1<?xml version='1.0' encoding='ISO-8859-1' standalone='no'?> 2<!DOCTYPE spec SYSTEM "spec.dtd" [ 3 4<!-- LAST TOUCHED BY: Tim Bray, 8 February 1997 --> 5 6<!-- The words 'FINAL EDIT' in comments mark places where changes 7need to be made after approval of the document by the ERB, before 8publication. --> 9 10<!ENTITY XML.version "1.0"> 11<!ENTITY doc.date "10 February 1998"> 12<!ENTITY iso6.doc.date "19980210"> 13<!ENTITY w3c.doc.date "02-Feb-1998"> 14<!ENTITY draft.day '10'> 15<!ENTITY draft.month 'February'> 16<!ENTITY draft.year '1998'> 17 18<!ENTITY WebSGML 19 'WebSGML Adaptations Annex to ISO 8879'> 20 21<!ENTITY lt "<"> 22<!ENTITY gt ">"> 23<!ENTITY xmlpio "'<?xml'"> 24<!ENTITY pic "'?>'"> 25<!ENTITY br "\n"> 26<!ENTITY cellback '#c0d9c0'> 27<!ENTITY mdash "--"> <!-- —, but nsgmls doesn't grok hex --> 28<!ENTITY com "--"> 29<!ENTITY como "--"> 30<!ENTITY comc "--"> 31<!ENTITY hcro "&#x"> 32<!-- <!ENTITY nbsp "�"> --> 33<!ENTITY nbsp " "> 34<!ENTITY magicents "<code>amp</code>, 35<code>lt</code>, 36<code>gt</code>, 37<code>apos</code>, 38<code>quot</code>"> 39 40<!-- audience and distribution status: for use at publication time --> 41<!ENTITY doc.audience "public review and discussion"> 42<!ENTITY doc.distribution "may be distributed freely, as long as 43all text and legal notices remain intact"> 44 45]> 46 47<!-- for Panorama *--> 48<?VERBATIM "eg" ?> 49 50<spec> 51<header> 52<title>Extensible Markup Language (XML) 1.0</title> 53<version></version> 54<w3c-designation>REC-xml-&iso6.doc.date;</w3c-designation> 55<w3c-doctype>W3C Recommendation</w3c-doctype> 56<pubdate><day>&draft.day;</day><month>&draft.month;</month><year>&draft.year;</year></pubdate> 57 58<publoc> 59<loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;"> 60http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;</loc> 61<loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.xml"> 62http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.xml</loc> 63<loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.html"> 64http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.html</loc> 65<loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.pdf"> 66http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.pdf</loc> 67<loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.ps"> 68http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.ps</loc> 69</publoc> 70<latestloc> 71<loc href="http://www.w3.org/TR/REC-xml"> 72http://www.w3.org/TR/REC-xml</loc> 73</latestloc> 74<prevlocs> 75<loc href="http://www.w3.org/TR/PR-xml-971208"> 76http://www.w3.org/TR/PR-xml-971208</loc> 77<!-- 78<loc href='http://www.w3.org/TR/WD-xml-961114'> 79http://www.w3.org/TR/WD-xml-961114</loc> 80<loc href='http://www.w3.org/TR/WD-xml-lang-970331'> 81http://www.w3.org/TR/WD-xml-lang-970331</loc> 82<loc href='http://www.w3.org/TR/WD-xml-lang-970630'> 83http://www.w3.org/TR/WD-xml-lang-970630</loc> 84<loc href='http://www.w3.org/TR/WD-xml-970807'> 85http://www.w3.org/TR/WD-xml-970807</loc> 86<loc href='http://www.w3.org/TR/WD-xml-971117'> 87http://www.w3.org/TR/WD-xml-971117</loc>--> 88</prevlocs> 89<authlist> 90<author><name>Tim Bray</name> 91<affiliation>Textuality and Netscape</affiliation> 92<email 93href="mailto:tbray@textuality.com">tbray@textuality.com</email></author> 94<author><name>Jean Paoli</name> 95<affiliation>Microsoft</affiliation> 96<email href="mailto:jeanpa@microsoft.com">jeanpa@microsoft.com</email></author> 97<author><name>C. M. Sperberg-McQueen</name> 98<affiliation>University of Illinois at Chicago</affiliation> 99<email href="mailto:cmsmcq@uic.edu">cmsmcq@uic.edu</email></author> 100</authlist> 101<abstract> 102<p>The Extensible Markup Language (XML) is a subset of 103SGML that is completely described in this document. Its goal is to 104enable generic SGML to be served, received, and processed on the Web 105in the way that is now possible with HTML. XML has been designed for 106ease of implementation and for interoperability with both SGML and 107HTML.</p> 108</abstract> 109<status> 110<p>This document has been reviewed by W3C Members and 111other interested parties and has been endorsed by the 112Director as a W3C Recommendation. It is a stable 113document and may be used as reference material or cited 114as a normative reference from another document. W3C's 115role in making the Recommendation is to draw attention 116to the specification and to promote its widespread 117deployment. This enhances the functionality and 118interoperability of the Web.</p> 119<p> 120This document specifies a syntax created by subsetting an existing, 121widely used international text processing standard (Standard 122Generalized Markup Language, ISO 8879:1986(E) as amended and 123corrected) for use on the World Wide Web. It is a product of the W3C 124XML Activity, details of which can be found at <loc 125href='http://www.w3.org/XML'>http://www.w3.org/XML</loc>. A list of 126current W3C Recommendations and other technical documents can be found 127at <loc href='http://www.w3.org/TR'>http://www.w3.org/TR</loc>. 128</p> 129<p>This specification uses the term URI, which is defined by <bibref 130ref="Berners-Lee"/>, a work in progress expected to update <bibref 131ref="RFC1738"/> and <bibref ref="RFC1808"/>. 132</p> 133<p>The list of known errors in this specification is 134available at 135<loc href='http://www.w3.org/XML/xml-19980210-errata'>http://www.w3.org/XML/xml-19980210-errata</loc>.</p> 136<p>Please report errors in this document to 137<loc href='mailto:xml-editor@w3.org'>xml-editor@w3.org</loc>. 138</p> 139</status> 140 141 142<pubstmt> 143<p>Chicago, Vancouver, Mountain View, et al.: 144World-Wide Web Consortium, XML Working Group, 1996, 1997.</p> 145</pubstmt> 146<sourcedesc> 147<p>Created in electronic form.</p> 148</sourcedesc> 149<langusage> 150<language id='EN'>English</language> 151<language id='ebnf'>Extended Backus-Naur Form (formal grammar)</language> 152</langusage> 153<revisiondesc> 154<slist> 155<sitem>1997-12-03 : CMSMcQ : yet further changes</sitem> 156<sitem>1997-12-02 : TB : further changes (see TB to XML WG, 1572 December 1997)</sitem> 158<sitem>1997-12-02 : CMSMcQ : deal with as many corrections and 159comments from the proofreaders as possible: 160entify hard-coded document date in pubdate element, 161change expansion of entity WebSGML, 162update status description as per Dan Connolly (am not sure 163about refernece to Berners-Lee et al.), 164add 'The' to abstract as per WG decision, 165move Relationship to Existing Standards to back matter and 166combine with References, 167re-order back matter so normative appendices come first, 168re-tag back matter so informative appendices are tagged informdiv1, 169remove XXX XXX from list of 'normative' specs in prose, 170move some references from Other References to Normative References, 171add RFC 1738, 1808, and 2141 to Other References (they are not 172normative since we do not require the processor to enforce any 173rules based on them), 174add reference to 'Fielding draft' (Berners-Lee et al.), 175move notation section to end of body, 176drop URIchar non-terminal and use SkipLit instead, 177lose stray reference to defunct nonterminal 'markupdecls', 178move reference to Aho et al. into appendix (Tim's right), 179add prose note saying that hash marks and fragment identifiers are 180NOT part of the URI formally speaking, and are NOT legal in 181system identifiers (processor 'may' signal an error). 182Work through: 183Tim Bray reacting to James Clark, 184Tim Bray on his own, 185Eve Maler, 186 187NOT DONE YET: 188change binary / text to unparsed / parsed. 189handle James's suggestion about < in attriubte values 190uppercase hex characters, 191namechar list, 192</sitem> 193<sitem>1997-12-01 : JB : add some column-width parameters</sitem> 194<sitem>1997-12-01 : CMSMcQ : begin round of changes to incorporate 195recent WG decisions and other corrections: 196binding sources of character encoding info (27 Aug / 3 Sept), 197correct wording of Faust quotation (restore dropped line), 198drop SDD from EncodingDecl, 199change text at version number 1.0, 200drop misleading (wrong!) sentence about ignorables and extenders, 201modify definition of PCData to make bar on msc grammatical, 202change grammar's handling of internal subset (drop non-terminal markupdecls), 203change definition of includeSect to allow conditional sections, 204add integral-declaration constraint on internal subset, 205drop misleading / dangerous sentence about relationship of 206entities with system storage objects, 207change table body tag to htbody as per EM change to DTD, 208add rule about space normalization in public identifiers, 209add description of how to generate our name-space rules from 210Unicode character database (needs further work!). 211</sitem> 212<sitem>1997-10-08 : TB : Removed %-constructs again, new rules 213for PE appearance.</sitem> 214<sitem>1997-10-01 : TB : Case-sensitive markup; cleaned up 215element-type defs, lotsa little edits for style</sitem> 216<sitem>1997-09-25 : TB : Change to elm's new DTD, with 217substantial detail cleanup as a side-effect</sitem> 218<sitem>1997-07-24 : CMSMcQ : correct error (lost *) in definition 219of ignoreSectContents (thanks to Makoto Murata)</sitem> 220<sitem>Allow all empty elements to have end-tags, consistent with 221SGML TC (as per JJC).</sitem> 222<sitem>1997-07-23 : CMSMcQ : pre-emptive strike on pending corrections: 223introduce the term 'empty-element tag', note that all empty elements 224may use it, and elements declared EMPTY must use it. 225Add WFC requiring encoding decl to come first in an entity. 226Redefine notations to point to PIs as well as binary entities. 227Change autodetection table by removing bytes 3 and 4 from 228examples with Byte Order Mark. 229Add content model as a term and clarify that it applies to both 230mixed and element content. 231</sitem> 232<sitem>1997-06-30 : CMSMcQ : change date, some cosmetic changes, 233changes to productions for choice, seq, Mixed, NotationType, 234Enumeration. Follow James Clark's suggestion and prohibit 235conditional sections in internal subset. TO DO: simplify 236production for ignored sections as a result, since we don't 237need to worry about parsers which don't expand PErefs finding 238a conditional section.</sitem> 239<sitem>1997-06-29 : TB : various edits</sitem> 240<sitem>1997-06-29 : CMSMcQ : further changes: 241Suppress old FINAL EDIT comments and some dead material. 242Revise occurrences of % in grammar to exploit Henry Thompson's pun, 243especially markupdecl and attdef. 244Remove RMD requirement relating to element content (?). 245</sitem> 246<sitem>1997-06-28 : CMSMcQ : Various changes for 1 July draft: 247Add text for draconian error handling (introduce 248the term Fatal Error). 249RE deleta est (changing wording from 250original announcement to restrict the requirement to validating 251parsers). 252Tag definition of validating processor and link to it. 253Add colon as name character. 254Change def of %operator. 255Change standard definitions of lt, gt, amp. 256Strip leading zeros from #x00nn forms.</sitem> 257<sitem>1997-04-02 : CMSMcQ : final corrections of editorial errors 258found in last night's proofreading. Reverse course once more on 259well-formed: Webster's Second hyphenates it, and that's enough 260for me.</sitem> 261<sitem>1997-04-01 : CMSMcQ : corrections from JJC, EM, HT, and self</sitem> 262<sitem>1997-03-31 : Tim Bray : many changes</sitem> 263<sitem>1997-03-29 : CMSMcQ : some Henry Thompson (on entity handling), 264some Charles Goldfarb, some ERB decisions (PE handling in miscellaneous 265declarations. Changed Ident element to accept def attribute. 266Allow normalization of Unicode characters. move def of systemliteral 267into section on literals.</sitem> 268<sitem>1997-03-28 : CMSMcQ : make as many corrections as possible, from 269Terry Allen, Norbert Mikula, James Clark, Jon Bosak, Henry Thompson, 270Paul Grosso, and self. Among other things: give in on "well formed" 271(Terry is right), tentatively rename QuotedCData as AttValue 272and Literal as EntityValue to be more informative, since attribute 273values are the <emph>only</emph> place QuotedCData was used, and 274vice versa for entity text and Literal. (I'd call it Entity Text, 275but 8879 uses that name for both internal and external entities.)</sitem> 276<sitem>1997-03-26 : CMSMcQ : resynch the two forks of this draft, reapply 277my changes dated 03-20 and 03-21. Normalize old 'may not' to 'must not' 278except in the one case where it meant 'may or may not'.</sitem> 279<sitem>1997-03-21 : TB : massive changes on plane flight from Chicago 280to Vancouver</sitem> 281<sitem>1997-03-21 : CMSMcQ : correct as many reported errors as possible. 282</sitem> 283<sitem>1997-03-20 : CMSMcQ : correct typos listed in CMSMcQ hand copy of spec.</sitem> 284<sitem>1997-03-20 : CMSMcQ : cosmetic changes preparatory to revision for 285WWW conference April 1997: restore some of the internal entity 286references (e.g. to docdate, etc.), change character xA0 to &nbsp; 287and define nbsp as &#160;, and refill a lot of paragraphs for 288legibility.</sitem> 289<sitem>1996-11-12 : CMSMcQ : revise using Tim's edits: 290Add list type of NUMBERED and change most lists either to 291BULLETS or to NUMBERED. 292Suppress QuotedNames, Names (not used). 293Correct trivial-grammar doc type decl. 294Rename 'marked section' as 'CDATA section' passim. 295Also edits from James Clark: 296Define the set of characters from which [^abc] subtracts. 297Charref should use just [0-9] not Digit. 298Location info needs cleaner treatment: remove? (ERB 299question). 300One example of a PI has wrong pic. 301Clarify discussion of encoding names. 302Encoding failure should lead to unspecified results; don't 303prescribe error recovery. 304Don't require exposure of entity boundaries. 305Ignore white space in element content. 306Reserve entity names of the form u-NNNN. 307Clarify relative URLs. 308And some of my own: 309Correct productions for content model: model cannot 310consist of a name, so "elements ::= cp" is no good. 311</sitem> 312<sitem>1996-11-11 : CMSMcQ : revise for style. 313Add new rhs to entity declaration, for parameter entities.</sitem> 314<sitem>1996-11-10 : CMSMcQ : revise for style. 315Fix / complete section on names, characters. 