termdef>
2302 <termdef id="dt-PE" term="Parameter entity">Parameter entities
2303 are parsed entities for use within the DTD.</termdef>
2304 These two types of entities use different forms of reference and
2305 are recognized in different contexts.
2306 Furthermore, they occupy different namespaces; a parameter entity and
2307 a general entity with the same name are two distinct entities.
2310 <div2 id="sec-references">
2311 <head>Character and Entity References</head>
2312 <p><termdef id="dt-charref" term="Character Reference">
2313 A <term>character reference</term> refers to a specific character in the
2314 ISO/IEC 10646 character set, for example one not directly accessible from
2315 available input devices.
2317 <head>Character Reference</head>
2318 <prod id="NT-CharRef"><lhs>CharRef</lhs>
2319 <rhs>'&#' [0-9]+ ';' </rhs>
2320 <rhs>| '&hcro;' [0-9a-fA-F]+ ';'</rhs>
2321 <wfc def="wf-Legalchar"/>
2324 <wfcnote id="wf-Legalchar">
2325 <head>Legal Character</head>
2326 <p>Characters referred to using character references must
2327 match the production for
2328 <termref def="NT-Char">Char</termref>.</p>
2330 If the character reference begins with "<code>&#x</code>", the digits and
2331 letters up to the terminating <code>;</code> provide a hexadecimal
2332 representation of the character's code point in ISO/IEC 10646.
2333 If it begins just with "<code>&#</code>", the digits up to the terminating
2334 <code>;</code> provide a decimal representation of the character's
2338 <p><termdef id="dt-entref" term="Entity Reference">An <term>entity
2339 reference</term> refers to the content of a named entity.</termdef>
2340 <termdef id="dt-GERef" term="General Entity Reference">References to
2341 parsed general entities
2342 use ampersand (<code>&</code>) and semicolon (<code>;</code>) as
2343 delimiters.</termdef>
2344 <termdef id="dt-PERef" term="Parameter-entity reference">
2345 <term>Parameter-entity references</term> use percent-sign (<code>%</code>) and
2347 (<code>;</code>) as delimiters.</termdef>
2350 <head>Entity Reference</head>
2351 <prod id="NT-Reference"><lhs>Reference</lhs>
2352 <rhs><nt def="NT-EntityRef">EntityRef</nt>
2353 | <nt def="NT-CharRef">CharRef</nt></rhs></prod>
2354 <prod id="NT-EntityRef"><lhs>EntityRef</lhs>
2355 <rhs>'&' <nt def="NT-Name">Name</nt> ';'</rhs>
2356 <wfc def="wf-entdeclared"/>
2357 <vc def="vc-entdeclared"/>
2358 <wfc def="textent"/>
2359 <wfc def="norecursion"/>
2361 <prod id="NT-PEReference"><lhs>PEReference</lhs>
2362 <rhs>'%' <nt def="NT-Name">Name</nt> ';'</rhs>
2363 <vc def="vc-entdeclared"/>
2364 <wfc def="norecursion"/>
2369 <wfcnote id="wf-entdeclared">
2370 <head>Entity Declared</head>
2371 <p>In a document without any DTD, a document with only an internal
2372 DTD subset which contains no parameter entity references, or a document with
2373 "<code>standalone='yes'</code>",
2374 the <nt def="NT-Name">Name</nt> given in the entity reference must
2375 <termref def="dt-match">match</termref> that in an
2376 <titleref href="sec-entity-decl">entity declaration</titleref>, except that
2377 well-formed documents need not declare
2378 any of the following entities: &magicents;.
2379 The declaration of a parameter entity must precede any reference to it.
2380 Similarly, the declaration of a general entity must precede any
2381 reference to it which appears in a default value in an attribute-list
2383 <p>Note that if entities are declared in the external subset or in
2384 external parameter entities, a non-validating processor is
2385 <titleref href="include-if-valid">not obligated to</titleref> read
2386 and process their declarations; for such documents, the rule that
2387 an entity must be declared is a well-formedness constraint only
2388 if <titleref href="sec-rmd">standalone='yes'</titleref>.</p>
2390 <vcnote id="vc-entdeclared">
2391 <head>Entity Declared</head>
2392 <p>In a document with an external subset or external parameter
2393 entities with "<code>standalone='no'</code>",
2394 the <nt def="NT-Name">Name</nt> given in the entity reference must <termref def="dt-match">match</termref> that in an
2395 <titleref href="sec-entity-decl">entity declaration</titleref>.
2396 For interoperability, valid documents should declare the entities
2397 &magicents;, in the form
2398 specified in <specref ref="sec-predefined-ent"/>.
2399 The declaration of a parameter entity must precede any reference to it.
2400 Similarly, the declaration of a general entity must precede any
2401 reference to it which appears in a default value in an attribute-list
2404 <!-- FINAL EDIT: is this duplication too clumsy? -->
2405 <wfcnote id="textent">
2406 <head>Parsed Entity</head>
2408 An entity reference must not contain the name of an <termref def="dt-unparsed">unparsed entity</termref>. Unparsed entities may be referred
2409 to only in <termref def="dt-attrval">attribute values</termref> declared to
2410 be of type <kw>ENTITY</kw> or <kw>ENTITIES</kw>.
2413 <wfcnote id="norecursion">
2414 <head>No Recursion</head>
2416 A parsed entity must not contain a recursive reference to itself,
2417 either directly or indirectly.
2420 <wfcnote id="indtd">
2423 Parameter-entity references may only appear in the
2424 <termref def="dt-doctype">DTD</termref>.
2427 <p>Examples of character and entity references:
2428 <eg>Type <key>less-than</key> (&hcro;3C;) to save options.
2429 This document was prepared on &docdate; and
2430 is classified &security-level;.</eg></p>
2431 <p>Example of a parameter-entity reference:
2432 <eg><![CDATA[<!-- declare the parameter entity "ISOLat2"... -->
2434 SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" >
2435 <!-- ... now reference it. -->
2436 %ISOLat2;]]></eg></p>
2439 <div2 id="sec-entity-decl">
2440 <head>Entity Declarations</head>
2442 <p><termdef id="dt-entdecl" term="entity declaration">
2443 Entities are declared thus:
2445 <head>Entity Declaration</head>
2446 <prodgroup pcw2="5" pcw4="18.5">
2447 <prod id="NT-EntityDecl"><lhs>EntityDecl</lhs>
2448 <rhs><nt def="NT-GEDecl">GEDecl</nt><!--</rhs><com>General entities</com>
2449 <rhs>--> | <nt def="NT-PEDecl">PEDecl</nt></rhs>
2450 <!--<com>Parameter entities</com>-->
2452 <prod id="NT-GEDecl"><lhs>GEDecl</lhs>
2453 <rhs>'<!ENTITY' <nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt>
2454 <nt def="NT-S">S</nt> <nt def="NT-EntityDef">EntityDef</nt>
2455 <nt def="NT-S">S</nt>? '>'</rhs>
2457 <prod id="NT-PEDecl"><lhs>PEDecl</lhs>
2458 <rhs>'<!ENTITY' <nt def="NT-S">S</nt> '%' <nt def="NT-S">S</nt>
2459 <nt def="NT-Name">Name</nt> <nt def="NT-S">S</nt>
2460 <nt def="NT-PEDef">PEDef</nt> <nt def="NT-S">S</nt>? '>'</rhs>
2461 <!--<com>Parameter entities</com>-->
2463 <prod id="NT-EntityDef"><lhs>EntityDef</lhs>
2464 <rhs><nt def="NT-EntityValue">EntityValue</nt>
2466 <rhs>-->| (<nt def="NT-ExternalID">ExternalID</nt>
2467 <nt def="NT-NDataDecl">NDataDecl</nt>?)</rhs>
2468 <!-- <nt def='NT-ExternalDef'>ExternalDef</nt></rhs> -->
2470 <!-- FINAL EDIT: what happened to WFs here? -->
2471 <prod id="NT-PEDef"><lhs>PEDef</lhs>
2472 <rhs><nt def="NT-EntityValue">EntityValue</nt>
2473 | <nt def="NT-ExternalID">ExternalID</nt></rhs></prod>
2476 The <nt def="NT-Name">Name</nt> identifies the entity in an
2477 <termref def="dt-entref">entity reference</termref> or, in the case of an
2478 unparsed entity, in the value of an <kw>ENTITY</kw> or <kw>ENTITIES</kw>
2480 If the same entity is declared more than once, the first declaration
2481 encountered is binding; at user option, an XML processor may issue a
2482 warning if entities are declared multiple times.</termdef>
2485 <div3 id="sec-internal-ent">
2486 <head>Internal Entities</head>
2488 <p><termdef id="dt-internent" term="Internal Entity Replacement Text">If
2489 the entity definition is an
2490 <nt def="NT-EntityValue">EntityValue</nt>,
2491 the defined entity is called an <term>internal entity</term>.
2492 There is no separate physical
2493 storage object, and the content of the entity is given in the
2494 declaration. </termdef>
2495 Note that some processing of entity and character references in the
2496 <termref def="dt-litentval">literal entity value</termref> may be required to
2497 produce the correct <termref def="dt-repltext">replacement
2498 text</termref>: see <specref ref="intern-replacement"/>.