316Add sections on parameter entities, conditional sections. 317Still to do: Add compatibility note on deterministic content models. 318Finish stylistic revision.</sitem> 319<sitem>1996-10-31 : TB : Add Entity Handling section</sitem> 320<sitem>1996-10-30 : TB : Clean up term & termdef. Slip in 321ERB decision re EMPTY.</sitem> 322<sitem>1996-10-28 : TB : Change DTD. Implement some of Michael's 323suggestions. Change comments back to //. Introduce language for 324XML namespace reservation. Add section on white-space handling. 325Lots more cleanup.</sitem> 326<sitem>1996-10-24 : CMSMcQ : quick tweaks, implement some ERB 327decisions. Characters are not integers. Comments are /* */ not //. 328Add bibliographic refs to 10646, HyTime, Unicode. 329Rename old Cdata as MsData since it's <emph>only</emph> seen 330in marked sections. Call them attribute-value pairs not 331name-value pairs, except once. Internal subset is optional, needs 332'?'. Implied attributes should be signaled to the app, not 333have values supplied by processor.</sitem> 334<sitem>1996-10-16 : TB : track down & excise all DSD references; 335introduce some EBNF for entity declarations.</sitem> 336<sitem>1996-10-?? : TB : consistency check, fix up scraps so 337they all parse, get formatter working, correct a few productions.</sitem> 338<sitem>1996-10-10/11 : CMSMcQ : various maintenance, stylistic, and 339organizational changes: 340Replace a few literals with xmlpio and 341pic entities, to make them consistent and ensure we can change pic 342reliably when the ERB votes. 343Drop paragraph on recognizers from notation section. 344Add match, exact match to terminology. 345Move old 2.2 XML Processors and Apps into intro. 346Mention comments, PIs, and marked sections in discussion of 347delimiter escaping. 348Streamline discussion of doctype decl syntax. 349Drop old section of 'PI syntax' for doctype decl, and add 350section on partial-DTD summary PIs to end of Logical Structures 351section. 352Revise DSD syntax section to use Tim's subset-in-a-PI 353mechanism.</sitem> 354<sitem>1996-10-10 : TB : eliminate name recognizers (and more?)</sitem> 355<sitem>1996-10-09 : CMSMcQ : revise for style, consistency through 2.3 356(Characters)</sitem> 357<sitem>1996-10-09 : CMSMcQ : re-unite everything for convenience, 358at least temporarily, and revise quickly</sitem> 359<sitem>1996-10-08 : TB : first major homogenization pass</sitem> 360<sitem>1996-10-08 : TB : turn "current" attribute on div type into 361CDATA</sitem> 362<sitem>1996-10-02 : TB : remould into skeleton + entities</sitem> 363<sitem>1996-09-30 : CMSMcQ : add a few more sections prior to exchange 364 with Tim.</sitem> 365<sitem>1996-09-20 : CMSMcQ : finish transcribing notes.</sitem> 366<sitem>1996-09-19 : CMSMcQ : begin transcribing notes for draft.</sitem> 367<sitem>1996-09-13 : CMSMcQ : made outline from notes of 09-06, 368do some housekeeping</sitem> 369</slist> 370</revisiondesc> 371</header> 372<body> 373<div1 id='sec-intro'> 374<head>Introduction</head> 375<p>Extensible Markup Language, abbreviated XML, describes a class of 376data objects called <termref def="dt-xml-doc">XML documents</termref> and 377partially describes the behavior of 378computer programs which process them. XML is an application profile or 379restricted form of SGML, the Standard Generalized Markup 380Language <bibref ref='ISO8879'/>. 381By construction, XML documents 382are conforming SGML documents. 383</p> 384<p>XML documents are made up of storage units called <termref 385def="dt-entity">entities</termref>, which contain either parsed 386or unparsed data. 387Parsed data is made up of <termref def="dt-character">characters</termref>, 388some 389of which form <termref def="dt-chardata">character data</termref>, 390and some of which form <termref def="dt-markup">markup</termref>. 391Markup encodes a description of the document's storage layout and 392logical structure. XML provides a mechanism to impose constraints on 393the storage layout and logical structure.</p> 394<p><termdef id="dt-xml-proc" term="XML Processor">A software module 395called an <term>XML processor</term> is used to read XML documents 396and provide access to their content and structure.</termdef> <termdef 397id="dt-app" term="Application">It is assumed that an XML processor is 398doing its work on behalf of another module, called the 399<term>application</term>.</termdef> This specification describes the 400required behavior of an XML processor in terms of how it must read XML 401data and the information it must provide to the application.</p> 402 403<div2 id='sec-origin-goals'> 404<head>Origin and Goals</head> 405<p>XML was developed by an XML Working Group (originally known as the 406SGML Editorial Review Board) formed under the auspices of the World 407Wide Web Consortium (W3C) in 1996. 408It was chaired by Jon Bosak of Sun 409Microsystems with the active participation of an XML Special 410Interest Group (previously known as the SGML Working Group) also 411organized by the W3C. The membership of the XML Working Group is given 412in an appendix. Dan Connolly served as the WG's contact with the W3C. 413</p> 414<p>The design goals for XML are:<olist> 415<item><p>XML shall be straightforwardly usable over the 416Internet.</p></item> 417<item><p>XML shall support a wide variety of applications.</p></item> 418<item><p>XML shall be compatible with SGML.</p></item> 419<item><p>It shall be easy to write programs which process XML 420documents.</p></item> 421<item><p>The number of optional features in XML is to be kept to the 422absolute minimum, ideally zero.</p></item> 423<item><p>XML documents should be human-legible and reasonably 424clear.</p></item> 425<item><p>The XML design should be prepared quickly.</p></item> 426<item><p>The design of XML shall be formal and concise.</p></item> 427<item><p>XML documents shall be easy to create.</p></item> 428<item><p>Terseness in XML markup is of minimal importance.</p></item></olist> 429</p> 430<p>This specification, 431together with associated standards 432(Unicode and ISO/IEC 10646 for characters, 433Internet RFC 1766 for language identification tags, 434ISO 639 for language name codes, and 435ISO 3166 for country name codes), 436provides all the information necessary to understand 437XML Version &XML.version; 438and construct computer programs to process it.</p> 439<p>This version of the XML specification 440<!-- is for &doc.audience;.--> 441&doc.distribution;.</p> 442 443</div2> 444 445 446 447 448<div2 id='sec-terminology'> 449<head>Terminology</head> 450 451<p>The terminology used to describe XML documents is defined in the body of 452this specification. 453The terms defined in the following list are used in building those 454definitions and in describing the actions of an XML processor: 455<glist> 456<gitem> 457<label>may</label> 458<def><p><termdef id="dt-may" term="May">Conforming documents and XML 459processors are permitted to but need not behave as 460described.</termdef></p></def> 461</gitem> 462<gitem> 463<label>must</label> 464<def><p>Conforming documents and XML processors 465are required to behave as described; otherwise they are in error. 466<!-- do NOT change this! this is what defines a violation of 467a 'must' clause as 'an error'. -MSM --> 468</p></def> 469</gitem> 470<gitem> 471<label>error</label> 472<def><p><termdef id='dt-error' term='Error' 473>A violation of the rules of this 474specification; results are 475undefined. Conforming software may detect and report an error and may 476recover from it.</termdef></p></def> 477</gitem> 478<gitem> 479<label>fatal error</label> 480<def><p><termdef id="dt-fatal" term="Fatal Error">An error 481which a conforming <termref def="dt-xml-proc">XML processor</termref> 482must detect and report to the application. 483After encountering a fatal error, the 484processor may continue 485processing the data to search for further errors and may report such 486errors to the application. In order to support correction of errors, 487the processor may make unprocessed data from the document (with 488intermingled character data and markup) available to the application. 489Once a fatal error is detected, however, the processor must not 490continue normal processing (i.e., it must not 491continue to pass character data and information about the document's 492logical structure to the application in the normal way). 493</termdef></p></def> 494</gitem> 495<gitem> 496<label>at user option</label> 497<def><p>Conforming software may or must (depending on the modal verb in the 498sentence) behave as described; if it does, it must 499provide users a means to enable or disable the behavior 500described.</p></def> 501</gitem> 502<gitem> 503<label>validity constraint</label> 504<def><p>A rule which applies to all 505<termref def="dt-valid">valid</termref> XML documents. 506Violations of validity constraints are errors; they must, at user option, 507be reported by 508<termref def="dt-validating">validating XML processors</termref>.</p></def> 509</gitem> 510<gitem> 511<label>well-formedness constraint</label> 512<def><p>A rule which applies to all <termref 513def="dt-wellformed">well-formed</termref> XML documents. 514Violations of well-formedness constraints are 515<termref def="dt-fatal">fatal errors</termref>.</p></def> 516</gitem> 517 518<gitem> 519<label>match</label> 520<def><p><termdef id="dt-match" term="match">(Of strings or names:) 521Two strings or names being compared must be identical. 522Characters with multiple possible representations in ISO/IEC 10646 (e.g. 523characters with 524both precomposed and base+diacritic forms) match only if they have the 525same representation in both strings. 526At user option, processors may normalize such characters to 527some canonical form. 528No case folding is performed. 529(Of strings and rules in the grammar:) 530A string matches a grammatical production if it belongs to the 531language generated by that production. 532(Of content and content models:) 533An element matches its declaration when it conforms 534in the fashion described in the constraint 535<specref ref='elementvalid'/>. 536</termdef> 537</p></def> 538</gitem> 539<gitem> 540<label>for compatibility</label> 541<def><p><termdef id="dt-compat" term="For Compatibility">A feature of 542XML included solely to ensure that XML remains compatible with SGML. 543</termdef></p></def> 544</gitem> 545<gitem> 546<label>for interoperability</label> 547<def><p><termdef id="dt-interop" term="For interoperability">A 548non-binding recommendation included to increase the chances that XML 549documents can be processed by the existing installed base of SGML 550processors which predate the 551&WebSGML;.</termdef></p></def> 552</gitem> 553</glist> 554</p> 555</div2> 556 557 558</div1> 559<!-- &Docs; --> 560 561<div1 id='sec-documents'> 562<head>Documents</head> 563 564<p><termdef id="dt-xml-doc" term="XML Document"> 565A data object is an 566<term>XML document</term> if it is 567<termref def="dt-wellformed">well-formed</termref>, as 568defined in this specification. 569A well-formed XML document may in addition be 570<termref def="dt-valid">valid</termref> if it meets certain further 571constraints.</termdef></p> 572 573<p>Each XML document has both a logical and a physical structure. 574Physically, the document is composed of units called <termref 575def="dt-entity">entities</termref>. An entity may <termref 576def="dt-entref">refer</termref> to other entities to cause their 577inclusion in the document. A document begins in a "root" or <termref 578def="dt-docent">document entity</termref>. 579Logically, the document is composed of declarations, elements, 580comments, 581character references, and 582processing 583instructions, all of which are indicated in the document by explicit 584markup. 585The logical and physical structures must nest properly, as described 586in <specref ref='wf-entities'/>. 587</p> 588 589<div2 id='sec-well-formed'> 590<head>Well-Formed XML Documents</head> 591 592<p><termdef id="dt-wellformed" term="Well-Formed"> 593A textual object is 594a well-formed XML document if:</termdef> 595<olist> 596<item><p>Taken as a whole, it 597matches the production labeled <nt def='NT-document'>document</nt>.</p></item> 598<item><p>It 599meets all the well-formedness constraints given in this specification.</p> 600</item> 601<item><p>Each of the <termref def='dt-parsedent'>parsed entities</termref> 602which is referenced directly or indirectly within the document is 603<titleref href='wf-entities'>well-formed</titleref>.</p></item> 604</olist></p> 605<p> 606<scrap lang='ebnf' id='document'> 607<head>Document</head> 608<prod id='NT-document'><lhs>document</lhs> 609<rhs><nt def='NT-prolog'>prolog</nt> 610<nt def='NT-element'>element</nt> 611<nt def='NT-Misc'>Misc</nt>*</rhs></prod> 612</scrap> 613</p> 614<p>Matching the <nt def="NT-document">document</nt> production 615implies that: 616<olist> 617<item><p>It contains one or more 618<termref def="dt-element">elements</termref>.</p> 619</item> 620<!--* N.B. some readers (notably JC) find the following 621paragraph awkward and redundant. I agree it's logically redundant: 622it *says* it is summarizing the logical implications of 623matching the grammar, and that means by definition it's 624logically redundant. I don't think it's rhetorically 625redundant or unnecessary, though, so I'm keeping it. It 626could however use some recasting when the editors are feeling 627stronger. -MSM *--> 628<item><p><termdef id="dt-root" term="Root Element">There is exactly 629one element, called the <term>root</term>, or document element, no 630part of which appears in the <termref 631def="dt-content">content</termref> of any other element.</termdef> 632For all other elements, if the start-tag is in the content of another 633element, the end-tag is in the content of the same element. More 634simply stated, the elements, delimited by start- and end-tags, nest 635properly within each other. 636</p></item> 637</olist> 638</p> 639<p><termdef id="dt-parentchild" term="Parent/Child">As a consequence 640of this, 641for each non-root element 642<code>C</code> in the document, there is one other element <code>P</code> 643in the document such that 644<code>C</code> is in the content of <code>P</code>, but is not in 645the content of any other element that is in the content of 646<code>P</code>. 