2500 <p>An internal entity is a <termref def="dt-parsedent">parsed
2501 entity</termref>.</p>
2502 <p>Example of an internal entity declaration:
2503 <eg><!ENTITY Pub-Status "This is a pre-release of the
2504 specification."></eg></p>
2507 <div3 id="sec-external-ent">
2508 <head>External Entities</head>
2510 <p><termdef id="dt-extent" term="External Entity">If the entity is not
2511 internal, it is an <term>external
2512 entity</term>, declared as follows:
2514 <head>External Entity Declaration</head>
2516 <prod id='NT-ExternalDef'><lhs>ExternalDef</lhs>
2518 <prod id="NT-ExternalID"><lhs>ExternalID</lhs>
2519 <rhs>'SYSTEM' <nt def="NT-S">S</nt>
2520 <nt def="NT-SystemLiteral">SystemLiteral</nt></rhs>
2521 <rhs>| 'PUBLIC' <nt def="NT-S">S</nt>
2522 <nt def="NT-PubidLiteral">PubidLiteral</nt>
2523 <nt def="NT-S">S</nt>
2524 <nt def="NT-SystemLiteral">SystemLiteral</nt>
2527 <prod id="NT-NDataDecl"><lhs>NDataDecl</lhs>
2528 <rhs><nt def="NT-S">S</nt> 'NDATA' <nt def="NT-S">S</nt>
2529 <nt def="NT-Name">Name</nt></rhs>
2530 <vc def="not-declared"/></prod>
2532 If the <nt def="NT-NDataDecl">NDataDecl</nt> is present, this is a
2533 general <termref def="dt-unparsed">unparsed
2534 entity</termref>; otherwise it is a parsed entity.</termdef></p>
2535 <vcnote id="not-declared">
2536 <head>Notation Declared</head>
2538 The <nt def="NT-Name">Name</nt> must match the declared name of a
2539 <termref def="dt-notation">notation</termref>.
2542 <p><termdef id="dt-sysid" term="System Identifier">The
2543 <nt def="NT-SystemLiteral">SystemLiteral</nt>
2544 is called the entity's <term>system identifier</term>. It is a URI,
2545 which may be used to retrieve the entity.</termdef>
2546 Note that the hash mark (<code>#</code>) and fragment identifier
2547 frequently used with URIs are not, formally, part of the URI itself;
2548 an XML processor may signal an error if a fragment identifier is
2549 given as part of a system identifier.
2550 Unless otherwise provided by information outside the scope of this
2551 specification (e.g. a special XML element type defined by a particular
2552 DTD, or a processing instruction defined by a particular application
2553 specification), relative URIs are relative to the location of the
2554 resource within which the entity declaration occurs.
2555 A URI might thus be relative to the
2556 <termref def="dt-docent">document entity</termref>, to the entity
2557 containing the <termref def="dt-doctype">external DTD subset</termref>,
2558 or to some other <termref def="dt-extent">external parameter entity</termref>.
2560 <p>An XML processor should handle a non-ASCII character in a URI by
2561 representing the character in UTF-8 as one or more bytes, and then
2562 escaping these bytes with the URI escaping mechanism (i.e., by
2563 converting each byte to %HH, where HH is the hexadecimal notation of the
2565 <p><termdef id="dt-pubid" term="Public identifier">
2566 In addition to a system identifier, an external identifier may
2567 include a <term>public identifier</term>.</termdef>
2568 An XML processor attempting to retrieve the entity's content may use the public
2569 identifier to try to generate an alternative URI. If the processor
2570 is unable to do so, it must use the URI specified in the system
2571 literal. Before a match is attempted, all strings
2572 of white space in the public identifier must be normalized to single space characters (#x20),
2573 and leading and trailing white space must be removed.</p>
2574 <p>Examples of external entity declarations:
2575 <eg><!ENTITY open-hatch
2576 SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml">
2577 <!ENTITY open-hatch
2578 PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN"
2579 "http://www.textuality.com/boilerplate/OpenHatch.xml">
2580 <!ENTITY hatch-pic
2581 SYSTEM "../grafix/OpenHatch.gif"
2582 NDATA gif ></eg></p>
2587 <div2 id="TextEntities">
2588 <head>Parsed Entities</head>
2589 <div3 id="sec-TextDecl">
2590 <head>The Text Declaration</head>
2591 <p>External parsed entities may each begin with a <term>text
2594 <head>Text Declaration</head>
2595 <prodgroup pcw4="12.5" pcw5="13">
2596 <prod id="NT-TextDecl"><lhs>TextDecl</lhs>
2598 <nt def="NT-VersionInfo">VersionInfo</nt>?
2599 <nt def="NT-EncodingDecl">EncodingDecl</nt>
2600 <nt def="NT-S">S</nt>? &pic;</rhs>
2605 <p>The text declaration must be provided literally, not
2606 by reference to a parsed entity.
2607 No text declaration may appear at any position other than the beginning of
2608 an external parsed entity.</p>
2610 <div3 id="wf-entities">
2611 <head>Well-Formed Parsed Entities</head>
2612 <p>The document entity is well-formed if it matches the production labeled
2613 <nt def="NT-document">document</nt>.
2615 parsed entity is well-formed if it matches the production labeled
2616 <nt def="NT-extParsedEnt">extParsedEnt</nt>.
2617 An external parameter
2618 entity is well-formed if it matches the production labeled
2619 <nt def="NT-extPE">extPE</nt>.
2621 <head>Well-Formed External Parsed Entity</head>
2622 <prod id="NT-extParsedEnt"><lhs>extParsedEnt</lhs>
2623 <rhs><nt def="NT-TextDecl">TextDecl</nt>?
2624 <nt def="NT-content">content</nt></rhs>
2626 <prod id="NT-extPE"><lhs>extPE</lhs>
2627 <rhs><nt def="NT-TextDecl">TextDecl</nt>?
2628 <nt def="NT-extSubsetDecl">extSubsetDecl</nt></rhs>
2631 An internal general parsed entity is well-formed if its replacement text
2632 matches the production labeled
2633 <nt def="NT-content">content</nt>.
2634 All internal parameter entities are well-formed by definition.
2636 <p>A consequence of well-formedness in entities is that the logical
2637 and physical structures in an XML document are properly nested; no
2638 <termref def="dt-stag">start-tag</termref>,
2639 <termref def="dt-etag">end-tag</termref>,
2640 <termref def="dt-empty">empty-element tag</termref>,
2641 <termref def="dt-element">element</termref>,
2642 <termref def="dt-comment">comment</termref>,
2643 <termref def="dt-pi">processing instruction</termref>,
2644 <termref def="dt-charref">character
2645 reference</termref>, or
2646 <termref def="dt-entref">entity reference</termref>
2647 can begin in one entity and end in another.</p>
2649 <div3 id="charencoding">
2650 <head>Character Encoding in Entities</head>
2652 <p>Each external parsed entity in an XML document may use a different
2653 encoding for its characters. All XML processors must be able to read
2654 entities in either UTF-8 or UTF-16.
2657 <p>Entities encoded in UTF-16 must
2658 begin with the Byte Order Mark described by ISO/IEC 10646 Annex E and
2659 Unicode Appendix B (the ZERO WIDTH NO-BREAK SPACE character, #xFEFF).
2660 This is an encoding signature, not part of either the markup or the
2661 character data of the XML document.
2662 XML processors must be able to use this character to
2663 differentiate between UTF-8 and UTF-16 encoded documents.</p>
2664 <p>Although an XML processor is required to read only entities in
2665 the UTF-8 and UTF-16 encodings, it is recognized that other encodings are
2666 used around the world, and it may be desired for XML processors
2667 to read entities that use them.
2668 Parsed entities which are stored in an encoding other than
2669 UTF-8 or UTF-16 must begin with a <titleref href="TextDecl">text
2670 declaration</titleref> containing an encoding declaration:
2672 <head>Encoding Declaration</head>
2673 <prod id="NT-EncodingDecl"><lhs>EncodingDecl</lhs>
2674 <rhs><nt def="NT-S">S</nt>
2675 'encoding' <nt def="NT-Eq">Eq</nt>
2676 ('"' <nt def="NT-EncName">EncName</nt> '"' |
2677 "'" <nt def="NT-EncName">EncName</nt> "'" )
2680 <prod id="NT-EncName"><lhs>EncName</lhs>
2681 <rhs>[A-Za-z] ([A-Za-z0-9._] | '-')*</rhs>
2682 <com>Encoding name contains only Latin characters</com>
2685 In the <termref def="dt-docent">document entity</termref>, the encoding
2686 declaration is part of the <termref def="dt-xmldecl">XML declaration</termref>.
2687 The <nt def="NT-EncName">EncName</nt> is the name of the encoding used.
2689 <!-- FINAL EDIT: check name of IANA and charset names -->
2690 <p>In an encoding declaration, the values
2691 "<code>UTF-8</code>",
2692 "<code>UTF-16</code>",
2693 "<code>ISO-10646-UCS-2</code>", and
2694 "<code>ISO-10646-UCS-4</code>" should be
2695 used for the various encodings and transformations of Unicode /
2696 ISO/IEC 10646, the values
2697 "<code>ISO-8859-1</code>",
2698 "<code>ISO-8859-2</code>", ...