647<code>P</code> is referred to as the 648<term>parent</term> of <code>C</code>, and <code>C</code> as a 649<term>child</term> of <code>P</code>.</termdef></p></div2> 650 651<div2 id="charsets"> 652<head>Characters</head> 653 654<p><termdef id="dt-text" term="Text">A parsed entity contains 655<term>text</term>, a sequence of 656<termref def="dt-character">characters</termref>, 657which may represent markup or character data.</termdef> 658<termdef id="dt-character" term="Character">A <term>character</term> 659is an atomic unit of text as specified by 660ISO/IEC 10646 <bibref ref="ISO10646"/>. 661Legal characters are tab, carriage return, line feed, and the legal 662graphic characters of Unicode and ISO/IEC 10646. 663The use of "compatibility characters", as defined in section 6.8 664of <bibref ref='Unicode'/>, is discouraged. 665</termdef> 666<scrap lang="ebnf" id="char32"> 667<head>Character Range</head> 668<prodgroup pcw2="4" pcw4="17.5" pcw5="11"> 669<prod id="NT-Char"><lhs>Char</lhs> 670<rhs>#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] 671| [#x10000-#x10FFFF]</rhs> 672<com>any Unicode character, excluding the 673surrogate blocks, FFFE, and FFFF.</com> </prod> 674</prodgroup> 675</scrap> 676</p> 677 678<p>The mechanism for encoding character code points into bit patterns may 679vary from entity to entity. All XML processors must accept the UTF-8 680and UTF-16 encodings of 10646; the mechanisms for signaling which of 681the two is in use, or for bringing other encodings into play, are 682discussed later, in <specref ref='charencoding'/>. 683</p> 684<!-- 685<p>Regardless of the specific encoding used, any character in the ISO/IEC 68610646 character set may be referred to by the decimal or hexadecimal 687equivalent of its 688UCS-4 code value. 689</p>--> 690</div2> 691 692<div2 id='sec-common-syn'> 693<head>Common Syntactic Constructs</head> 694 695<p>This section defines some symbols used widely in the grammar.</p> 696<p><nt def="NT-S">S</nt> (white space) consists of one or more space (#x20) 697characters, carriage returns, line feeds, or tabs. 698 699<scrap lang="ebnf" id='white'> 700<head>White Space</head> 701<prodgroup pcw2="4" pcw4="17.5" pcw5="11"> 702<prod id='NT-S'><lhs>S</lhs> 703<rhs>(#x20 | #x9 | #xD | #xA)+</rhs> 704</prod> 705</prodgroup> 706</scrap></p> 707<p>Characters are classified for convenience as letters, digits, or other 708characters. Letters consist of an alphabetic or syllabic 709base character possibly 710followed by one or more combining characters, or of an ideographic 711character. 712Full definitions of the specific characters in each class 713are given in <specref ref='CharClasses'/>.</p> 714<p><termdef id="dt-name" term="Name">A <term>Name</term> is a token 715beginning with a letter or one of a few punctuation characters, and continuing 716with letters, digits, hyphens, underscores, colons, or full stops, together 717known as name characters.</termdef> 718Names beginning with the string "<code>xml</code>", or any string 719which would match <code>(('X'|'x') ('M'|'m') ('L'|'l'))</code>, are 720reserved for standardization in this or future versions of this 721specification. 722</p> 723<note> 724<p>The colon character within XML names is reserved for experimentation with 725name spaces. 726Its meaning is expected to be 727standardized at some future point, at which point those documents 728using the colon for experimental purposes may need to be updated. 729(There is no guarantee that any name-space mechanism 730adopted for XML will in fact use the colon as a name-space delimiter.) 731In practice, this means that authors should not use the colon in XML 732names except as part of name-space experiments, but that XML processors 733should accept the colon as a name character.</p> 734</note> 735<p>An 736<nt def='NT-Nmtoken'>Nmtoken</nt> (name token) is any mixture of 737name characters. 738<scrap lang='ebnf'> 739<head>Names and Tokens</head> 740<prod id='NT-NameChar'><lhs>NameChar</lhs> 741<rhs><nt def="NT-Letter">Letter</nt> 742| <nt def='NT-Digit'>Digit</nt> 743| '.' | '-' | '_' | ':' 744| <nt def='NT-CombiningChar'>CombiningChar</nt> 745| <nt def='NT-Extender'>Extender</nt></rhs> 746</prod> 747<prod id='NT-Name'><lhs>Name</lhs> 748<rhs>(<nt def='NT-Letter'>Letter</nt> | '_' | ':') 749(<nt def='NT-NameChar'>NameChar</nt>)*</rhs></prod> 750<prod id='NT-Names'><lhs>Names</lhs> 751<rhs><nt def='NT-Name'>Name</nt> 752(<nt def='NT-S'>S</nt> <nt def='NT-Name'>Name</nt>)*</rhs></prod> 753<prod id='NT-Nmtoken'><lhs>Nmtoken</lhs> 754<rhs>(<nt def='NT-NameChar'>NameChar</nt>)+</rhs></prod> 755<prod id='NT-Nmtokens'><lhs>Nmtokens</lhs> 756<rhs><nt def='NT-Nmtoken'>Nmtoken</nt> (<nt def='NT-S'>S</nt> <nt def='NT-Nmtoken'>Nmtoken</nt>)*</rhs></prod> 757</scrap> 758</p> 759<p>Literal data is any quoted string not containing 760the quotation mark used as a delimiter for that string. 761Literals are used 762for specifying the content of internal entities 763(<nt def='NT-EntityValue'>EntityValue</nt>), 764the values of attributes (<nt def='NT-AttValue'>AttValue</nt>), 765and external identifiers 766(<nt def="NT-SystemLiteral">SystemLiteral</nt>). 767Note that a <nt def='NT-SystemLiteral'>SystemLiteral</nt> 768can be parsed without scanning for markup. 769<scrap lang='ebnf'> 770<head>Literals</head> 771<prod id='NT-EntityValue'><lhs>EntityValue</lhs> 772<rhs>'"' 773([^%&"] 774| <nt def='NT-PEReference'>PEReference</nt> 775| <nt def='NT-Reference'>Reference</nt>)* 776'"' 777</rhs> 778<rhs>| 779"'" 780([^%&'] 781| <nt def='NT-PEReference'>PEReference</nt> 782| <nt def='NT-Reference'>Reference</nt>)* 783"'"</rhs> 784</prod> 785<prod id='NT-AttValue'><lhs>AttValue</lhs> 786<rhs>'"' 787([^<&"] 788| <nt def='NT-Reference'>Reference</nt>)* 789'"' 790</rhs> 791<rhs>| 792"'" 793([^<&'] 794| <nt def='NT-Reference'>Reference</nt>)* 795"'"</rhs> 796</prod> 797<prod id="NT-SystemLiteral"><lhs>SystemLiteral</lhs> 798<rhs>('"' [^"]* '"') | ("'" [^']* "'") 799</rhs> 800</prod> 801<prod id="NT-PubidLiteral"><lhs>PubidLiteral</lhs> 802<rhs>'"' <nt def='NT-PubidChar'>PubidChar</nt>* 803'"' 804| "'" (<nt def='NT-PubidChar'>PubidChar</nt> - "'")* "'"</rhs> 805</prod> 806<prod id="NT-PubidChar"><lhs>PubidChar</lhs> 807<rhs>#x20 | #xD | #xA 808| [a-zA-Z0-9] 809| [-'()+,./:=?;!*#@$_%]</rhs> 810</prod> 811</scrap> 812</p> 813 814</div2> 815 816<div2 id='syntax'> 817<head>Character Data and Markup</head> 818 819<p><termref def='dt-text'>Text</termref> consists of intermingled 820<termref def="dt-chardata">character 821data</termref> and markup. 822<termdef id="dt-markup" term="Markup"><term>Markup</term> takes the form of 823<termref def="dt-stag">start-tags</termref>, 824<termref def="dt-etag">end-tags</termref>, 825<termref def="dt-empty">empty-element tags</termref>, 826<termref def="dt-entref">entity references</termref>, 827<termref def="dt-charref">character references</termref>, 828<termref def="dt-comment">comments</termref>, 829<termref def="dt-cdsection">CDATA section</termref> delimiters, 830<termref def="dt-doctype">document type declarations</termref>, and 831<termref def="dt-pi">processing instructions</termref>. 832</termdef> 833</p> 834<p><termdef id="dt-chardata" term="Character Data">All text that is not markup 835constitutes the <term>character data</term> of 836the document.</termdef></p> 837<p>The ampersand character (&) and the left angle bracket (<) 838may appear in their literal form <emph>only</emph> when used as markup 839delimiters, or within a <termref def="dt-comment">comment</termref>, a 840<termref def="dt-pi">processing instruction</termref>, 841or a <termref def="dt-cdsection">CDATA section</termref>. 842 843They are also legal within the <termref def='dt-litentval'>literal entity 844value</termref> of an internal entity declaration; see 845<specref ref='wf-entities'/>. 846<!-- FINAL EDIT: restore internal entity decl or leave it out. --> 847If they are needed elsewhere, 848they must be <termref def="dt-escape">escaped</termref> 849using either <termref def='dt-charref'>numeric character references</termref> 850or the strings 851"<code>&amp;</code>" and "<code>&lt;</code>" respectively. 852The right angle 853bracket (>) may be represented using the string 854"<code>&gt;</code>", and must, <termref def='dt-compat'>for 855compatibility</termref>, 856be escaped using 857"<code>&gt;</code>" or a character reference 858when it appears in the string 859"<code>]]></code>" 860in content, 861when that string is not marking the end of 862a <termref def="dt-cdsection">CDATA section</termref>. 863</p> 864<p> 865In the content of elements, character data 866is any string of characters which does 867not contain the start-delimiter of any markup. 868In a CDATA section, character data 869is any string of characters not including the CDATA-section-close 870delimiter, "<code>]]></code>".</p> 871<p> 872To allow attribute values to contain both single and double quotes, the 873apostrophe or single-quote character (') may be represented as 874"<code>&apos;</code>", and the double-quote character (") as 875"<code>&quot;</code>". 876<scrap lang="ebnf"> 877<head>Character Data</head> 878<prod id='NT-CharData'> 879<lhs>CharData</lhs> 880<rhs>[^<&]* - ([^<&]* ']]>' [^<&]*)</rhs> 881</prod> 882</scrap> 883</p> 884</div2> 885 886<div2 id='sec-comments'> 887<head>Comments</head> 888 889<p><termdef id="dt-comment" term="Comment"><term>Comments</term> may 890appear anywhere in a document outside other 891<termref def='dt-markup'>markup</termref>; in addition, 892they may appear within the document type declaration 893at places allowed by the grammar. 894They are not part of the document's <termref def="dt-chardata">character 895data</termref>; an XML 896processor may, but need not, make it possible for an application to 897retrieve the text of comments. 898<termref def="dt-compat">For compatibility</termref>, the string 899"<code>--</code>" (double-hyphen) must not occur within 900comments. 901<scrap lang="ebnf"> 902<head>Comments</head> 903<prod id='NT-Comment'><lhs>Comment</lhs> 904<rhs>'<!--' 905((<nt def='NT-Char'>Char</nt> - '-') 906| ('-' (<nt def='NT-Char'>Char</nt> - '-')))* 907'-->'</rhs> 908</prod> 909</scrap> 910</termdef></p> 911<p>An example of a comment: 912<eg><!&como; declarations for <head> & <body> &comc;></eg> 913</p> 914</div2> 915 916<div2 id='sec-pi'> 917<head>Processing Instructions</head> 918 919<p><termdef id="dt-pi" term="Processing instruction"><term>Processing 920instructions</term> (PIs) allow documents to contain instructions 921for applications. 922 923<scrap lang="ebnf"> 924<head>Processing Instructions</head> 925<prod id='NT-PI'><lhs>PI</lhs> 926<rhs>'<?' <nt def='NT-PITarget'>PITarget</nt> 927(<nt def='NT-S'>S</nt> 928(<nt def='NT-Char'>Char</nt>* - 929(<nt def='NT-Char'>Char</nt>* &pic; <nt def='NT-Char'>Char</nt>*)))? 930&pic;</rhs></prod> 931<prod id='NT-PITarget'><lhs>PITarget</lhs> 932<rhs><nt def='NT-Name'>Name</nt> - 933(('X' | 'x') ('M' | 'm') ('L' | 'l'))</rhs> 934</prod> 935</scrap></termdef> 936PIs are not part of the document's <termref def="dt-chardata">character 937data</termref>, but must be passed through to the application. The 938PI begins with a target (<nt def='NT-PITarget'>PITarget</nt>) used 939to identify the application to which the instruction is directed. 940The target names "<code>XML</code>", "<code>xml</code>", and so on are 941reserved for standardization in this or future versions of this 942specification. 943The 944XML <termref def='dt-notation'>Notation</termref> mechanism 945may be used for 946formal declaration of PI targets. 947</p> 948</div2> 949 950<div2 id='sec-cdata-sect'> 951<head>CDATA Sections</head> 952 953<p><termdef id="dt-cdsection" term="CDATA Section"><term>CDATA sections</term> 954may occur 955anywhere character data may occur; they are 956used to escape blocks of text containing characters which would 957otherwise be recognized as markup. CDATA sections begin with the 958string "<code><![CDATA[</code>" and end with the string 959"<code>]]></code>": 960<scrap lang="ebnf"> 961<head>CDATA Sections</head> 962<prod id='NT-CDSect'><lhs>CDSect</lhs> 963<rhs><nt def='NT-CDStart'>CDStart</nt> 964<nt def='NT-CData'>CData</nt> 965<nt def='NT-CDEnd'>CDEnd</nt></rhs></prod> 966<prod id='NT-CDStart'><lhs>CDStart</lhs> 967<rhs>'<![CDATA['</rhs> 968</prod> 969<prod id='NT-CData'><lhs>CData</lhs> 970<rhs>(<nt def='NT-Char'>Char</nt>* - 971(<nt def='NT-Char'>Char</nt>* ']]>' <nt def='NT-Char'>Char</nt>*)) 972</rhs> 973</prod> 974<prod id='NT-CDEnd'><lhs>CDEnd</lhs> 975<rhs>']]>'</rhs> 976</prod> 977</scrap> 978 979Within a CDATA section, only the <nt def='NT-CDEnd'>CDEnd</nt> string is 980recognized as markup, so that left angle brackets and ampersands may occur in 981their literal form; they need not (and cannot) be escaped using 982"<code>&lt;</code>" and "<code>&amp;</code>". CDATA sections 983cannot nest.</termdef> 984</p> 985 986<p>An example of a CDATA section, in which "<code><greeting></code>" and 987"<code></greeting></code>" 988are recognized as <termref def='dt-chardata'>character data</termref>, not 989<termref def='dt-markup'>markup</termref>: 990<eg><![CDATA[<greeting>Hello, world!</greeting>]]></eg> 991</p> 992</div2> 993 994<div2 id='sec-prolog-dtd'> 995<head>Prolog and Document Type Declaration</head> 996 997<p><termdef id='dt-xmldecl' term='XML Declaration'>XML documents 998may, and should, 999begin with an <term>XML declaration</term> which specifies 1000the version of 1001XML being used.</termdef> 1002For example, the following is a complete XML document, <termref 1003def="dt-wellformed">well-formed</termref> but not 1004<termref def="dt-valid">valid</termref>: 1005<eg><![CDATA[<?xml version="1.0"?> 1006<greeting>Hello, world!</greeting> 1007]]></eg> 1008and so is this: 1009<eg><![CDATA[<greeting>Hello, world!</greeting> 1010]]></eg> 1011</p> 1012 1013<p>The version number "<code>1.0</code>" should be used to indicate 1014conformance to this version of this specification; it is an error 1015for a document to use the value "<code>1.0</code>" 1016if it does not conform to this version of this specification. 1017It is the intent 1018of the XML working group to give later versions of this specification 1019numbers other than "<code>1.0</code>", but this intent does not 1020indicate a 1021commitment to produce any future versions of XML, nor if any are produced, to 1022use any particular numbering scheme. 1023Since future versions are not ruled out, this construct is provided 1024as a means to allow the possibility of automatic version recognition, should 1025it become necessary. 1026Processors may signal an error if they receive documents labeled with 1027versions they do not support. 1028</p> 1029<p>The function of the markup in an XML document is to describe its 1030storage and logical structure and to associate attribute-value pairs 1031with its logical structures. XML provides a mechanism, the <termref 1032def="dt-doctype">document type declaration</termref>, to define 1033constraints on the logical structure and to support the use of 1034predefined storage units. 1035 1036<termdef id="dt-valid" term="Validity">An XML document is 1037<term>valid</term> if it has an associated document type 1038declaration and if the document 1039complies with the constraints expressed in it.</termdef></p> 1040<p>The document type declaration must appear before 1041the first <termref def="dt-element">element</termref> in the document. 1042<scrap lang="ebnf" id='xmldoc'> 1043<head>Prolog</head> 1044<prodgroup pcw2="6" pcw4="17.5" pcw5="9"> 1045<prod id='NT-prolog'><lhs>prolog</lhs> 1046<rhs><nt def='NT-XMLDecl'>XMLDecl</nt>? 1047<nt def='NT-Misc'>Misc</nt>* 1048(<nt def='NT-doctypedecl'>doctypedecl</nt> 1049<nt def='NT-Misc'>Misc</nt>*)?</rhs></prod> 1050<prod id='NT-XMLDecl'><lhs>XMLDecl</lhs> 1051<rhs>&xmlpio; 1052<nt def='NT-VersionInfo'>VersionInfo</nt> 1053<nt def='NT-EncodingDecl'>EncodingDecl</nt>? 1054<nt def='NT-SDDecl'>SDDecl</nt>? 1055<nt def="NT-S">S</nt>? 1056&pic;</rhs> 1057</prod> 1058<prod id='NT-VersionInfo'><lhs>VersionInfo</lhs> 1059<rhs><nt def="NT-S">S</nt> 'version' <nt def='NT-Eq'>Eq</nt> 1060(' <nt def="NT-VersionNum">VersionNum</nt> ' 1061| " <nt def="NT-VersionNum">VersionNum</nt> ")</rhs> 1062</prod> 1063<prod id='NT-Eq'><lhs>Eq</lhs> 1064<rhs><nt def='NT-S'>S</nt>? '=' <nt def='NT-S'>S</nt>?</rhs></prod> 1065<prod id="NT-VersionNum"> 1066<lhs>VersionNum</lhs> 1067<rhs>([a-zA-Z0-9_.:] | '-')+</rhs> 1068</prod> 1069<prod id='NT-Misc'><lhs>Misc</lhs> 1070<rhs><nt def='NT-Comment'>Comment</nt> | <nt def='NT-PI'>PI</nt> | 1071<nt def='NT-S'>S</nt></rhs></prod> 1072</prodgroup> 1073</scrap></p> 1074 1075<p><termdef id="dt-doctype" term="Document Type Declaration">The XML 1076<term>document type declaration</term> 1077contains or points to 1078<termref def='dt-markupdecl'>markup declarations</termref> 1079that provide a grammar for a 1080class of documents. 1081This grammar is known as a document type definition, 1082or <term>DTD</term>. 1083The document type declaration can point to an external subset (a 1084special kind of 1085<termref def='dt-extent'>external entity</termref>) containing markup 1086declarations, or can 1087contain the markup declarations directly in an internal subset, or can do 1088both. 1089The DTD for a document consists of both subsets taken 1090together.</termdef> 1091</p> 1092<p><termdef id="dt-markupdecl" term="markup declaration"> 1093A <term>markup declaration</term> is 1094an <termref def="dt-eldecl">element type declaration</termref>, 1095an <termref def="dt-attdecl">attribute-list declaration</termref>, 1096an <termref def="dt-entdecl">entity declaration</termref>, or 1097a <termref def="dt-notdecl">notation declaration</termref>. 1098</termdef> 1099These declarations may be contained in whole or in part 1100within <termref def='dt-PE'>parameter entities</termref>, 1101as described in the well-formedness and validity constraints below. 1102For fuller information, see 1103<specref ref="sec-physical-struct"/>.</p> 1104<scrap lang="ebnf" id='dtd'> 1105<head>Document Type Definition</head> 1106<prodgroup pcw2="6" pcw4="17.5" pcw5="9"> 1107<prod id='NT-doctypedecl'><lhs>doctypedecl</lhs> 1108<rhs>'<!DOCTYPE' <nt def='NT-S'>S</nt> 1109<nt def='NT-Name'>Name</nt> (<nt def='NT-S'>S</nt> 1110<nt def='NT-ExternalID'>ExternalID</nt>)? 1111<nt def='NT-S'>S</nt>? ('[' 1112(<nt def='NT-markupdecl'>markupdecl</nt> 1113| <nt def='NT-PEReference'>PEReference</nt> 1114| <nt def='NT-S'>S</nt>)* 1115']' 1116<nt def='NT-S'>S</nt>?)? '>'</rhs> 1117<vc def="vc-roottype"/> 1118</prod> 1119<prod id='NT-markupdecl'><lhs>markupdecl</lhs> 1120<rhs><nt def='NT-elementdecl'>elementdecl</nt> 1121| <nt def='NT-AttlistDecl'>AttlistDecl</nt> 1122| <nt def='NT-EntityDecl'>EntityDecl</nt> 1123| <nt def='NT-NotationDecl'>NotationDecl</nt> 1124| <nt def='NT-PI'>PI</nt> 1125| <nt def='NT-Comment'>Comment</nt> 1126</rhs> 1127<vc def='vc-PEinMarkupDecl'/> 1128<wfc def="wfc-PEinInternalSubset"/> 1129</prod> 1130 1131</prodgroup> 1132</scrap> 1133 1134<p>The markup declarations may be made up in whole or in part of 1135the <termref def='dt-repltext'>replacement text</termref> of 1136<termref def='dt-PE'>parameter entities</termref>. 1137The productions later in this specification for 1138individual nonterminals (<nt def='NT-elementdecl'>elementdecl</nt>, 1139<nt def='NT-AttlistDecl'>AttlistDecl</nt>, and so on) describe 1140the declarations <emph>after</emph> all the parameter entities have been 1141<termref def='dt-include'>included</termref>.</p> 1142 1143<vcnote id="vc-roottype"> 1144<head>Root Element Type</head> 1145<p> 1146The <nt def='NT-Name'>Name</nt> in the document type declaration must 1147match the element type of the <termref def='dt-root'>root element</termref>. 1148</p> 1149</vcnote> 1150 1151<vcnote id='vc-PEinMarkupDecl'> 1152<head>Proper Declaration/PE Nesting</head> 1153<p>Parameter-entity 1154<termref def='dt-repltext'>replacement text</termref> must be properly nested 1155with markup declarations. 1156That is to say, if either the first character 1157or the last character of a markup 1158declaration (<nt def='NT-markupdecl'>markupdecl</nt> above) 1159is contained in the replacement text for a 1160<termref def='dt-PERef'>parameter-entity reference</termref>, 1161both must be contained in the same replacement text.</p> 1162</vcnote> 1163<wfcnote id="wfc-PEinInternalSubset"> 1164<head>PEs in Internal Subset</head> 1165<p>In the internal DTD subset, 1166<termref def='dt-PERef'>parameter-entity references</termref> 1167can occur only where markup declarations can occur, not 1168within markup declarations. (This does not apply to 1169references that occur in 1170external parameter entities or to the external subset.) 1171</p> 1172</wfcnote> 1173<p> 1174Like the internal subset, the external subset and 1175any external parameter entities referred to in the DTD 1176must consist of a series of complete markup declarations of the types 1177allowed by the non-terminal symbol 1178<nt def="NT-markupdecl">markupdecl</nt>, interspersed with white space 1179or <termref def="dt-PERef">parameter-entity references</termref>. 1180However, portions of the contents 1181of the 1182external subset or of external parameter entities may conditionally be ignored 1183by using 1184the <termref def="dt-cond-section">conditional section</termref> 1185construct; this is not allowed in the internal subset. 1186 1187<scrap id="ext-Subset"> 1188<head>External Subset</head> 1189<prodgroup pcw2="6" pcw4="17.5" pcw5="9"> 1190<prod id='NT-extSubset'><lhs>extSubset</lhs> 1191<rhs><nt def='NT-TextDecl'>TextDecl</nt>? 1192<nt def='NT-extSubsetDecl'>extSubsetDecl</nt></rhs></prod> 1193<prod id='NT-extSubsetDecl'><lhs>extSubsetDecl</lhs> 1194<rhs>( 1195<nt def='NT-markupdecl'>markupdecl</nt> 1196| <nt def='NT-conditionalSect'>conditionalSect</nt> 1197| <nt def='NT-PEReference'>PEReference</nt> 1198| <nt def='NT-S'>S</nt> 1199)*</rhs> 1200</prod> 1201</prodgroup> 1202</scrap></p> 1203<p>The external subset and external parameter entities also differ 1204from the internal subset in that in them, 1205<termref def="dt-PERef">parameter-entity references</termref> 1206are permitted <emph>within</emph> markup declarations, 1207not only <emph>between</emph> markup declarations.</p> 1208<p>An example of an XML document with a document type declaration: 1209<eg><![CDATA[<?xml version="1.0"?> 1210<!DOCTYPE greeting SYSTEM "hello.dtd"> 1211<greeting>Hello, world!</greeting> 1212]]></eg> 1213The <termref def="dt-sysid">system identifier</termref> 1214"<code>hello.dtd</code>" gives the URI of a DTD for the document.</p> 1215<p>The declarations can also be given locally, as in this 1216example: 1217<eg><![CDATA[<?xml version="1.0" encoding="UTF-8" ?> 1218<!DOCTYPE greeting [ 1219 <!ELEMENT greeting (#PCDATA)> 1220]> 1221<greeting>Hello, world!</greeting> 1222]]></eg> 1223If both the external and internal subsets are used, the 1224internal subset is considered to occur before the external subset. 1225<!-- 'is considered to'? boo. whazzat mean? --> 1226This has the effect that entity and attribute-list declarations in the 1227internal subset take precedence over those in the external subset. 1228</p> 1229</div2> 1230 1231<div2 id='sec-rmd'> 1232<head>Standalone Document Declaration</head> 1233<p>Markup declarations can affect the content of the document, 1234as passed from an <termref def="dt-xml-proc">XML processor</termref> 1235to an application; examples are attribute defaults and entity 1236declarations. 1237The standalone document declaration, 1238which may appear as a component of the XML declaration, signals 1239whether or not there are such declarations which appear external to 1240the <termref def='dt-docent'>document entity</termref>. 1241<scrap lang="ebnf" id='fulldtd'> 1242<head>Standalone Document Declaration</head> 1243<prodgroup pcw2="4" pcw4="19.5" pcw5="9"> 1244<prod id='NT-SDDecl'><lhs>SDDecl</lhs> 1245<rhs> 1246<nt def="NT-S">S</nt> 1247'standalone' <nt def='NT-Eq'>Eq</nt> 1248(("'" ('yes' | 'no') "'") | ('"' ('yes' | 'no') '"')) 1249</rhs> 1250<vc def='vc-check-rmd'/></prod> 1251</prodgroup> 1252</scrap></p> 1253<p> 1254In a standalone document declaration, the value "<code>yes</code>" indicates 1255that there 1256are no markup declarations external to the <termref def='dt-docent'>document 1257entity</termref> (either in the DTD external subset, or in an 1258external parameter entity referenced from the internal subset) 1259which affect the information passed from the XML processor to 1260the application. 1261The value "<code>no</code>" indicates that there are or may be such 1262external markup declarations. 1263Note that the standalone document declaration only 1264denotes the presence of external <emph>declarations</emph>; the presence, in a 1265document, of 1266references to external <emph>entities</emph>, when those entities are 1267internally declared, 1268does not change its standalone status.</p> 1269<p>If there are no external markup declarations, the standalone document 1270declaration has no meaning. 1271If there are external markup declarations but there is no standalone 1272document declaration, the value "<code>no</code>" is assumed.</p> 1273<p>Any XML document for which <code>standalone="no"</code> holds can 1274be converted algorithmically to a standalone document, 1275which may be desirable for some network delivery applications.</p> 1276<vcnote id='vc-check-rmd'> 1277<head>Standalone Document Declaration</head> 1278<p>The standalone document declaration must have 1279the value "<code>no</code>" if any external markup declarations 1280contain declarations of:</p><ulist> 1281<item><p>attributes with <termref def="dt-default">default</termref> values, if 1282elements to which 1283these attributes apply appear in the document without 1284specifications of values for these attributes, or</p></item> 1285<item><p>entities (other than &magicents;), 1286if <termref def="dt-entref">references</termref> to those 1287entities appear in the document, or</p> 1288</item> 1289<item><p>attributes with values subject to 1290<titleref href='AVNormalize'>normalization</titleref>, where the 1291attribute appears in the document with a value which will 1292change as a result of normalization, or</p> 1293</item> 1294<item> 1295<p>element types with <termref def="dt-elemcontent">element content</termref>, 1296if white space occurs 1297directly within any instance of those types. 1298</p></item> 1299</ulist> 1300 1301</vcnote> 1302<p>An example XML declaration with a standalone document declaration:<eg 1303><?xml version="&XML.version;" standalone='yes'?></eg></p> 1304</div2> 1305<div2 id='sec-white-space'> 1306<head>White Space Handling</head> 1307 1308<p>In editing XML documents, it is often convenient to use "white space" 1309(spaces, tabs, and blank lines, denoted by the nonterminal 1310<nt def='NT-S'>S</nt> in this specification) to 1311set apart the markup for greater readability. Such white space is typically 1312not intended for inclusion in the delivered version of the document. 1313On the other hand, "significant" white space that should be preserved in the 1314delivered version is common, for example in poetry and 1315source code.</p> 1316<p>An <termref def='dt-xml-proc'>XML processor</termref> 1317must always pass all characters in a document that are not 1318markup through to the application. A <termref def='dt-validating'> 1319validating XML processor</termref> must also inform the application 1320which of these characters constitute white space appearing 1321in <termref def="dt-elemcontent">element content</termref>. 1322</p> 1323<p>A special <termref def='dt-attr'>attribute</termref> 1324named <kw>xml:space</kw> may be attached to an element 1325to signal an intention that in that element, 1326white space should be preserved by applications. 1327In valid documents, this attribute, like any other, must be 1328<termref def="dt-attdecl">declared</termref> if it is used. 1329When declared, it must be given as an 1330<termref def='dt-enumerated'>enumerated type</termref> whose only 1331possible values are "<code>default</code>" and "<code>preserve</code>". 1332For example:<eg><![CDATA[ <!ATTLIST poem xml:space (default|preserve) 'preserve'>]]></eg></p> 1333<p>The value "<code>default</code>" signals that applications' 1334default white-space processing modes are acceptable for this element; the 1335value "<code>preserve</code>" indicates the intent that applications preserve 1336all the white space. 1337This declared intent is considered to apply to all elements within the content 1338of the element where it is specified, unless overriden with another instance 1339of the <kw>xml:space</kw> attribute. 