2699 "<code>ISO-8859-9</code>" should be used for the parts of ISO 8859, and
2701 "<code>ISO-2022-JP</code>",
2702 "<code>Shift_JIS</code>", and
2703 "<code>EUC-JP</code>"
2704 should be used for the various encoded forms of JIS X-0208-1997. XML
2705 processors may recognize other encodings; it is recommended that
2706 character encodings registered (as <emph>charset</emph>s)
2707 with the Internet Assigned Numbers
2708 Authority <bibref ref="IANA"/>, other than those just listed, should be
2710 using their registered names.
2711 Note that these registered names are defined to be
2712 case-insensitive, so processors wishing to match against them
2713 should do so in a case-insensitive
2715 <p>In the absence of information provided by an external
2716 transport protocol (e.g. HTTP or MIME),
2717 it is an <termref def="dt-error">error</termref> for an entity including
2718 an encoding declaration to be presented to the XML processor
2719 in an encoding other than that named in the declaration,
2720 for an encoding declaration to occur other than at the beginning
2721 of an external entity, or for
2722 an entity which begins with neither a Byte Order Mark nor an encoding
2723 declaration to use an encoding other than UTF-8.
2724 Note that since ASCII
2725 is a subset of UTF-8, ordinary ASCII entities do not strictly need
2726 an encoding declaration.</p>
2728 <p>It is a <termref def="dt-fatal">fatal error</termref> when an XML processor
2729 encounters an entity with an encoding that it is unable to process.</p>
2730 <p>Examples of encoding declarations:
2731 <eg><?xml encoding='UTF-8'?>
2732 <?xml encoding='EUC-JP'?></eg></p>
2736 <head>XML Processor Treatment of Entities and References</head>
2737 <p>The table below summarizes the contexts in which character references,
2738 entity references, and invocations of unparsed entities might appear and the
2739 required behavior of an <termref def="dt-xml-proc">XML processor</termref> in
2741 The labels in the leftmost column describe the recognition context:
2743 <gitem><label>Reference in Content</label>
2744 <def><p>as a reference
2745 anywhere after the <termref def="dt-stag">start-tag</termref> and
2746 before the <termref def="dt-etag">end-tag</termref> of an element; corresponds
2747 to the nonterminal <nt def="NT-content">content</nt>.</p></def>
2750 <label>Reference in Attribute Value</label>
2751 <def><p>as a reference within either the value of an attribute in a
2752 <termref def="dt-stag">start-tag</termref>, or a default
2753 value in an <termref def="dt-attdecl">attribute declaration</termref>;
2754 corresponds to the nonterminal
2755 <nt def="NT-AttValue">AttValue</nt>.</p></def></gitem>
2757 <label>Occurs as Attribute Value</label>
2758 <def><p>as a <nt def="NT-Name">Name</nt>, not a reference, appearing either as
2760 attribute which has been declared as type <kw>ENTITY</kw>, or as one of
2761 the space-separated tokens in the value of an attribute which has been
2762 declared as type <kw>ENTITIES</kw>.</p>
2764 <gitem><label>Reference in Entity Value</label>
2765 <def><p>as a reference
2766 within a parameter or internal entity's
2767 <termref def="dt-litentval">literal entity value</termref> in
2768 the entity's declaration; corresponds to the nonterminal
2769 <nt def="NT-EntityValue">EntityValue</nt>.</p></def></gitem>
2770 <gitem><label>Reference in DTD</label>
2771 <def><p>as a reference within either the internal or external subsets of the
2772 <termref def="dt-doctype">DTD</termref>, but outside
2773 of an <nt def="NT-EntityValue">EntityValue</nt> or
2774 <nt def="NT-AttValue">AttValue</nt>.</p></def>
2777 <htable border="1" cellpadding="7" align="center">
2779 <tr><td bgcolor="&cellback;" rowspan="2" colspan="1"/>
2780 <td bgcolor="&cellback;" align="center" valign="bottom" colspan="4">Entity Type</td>
2781 <td bgcolor="&cellback;" rowspan="2" align="center">Character</td>
2783 <tr align="center" valign="bottom">
2784 <td bgcolor="&cellback;">Parameter</td>
2785 <td bgcolor="&cellback;">Internal
2787 <td bgcolor="&cellback;">External Parsed
2789 <td bgcolor="&cellback;">Unparsed</td>
2791 <tr align="center" valign="middle">
2793 <td bgcolor="&cellback;" align="right">Reference
2795 <td bgcolor="&cellback;"><titleref href="not-recognized">Not recognized</titleref></td>
2796 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td>
2797 <td bgcolor="&cellback;"><titleref href="include-if-valid">Included if validating</titleref></td>
2798 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
2799 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td>
2801 <tr align="center" valign="middle">
2802 <td bgcolor="&cellback;" align="right">Reference
2803 in Attribute Value</td>
2804 <td bgcolor="&cellback;"><titleref href="not-recognized">Not recognized</titleref></td>
2805 <td bgcolor="&cellback;"><titleref href="inliteral">Included in literal</titleref></td>
2806 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
2807 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
2808 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td>
2810 <tr align="center" valign="middle">
2811 <td bgcolor="&cellback;" align="right">Occurs as
2812 Attribute Value</td>
2813 <td bgcolor="&cellback;"><titleref href="not-recognized">Not recognized</titleref></td>
2814 <td bgcolor="&cellback;"><titleref href="not-recognized">Forbidden</titleref></td>
2815 <td bgcolor="&cellback;"><titleref href="not-recognized">Forbidden</titleref></td>
2816 <td bgcolor="&cellback;"><titleref href="notify">Notify</titleref></td>
2817 <td bgcolor="&cellback;"><titleref href="not recognized">Not recognized</titleref></td>
2819 <tr align="center" valign="middle">
2820 <td bgcolor="&cellback;" align="right">Reference
2822 <td bgcolor="&cellback;"><titleref href="inliteral">Included in literal</titleref></td>
2823 <td bgcolor="&cellback;"><titleref href="bypass">Bypassed</titleref></td>
2824 <td bgcolor="&cellback;"><titleref href="bypass">Bypassed</titleref></td>
2825 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
2826 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td>
2828 <tr align="center" valign="middle">
2829 <td bgcolor="&cellback;" align="right">Reference
2831 <td bgcolor="&cellback;"><titleref href="as-PE">Included as PE</titleref></td>
2832 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
2833 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
2834 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
2835 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
2839 <div3 id="not-recognized">
2840 <head>Not Recognized</head>
2841 <p>Outside the DTD, the <code>%</code> character has no
2842 special significance; thus, what would be parameter entity references in the
2843 DTD are not recognized as markup in <nt def="NT-content">content</nt>.
2844 Similarly, the names of unparsed entities are not recognized except
2845 when they appear in the value of an appropriately declared attribute.
2848 <div3 id="included">
2849 <head>Included</head>
2850 <p><termdef id="dt-include" term="Include">An entity is
2851 <term>included</term> when its
2852 <termref def="dt-repltext">replacement text</termref> is retrieved
2853 and processed, in place of the reference itself,
2854 as though it were part of the document at the location the
2855 reference was recognized.
2856 The replacement text may contain both
2857 <termref def="dt-chardata">character data</termref>
2858 and (except for parameter entities) <termref def="dt-markup">markup</termref>,
2859 which must be recognized in
2860 the usual way, except that the replacement text of entities used to escape
2861 markup delimiters (the entities &magicents;) is always treated as
2862 data. (The string "<code>AT&amp;T;</code>" expands to
2863 "<code>AT&T;</code>" and the remaining ampersand is not recognized
2864 as an entity-reference delimiter.)
2865 A character reference is <term>included</term> when the indicated
2866 character is processed in place of the reference itself.
2869 <div3 id="include-if-valid">
2870 <head>Included If Validating</head>
2871 <p>When an XML processor recognizes a reference to a parsed entity, in order
2872 to <termref def="dt-valid">validate</termref>
2873 the document, the processor must
2874 <termref def="dt-include">include</termref> its
2876 If the entity is external, and the processor is not
2877 attempting to validate the XML document, the
2878 processor <termref def="dt-may">may</termref>, but need not,
2879 include the entity's replacement text.
2880 If a non-validating parser does not include the replacement text,
2881 it must inform the application that it recognized, but did not
2882 read, the entity.</p>
2883 <p>This rule is based on the recognition that the automatic inclusion
2884 provided by the SGML and XML entity mechanism, primarily designed
2885 to support modularity in authoring, is not necessarily
2886 appropriate for other applications, in particular document browsing.
2887 Browsers, for example, when encountering an external parsed entity reference,
2888 might choose to provide a visual indication of the entity's
2889 presence and retrieve it for display only on demand.
2892 <div3 id="forbidden">
2893 <head>Forbidden</head>
2894 <p>The following are forbidden, and constitute
2895 <termref def="dt-fatal">fatal</termref> errors:
2897 <item><p>the appearance of a reference to an
2898 <termref def="dt-unparsed">unparsed entity</termref>.