1340</p> 1341<p>The <termref def='dt-root'>root element</termref> of any document 1342is considered to have signaled no intentions as regards application space 1343handling, unless it provides a value for 1344this attribute or the attribute is declared with a default value. 1345</p> 1346 1347</div2> 1348<div2 id='sec-line-ends'> 1349<head>End-of-Line Handling</head> 1350<p>XML <termref def='dt-parsedent'>parsed entities</termref> are often stored in 1351computer files which, for editing convenience, are organized into lines. 1352These lines are typically separated by some combination of the characters 1353carriage-return (#xD) and line-feed (#xA).</p> 1354<p>To simplify the tasks of <termref def='dt-app'>applications</termref>, 1355wherever an external parsed entity or the literal entity value 1356of an internal parsed entity contains either the literal 1357two-character sequence "#xD#xA" or a standalone literal 1358#xD, an <termref def='dt-xml-proc'>XML processor</termref> must 1359pass to the application the single character #xA. 1360(This behavior can 1361conveniently be produced by normalizing all 1362line breaks to #xA on input, before parsing.) 1363</p> 1364</div2> 1365<div2 id='sec-lang-tag'> 1366<head>Language Identification</head> 1367<p>In document processing, it is often useful to 1368identify the natural or formal language 1369in which the content is 1370written. 1371A special <termref def="dt-attr">attribute</termref> named 1372<kw>xml:lang</kw> may be inserted in 1373documents to specify the 1374language used in the contents and attribute values 1375of any element in an XML document. 1376In valid documents, this attribute, like any other, must be 1377<termref def="dt-attdecl">declared</termref> if it is used. 1378The values of the attribute are language identifiers as defined 1379by <bibref ref="RFC1766"/>, "Tags for the Identification of Languages": 1380<scrap lang='ebnf'> 1381<head>Language Identification</head> 1382<prod id='NT-LanguageID'><lhs>LanguageID</lhs> 1383<rhs><nt def='NT-Langcode'>Langcode</nt> 1384('-' <nt def='NT-Subcode'>Subcode</nt>)*</rhs></prod> 1385<prod id='NT-Langcode'><lhs>Langcode</lhs> 1386<rhs><nt def='NT-ISO639Code'>ISO639Code</nt> | 1387<nt def='NT-IanaCode'>IanaCode</nt> | 1388<nt def='NT-UserCode'>UserCode</nt></rhs> 1389</prod> 1390<prod id='NT-ISO639Code'><lhs>ISO639Code</lhs> 1391<rhs>([a-z] | [A-Z]) ([a-z] | [A-Z])</rhs></prod> 1392<prod id='NT-IanaCode'><lhs>IanaCode</lhs> 1393<rhs>('i' | 'I') '-' ([a-z] | [A-Z])+</rhs></prod> 1394<prod id='NT-UserCode'><lhs>UserCode</lhs> 1395<rhs>('x' | 'X') '-' ([a-z] | [A-Z])+</rhs></prod> 1396<prod id='NT-Subcode'><lhs>Subcode</lhs> 1397<rhs>([a-z] | [A-Z])+</rhs></prod> 1398</scrap> 1399The <nt def='NT-Langcode'>Langcode</nt> may be any of the following: 1400<ulist> 1401<item><p>a two-letter language code as defined by 1402<bibref ref="ISO639"/>, "Codes 1403for the representation of names of languages"</p></item> 1404<item><p>a language identifier registered with the Internet 1405Assigned Numbers Authority <bibref ref='IANA'/>; these begin with the 1406prefix "<code>i-</code>" (or "<code>I-</code>")</p></item> 1407<item><p>a language identifier assigned by the user, or agreed on 1408between parties in private use; these must begin with the 1409prefix "<code>x-</code>" or "<code>X-</code>" in order to ensure that they do not conflict 1410with names later standardized or registered with IANA</p></item> 1411</ulist></p> 1412<p>There may be any number of <nt def='NT-Subcode'>Subcode</nt> segments; if 1413the first 1414subcode segment exists and the Subcode consists of two 1415letters, then it must be a country code from 1416<bibref ref="ISO3166"/>, "Codes 1417for the representation of names of countries." 1418If the first 1419subcode consists of more than two letters, it must be 1420a subcode for the language in question registered with IANA, 1421unless the <nt def='NT-Langcode'>Langcode</nt> begins with the prefix 1422"<code>x-</code>" or 1423"<code>X-</code>". </p> 1424<p>It is customary to give the language code in lower case, and 1425the country code (if any) in upper case. 1426Note that these values, unlike other names in XML documents, 1427are case insensitive.</p> 1428<p>For example: 1429<eg><![CDATA[<p xml:lang="en">The quick brown fox jumps over the lazy dog.</p> 1430<p xml:lang="en-GB">What colour is it?</p> 1431<p xml:lang="en-US">What color is it?</p> 1432<sp who="Faust" desc='leise' xml:lang="de"> 1433 <l>Habe nun, ach! Philosophie,</l> 1434 <l>Juristerei, und Medizin</l> 1435 <l>und leider auch Theologie</l> 1436 <l>durchaus studiert mit hei�em Bem�h'n.</l> 1437 </sp>]]></eg></p> 1438<!--<p>The xml:lang value is considered to apply both to the contents of an 1439element and 1440(unless otherwise via attribute default values) to the 1441values of all of its attributes with free-text (CDATA) values. --> 1442<p>The intent declared with <kw>xml:lang</kw> is considered to apply to 1443all attributes and content of the element where it is specified, 1444unless overridden with an instance of <kw>xml:lang</kw> 1445on another element within that content.</p> 1446<!-- 1447If no 1448value is specified for xml:lang on an element, and no default value is 1449defined for it in the DTD, then the xml:lang attribute of any element 1450takes the same value it has in the parent element, if any. The two 1451technical terms in the following example both have the same effective 1452value for xml:lang: 1453 1454 <p xml:lang="en">Here the keywords are 1455 <term xml:lang="en">shift</term> and 1456 <term>reduce</term>. ...</p> 1457 1458The application, not the XML processor, is responsible for this ' 1459inheritance' of attribute values. 1460--> 1461<p>A simple declaration for <kw>xml:lang</kw> might take 1462the form 1463<eg>xml:lang NMTOKEN #IMPLIED</eg> 1464but specific default values may also be given, if appropriate. In a 1465collection of French poems for English students, with glosses and 1466notes in English, the xml:lang attribute might be declared this way: 1467<eg><![CDATA[ <!ATTLIST poem xml:lang NMTOKEN 'fr'> 1468 <!ATTLIST gloss xml:lang NMTOKEN 'en'> 1469 <!ATTLIST note xml:lang NMTOKEN 'en'>]]></eg> 1470</p> 1471 1472</div2> 1473</div1> 1474<!-- &Elements; --> 1475 1476<div1 id='sec-logical-struct'> 1477<head>Logical Structures</head> 1478 1479<p><termdef id="dt-element" term="Element">Each <termref 1480def="dt-xml-doc">XML document</termref> contains one or more 1481<term>elements</term>, the boundaries of which are 1482either delimited by <termref def="dt-stag">start-tags</termref> 1483and <termref def="dt-etag">end-tags</termref>, or, for <termref 1484def="dt-empty">empty</termref> elements, by an <termref 1485def="dt-eetag">empty-element tag</termref>. Each element has a type, 1486identified by name, sometimes called its "generic 1487identifier" (GI), and may have a set of 1488attribute specifications.</termdef> Each attribute specification 1489has a <termref 1490def="dt-attrname">name</termref> and a <termref 1491def="dt-attrval">value</termref>. 1492</p> 1493<scrap lang='ebnf'><head>Element</head> 1494<prod id='NT-element'><lhs>element</lhs> 1495<rhs><nt def='NT-EmptyElemTag'>EmptyElemTag</nt></rhs> 1496<rhs>| <nt def='NT-STag'>STag</nt> <nt def='NT-content'>content</nt> 1497<nt def='NT-ETag'>ETag</nt></rhs> 1498<wfc def='GIMatch'/> 1499<vc def='elementvalid'/> 1500</prod> 1501</scrap> 1502<p>This specification does not constrain the semantics, use, or (beyond 1503syntax) names of the element types and attributes, except that names 1504beginning with a match to <code>(('X'|'x')('M'|'m')('L'|'l'))</code> 1505are reserved for standardization in this or future versions of this 1506specification. 1507</p> 1508<wfcnote id='GIMatch'> 1509<head>Element Type Match</head> 1510<p> 1511The <nt def='NT-Name'>Name</nt> in an element's end-tag must match 1512the element type in 1513the start-tag. 1514</p> 1515</wfcnote> 1516<vcnote id='elementvalid'> 1517<head>Element Valid</head> 1518<p>An element is 1519valid if 1520there is a declaration matching 1521<nt def='NT-elementdecl'>elementdecl</nt> where the 1522<nt def='NT-Name'>Name</nt> matches the element type, and 1523one of the following holds:</p> 1524<olist> 1525<item><p>The declaration matches <kw>EMPTY</kw> and the element has no 1526<termref def='dt-content'>content</termref>.</p></item> 1527<item><p>The declaration matches <nt def='NT-children'>children</nt> and 1528the sequence of 1529<termref def="dt-parentchild">child elements</termref> 1530belongs to the language generated by the regular expression in 1531the content model, with optional white space (characters 1532matching the nonterminal <nt def='NT-S'>S</nt>) between each pair 1533of child elements.</p></item> 1534<item><p>The declaration matches <nt def='NT-Mixed'>Mixed</nt> and 1535the content consists of <termref def='dt-chardata'>character 1536data</termref> and <termref def='dt-parentchild'>child elements</termref> 1537whose types match names in the content model.</p></item> 1538<item><p>The declaration matches <kw>ANY</kw>, and the types 1539of any <termref def='dt-parentchild'>child elements</termref> have 1540been declared.</p></item> 1541</olist> 1542</vcnote> 1543 1544<div2 id='sec-starttags'> 1545<head>Start-Tags, End-Tags, and Empty-Element Tags</head> 1546 1547<p><termdef id="dt-stag" term="Start-Tag">The beginning of every 1548non-empty XML element is marked by a <term>start-tag</term>. 1549<scrap lang='ebnf'> 1550<head>Start-tag</head> 1551<prodgroup pcw2="6" pcw4="15" pcw5="11.5"> 1552<prod id='NT-STag'><lhs>STag</lhs> 1553<rhs>'<' <nt def='NT-Name'>Name</nt> 1554(<nt def='NT-S'>S</nt> <nt def='NT-Attribute'>Attribute</nt>)* 1555<nt def='NT-S'>S</nt>? '>'</rhs> 1556<wfc def="uniqattspec"/> 1557</prod> 1558<prod id='NT-Attribute'><lhs>Attribute</lhs> 1559<rhs><nt def='NT-Name'>Name</nt> <nt def='NT-Eq'>Eq</nt> 1560<nt def='NT-AttValue'>AttValue</nt></rhs> 1561<vc def='ValueType'/> 1562<wfc def='NoExternalRefs'/> 1563<wfc def='CleanAttrVals'/></prod> 1564</prodgroup> 1565</scrap> 1566The <nt def='NT-Name'>Name</nt> in 1567the start- and end-tags gives the 1568element's <term>type</term>.</termdef> 1569<termdef id="dt-attr" term="Attribute"> 1570The <nt def='NT-Name'>Name</nt>-<nt def='NT-AttValue'>AttValue</nt> pairs are 1571referred to as 1572the <term>attribute specifications</term> of the element</termdef>, 1573<termdef id="dt-attrname" term="Attribute Name">with the 1574<nt def='NT-Name'>Name</nt> in each pair 1575referred to as the <term>attribute name</term></termdef> and 1576<termdef id="dt-attrval" term="Attribute Value">the content of the 1577<nt def='NT-AttValue'>AttValue</nt> (the text between the 1578<code>'</code> or <code>"</code> delimiters) 1579as the <term>attribute value</term>.</termdef> 1580</p> 1581<wfcnote id='uniqattspec'> 1582<head>Unique Att Spec</head> 1583<p> 1584No attribute name may appear more than once in the same start-tag 1585or empty-element tag. 1586</p> 1587</wfcnote> 1588<vcnote id='ValueType'> 1589<head>Attribute Value Type</head> 1590<p> 1591The attribute must have been declared; the value must be of the type 1592declared for it. 1593(For attribute types, see <specref ref='attdecls'/>.) 1594</p> 1595</vcnote> 1596<wfcnote id='NoExternalRefs'> 1597<head>No External Entity References</head> 1598<p> 1599Attribute values cannot contain direct or indirect entity references 1600to external entities. 1601</p> 1602</wfcnote> 1603<wfcnote id='CleanAttrVals'> 1604<head>No <code><</code> in Attribute Values</head> 1605<p>The <termref def='dt-repltext'>replacement text</termref> of any entity 1606referred to directly or indirectly in an attribute 1607value (other than "<code>&lt;</code>") must not contain 1608a <code><</code>. 1609</p></wfcnote> 1610<p>An example of a start-tag: 1611<eg><termdef id="dt-dog" term="dog"></eg></p> 1612<p><termdef id="dt-etag" term="End Tag">The end of every element 1613that begins with a start-tag must 1614be marked by an <term>end-tag</term> 1615containing a name that echoes the element's type as given in the 1616start-tag: 1617<scrap lang='ebnf'> 1618<head>End-tag</head> 1619<prodgroup pcw2="6" pcw4="15" pcw5="11.5"> 1620<prod id='NT-ETag'><lhs>ETag</lhs> 1621<rhs>'</' <nt def='NT-Name'>Name</nt> 1622<nt def='NT-S'>S</nt>? '>'</rhs></prod> 1623</prodgroup> 1624</scrap> 1625</termdef></p> 1626<p>An example of an end-tag:<eg></termdef></eg></p> 1627<p><termdef id="dt-content" term="Content">The 1628<termref def='dt-text'>text</termref> between the start-tag and 1629end-tag is called the element's 1630<term>content</term>: 1631<scrap lang='ebnf'> 1632<head>Content of Elements</head> 1633<prodgroup pcw2="6" pcw4="15" pcw5="11.5"> 1634<prod id='NT-content'><lhs>content</lhs> 1635<rhs>(<nt def='NT-element'>element</nt> | <nt def='NT-CharData'>CharData</nt> 1636| <nt def='NT-Reference'>Reference</nt> | <nt def='NT-CDSect'>CDSect</nt> 1637| <nt def='NT-PI'>PI</nt> | <nt def='NT-Comment'>Comment</nt>)*</rhs> 1638</prod> 1639</prodgroup> 1640</scrap> 1641</termdef></p> 1642<p><termdef id="dt-empty" term="Empty">If an element is <term>empty</term>, 1643it must be represented either by a start-tag immediately followed 1644by an end-tag or by an empty-element tag.</termdef> 1645<termdef id="dt-eetag" term="empty-element tag">An 1646<term>empty-element tag</term> takes a special form: 1647<scrap lang='ebnf'> 1648<head>Tags for Empty Elements</head> 1649<prodgroup pcw2="6" pcw4="15" pcw5="11.5"> 1650<prod id='NT-EmptyElemTag'><lhs>EmptyElemTag</lhs> 1651<rhs>'<' <nt def='NT-Name'>Name</nt> (<nt def='NT-S'>S</nt> 1652<nt def='NT-Attribute'>Attribute</nt>)* <nt def='NT-S'>S</nt>? 1653'/>'</rhs> 1654<wfc def="uniqattspec"/> 1655</prod> 1656</prodgroup> 1657</scrap> 1658</termdef></p> 1659<p>Empty-element tags may be used for any element which has no 1660content, whether or not it is declared using the keyword 1661<kw>EMPTY</kw>. 1662<termref def='dt-interop'>For interoperability</termref>, the empty-element 1663tag must be used, and can only be used, for elements which are 1664<termref def='dt-eldecl'>declared</termref> <kw>EMPTY</kw>.