2900 <item><p>the appearance of any character or general-entity reference in the
2901 DTD except within an <nt def="NT-EntityValue">EntityValue</nt> or
2902 <nt def="NT-AttValue">AttValue</nt>.</p></item>
2903 <item><p>a reference to an external entity in an attribute value.</p>
2908 <div3 id="inliteral">
2909 <head>Included in Literal</head>
2910 <p>When an <termref def="dt-entref">entity reference</termref> appears in an
2911 attribute value, or a parameter entity reference appears in a literal entity
2912 value, its <termref def="dt-repltext">replacement text</termref> is
2913 processed in place of the reference itself as though it
2914 were part of the document at the location the reference was recognized,
2915 except that a single or double quote character in the replacement text
2916 is always treated as a normal data character and will not terminate the
2918 For example, this is well-formed:
2919 <eg><![CDATA[<!ENTITY % YN '"Yes"' >
2920 <!ENTITY WhatHeSaid "He said &YN;" >]]></eg>
2922 <eg><!ENTITY EndAttr "27'" >
2923 <element attribute='a-&EndAttr;></eg>
2927 <p>When the name of an <termref def="dt-unparsed">unparsed
2928 entity</termref> appears as a token in the
2929 value of an attribute of declared type <kw>ENTITY</kw> or <kw>ENTITIES</kw>,
2930 a validating processor must inform the
2931 application of the <termref def="dt-sysid">system</termref>
2932 and <termref def="dt-pubid">public</termref> (if any)
2933 identifiers for both the entity and its associated
2934 <termref def="dt-notation">notation</termref>.</p>
2937 <head>Bypassed</head>
2938 <p>When a general entity reference appears in the
2939 <nt def="NT-EntityValue">EntityValue</nt> in an entity declaration,
2940 it is bypassed and left as is.</p>
2943 <head>Included as PE</head>
2944 <p>Just as with external parsed entities, parameter entities
2945 need only be <titleref href="include-if-valid">included if
2946 validating</titleref>.
2947 When a parameter-entity reference is recognized in the DTD
2949 <termref def="dt-repltext">replacement
2950 text</termref> is enlarged by the attachment of one leading and one following
2951 space (#x20) character; the intent is to constrain the replacement
2953 entities to contain an integral number of grammatical tokens in the DTD.
2958 <div2 id="intern-replacement">
2959 <head>Construction of Internal Entity Replacement Text</head>
2960 <p>In discussing the treatment
2961 of internal entities, it is
2962 useful to distinguish two forms of the entity's value.
2963 <termdef id="dt-litentval" term="Literal Entity Value">The <term>literal
2964 entity value</term> is the quoted string actually
2965 present in the entity declaration, corresponding to the
2966 non-terminal <nt def="NT-EntityValue">EntityValue</nt>.</termdef>
2967 <termdef id="dt-repltext" term="Replacement Text">The <term>replacement
2968 text</term> is the content of the entity, after
2969 replacement of character references and parameter-entity
2973 <p>The literal entity value
2974 as given in an internal entity declaration
2975 (<nt def="NT-EntityValue">EntityValue</nt>) may contain character,
2976 parameter-entity, and general-entity references.
2977 Such references must be contained entirely within the
2978 literal entity value.
2979 The actual replacement text that is
2980 <termref def="dt-include">included</termref> as described above
2981 must contain the <emph>replacement text</emph> of any
2982 parameter entities referred to, and must contain the character
2983 referred to, in place of any character references in the
2984 literal entity value; however,
2985 general-entity references must be left as-is, unexpanded.
2986 For example, given the following declarations:
2988 <eg><![CDATA[<!ENTITY % pub "Éditions Gallimard" >
2989 <!ENTITY rights "All rights reserved" >
2990 <!ENTITY book "La Peste: Albert Camus,
2991 © 1947 %pub;. &rights;" >]]></eg>
2992 then the replacement text for the entity "<code>book</code>" is:
2993 <eg>La Peste: Albert Camus,
2994 © 1947 Éditions Gallimard. &rights;</eg>
2995 The general-entity reference "<code>&rights;</code>" would be expanded
2996 should the reference "<code>&book;</code>" appear in the document's
2997 content or an attribute value.</p>
2998 <p>These simple rules may have complex interactions; for a detailed
2999 discussion of a difficult example, see
3000 <specref ref="sec-entexpand"/>.
3004 <div2 id="sec-predefined-ent">
3005 <head>Predefined Entities</head>
3006 <p><termdef id="dt-escape" term="escape">Entity and character
3007 references can both be used to <term>escape</term> the left angle bracket,
3008 ampersand, and other delimiters. A set of general entities
3009 (&magicents;) is specified for this purpose.
3010 Numeric character references may also be used; they are
3011 expanded immediately when recognized and must be treated as
3012 character data, so the numeric character references
3013 "<code>&#60;</code>" and "<code>&#38;</code>" may be used to
3014 escape <code><</code> and <code>&</code> when they occur
3015 in character data.</termdef></p>
3016 <p>All XML processors must recognize these entities whether they
3017 are declared or not.
3018 <termref def="dt-interop">For interoperability</termref>,
3019 valid XML documents should declare these
3020 entities, like any others, before using them.
3021 If the entities in question are declared, they must be declared
3022 as internal entities whose replacement text is the single
3023 character being escaped or a character reference to
3024 that character, as shown below.
3025 <eg><![CDATA[<!ENTITY lt "&#60;">
3026 <!ENTITY gt ">">
3027 <!ENTITY amp "&#38;">
3028 <!ENTITY apos "'">
3029 <!ENTITY quot """>
3031 Note that the <code><</code> and <code>&</code> characters
3032 in the declarations of "<code>lt</code>" and "<code>amp</code>"
3033 are doubly escaped to meet the requirement that entity replacement
3038 <div2 id="Notations">
3039 <head>Notation Declarations</head>
3041 <p><termdef id="dt-notation" term="Notation"><term>Notations</term> identify by
3042 name the format of <termref def="dt-extent">unparsed
3043 entities</termref>, the
3044 format of elements which bear a notation attribute,
3045 or the application to which
3046 a <termref def="dt-pi">processing instruction</termref> is
3047 addressed.</termdef></p>
3048 <p><termdef id="dt-notdecl" term="Notation Declaration">
3049 <term>Notation declarations</term>
3050 provide a name for the notation, for use in
3051 entity and attribute-list declarations and in attribute specifications,
3052 and an external identifier for the notation which may allow an XML
3053 processor or its client application to locate a helper application
3054 capable of processing data in the given notation.
3056 <head>Notation Declarations</head>
3057 <prod id="NT-NotationDecl"><lhs>NotationDecl</lhs>
3058 <rhs>'<!NOTATION' <nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt>
3059 <nt def="NT-S">S</nt>
3060 (<nt def="NT-ExternalID">ExternalID</nt> |
3061 <nt def="NT-PublicID">PublicID</nt>)
3062 <nt def="NT-S">S</nt>? '>'</rhs></prod>
3063 <prod id="NT-PublicID"><lhs>PublicID</lhs>
3064 <rhs>'PUBLIC' <nt def="NT-S">S</nt>
3065 <nt def="NT-PubidLiteral">PubidLiteral</nt>
3069 <p>XML processors must provide applications with the name and external
3070 identifier(s) of any notation declared and referred to in an attribute
3071 value, attribute definition, or entity declaration. They may
3072 additionally resolve the external identifier into the
3073 <termref def="dt-sysid">system identifier</termref>,
3074 file name, or other information needed to allow the
3075 application to call a processor for data in the notation described. (It
3076 is not an error, however, for XML documents to declare and refer to
3077 notations for which notation-specific applications are not available on
3078 the system where the XML processor or application is running.)</p>
3082 <div2 id="sec-doc-entity">
3083 <head>Document Entity</head>
3085 <p><termdef id="dt-docent" term="Document Entity">The <term>document
3086 entity</term> serves as the root of the entity
3087 tree and a starting-point for an <termref def="dt-xml-proc">XML
3088 processor</termref>.</termdef>
3089 This specification does
3090 not specify how the document entity is to be located by an XML
3091 processor; unlike other entities, the document entity has no name and might
3092 well appear on a processor input stream
3093 without any identification at all.</p>
3098 <!-- &Conformance; -->
3100 <div1 id="sec-conformance">
3101 <head>Conformance</head>
3103 <div2 id="proc-types">
3104 <head>Validating and Non-Validating Processors</head>
3105 <p>Conforming <termref def="dt-xml-proc">XML processors</termref> fall into two
3106 classes: validating and non-validating.</p>
3107 <p>Validating and non-validating processors alike must report
3108 violations of this specification's well-formedness constraints
3109 in the content of the
3110 <termref def="dt-docent">document entity</termref> and any
3111 other <termref def="dt-parsedent">parsed entities</termref> that
3113 <p><termdef id="dt-validating" term="Validating Processor">
3114 <term>Validating processors</term> must report
3115 violations of the constraints expressed by the declarations in the
3116 <termref def="dt-doctype">DTD</termref>, and
3117 failures to fulfill the validity constraints given
3118 in this specification.
3120 To accomplish this, validating XML processors must read and process the entire
3121 DTD and all external parsed entities referenced in the document.
3123 <p>Non-validating processors are required to check only the
3124 <termref def="dt-docent">document entity</termref>, including
3125 the entire internal DTD subset, for well-formedness.