</p> 1665<p>Examples of empty elements: 1666<eg><IMG align="left" 1667 src="http://www.w3.org/Icons/WWW/w3c_home" /> 1668<br></br> 1669<br/></eg></p> 1670</div2> 1671 1672<div2 id='elemdecls'> 1673<head>Element Type Declarations</head> 1674 1675<p>The <termref def="dt-element">element</termref> structure of an 1676<termref def="dt-xml-doc">XML document</termref> may, for 1677<termref def="dt-valid">validation</termref> purposes, 1678be constrained 1679using element type and attribute-list declarations. 1680An element type declaration constrains the element's 1681<termref def="dt-content">content</termref>. 1682</p> 1683 1684<p>Element type declarations often constrain which element types can 1685appear as <termref def="dt-parentchild">children</termref> of the element. 1686At user option, an XML processor may issue a warning 1687when a declaration mentions an element type for which no declaration 1688is provided, but this is not an error.</p> 1689<p><termdef id="dt-eldecl" term="Element Type declaration">An <term>element 1690type declaration</term> takes the form: 1691<scrap lang='ebnf'> 1692<head>Element Type Declaration</head> 1693<prodgroup pcw2="5.5" pcw4="18" pcw5="9"> 1694<prod id='NT-elementdecl'><lhs>elementdecl</lhs> 1695<rhs>'<!ELEMENT' <nt def='NT-S'>S</nt> 1696<nt def='NT-Name'>Name</nt> 1697<nt def='NT-S'>S</nt> 1698<nt def='NT-contentspec'>contentspec</nt> 1699<nt def='NT-S'>S</nt>? '>'</rhs> 1700<vc def='EDUnique'/></prod> 1701<prod id='NT-contentspec'><lhs>contentspec</lhs> 1702<rhs>'EMPTY' 1703| 'ANY' 1704| <nt def='NT-Mixed'>Mixed</nt> 1705| <nt def='NT-children'>children</nt> 1706</rhs> 1707</prod> 1708</prodgroup> 1709</scrap> 1710where the <nt def='NT-Name'>Name</nt> gives the element type 1711being declared.</termdef> 1712</p> 1713 1714<vcnote id='EDUnique'> 1715<head>Unique Element Type Declaration</head> 1716<p> 1717No element type may be declared more than once. 1718</p> 1719</vcnote> 1720 1721<p>Examples of element type declarations: 1722<eg><!ELEMENT br EMPTY> 1723<!ELEMENT p (#PCDATA|emph)* > 1724<!ELEMENT %name.para; %content.para; > 1725<!ELEMENT container ANY></eg></p> 1726 1727<div3 id='sec-element-content'> 1728<head>Element Content</head> 1729 1730<p><termdef id='dt-elemcontent' term='Element content'>An element <termref 1731def="dt-stag">type</termref> has 1732<term>element content</term> when elements of that 1733type must contain only <termref def='dt-parentchild'>child</termref> 1734elements (no character data), optionally separated by 1735white space (characters matching the nonterminal 1736<nt def='NT-S'>S</nt>). 1737</termdef> 1738In this case, the 1739constraint includes a content model, a simple grammar governing 1740the allowed types of the child 1741elements and the order in which they are allowed to appear. 1742The grammar is built on 1743content particles (<nt def='NT-cp'>cp</nt>s), which consist of names, 1744choice lists of content particles, or 1745sequence lists of content particles: 1746<scrap lang='ebnf'> 1747<head>Element-content Models</head> 1748<prodgroup pcw2="5.5" pcw4="16" pcw5="11"> 1749<prod id='NT-children'><lhs>children</lhs> 1750<rhs>(<nt def='NT-choice'>choice</nt> 1751| <nt def='NT-seq'>seq</nt>) 1752('?' | '*' | '+')?</rhs></prod> 1753<prod id='NT-cp'><lhs>cp</lhs> 1754<rhs>(<nt def='NT-Name'>Name</nt> 1755| <nt def='NT-choice'>choice</nt> 1756| <nt def='NT-seq'>seq</nt>) 1757('?' | '*' | '+')?</rhs></prod> 1758<prod id='NT-choice'><lhs>choice</lhs> 1759<rhs>'(' <nt def='NT-S'>S</nt>? cp 1760( <nt def='NT-S'>S</nt>? '|' <nt def='NT-S'>S</nt>? <nt def='NT-cp'>cp</nt> )* 1761<nt def='NT-S'>S</nt>? ')'</rhs> 1762<vc def='vc-PEinGroup'/></prod> 1763<prod id='NT-seq'><lhs>seq</lhs> 1764<rhs>'(' <nt def='NT-S'>S</nt>? cp 1765( <nt def='NT-S'>S</nt>? ',' <nt def='NT-S'>S</nt>? <nt def='NT-cp'>cp</nt> )* 1766<nt def='NT-S'>S</nt>? ')'</rhs> 1767<vc def='vc-PEinGroup'/></prod> 1768 1769</prodgroup> 1770</scrap> 1771where each <nt def='NT-Name'>Name</nt> is the type of an element which may 1772appear as a <termref def="dt-parentchild">child</termref>. 1773Any content 1774particle in a choice list may appear in the <termref 1775def="dt-elemcontent">element content</termref> at the location where 1776the choice list appears in the grammar; 1777content particles occurring in a sequence list must each 1778appear in the <termref def="dt-elemcontent">element content</termref> in the 1779order given in the list. 1780The optional character following a name or list governs 1781whether the element or the content particles in the list may occur one 1782or more (<code>+</code>), zero or more (<code>*</code>), or zero or 1783one times (<code>?</code>). 1784The absence of such an operator means that the element or content particle 1785must appear exactly once. 1786This syntax 1787and meaning are identical to those used in the productions in this 1788specification.</p> 1789<p> 1790The content of an element matches a content model if and only if it is 1791possible to trace out a path through the content model, obeying the 1792sequence, choice, and repetition operators and matching each element in 1793the content against an element type in the content model. <termref 1794def='dt-compat'>For compatibility</termref>, it is an error 1795if an element in the document can 1796match more than one occurrence of an element type in the content model. 1797For more information, see <specref ref="determinism"/>. 1798<!-- appendix <specref ref="determinism"/>. --> 1799<!-- appendix on deterministic content models. --> 1800</p> 1801<vcnote id='vc-PEinGroup'> 1802<head>Proper Group/PE Nesting</head> 1803<p>Parameter-entity 1804<termref def='dt-repltext'>replacement text</termref> must be properly nested 1805with parenthetized groups. 1806That is to say, if either of the opening or closing parentheses 1807in a <nt def='NT-choice'>choice</nt>, <nt def='NT-seq'>seq</nt>, or 1808<nt def='NT-Mixed'>Mixed</nt> construct 1809is contained in the replacement text for a 1810<termref def='dt-PERef'>parameter entity</termref>, 1811both must be contained in the same replacement text.</p> 1812<p><termref def='dt-interop'>For interoperability</termref>, 1813if a parameter-entity reference appears in a 1814<nt def='NT-choice'>choice</nt>, <nt def='NT-seq'>seq</nt>, or 1815<nt def='NT-Mixed'>Mixed</nt> construct, its replacement text 1816should not be empty, and 1817neither the first nor last non-blank 1818character of the replacement text should be a connector 1819(<code>|</code> or <code>,</code>). 1820</p> 1821</vcnote> 1822<p>Examples of element-content models: 1823<eg><!ELEMENT spec (front, body, back?)> 1824<!ELEMENT div1 (head, (p | list | note)*, div2*)> 1825<!ELEMENT dictionary-body (%div.mix; | %dict.mix;)*></eg></p> 1826</div3> 1827 1828<div3 id='sec-mixed-content'> 1829<head>Mixed Content</head> 1830 1831<p><termdef id='dt-mixed' term='Mixed Content'>An element 1832<termref def='dt-stag'>type</termref> has 1833<term>mixed content</term> when elements of that type may contain 1834character data, optionally interspersed with 1835<termref def="dt-parentchild">child</termref> elements.</termdef> 1836In this case, the types of the child elements 1837may be constrained, but not their order or their number of occurrences: 1838<scrap lang='ebnf'> 1839<head>Mixed-content Declaration</head> 1840<prodgroup pcw2="5.5" pcw4="16" pcw5="11"> 1841<prod id='NT-Mixed'><lhs>Mixed</lhs> 1842<rhs>'(' <nt def='NT-S'>S</nt>? 1843'#PCDATA' 1844(<nt def='NT-S'>S</nt>? 1845'|' 1846<nt def='NT-S'>S</nt>? 1847<nt def='NT-Name'>Name</nt>)* 1848<nt def='NT-S'>S</nt>? 1849')*' </rhs> 1850<rhs>| '(' <nt def='NT-S'>S</nt>? '#PCDATA' <nt def='NT-S'>S</nt>? ')' 1851</rhs><vc def='vc-PEinGroup'/> 1852<vc def='vc-MixedChildrenUnique'/> 1853</prod> 1854 1855</prodgroup> 1856</scrap> 1857where the <nt def='NT-Name'>Name</nt>s give the types of elements 1858that may appear as children. 1859</p> 1860<vcnote id='vc-MixedChildrenUnique'> 1861<head>No Duplicate Types</head> 1862<p>The same name must not appear more than once in a single mixed-content 1863declaration. 1864</p></vcnote> 1865<p>Examples of mixed content declarations: 1866<eg><!ELEMENT p (#PCDATA|a|ul|b|i|em)*> 1867<!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* > 1868<!ELEMENT b (#PCDATA)></eg></p> 1869</div3> 1870</div2> 1871 1872<div2 id='attdecls'> 1873<head>Attribute-List Declarations</head> 1874 1875<p><termref def="dt-attr">Attributes</termref> are used to associate 1876name-value pairs with <termref def="dt-element">elements</termref>. 1877Attribute specifications may appear only within <termref 1878def="dt-stag">start-tags</termref> 1879and <termref def="dt-eetag">empty-element tags</termref>; 1880thus, the productions used to 1881recognize them appear in <specref ref='sec-starttags'/>. 1882Attribute-list 1883declarations may be used: 1884<ulist> 1885<item><p>To define the set of attributes pertaining to a given 1886element type.</p></item> 1887<item><p>To establish type constraints for these 1888attributes.</p></item> 1889<item><p>To provide <termref def="dt-default">default values</termref> 1890for attributes.</p></item> 1891</ulist> 1892</p> 1893<p><termdef id="dt-attdecl" term="Attribute-List Declaration"> 1894<term>Attribute-list declarations</term> specify the name, data type, and default 1895value (if any) of each attribute associated with a given element type: 1896<scrap lang='ebnf'> 1897<head>Attribute-list Declaration</head> 1898<prod id='NT-AttlistDecl'><lhs>AttlistDecl</lhs> 1899<rhs>'<!ATTLIST' <nt def='NT-S'>S</nt> 1900<nt def='NT-Name'>Name</nt> 1901<nt def='NT-AttDef'>AttDef</nt>* 1902<nt def='NT-S'>S</nt>? '>'</rhs> 1903</prod> 1904<prod id='NT-AttDef'><lhs>AttDef</lhs> 1905<rhs><nt def='NT-S'>S</nt> <nt def='NT-Name'>Name</nt> 1906<nt def='NT-S'>S</nt> <nt def='NT-AttType'>AttType</nt> 1907<nt def='NT-S'>S</nt> <nt def='NT-DefaultDecl'>DefaultDecl</nt></rhs> 1908</prod> 1909</scrap> 1910The <nt def="NT-Name">Name</nt> in the 1911<nt def='NT-AttlistDecl'>AttlistDecl</nt> rule is the type of an element. At 1912user option, an XML processor may issue a warning if attributes are 1913declared for an element type not itself declared, but this is not an 1914error. The <nt def='NT-Name'>Name</nt> in the 1915<nt def='NT-AttDef'>AttDef</nt> rule is 1916the name of the attribute.</termdef></p> 1917<p> 1918When more than one <nt def='NT-AttlistDecl'>AttlistDecl</nt> is provided for a 1919given element type, the contents of all those provided are merged. When 1920more than one definition is provided for the same attribute of a 1921given element type, the first declaration is binding and later 1922declarations are ignored. 1923<termref def='dt-interop'>For interoperability,</termref> writers of DTDs 1924may choose to provide at most one attribute-list declaration 1925for a given element type, at most one attribute definition 1926for a given attribute name, and at least one attribute definition 1927in each attribute-list declaration. 1928For interoperability, an XML processor may at user option 1929issue a warning when more than one attribute-list declaration is 1930provided for a given element type, or more than one attribute definition 1931is provided 1932for a given attribute, but this is not an error. 1933</p> 1934 1935<div3 id='sec-attribute-types'> 1936<head>Attribute Types</head> 1937 1938<p>XML attribute types are of three kinds: a string type, a 1939set of tokenized types, and enumerated types. The string type may take 1940any literal string as a value; the tokenized types have varying lexical 1941and semantic constraints, as noted: 1942<scrap lang='ebnf'> 1943<head>Attribute Types</head> 1944<prodgroup pcw4="14" pcw5="11.5"> 1945<prod id='NT-AttType'><lhs>AttType</lhs> 1946<rhs><nt def='NT-StringType'>StringType</nt> 1947| <nt def='NT-TokenizedType'>TokenizedType</nt> 1948| <nt def='NT-EnumeratedType'>EnumeratedType</nt> 1949</rhs> 1950</prod> 1951<prod id='NT-StringType'><lhs>StringType</lhs> 1952<rhs>'CDATA'</rhs> 1953</prod> 1954<prod id='NT-TokenizedType'><lhs>TokenizedType</lhs> 1955<rhs>'ID'</rhs> 1956<vc def='id'/> 1957<vc def='one-id-per-el'/> 1958<vc def='id-default'/> 1959<rhs>| 'IDREF'</rhs> 1960<vc def='idref'/> 1961<rhs>| 'IDREFS'</rhs> 1962<vc def='idref'/> 1963<rhs>| 'ENTITY'</rhs> 1964<vc def='entname'/> 1965<rhs>| 'ENTITIES'</rhs> 1966<vc def='entname'/> 1967<rhs>| 'NMTOKEN'</rhs> 1968<vc def='nmtok'/> 1969<rhs>| 'NMTOKENS'</rhs> 1970<vc def='nmtok'/></prod> 1971</prodgroup> 1972</scrap> 1973</p> 1974<vcnote id='id' > 1975<head>ID</head> 1976<p> 1977Values of type <kw>ID</kw> must match the 1978<nt def='NT-Name'>Name</nt> production. 1979A name must not appear more than once in 1980an XML document as a value of this type; i.e., ID values must uniquely 1981identify the elements which bear them. 1982</p> 1983</vcnote> 1984<vcnote id='one-id-per-el'> 1985<head>One ID per Element Type</head> 1986<p>No element type may have more than one ID attribute specified.</p> 1987</vcnote> 1988<vcnote id='id-default'> 1989<head>ID Attribute Default</head> 1990<p>An ID attribute must have a declared default of <kw>#IMPLIED</kw> or 1991<kw>#REQUIRED</kw>.</p> 1992</vcnote> 1993<vcnote id='idref'> 1994<head>IDREF</head> 1995<p> 1996Values of type <kw>IDREF</kw> must match 1997the <nt def="NT-Name">Name</nt> production, and 1998values of type <kw>IDREFS</kw> must match 1999<nt def="NT-Names">Names</nt>; 2000each <nt def='NT-Name'>Name</nt> must match the value of an ID attribute on 2001some element in the XML document; i.e. <kw>IDREF</kw> values must 2002match the value of some ID attribute. 2003</p> 2004</vcnote> 2005<vcnote id='entname'> 2006<head>Entity Name</head> 2007<p> 2008Values of type <kw>ENTITY</kw> 2009must match the <nt def="NT-Name">Name</nt> production, 2010values of type <kw>ENTITIES</kw> must match 2011<nt def="NT-Names">Names</nt>; 2012each <nt def="NT-Name">Name</nt> must 2013match the 2014name of an <termref def="dt-unparsed">unparsed entity</termref> declared in the 2015<termref def="dt-doctype">DTD</termref>. 2016</p> 2017</vcnote> 2018<vcnote id='nmtok'> 2019<head>Name Token</head> 2020<p> 2021Values of type <kw>NMTOKEN</kw> must match the 2022<nt def="NT-Nmtoken">Nmtoken</nt> production; 2023values of type <kw>NMTOKENS</kw> must 2024match <termref def="NT-Nmtokens">Nmtokens</termref>. 2025</p> 2026</vcnote> 2027<!-- why? 2028<p>The XML processor must normalize attribute values before 2029passing them to the application, as described in 2030<specref ref="AVNormalize"/>.