3126 <termdef id="dt-use-mdecl" term="Process Declarations">
3127 While they are not required to check the document for validity,
3128 they are required to
3129 <term>process</term> all the declarations they read in the
3130 internal DTD subset and in any parameter entity that they
3131 read, up to the first reference
3132 to a parameter entity that they do <emph>not</emph> read; that is to
3134 use the information in those declarations to
3135 <titleref href="AVNormalize">normalize</titleref> attribute values,
3136 <titleref href="included">include</titleref> the replacement text of
3137 internal entities, and supply
3138 <titleref href="sec-attr-defaults">default attribute values</titleref>.
3140 They must not <termref def="dt-use-mdecl">process</termref>
3141 <termref def="dt-entdecl">entity declarations</termref> or
3142 <termref def="dt-attdecl">attribute-list declarations</termref>
3143 encountered after a reference to a parameter entity that is not
3144 read, since the entity may have contained overriding declarations.
3147 <div2 id="safe-behavior">
3148 <head>Using XML Processors</head>
3149 <p>The behavior of a validating XML processor is highly predictable; it
3150 must read every piece of a document and report all well-formedness and
3151 validity violations.
3152 Less is required of a non-validating processor; it need not read any
3153 part of the document other than the document entity.
3154 This has two effects that may be important to users of XML processors:
3156 <item><p>Certain well-formedness errors, specifically those that require
3157 reading external entities, may not be detected by a non-validating processor.
3158 Examples include the constraints entitled
3159 <titleref href="wf-entdeclared">Entity Declared</titleref>,
3160 <titleref href="wf-textent">Parsed Entity</titleref>, and
3161 <titleref href="wf-norecursion">No Recursion</titleref>, as well
3162 as some of the cases described as
3163 <titleref href="forbidden">forbidden</titleref> in
3164 <specref ref="entproc"/>.</p></item>
3165 <item><p>The information passed from the processor to the application may
3166 vary, depending on whether the processor reads
3167 parameter and external entities.
3168 For example, a non-validating processor may not
3169 <titleref href="AVNormalize">normalize</titleref> attribute values,
3170 <titleref href="included">include</titleref> the replacement text of
3171 internal entities, or supply
3172 <titleref href="sec-attr-defaults">default attribute values</titleref>,
3173 where doing so depends on having read declarations in
3174 external or parameter entities.</p></item>
3177 <p>For maximum reliability in interoperating between different XML
3178 processors, applications which use non-validating processors should not
3179 rely on any behaviors not required of such processors.
3180 Applications which require facilities such as the use of default
3181 attributes or internal entities which are declared in external
3182 entities should use validating XML processors.</p>
3186 <div1 id="sec-notation">
3187 <head>Notation</head>
3189 <p>The formal grammar of XML is given in this specification using a simple
3190 Extended Backus-Naur Form (EBNF) notation. Each rule in the grammar defines
3191 one symbol, in the form
3192 <eg>symbol ::= expression</eg></p>
3193 <p>Symbols are written with an initial capital letter if they are
3194 defined by a regular expression, or with an initial lower case letter
3196 Literal strings are quoted.
3200 <p>Within the expression on the right-hand side of a rule, the following
3201 expressions are used to match strings of one or more characters:
3204 <label><code>#xN</code></label>
3205 <def><p>where <code>N</code> is a hexadecimal integer, the
3206 expression matches the character in ISO/IEC 10646 whose canonical
3208 code value, when interpreted as an unsigned binary number, has
3209 the value indicated. The number of leading zeros in the
3210 <code>#xN</code> form is insignificant; the number of leading
3211 zeros in the corresponding code value
3212 is governed by the character
3213 encoding in use and is not significant for XML.</p></def>
3216 <label><code>[a-zA-Z]</code>, <code>[#xN-#xN]</code></label>
3217 <def><p>matches any <termref def="dt-character">character</termref>
3218 with a value in the range(s) indicated (inclusive).</p></def>
3221 <label><code>[^a-z]</code>, <code>[^#xN-#xN]</code></label>
3222 <def><p>matches any <termref def="dt-character">character</termref>
3223 with a value <emph>outside</emph> the
3224 range indicated.</p></def>
3227 <label><code>[^abc]</code>, <code>[^#xN#xN#xN]</code></label>
3228 <def><p>matches any <termref def="dt-character">character</termref>
3229 with a value not among the characters given.</p></def>
3232 <label><code>"string"</code></label>
3233 <def><p>matches a literal string <termref def="dt-match">matching</termref>
3234 that given inside the double quotes.</p></def>
3237 <label><code>'string'</code></label>
3238 <def><p>matches a literal string <termref def="dt-match">matching</termref>
3239 that given inside the single quotes.</p></def>
3242 These symbols may be combined to match more complex patterns as follows,
3243 where <code>A</code> and <code>B</code> represent simple expressions:
3246 <label>(<code>expression</code>)</label>
3247 <def><p><code>expression</code> is treated as a unit
3248 and may be combined as described in this list.</p></def>
3251 <label><code>A?</code></label>
3252 <def><p>matches <code>A</code> or nothing; optional <code>A</code>.</p></def>
3255 <label><code>A B</code></label>
3256 <def><p>matches <code>A</code> followed by <code>B</code>.</p></def>
3259 <label><code>A | B</code></label>
3260 <def><p>matches <code>A</code> or <code>B</code> but not both.</p></def>
3263 <label><code>A - B</code></label>
3264 <def><p>matches any string that matches <code>A</code> but does not match
3269 <label><code>A+</code></label>
3270 <def><p>matches one or more occurrences of <code>A</code>.</p></def>
3273 <label><code>A*</code></label>
3274 <def><p>matches zero or more occurrences of <code>A</code>.</p></def>
3278 Other notations used in the productions are:
3281 <label><code>/* ... */</code></label>
3282 <def><p>comment.</p></def>
3285 <label><code>[ wfc: ... ]</code></label>
3286 <def><p>well-formedness constraint; this identifies by name a
3288 <termref def="dt-wellformed">well-formed</termref> documents
3289 associated with a production.</p></def>
3292 <label><code>[ vc: ... ]</code></label>
3293 <def><p>validity constraint; this identifies by name a constraint on
3294 <termref def="dt-valid">valid</termref> documents associated with
3295 a production.</p></def>
3306 <div1 id="sec-bibliography">
3308 <head>References</head>
3309 <div2 id="sec-existing-stds">
3310 <head>Normative References</head>
3313 <bibl id="IANA" key="IANA">
3314 (Internet Assigned Numbers Authority) <emph>Official Names for
3315 Character Sets</emph>,
3316 ed. Keld Simonsen et al.
3317 See <loc href="ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets">ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets</loc>.
3320 <bibl id="RFC1766" key="IETF RFC 1766">
3321 IETF (Internet Engineering Task Force).
3322 <emph>RFC 1766: Tags for the Identification of Languages</emph>,
3327 <bibl id="ISO639" key="ISO 639">
3328 (International Organization for Standardization).
3329 <emph>ISO 639:1988 (E).
3330 Code for the representation of names of languages.</emph>
3331 [Geneva]: International Organization for
3332 Standardization, 1988.</bibl>
3334 <bibl id="ISO3166" key="ISO 3166">
3335 (International Organization for Standardization).
3336 <emph>ISO 3166-1:1997 (E).
3337 Codes for the representation of names of countries and their subdivisions
3338 — Part 1: Country codes</emph>
3339 [Geneva]: International Organization for
3340 Standardization, 1997.</bibl>
3342 <bibl id="ISO10646" key="ISO/IEC 10646">ISO
3343 (International Organization for Standardization).
3344 <emph>ISO/IEC 10646-1993 (E). Information technology — Universal
3345 Multiple-Octet Coded Character Set (UCS) — Part 1:
3346 Architecture and Basic Multilingual Plane.</emph>
3347 [Geneva]: International Organization for
3348 Standardization, 1993 (plus amendments AM 1 through AM 7).
3351 <bibl id="Unicode" key="Unicode">The Unicode Consortium.
3352 <emph>The Unicode Standard, Version 2.0.</emph>
3353 Reading, Mass.: Addison-Wesley Developers Press, 1996.</bibl>
3359 <div2><head>Other References</head>
3363 <bibl id="Aho" key="Aho/Ullman">Aho, Alfred V.,
3364 Ravi Sethi, and Jeffrey D. Ullman.
3365 <emph>Compilers: Principles, Techniques, and Tools</emph>.
3366 Reading: Addison-Wesley, 1986, rpt. corr. 1988.</bibl>
3368 <bibl id="Berners-Lee" xml-link="simple" key="Berners-Lee et al.">
3369 Berners-Lee, T., R. Fielding, and L. Masinter.
3370 <emph>Uniform Resource Identifiers (URI): Generic Syntax and
3373 (Work in progress; see updates to RFC1738.)</bibl>
3375 <bibl id="ABK" key="Brüggemann-Klein">Brüggemann-Klein, Anne.
3376 <emph>Regular Expressions into Finite Automata</emph>.
3377 Extended abstract in I. Simon, Hrsg., LATIN 1992,
3378 S. 97-98. Springer-Verlag, Berlin 1992.
3379 Full Version in Theoretical Computer Science 120: 197-213, 1993.
3383 <bibl id="ABKDW" key="Brüggemann-Klein and Wood">Brüggemann-Klein, Anne,
3385 <emph>Deterministic Regular Languages</emph>.
3386 Universität Freiburg, Institut für Informatik,
3387 Bericht 38, Oktober 1991.
3390 <bibl id="Clark" key="Clark">James Clark.