</p>--> 2031<p><termdef id='dt-enumerated' term='Enumerated Attribute 2032Values'><term>Enumerated attributes</term> can take one 2033of a list of values provided in the declaration</termdef>. There are two 2034kinds of enumerated types: 2035<scrap lang='ebnf'> 2036<head>Enumerated Attribute Types</head> 2037<prod id='NT-EnumeratedType'><lhs>EnumeratedType</lhs> 2038<rhs><nt def='NT-NotationType'>NotationType</nt> 2039| <nt def='NT-Enumeration'>Enumeration</nt> 2040</rhs></prod> 2041<prod id='NT-NotationType'><lhs>NotationType</lhs> 2042<rhs>'NOTATION' 2043<nt def='NT-S'>S</nt> 2044'(' 2045<nt def='NT-S'>S</nt>? 2046<nt def='NT-Name'>Name</nt> 2047(<nt def='NT-S'>S</nt>? '|' <nt def='NT-S'>S</nt>? 2048<nt def='NT-Name'>Name</nt>)* 2049<nt def='NT-S'>S</nt>? ')' 2050</rhs> 2051<vc def='notatn' /></prod> 2052<prod id='NT-Enumeration'><lhs>Enumeration</lhs> 2053<rhs>'(' <nt def='NT-S'>S</nt>? 2054<nt def='NT-Nmtoken'>Nmtoken</nt> 2055(<nt def='NT-S'>S</nt>? '|' 2056<nt def='NT-S'>S</nt>? 2057<nt def='NT-Nmtoken'>Nmtoken</nt>)* 2058<nt def='NT-S'>S</nt>? 2059')'</rhs> 2060<vc def='enum'/></prod> 2061</scrap> 2062A <kw>NOTATION</kw> attribute identifies a 2063<termref def='dt-notation'>notation</termref>, declared in the 2064DTD with associated system and/or public identifiers, to 2065be used in interpreting the element to which the attribute 2066is attached. 2067</p> 2068 2069<vcnote id='notatn'> 2070<head>Notation Attributes</head> 2071<p> 2072Values of this type must match 2073one of the <titleref href='Notations'>notation</titleref> names included in 2074the declaration; all notation names in the declaration must 2075be declared. 2076</p> 2077</vcnote> 2078<vcnote id='enum'> 2079<head>Enumeration</head> 2080<p> 2081Values of this type 2082must match one of the <nt def='NT-Nmtoken'>Nmtoken</nt> tokens in the 2083declaration. 2084</p> 2085</vcnote> 2086<p><termref def='dt-interop'>For interoperability,</termref> the same 2087<nt def='NT-Nmtoken'>Nmtoken</nt> should not occur more than once in the 2088enumerated attribute types of a single element type. 2089</p> 2090</div3> 2091 2092<div3 id='sec-attr-defaults'> 2093<head>Attribute Defaults</head> 2094 2095<p>An <termref def="dt-attdecl">attribute declaration</termref> provides 2096information on whether 2097the attribute's presence is required, and if not, how an XML processor should 2098react if a declared attribute is absent in a document. 2099<scrap lang='ebnf'> 2100<head>Attribute Defaults</head> 2101<prodgroup pcw4="14" pcw5="11.5"> 2102<prod id='NT-DefaultDecl'><lhs>DefaultDecl</lhs> 2103<rhs>'#REQUIRED' 2104| '#IMPLIED' </rhs> 2105<rhs>| (('#FIXED' S)? <nt def='NT-AttValue'>AttValue</nt>)</rhs> 2106<vc def='RequiredAttr'/> 2107<vc def='defattrvalid'/> 2108<wfc def="CleanAttrVals"/> 2109<vc def='FixedAttr'/> 2110</prod> 2111</prodgroup> 2112</scrap> 2113 2114</p> 2115<p>In an attribute declaration, <kw>#REQUIRED</kw> means that the 2116attribute must always be provided, <kw>#IMPLIED</kw> that no default 2117value is provided. 2118<!-- not any more!! 2119<kw>#IMPLIED</kw> means that if the attribute is omitted 2120from an element of this type, 2121the XML processor must inform the application 2122that no value was specified; no constraint is placed on the behavior 2123of the application. --> 2124<termdef id="dt-default" term="Attribute Default">If the 2125declaration 2126is neither <kw>#REQUIRED</kw> nor <kw>#IMPLIED</kw>, then the 2127<nt def='NT-AttValue'>AttValue</nt> value contains the declared 2128<term>default</term> value; the <kw>#FIXED</kw> keyword states that 2129the attribute must always have the default value. 2130If a default value 2131is declared, when an XML processor encounters an omitted attribute, it 2132is to behave as though the attribute were present with 2133the declared default value.</termdef></p> 2134<vcnote id='RequiredAttr'> 2135<head>Required Attribute</head> 2136<p>If the default declaration is the keyword <kw>#REQUIRED</kw>, then 2137the attribute must be specified for 2138all elements of the type in the attribute-list declaration. 2139</p></vcnote> 2140<vcnote id='defattrvalid'> 2141<head>Attribute Default Legal</head> 2142<p> 2143The declared 2144default value must meet the lexical constraints of the declared attribute type. 2145</p> 2146</vcnote> 2147<vcnote id='FixedAttr'> 2148<head>Fixed Attribute Default</head> 2149<p>If an attribute has a default value declared with the 2150<kw>#FIXED</kw> keyword, instances of that attribute must 2151match the default value. 2152</p></vcnote> 2153 2154<p>Examples of attribute-list declarations: 2155<eg><!ATTLIST termdef 2156 id ID #REQUIRED 2157 name CDATA #IMPLIED> 2158<!ATTLIST list 2159 type (bullets|ordered|glossary) "ordered"> 2160<!ATTLIST form 2161 method CDATA #FIXED "POST"></eg></p> 2162</div3> 2163<div3 id='AVNormalize'> 2164<head>Attribute-Value Normalization</head> 2165<p>Before the value of an attribute is passed to the application 2166or checked for validity, the 2167XML processor must normalize it as follows: 2168<ulist> 2169<item><p>a character reference is processed by appending the referenced 2170character to the attribute value</p></item> 2171<item><p>an entity reference is processed by recursively processing the 2172replacement text of the entity</p></item> 2173<item><p>a whitespace character (#x20, #xD, #xA, #x9) is processed by 2174appending #x20 to the normalized value, except that only a single #x20 2175is appended for a "#xD#xA" sequence that is part of an external 2176parsed entity or the literal entity value of an internal parsed 2177entity</p></item> 2178<item><p>other characters are processed by appending them to the normalized 2179value</p> 2180</item></ulist> 2181</p> 2182<p>If the declared value is not CDATA, then the XML processor must 2183further process the normalized attribute value by discarding any 2184leading and trailing space (#x20) characters, and by replacing 2185sequences of space (#x20) characters by a single space (#x20) 2186character.</p> 2187<p> 2188All attributes for which no declaration has been read should be treated 2189by a non-validating parser as if declared 2190<kw>CDATA</kw>. 2191</p> 2192</div3> 2193</div2> 2194<div2 id='sec-condition-sect'> 2195<head>Conditional Sections</head> 2196<p><termdef id='dt-cond-section' term='conditional section'> 2197<term>Conditional sections</term> are portions of the 2198<termref def='dt-doctype'>document type declaration external subset</termref> 2199which are 2200included in, or excluded from, the logical structure of the DTD based on 2201the keyword which governs them.</termdef> 2202<scrap lang='ebnf'> 2203<head>Conditional Section</head> 2204<prodgroup pcw2="9" pcw4="14.5"> 2205<prod id='NT-conditionalSect'><lhs>conditionalSect</lhs> 2206<rhs><nt def='NT-includeSect'>includeSect</nt> 2207| <nt def='NT-ignoreSect'>ignoreSect</nt> 2208</rhs> 2209</prod> 2210<prod id='NT-includeSect'><lhs>includeSect</lhs> 2211<rhs>'<![' S? 'INCLUDE' S? '[' 2212 2213<nt def="NT-extSubsetDecl">extSubsetDecl</nt> 2214']]>' 2215</rhs> 2216</prod> 2217<prod id='NT-ignoreSect'><lhs>ignoreSect</lhs> 2218<rhs>'<![' S? 'IGNORE' S? '[' 2219<nt def="NT-ignoreSectContents">ignoreSectContents</nt>* 2220']]>'</rhs> 2221</prod> 2222 2223<prod id='NT-ignoreSectContents'><lhs>ignoreSectContents</lhs> 2224<rhs><nt def='NT-Ignore'>Ignore</nt> 2225('<![' <nt def='NT-ignoreSectContents'>ignoreSectContents</nt> ']]>' 2226<nt def='NT-Ignore'>Ignore</nt>)*</rhs></prod> 2227<prod id='NT-Ignore'><lhs>Ignore</lhs> 2228<rhs><nt def='NT-Char'>Char</nt>* - 2229(<nt def='NT-Char'>Char</nt>* ('<![' | ']]>') 2230<nt def='NT-Char'>Char</nt>*) 2231</rhs></prod> 2232 2233</prodgroup> 2234</scrap> 2235</p> 2236<p>Like the internal and external DTD subsets, a conditional section 2237may contain one or more complete declarations, 2238comments, processing instructions, 2239or nested conditional sections, intermingled with white space. 2240</p> 2241<p>If the keyword of the 2242conditional section is <kw>INCLUDE</kw>, then the contents of the conditional 2243section are part of the DTD. 2244If the keyword of the conditional 2245section is <kw>IGNORE</kw>, then the contents of the conditional section are 2246not logically part of the DTD. 2247Note that for reliable parsing, the contents of even ignored 2248conditional sections must be read in order to 2249detect nested conditional sections and ensure that the end of the 2250outermost (ignored) conditional section is properly detected. 2251If a conditional section with a 2252keyword of <kw>INCLUDE</kw> occurs within a larger conditional 2253section with a keyword of <kw>IGNORE</kw>, both the outer and the 2254inner conditional sections are ignored.</p> 2255<p>If the keyword of the conditional section is a 2256parameter-entity reference, the parameter entity must be replaced by its 2257content before the processor decides whether to 2258include or ignore the conditional section.</p> 2259<p>An example: 2260<eg><!ENTITY % draft 'INCLUDE' > 2261<!ENTITY % final 'IGNORE' > 2262 2263<![%draft;[ 2264<!ELEMENT book (comments*, title, body, supplements?)> 2265]]> 2266<![%final;[ 2267<!ELEMENT book (title, body, supplements?)> 2268]]> 2269</eg> 2270</p> 2271</div2> 2272 2273 2274<!-- 2275<div2 id='sec-pass-to-app'> 2276<head>XML Processor Treatment of Logical Structure</head> 2277<p>When an XML processor encounters a start-tag, it must make 2278at least the following information available to the application: 2279<ulist> 2280<item> 2281<p>the element type's generic identifier</p> 2282</item> 2283<item> 2284<p>the names of attributes known to apply to this element type 2285(validating processors must make available names of all attributes 2286declared for the element type; non-validating processors must 2287make available at least the names of the attributes for which 2288values are specified. 2289</p> 2290</item> 2291</ulist> 2292</p> 2293</div2> 2294--> 2295 2296</div1> 2297<!-- &Entities; --> 2298 2299<div1 id='sec-physical-struct'> 2300<head>Physical Structures</head> 2301 2302<p><termdef id="dt-entity" term="Entity">An XML document may consist 2303of one or many storage units. These are called 2304<term>entities</term>; they all have <term>content</term> and are all 2305(except for the document entity, see below, and 2306the <termref def='dt-doctype'>external DTD subset</termref>) 2307identified by <term>name</term>. 2308</termdef> 2309Each XML document has one entity 2310called the <termref def="dt-docent">document entity</termref>, which serves 2311as the starting point for the <termref def="dt-xml-proc">XML 2312processor</termref> and may contain the whole document.</p> 2313<p>Entities may be either parsed or unparsed. 2314<termdef id="dt-parsedent" term="Text Entity">A <term>parsed entity's</term> 2315contents are referred to as its 2316<termref def='dt-repltext'>replacement text</termref>; 2317this <termref def="dt-text">text</termref> is considered an 2318integral part of the document.</termdef></p> 2319 2320<p><termdef id="dt-unparsed" term="Unparsed Entity">An 2321<term>unparsed entity</term> 2322is a resource whose contents may or may not be 2323<termref def='dt-text'>text</termref>, and if text, may not be XML. 2324Each unparsed entity 2325has an associated <termref 2326def="dt-notation">notation</termref>, identified by name. 2327Beyond a requirement 2328that an XML processor make the identifiers for the entity and 2329notation available to the application, 2330XML places no constraints on the contents of unparsed entities.</termdef> 2331</p> 2332<p> 2333Parsed entities are invoked by name using entity references; 2334unparsed entities by name, given in the value of <kw>ENTITY</kw> 2335or <kw>ENTITIES</kw> 2336attributes.</p> 2337<p><termdef id='gen-entity' term='general entity' 2338><term>General entities</term> 2339are entities for use within the document content. 2340In this specification, general entities are sometimes referred 2341to with the unqualified term <emph>entity</emph> when this leads 2342to no ambiguity.</termdef> 2343<termdef id='dt-PE' term='Parameter entity'>Parameter entities 2344are parsed entities for use within the DTD.</termdef> 2345These two types of entities use different forms of reference and 2346are recognized in different contexts. 2347Furthermore, they occupy different namespaces; a parameter entity and 2348a general entity with the same name are two distinct entities. 2349</p> 2350 2351<div2 id='sec-references'> 2352<head>Character and Entity References</head> 2353<p><termdef id="dt-charref" term="Character Reference"> 2354A <term>character reference</term> refers to a specific character in the 2355ISO/IEC 10646 character set, for example one not directly accessible from 2356available input devices. 2357<scrap lang='ebnf'> 2358<head>Character Reference</head> 2359<prod id='NT-CharRef'><lhs>CharRef</lhs> 2360<rhs>'&#' [0-9]+ ';' </rhs> 2361<rhs>| '&hcro;' [0-9a-fA-F]+ ';'</rhs> 2362<wfc def="wf-Legalchar"/> 2363</prod> 2364</scrap> 2365<wfcnote id="wf-Legalchar"> 2366<head>Legal Character</head> 2367<p>Characters referred to using character references must 2368match the production for 2369<termref def="NT-Char">Char</termref>.</p> 2370</wfcnote> 2371If the character reference begins with "<code>&#x</code>", the digits and 2372letters up to the terminating <code>;</code> provide a hexadecimal 2373representation of the character's code point in ISO/IEC 10646. 2374If it begins just with "<code>&#</code>", the digits up to the terminating 2375<code>;</code> provide a decimal representation of the character's 2376code point. 2377</termdef> 2378</p> 2379<p><termdef id="dt-entref" term="Entity Reference">An <term>entity 2380reference</term> refers to the content of a named entity.</termdef> 2381<termdef id='dt-GERef' term='General Entity Reference'>References to 2382parsed general entities 2383use ampersand (<code>&</code>) and semicolon (<code>;</code>) as 2384delimiters.</termdef> 2385<termdef id='dt-PERef' term='Parameter-entity reference'> 2386<term>Parameter-entity references</term> use percent-sign (<code>%</code>) and 2387semicolon 2388(<code>;</code>) as delimiters.