3391 Comparison of SGML and XML. See
3392 <loc href="http://www.w3.org/TR/NOTE-sgml-xml-971215">http://www.w3.org/TR/NOTE-sgml-xml-971215</loc>.
3394 <bibl id="RFC1738" xml-link="simple" key="IETF RFC1738">
3395 IETF (Internet Engineering Task Force).
3396 <emph>RFC 1738: Uniform Resource Locators (URL)</emph>,
3397 ed. T. Berners-Lee, L. Masinter, M. McCahill.
3401 <bibl id="RFC1808" xml-link="simple" key="IETF RFC1808">
3402 IETF (Internet Engineering Task Force).
3403 <emph>RFC 1808: Relative Uniform Resource Locators</emph>,
3408 <bibl id="RFC2141" xml-link="simple" key="IETF RFC2141">
3409 IETF (Internet Engineering Task Force).
3410 <emph>RFC 2141: URN Syntax</emph>,
3415 <bibl id="ISO8879" key="ISO 8879">ISO
3416 (International Organization for Standardization).
3417 <emph>ISO 8879:1986(E). Information processing — Text and Office
3418 Systems — Standard Generalized Markup Language (SGML).</emph> First
3419 edition — 1986-10-15. [Geneva]: International Organization for
3420 Standardization, 1986.
3424 <bibl id="ISO10744" key="ISO/IEC 10744">ISO
3425 (International Organization for Standardization).
3426 <emph>ISO/IEC 10744-1992 (E). Information technology —
3427 Hypermedia/Time-based Structuring Language (HyTime).
3429 [Geneva]: International Organization for
3430 Standardization, 1992.
3431 <emph>Extended Facilities Annexe.</emph>
3432 [Geneva]: International Organization for
3433 Standardization, 1996.
3441 <div1 id="CharClasses">
3442 <head>Character Classes</head>
3443 <p>Following the characteristics defined in the Unicode standard,
3444 characters are classed as base characters (among others, these
3445 contain the alphabetic characters of the Latin alphabet, without
3446 diacritics), ideographic characters, and combining characters (among
3447 others, this class contains most diacritics); these classes combine
3448 to form the class of letters. Digits and extenders are
3450 <scrap lang="ebnf" id="CHARACTERS">
3451 <head>Characters</head>
3452 <prodgroup pcw3="3" pcw4="15">
3453 <prod id="NT-Letter"><lhs>Letter</lhs>
3454 <rhs><nt def="NT-BaseChar">BaseChar</nt>
3455 | <nt def="NT-Ideographic">Ideographic</nt></rhs> </prod>
3456 <prod id="NT-BaseChar"><lhs>BaseChar</lhs>
3457 <rhs>[#x0041-#x005A]
3458 | [#x0061-#x007A]
3459 | [#x00C0-#x00D6]
3460 | [#x00D8-#x00F6]
3461 | [#x00F8-#x00FF]
3462 | [#x0100-#x0131]
3463 | [#x0134-#x013E]
3464 | [#x0141-#x0148]
3465 | [#x014A-#x017E]
3466 | [#x0180-#x01C3]
3467 | [#x01CD-#x01F0]
3468 | [#x01F4-#x01F5]
3469 | [#x01FA-#x0217]
3470 | [#x0250-#x02A8]
3471 | [#x02BB-#x02C1]
3473 | [#x0388-#x038A]
3475 | [#x038E-#x03A1]
3476 | [#x03A3-#x03CE]
3477 | [#x03D0-#x03D6]
3482 | [#x03E2-#x03F3]
3483 | [#x0401-#x040C]
3484 | [#x040E-#x044F]
3485 | [#x0451-#x045C]
3486 | [#x045E-#x0481]
3487 | [#x0490-#x04C4]
3488 | [#x04C7-#x04C8]
3489 | [#x04CB-#x04CC]
3490 | [#x04D0-#x04EB]
3491 | [#x04EE-#x04F5]
3492 | [#x04F8-#x04F9]
3493 | [#x0531-#x0556]
3495 | [#x0561-#x0586]
3496 | [#x05D0-#x05EA]
3497 | [#x05F0-#x05F2]
3498 | [#x0621-#x063A]
3499 | [#x0641-#x064A]
3500 | [#x0671-#x06B7]
3501 | [#x06BA-#x06BE]
3502 | [#x06C0-#x06CE]
3503 | [#x06D0-#x06D3]
3505 | [#x06E5-#x06E6]
3506 | [#x0905-#x0939]
3508 | [#x0958-#x0961]
3509 | [#x0985-#x098C]
3510 | [#x098F-#x0990]
3511 | [#x0993-#x09A8]
3512 | [#x09AA-#x09B0]
3514 | [#x09B6-#x09B9]
3515 | [#x09DC-#x09DD]
3516 | [#x09DF-#x09E1]
3517 | [#x09F0-#x09F1]
3518 | [#x0A05-#x0A0A]
3519 | [#x0A0F-#x0A10]
3520 | [#x0A13-#x0A28]
3521 | [#x0A2A-#x0A30]
3522 | [#x0A32-#x0A33]
3523 | [#x0A35-#x0A36]
3524 | [#x0A38-#x0A39]
3525 | [#x0A59-#x0A5C]
3527 | [#x0A72-#x0A74]
3528 | [#x0A85-#x0A8B]
3530 | [#x0A8F-#x0A91]
3531 | [#x0A93-#x0AA8]
3532 | [#x0AAA-#x0AB0]
3533 | [#x0AB2-#x0AB3]
3534 | [#x0AB5-#x0AB9]
3537 | [#x0B05-#x0B0C]
3538 | [#x0B0F-#x0B10]
3539 | [#x0B13-#x0B28]
3540 | [#x0B2A-#x0B30]
3541 | [#x0B32-#x0B33]
3542 | [#x0B36-#x0B39]
3544 | [#x0B5C-#x0B5D]
3545 | [#x0B5F-#x0B61]
3546 | [#x0B85-#x0B8A]
3547 | [#x0B8E-#x0B90]
3548 | [#x0B92-#x0B95]
3549 | [#x0B99-#x0B9A]
3551 | [#x0B9E-#x0B9F]
3552 | [#x0BA3-#x0BA4]
3553 | [#x0BA8-#x0BAA]
3554 | [#x0BAE-#x0BB5]
3555 | [#x0BB7-#x0BB9]
3556 | [#x0C05-#x0C0C]
3557 | [#x0C0E-#x0C10]
3558 | [#x0C12-#x0C28]
3559 | [#x0C2A-#x0C33]
3560 | [#x0C35-#x0C39]
3561 | [#x0C60-#x0C61]
3562 | [#x0C85-#x0C8C]
3563 | [#x0C8E-#x0C90]
3564 | [#x0C92-#x0CA8]
3565 | [#x0CAA-#x0CB3]
3566 | [#x0CB5-#x0CB9]
3568 | [#x0CE0-#x0CE1]
3569 | [#x0D05-#x0D0C]
3570 | [#x0D0E-#x0D10]
3571 | [#x0D12-#x0D28]
3572 | [#x0D2A-#x0D39]
3573 | [#x0D60-#x0D61]
3574 | [#x0E01-#x0E2E]
3576 | [#x0E32-#x0E33]
3577 | [#x0E40-#x0E45]
3578 | [#x0E81-#x0E82]
3580 | [#x0E87-#x0E88]
3583 | [#x0E94-#x0E97]
3584 | [#x0E99-#x0E9F]
3585 | [#x0EA1-#x0EA3]
3588 | [#x0EAA-#x0EAB]
3589 | [#x0EAD-#x0EAE]
3591 | [#x0EB2-#x0EB3]
3593 | [#x0EC0-#x0EC4]
3594 | [#x0F40-#x0F47]
3595 | [#x0F49-#x0F69]
3596 | [#x10A0-#x10C5]
3597 | [#x10D0-#x10F6]
3599 | [#x1102-#x1103]
3600 | [#x1105-#x1107]
3602 | [#x110B-#x110C]
3603 | [#x110E-#x1112]
3610 | [#x1154-#x1155]
3612 | [#x115F-#x1161]
3617 | [#x116D-#x116E]
3618 | [#x1172-#x1173]
3623 | [#x11AE-#x11AF]
3624 | [#x11B7-#x11B8]
3626 | [#x11BC-#x11C2]
3630 | [#x1E00-#x1E9B]
3631 | [#x1EA0-#x1EF9]
3632 | [#x1F00-#x1F15]
3633 | [#x1F18-#x1F1D]
3634 | [#x1F20-#x1F45]
3635 | [#x1F48-#x1F4D]
3636 | [#x1F50-#x1F57]
3640 | [#x1F5F-#x1F7D]
3641 | [#x1F80-#x1FB4]
3642 | [#x1FB6-#x1FBC]
3644 | [#x1FC2-#x1FC4]
3645 | [#x1FC6-#x1FCC]
3646 | [#x1FD0-#x1FD3]
3647 | [#x1FD6-#x1FDB]
3648 | [#x1FE0-#x1FEC]
3649 | [#x1FF2-#x1FF4]
3650 | [#x1FF6-#x1FFC]
3652 | [#x212A-#x212B]
3654 | [#x2180-#x2182]
3655 | [#x3041-#x3094]
3656 | [#x30A1-#x30FA]
3657 | [#x3105-#x312C]
3658 | [#xAC00-#xD7A3]
3660 <prod id="NT-Ideographic"><lhs>Ideographic</lhs>
3661 <rhs>[#x4E00-#x9FA5]
3663 | [#x3021-#x3029]
3665 <prod id="NT-CombiningChar"><lhs>CombiningChar</lhs>
3666 <rhs>[#x0300-#x0345]
3667 | [#x0360-#x0361]
3668 | [#x0483-#x0486]
3669 | [#x0591-#x05A1]
3670 | [#x05A3-#x05B9]
3671 | [#x05BB-#x05BD]
3673 | [#x05C1-#x05C2]
3675 | [#x064B-#x0652]
3677 | [#x06D6-#x06DC]
3678 | [#x06DD-#x06DF]
3679 | [#x06E0-#x06E4]
3680 | [#x06E7-#x06E8]
3681 | [#x06EA-#x06ED]
3682 | [#x0901-#x0903]
3684 | [#x093E-#x094C]
3686 | [#x0951-#x0954]
3687 | [#x0962-#x0963]
3688 | [#x0981-#x0983]
3692 | [#x09C0-#x09C4]
3693 | [#x09C7-#x09C8]
3694 | [#x09CB-#x09CD]
3696 | [#x09E2-#x09E3]
3701 | [#x0A40-#x0A42]
3702 | [#x0A47-#x0A48]
3703 | [#x0A4B-#x0A4D]
3704 | [#x0A70-#x0A71]
3705 | [#x0A81-#x0A83]
3707 | [#x0ABE-#x0AC5]
3708 | [#x0AC7-#x0AC9]
3709 | [#x0ACB-#x0ACD]
3710 | [#x0B01-#x0B03]
3712 | [#x0B3E-#x0B43]
3713 | [#x0B47-#x0B48]
3714 | [#x0B4B-#x0B4D]
3715 | [#x0B56-#x0B57]
3716 | [#x0B82-#x0B83]
3717 | [#x0BBE-#x0BC2]
3718 | [#x0BC6-#x0BC8]
3719 | [#x0BCA-#x0BCD]
3721 | [#x0C01-#x0C03]
3722 | [#x0C3E-#x0C44]
3723 | [#x0C46-#x0C48]
3724 | [#x0C4A-#x0C4D]
3725 | [#x0C55-#x0C56]
3726 | [#x0C82-#x0C83]
3727 | [#x0CBE-#x0CC4]
3728 | [#x0CC6-#x0CC8]
3729 | [#x0CCA-#x0CCD]
3730 | [#x0CD5-#x0CD6]
3731 | [#x0D02-#x0D03]
3732 | [#x0D3E-#x0D43]
3733 | [#x0D46-#x0D48]
3734 | [#x0D4A-#x0D4D]
3737 | [#x0E34-#x0E3A]
3738 | [#x0E47-#x0E4E]
3740 | [#x0EB4-#x0EB9]
3741 | [#x0EBB-#x0EBC]
3742 | [#x0EC8-#x0ECD]
3743 | [#x0F18-#x0F19]
3749 | [#x0F71-#x0F84]
3750 | [#x0F86-#x0F8B]
3751 | [#x0F90-#x0F95]
3753 | [#x0F99-#x0FAD]
3754 | [#x0FB1-#x0FB7]
3756 | [#x20D0-#x20DC]
3758 | [#x302A-#x302F]
3762 <prod id="NT-Digit"><lhs>Digit</lhs>
3763 <rhs>[#x0030-#x0039]
3764 | [#x0660-#x0669]
3765 | [#x06F0-#x06F9]
3766 | [#x0966-#x096F]
3767 | [#x09E6-#x09EF]
3768 | [#x0A66-#x0A6F]
3769 | [#x0AE6-#x0AEF]
3770 | [#x0B66-#x0B6F]
3771 | [#x0BE7-#x0BEF]
3772 | [#x0C66-#x0C6F]
3773 | [#x0CE6-#x0CEF]
3774 | [#x0D66-#x0D6F]
3775 | [#x0E50-#x0E59]
3776 | [#x0ED0-#x0ED9]
3777 | [#x0F20-#x0F29]
3779 <prod id="NT-Extender"><lhs>Extender</lhs>
3788 | [#x3031-#x3035]
3789 | [#x309D-#x309E]
3790 | [#x30FC-#x30FE]
3796 <p>The character classes defined here can be derived from the
3797 Unicode character database as follows:
3800 <p>Name start characters must have one of the categories Ll, Lu,
3804 <p>Name characters other than Name-start characters
3805 must have one of the categories Mc, Me, Mn, Lm, or Nd.</p>
3808 <p>Characters in the compatibility area (i.e. with character code
3809 greater than #xF900 and less than #xFFFE) are not allowed in XML
3813 <p>Characters which have a font or compatibility decomposition (i.e. those
3814 with a "compatibility formatting tag" in field 5 of the database --
3815 marked by field 5 beginning with a "<") are not allowed.</p>
3818 <p>The following characters are treated as name-start characters
3819 rather than name characters, because the property file classifies
3820 them as Alphabetic: [#x02BB-#x02C1], #x0559, #x06E5, #x06E6.</p>
3823 <p>Characters #x20DD-#x20E0 are excluded (in accordance with
3824 Unicode, section 5.14).</p>
3827 <p>Character #x00B7 is classified as an extender, because the
3828 property list so identifies it.</p>
3831 <p>Character #x0387 is added as a name character, because #x00B7
3832 is its canonical equivalent.</p>
3835 <p>Characters ':' and '_' are allowed as name-start characters.</p>
3838 <p>Characters '-' and '.' are allowed as name characters.</p>
3843 <inform-div1 id="sec-xml-and-sgml">
3844 <head>XML and SGML</head>
3846 <p>XML is designed to be a subset of SGML, in that every
3847 <termref def="dt-valid">valid</termref> XML document should also be a
3848 conformant SGML document.
3849 For a detailed comparison of the additional restrictions that XML places on
3850 documents beyond those of SGML, see <bibref ref="Clark"/>.
3853 <inform-div1 id="sec-entexpand">
3854 <head>Expansion of Entity and Character References</head>
3855 <p>This appendix contains some examples illustrating the
3856 sequence of entity- and character-reference recognition and
3857 expansion, as specified in <specref ref="entproc"/>.</p>
3859 If the DTD contains the declaration
3860 <eg><![CDATA[<!ENTITY example "<p>An ampersand (&#38;) may be escaped
3861 numerically (&#38;#38;) or with a general entity
3864 then the XML processor will recognize the character references
3865 when it parses the entity declaration, and resolve them before
3866 storing the following string as the
3867 value of the entity "<code>example</code>":
3868 <eg><![CDATA[<p>An ampersand (&) may be escaped
3869 numerically (&#38;) or with a general entity
3872 A reference in the document to "<code>&example;</code>"
3873 will cause the text to be reparsed, at which time the
3874 start- and end-tags of the "<code>p</code>" element will be recognized
3875 and the three references will be recognized and expanded,
3876 resulting in a "<code>p</code>" element with the following content
3877 (all data, no delimiters or markup):
3878 <eg><![CDATA[An ampersand (&) may be escaped
3879 numerically (&) or with a general entity
3883 <p>A more complex example will illustrate the rules and their
3884 effects fully. In the following example, the line numbers are
3885 solely for reference.
3886 <eg><![CDATA[1 <?xml version='1.0'?>
3888 3 <!ELEMENT test (#PCDATA) >
3889 4 <!ENTITY % xx '%zz;'>
3890 5 <!ENTITY % zz '<!ENTITY tricky "error-prone" >' >
3893 8 <test>This sample shows a &tricky; method.</test>
3895 This produces the following:
3896 <ulist spacing="compact">
3897 <item><p>in line 4, the reference to character 37 is expanded immediately,
3898 and the parameter entity "<code>xx</code>" is stored in the symbol
3899 table with the value "<code>%zz;</code>". Since the replacement text
3900 is not rescanned, the reference to parameter entity "<code>zz</code>"
3901 is not recognized. (And it would be an error if it were, since
3902 "<code>zz</code>" is not yet declared.)</p></item>
3903 <item><p>in line 5, the character reference "<code>&#60;</code>" is
3904 expanded immediately and the parameter entity "<code>zz</code>" is
3905 stored with the replacement text
3906 "<code><!ENTITY tricky "error-prone" ></code>",
3907 which is a well-formed entity declaration.</p></item>
3908 <item><p>in line 6, the reference to "<code>xx</code>" is recognized,
3909 and the replacement text of "<code>xx</code>" (namely
3910 "<code>%zz;</code>") is parsed. The reference to "<code>zz</code>"
3911 is recognized in its turn, and its replacement text
3912 ("<code><!ENTITY tricky "error-prone" ></code>") is parsed.
3913 The general entity "<code>tricky</code>" has now been
3914 declared, with the replacement text "<code>error-prone</code>".</p></item>
3916 in line 8, the reference to the general entity "<code>tricky</code>" is
3917 recognized, and it is expanded, so the full content of the
3918 "<code>test</code>" element is the self-describing (and ungrammatical) string
3919 <emph>This sample shows a error-prone method.</emph>
3924 <inform-div1 id="determinism">
3925 <head>Deterministic Content Models</head>
3926 <p><termref def="dt-compat">For compatibility</termref>, it is
3928 that content models in element type declarations be deterministic.
3930 <!-- FINAL EDIT: WebSGML allows ambiguity? -->
3932 requires deterministic content models (it calls them
3933 "unambiguous"); XML processors built using SGML systems may
3934 flag non-deterministic content models as errors.</p>
3935 <p>For example, the content model <code>((b, c) | (b, d))</code> is
3936 non-deterministic, because given an initial <code>b</code> the parser
3937 cannot know which <code>b</code> in the model is being matched without
3938 looking ahead to see which element follows the <code>b</code>.
3939 In this case, the two references to
3940 <code>b</code> can be collapsed
3941 into a single reference, making the model read
3942 <code>(b, (c | d))</code>. An initial <code>b</code> now clearly
3943 matches only a single name in the content model. The parser doesn't
3944 need to look ahead to see what follows; either <code>c</code> or
3945 <code>d</code> would be accepted.</p>
3946 <p>More formally: a finite state automaton may be constructed from the
3947 content model using the standard algorithms, e.g. algorithm 3.5
3949 of Aho, Sethi, and Ullman <bibref ref="Aho"/>.
3950 In many such algorithms, a follow set is constructed for each
3951 position in the regular expression (i.e., each leaf
3953 syntax tree for the regular expression);
3954 if any position has a follow set in which
3955 more than one following position is
3956 labeled with the same element type name,
3957 then the content model is in error
3958 and may be reported as an error.
3960 <p>Algorithms exist which allow many but not all non-deterministic
3961 content models to be reduced automatically to equivalent deterministic
3962 models; see Brüggemann-Klein 1991 <bibref ref="ABK"/>.</p>
3964 <inform-div1 id="sec-guessing">
3965 <head>Autodetection of Character Encodings</head>
3966 <p>The XML encoding declaration functions as an internal label on each
3967 entity, indicating which character encoding is in use. Before an XML
3968 processor can read the internal label, however, it apparently has to
3969 know what character encoding is in use—which is what the internal label
3970 is trying to indicate. In the general case, this is a hopeless
3971 situation. It is not entirely hopeless in XML, however, because XML
3972 limits the general case in two ways: each implementation is assumed
3973 to support only a finite set of character encodings, and the XML
3974 encoding declaration is restricted in position and content in order to
3975 make it feasible to autodetect the character encoding in use in each
3976 entity in normal cases. Also, in many cases other sources of information
3977 are available in addition to the XML data stream itself.
3978 Two cases may be distinguished,
3979 depending on whether the XML entity is presented to the
3980 processor without, or with, any accompanying
3981 (external) information. We consider the first case first.
3984 Because each XML entity not in UTF-8 or UTF-16 format <emph>must</emph>
3985 begin with an XML encoding declaration, in which the first characters
3986 must be '<code><?xml</code>', any conforming processor can detect,
3987 after two to four octets of input, which of the following cases apply.
3988 In reading this list, it may help to know that in UCS-4, '<' is
3989 "<code>#x0000003C</code>" and '?' is "<code>#x0000003F</code>", and the Byte
3990 Order Mark required of UTF-16 data streams is "<code>#xFEFF</code>".</p>
3994 <p><code>00 00 00 3C</code>: UCS-4, big-endian machine (1234 order)</p>
3997 <p><code>3C 00 00 00</code>: UCS-4, little-endian machine (4321 order)</p>
4000 <p><code>00 00 3C 00</code>: UCS-4, unusual octet order (2143)</p>
4003 <p><code>00 3C 00 00</code>: UCS-4, unusual octet order (3412)</p>
4006 <p><code>FE FF</code>: UTF-16, big-endian</p>
4009 <p><code>FF FE</code>: UTF-16, little-endian</p>
4012 <p><code>00 3C 00 3F</code>: UTF-16, big-endian, no Byte Order Mark
4013 (and thus, strictly speaking, in error)</p>
4016 <p><code>3C 00 3F 00</code>: UTF-16, little-endian, no Byte Order Mark
4017 (and thus, strictly speaking, in error)</p>
4020 <p><code>3C 3F 78 6D</code>: UTF-8, ISO 646, ASCII, some part of ISO 8859,
4021 Shift-JIS, EUC, or any other 7-bit, 8-bit, or mixed-width encoding
4022 which ensures that the characters of ASCII have their normal positions,
4024 and values; the actual encoding declaration must be read to
4025 detect which of these applies, but since all of these encodings
4026 use the same bit patterns for the ASCII characters, the encoding
4027 declaration itself may be read reliably
4031 <p><code>4C 6F A7 94</code>: EBCDIC (in some flavor; the full
4032 encoding declaration must be read to tell which code page is in
4036 <p>other: UTF-8 without an encoding declaration, or else
4037 the data stream is corrupt, fragmentary, or enclosed in
4038 a wrapper of some kind</p>
4043 This level of autodetection is enough to read the XML encoding
4044 declaration and parse the character-encoding identifier, which is
4045 still necessary to distinguish the individual members of each family
4046 of encodings (e.g. to tell UTF-8 from 8859, and the parts of 8859
4047 from each other, or to distinguish the specific EBCDIC code page in
4051 Because the contents of the encoding declaration are restricted to
4052 ASCII characters, a processor can reliably read the entire encoding
4053 declaration as soon as it has detected which family of encodings is in
4054 use. Since in practice, all widely used character encodings fall into
4055 one of the categories above, the XML encoding declaration allows
4056 reasonably reliable in-band labeling of character encodings, even when
4057 external sources of information at the operating-system or
4058 transport-protocol level are unreliable.
4061 Once the processor has detected the character encoding in use, it can
4062 act appropriately, whether by invoking a separate input routine for
4063 each case, or by calling the proper conversion function on each
4067 Like any self-labeling system, the XML encoding declaration will not
4068 work if any software changes the entity's character set or encoding
4069 without updating the encoding declaration. Implementors of
4070 character-encoding routines should be careful to ensure the accuracy
4071 of the internal and external information used to label the entity.
4073 <p>The second possible case occurs when the XML entity is accompanied
4074 by encoding information, as in some file systems and some network
4076 When multiple sources of information are available,
4079 priority and the preferred method of handling conflict should be
4080 specified as part of the higher-level protocol used to deliver XML.
4081 Rules for the relative priority of the internal label and the
4082 MIME-type label in an external header, for example, should be part of the
4083 RFC document defining the text/xml and application/xml MIME types. In
4084 the interests of interoperability, however, the following rules
4087 <item><p>If an XML entity is in a file, the Byte-Order Mark
4088 and encoding-declaration PI are used (if present) to determine the
4089 character encoding. All other heuristics and sources of information
4090 are solely for error recovery.
4092 <item><p>If an XML entity is delivered with a
4093 MIME type of text/xml, then the <code>charset</code> parameter
4094 on the MIME type determines the
4095 character encoding method; all other heuristics and sources of
4096 information are solely for error recovery.
4098 <item><p>If an XML entity is delivered
4100 MIME type of application/xml, then the Byte-Order Mark and
4101 encoding-declaration PI are used (if present) to determine the
4102 character encoding. All other heuristics and sources of
4103 information are solely for error recovery.
4106 These rules apply only in the absence of protocol-level documentation;
4107 in particular, when the MIME types text/xml and application/xml are
4108 defined, the recommendations of the relevant RFC will supersede
4114 <inform-div1 id="sec-xml-wg">
4115 <head>W3C XML Working Group</head>
4117 <p>This specification was prepared and approved for publication by the
4118 W3C XML Working Group (WG). WG approval of this specification does
4119 not necessarily imply that all WG members voted for its approval.
4120 The current and former members of the XML WG are:</p>
4123 <member><name>Jon Bosak, Sun</name><role>Chair</role></member>
4124 <member><name>James Clark</name><role>Technical Lead</role></member>
4125 <member><name>Tim Bray, Textuality and Netscape</name><role>XML Co-editor</role></member>
4126 <member><name>Jean Paoli, Microsoft</name><role>XML Co-editor</role></member>
4127 <member><name>C. M. Sperberg-McQueen, U. of Ill.</name><role>XML
4128 Co-editor</role></member>
4129 <member><name>Dan Connolly, W3C</name><role>W3C Liaison</role></member>
4130 <member><name>Paula Angerstein, Texcel</name></member>
4131 <member><name>Steve DeRose, INSO</name></member>
4132 <member><name>Dave Hollander, HP</name></member>
4133 <member><name>Eliot Kimber, ISOGEN</name></member>
4134 <member><name>Eve Maler, ArborText</name></member>
4135 <member><name>Tom Magliery, NCSA</name></member>
4136 <member><name>Murray Maloney, Muzmo and Grif</name></member>
4137 <member><name>Makoto Murata, Fuji Xerox Information Systems</name></member>
4138 <member><name>Joel Nava, Adobe</name></member>
4139 <member><name>Conleth O'Connell, Vignette</name></member>
4140 <member><name>Peter Sharpe, SoftQuad</name></member>
4141 <member><name>John Tigue, DataChannel</name></member>
4147 <!-- Keep this comment at the end of the file
4150 sgml-default-dtd-file:"~/sgml/spec.ced"