</termdef> 2389</p> 2390<scrap lang="ebnf"> 2391<head>Entity Reference</head> 2392<prod id='NT-Reference'><lhs>Reference</lhs> 2393<rhs><nt def='NT-EntityRef'>EntityRef</nt> 2394| <nt def='NT-CharRef'>CharRef</nt></rhs></prod> 2395<prod id='NT-EntityRef'><lhs>EntityRef</lhs> 2396<rhs>'&' <nt def='NT-Name'>Name</nt> ';'</rhs> 2397<wfc def='wf-entdeclared'/> 2398<vc def='vc-entdeclared'/> 2399<wfc def='textent'/> 2400<wfc def='norecursion'/> 2401</prod> 2402<prod id='NT-PEReference'><lhs>PEReference</lhs> 2403<rhs>'%' <nt def='NT-Name'>Name</nt> ';'</rhs> 2404<vc def='vc-entdeclared'/> 2405<wfc def='norecursion'/> 2406<wfc def='indtd'/> 2407</prod> 2408</scrap> 2409 2410<wfcnote id='wf-entdeclared'> 2411<head>Entity Declared</head> 2412<p>In a document without any DTD, a document with only an internal 2413DTD subset which contains no parameter entity references, or a document with 2414"<code>standalone='yes'</code>", 2415the <nt def='NT-Name'>Name</nt> given in the entity reference must 2416<termref def="dt-match">match</termref> that in an 2417<titleref href='sec-entity-decl'>entity declaration</titleref>, except that 2418well-formed documents need not declare 2419any of the following entities: &magicents;. 2420The declaration of a parameter entity must precede any reference to it. 2421Similarly, the declaration of a general entity must precede any 2422reference to it which appears in a default value in an attribute-list 2423declaration.</p> 2424<p>Note that if entities are declared in the external subset or in 2425external parameter entities, a non-validating processor is 2426<titleref href='include-if-valid'>not obligated to</titleref> read 2427and process their declarations; for such documents, the rule that 2428an entity must be declared is a well-formedness constraint only 2429if <titleref href='sec-rmd'>standalone='yes'</titleref>.</p> 2430</wfcnote> 2431<vcnote id="vc-entdeclared"> 2432<head>Entity Declared</head> 2433<p>In a document with an external subset or external parameter 2434entities with "<code>standalone='no'</code>", 2435the <nt def='NT-Name'>Name</nt> given in the entity reference must <termref 2436def="dt-match">match</termref> that in an 2437<titleref href='sec-entity-decl'>entity declaration</titleref>. 2438For interoperability, valid documents should declare the entities 2439&magicents;, in the form 2440specified in <specref ref="sec-predefined-ent"/>. 2441The declaration of a parameter entity must precede any reference to it. 2442Similarly, the declaration of a general entity must precede any 2443reference to it which appears in a default value in an attribute-list 2444declaration.</p> 2445</vcnote> 2446<!-- FINAL EDIT: is this duplication too clumsy? --> 2447<wfcnote id='textent'> 2448<head>Parsed Entity</head> 2449<p> 2450An entity reference must not contain the name of an <termref 2451def="dt-unparsed">unparsed entity</termref>. Unparsed entities may be referred 2452to only in <termref def="dt-attrval">attribute values</termref> declared to 2453be of type <kw>ENTITY</kw> or <kw>ENTITIES</kw>. 2454</p> 2455</wfcnote> 2456<wfcnote id='norecursion'> 2457<head>No Recursion</head> 2458<p> 2459A parsed entity must not contain a recursive reference to itself, 2460either directly or indirectly. 2461</p> 2462</wfcnote> 2463<wfcnote id='indtd'> 2464<head>In DTD</head> 2465<p> 2466Parameter-entity references may only appear in the 2467<termref def='dt-doctype'>DTD</termref>. 2468</p> 2469</wfcnote> 2470<p>Examples of character and entity references: 2471<eg>Type <key>less-than</key> (&hcro;3C;) to save options. 2472This document was prepared on &docdate; and 2473is classified &security-level;.</eg></p> 2474<p>Example of a parameter-entity reference: 2475<eg><![CDATA[<!-- declare the parameter entity "ISOLat2"... --> 2476<!ENTITY % ISOLat2 2477 SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" > 2478<!-- ... now reference it. --> 2479%ISOLat2;]]></eg></p> 2480</div2> 2481 2482<div2 id='sec-entity-decl'> 2483<head>Entity Declarations</head> 2484 2485<p><termdef id="dt-entdecl" term="entity declaration"> 2486Entities are declared thus: 2487<scrap lang='ebnf'> 2488<head>Entity Declaration</head> 2489<prodgroup pcw2="5" pcw4="18.5"> 2490<prod id='NT-EntityDecl'><lhs>EntityDecl</lhs> 2491<rhs><nt def="NT-GEDecl">GEDecl</nt><!--</rhs><com>General entities</com> 2492<rhs>--> | <nt def="NT-PEDecl">PEDecl</nt></rhs> 2493<!--<com>Parameter entities</com>--> 2494</prod> 2495<prod id='NT-GEDecl'><lhs>GEDecl</lhs> 2496<rhs>'<!ENTITY' <nt def='NT-S'>S</nt> <nt def='NT-Name'>Name</nt> 2497<nt def='NT-S'>S</nt> <nt def='NT-EntityDef'>EntityDef</nt> 2498<nt def='NT-S'>S</nt>? '>'</rhs> 2499</prod> 2500<prod id='NT-PEDecl'><lhs>PEDecl</lhs> 2501<rhs>'<!ENTITY' <nt def='NT-S'>S</nt> '%' <nt def='NT-S'>S</nt> 2502<nt def='NT-Name'>Name</nt> <nt def='NT-S'>S</nt> 2503<nt def='NT-PEDef'>PEDef</nt> <nt def='NT-S'>S</nt>? '>'</rhs> 2504<!--<com>Parameter entities</com>--> 2505</prod> 2506<prod id='NT-EntityDef'><lhs>EntityDef</lhs> 2507<rhs><nt def='NT-EntityValue'>EntityValue</nt> 2508<!--</rhs> 2509<rhs>-->| (<nt def='NT-ExternalID'>ExternalID</nt> 2510<nt def='NT-NDataDecl'>NDataDecl</nt>?)</rhs> 2511<!-- <nt def='NT-ExternalDef'>ExternalDef</nt></rhs> --> 2512</prod> 2513<!-- FINAL EDIT: what happened to WFs here? --> 2514<prod id='NT-PEDef'><lhs>PEDef</lhs> 2515<rhs><nt def='NT-EntityValue'>EntityValue</nt> 2516| <nt def='NT-ExternalID'>ExternalID</nt></rhs></prod> 2517</prodgroup> 2518</scrap> 2519The <nt def='NT-Name'>Name</nt> identifies the entity in an 2520<termref def="dt-entref">entity reference</termref> or, in the case of an 2521unparsed entity, in the value of an <kw>ENTITY</kw> or <kw>ENTITIES</kw> 2522attribute. 2523If the same entity is declared more than once, the first declaration 2524encountered is binding; at user option, an XML processor may issue a 2525warning if entities are declared multiple times.</termdef> 2526</p> 2527 2528<div3 id='sec-internal-ent'> 2529<head>Internal Entities</head> 2530 2531<p><termdef id='dt-internent' term="Internal Entity Replacement Text">If 2532the entity definition is an 2533<nt def='NT-EntityValue'>EntityValue</nt>, 2534the defined entity is called an <term>internal entity</term>. 2535There is no separate physical 2536storage object, and the content of the entity is given in the 2537declaration. </termdef> 2538Note that some processing of entity and character references in the 2539<termref def='dt-litentval'>literal entity value</termref> may be required to 2540produce the correct <termref def='dt-repltext'>replacement 2541text</termref>: see <specref ref='intern-replacement'/>. 2542</p> 2543<p>An internal entity is a <termref def="dt-parsedent">parsed 2544entity</termref>.</p> 2545<p>Example of an internal entity declaration: 2546<eg><!ENTITY Pub-Status "This is a pre-release of the 2547 specification."></eg></p> 2548</div3> 2549 2550<div3 id='sec-external-ent'> 2551<head>External Entities</head> 2552 2553<p><termdef id="dt-extent" term="External Entity">If the entity is not 2554internal, it is an <term>external 2555entity</term>, declared as follows: 2556<scrap lang='ebnf'> 2557<head>External Entity Declaration</head> 2558<!-- 2559<prod id='NT-ExternalDef'><lhs>ExternalDef</lhs> 2560<rhs></prod> --> 2561<prod id='NT-ExternalID'><lhs>ExternalID</lhs> 2562<rhs>'SYSTEM' <nt def='NT-S'>S</nt> 2563<nt def='NT-SystemLiteral'>SystemLiteral</nt></rhs> 2564<rhs>| 'PUBLIC' <nt def='NT-S'>S</nt> 2565<nt def='NT-PubidLiteral'>PubidLiteral</nt> 2566<nt def='NT-S'>S</nt> 2567<nt def='NT-SystemLiteral'>SystemLiteral</nt> 2568</rhs> 2569</prod> 2570<prod id='NT-NDataDecl'><lhs>NDataDecl</lhs> 2571<rhs><nt def='NT-S'>S</nt> 'NDATA' <nt def='NT-S'>S</nt> 2572<nt def='NT-Name'>Name</nt></rhs> 2573<vc def='not-declared'/></prod> 2574</scrap> 2575If the <nt def='NT-NDataDecl'>NDataDecl</nt> is present, this is a 2576general <termref def="dt-unparsed">unparsed 2577entity</termref>; otherwise it is a parsed entity.</termdef></p> 2578<vcnote id='not-declared'> 2579<head>Notation Declared</head> 2580<p> 2581The <nt def='NT-Name'>Name</nt> must match the declared name of a 2582<termref def="dt-notation">notation</termref>. 2583</p> 2584</vcnote> 2585<p><termdef id="dt-sysid" term="System Identifier">The 2586<nt def='NT-SystemLiteral'>SystemLiteral</nt> 2587is called the entity's <term>system identifier</term>. It is a URI, 2588which may be used to retrieve the entity.</termdef> 2589Note that the hash mark (<code>#</code>) and fragment identifier 2590frequently used with URIs are not, formally, part of the URI itself; 2591an XML processor may signal an error if a fragment identifier is 2592given as part of a system identifier. 2593Unless otherwise provided by information outside the scope of this 2594specification (e.g. a special XML element type defined by a particular 2595DTD, or a processing instruction defined by a particular application 2596specification), relative URIs are relative to the location of the 2597resource within which the entity declaration occurs. 2598A URI might thus be relative to the 2599<termref def='dt-docent'>document entity</termref>, to the entity 2600containing the <termref def='dt-doctype'>external DTD subset</termref>, 2601or to some other <termref def='dt-extent'>external parameter entity</termref>. 2602</p> 2603<p>An XML processor should handle a non-ASCII character in a URI by 2604representing the character in UTF-8 as one or more bytes, and then 2605escaping these bytes with the URI escaping mechanism (i.e., by 2606converting each byte to %HH, where HH is the hexadecimal notation of the 2607byte value).</p> 2608<p><termdef id="dt-pubid" term="Public identifier"> 2609In addition to a system identifier, an external identifier may 2610include a <term>public identifier</term>.</termdef> 2611An XML processor attempting to retrieve the entity's content may use the public 2612identifier to try to generate an alternative URI. If the processor 2613is unable to do so, it must use the URI specified in the system 2614literal. Before a match is attempted, all strings 2615of white space in the public identifier must be normalized to single space characters (#x20), 2616and leading and trailing white space must be removed.</p> 2617<p>Examples of external entity declarations: 2618<eg><!ENTITY open-hatch 2619 SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml"> 2620<!ENTITY open-hatch 2621 PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN" 2622 "http://www.textuality.com/boilerplate/OpenHatch.xml"> 2623<!ENTITY hatch-pic 2624 SYSTEM "/grafix/OpenHatch.gif" 2625 NDATA gif ></eg></p> 2626</div3> 2627 2628</div2> 2629 2630<div2 id='TextEntities'> 2631<head>Parsed Entities</head> 2632<div3 id='sec-TextDecl'> 2633<head>The Text Declaration</head> 2634<p>External parsed entities may each begin with a <term>text 2635declaration</term>. 2636<scrap lang='ebnf'> 2637<head>Text Declaration</head> 2638<prodgroup pcw4="12.5" pcw5="13"> 2639<prod id='NT-TextDecl'><lhs>TextDecl</lhs> 2640<rhs>&xmlpio; 2641<nt def='NT-VersionInfo'>VersionInfo</nt>? 2642<nt def='NT-EncodingDecl'>EncodingDecl</nt> 2643<nt def='NT-S'>S</nt>? &pic;</rhs> 2644</prod> 2645</prodgroup> 2646</scrap> 2647</p> 2648<p>The text declaration must be provided literally, not 2649by reference to a parsed entity. 2650No text declaration may appear at any position other than the beginning of 2651an external parsed entity.</p> 2652</div3> 2653<div3 id='wf-entities'> 2654<head>Well-Formed Parsed Entities</head> 2655<p>The document entity is well-formed if it matches the production labeled 2656<nt def='NT-document'>document</nt>. 2657An external general 2658parsed entity is well-formed if it matches the production labeled 2659<nt def='NT-extParsedEnt'>extParsedEnt</nt>. 2660An external parameter 2661entity is well-formed if it matches the production labeled 2662<nt def='NT-extPE'>extPE</nt>. 2663<scrap lang='ebnf'> 2664<head>Well-Formed External Parsed Entity</head> 2665<prod id='NT-extParsedEnt'><lhs>extParsedEnt</lhs> 2666<rhs><nt def='NT-TextDecl'>TextDecl</nt>? 2667<nt def='NT-content'>content</nt></rhs> 2668</prod> 2669<prod id='NT-extPE'><lhs>extPE</lhs> 2670<rhs><nt def='NT-TextDecl'>TextDecl</nt>? 2671<nt def='NT-extSubsetDecl'>extSubsetDecl</nt></rhs> 2672</prod> 2673</scrap> 2674An internal general parsed entity is well-formed if its replacement text 2675matches the production labeled 2676<nt def='NT-content'>content</nt>. 2677All internal parameter entities are well-formed by definition. 2678</p> 2679<p>A consequence of well-formedness in entities is that the logical 2680and physical structures in an XML document are properly nested; no 2681<termref def='dt-stag'>start-tag</termref>, 2682<termref def='dt-etag'>end-tag</termref>, 2683<termref def="dt-empty">empty-element tag</termref>, 2684<termref def='dt-element'>element</termref>, 2685<termref def='dt-comment'>comment</termref>, 2686<termref def='dt-pi'>processing instruction</termref>, 2687<termref def='dt-charref'>character 2688reference</termref>, or 2689<termref def='dt-entref'>entity reference</termref> 2690can begin in one entity and end in another.</p> 2691</div3> 2692<div3 id='charencoding'> 2693<head>Character Encoding in Entities</head> 2694 2695<p>Each external parsed entity in an XML document may use a different 2696encoding for its characters. All XML processors must be able to read 2697entities in either UTF-8 or UTF-16. 2698 2699</p> 2700<p>Entities encoded in UTF-16 must 2701begin with the Byte Order Mark described by ISO/IEC 10646 Annex E and 2702Unicode Appendix B (the ZERO WIDTH NO-BREAK SPACE character, #xFEFF). 2703This is an encoding signature, not part of either the markup or the 2704character data of the XML document. 2705XML processors must be able to use this character to 2706differentiate between UTF-8 and UTF-16 encoded documents.</p> 2707<p>Although an XML processor is required to read only entities in 2708the UTF-8 and UTF-16 encodings, it is recognized that other encodings are 2709used around the world, and it may be desired for XML processors 2710to read entities that use them. 2711Parsed entities which are stored in an encoding other than 2712UTF-8 or UTF-16 must begin with a <titleref href='TextDecl'>text 2713declaration</titleref> containing an encoding declaration: 2714<scrap lang='ebnf'> 2715<head>Encoding Declaration</head> 2716<prod id='NT-EncodingDecl'><lhs>EncodingDecl</lhs> 2717<rhs><nt def="NT-S">S</nt> 2718'encoding' <nt def='NT-Eq'>Eq</nt> 2719('"' <nt def='NT-EncName'>EncName</nt> '"' | 2720"'" <nt def='NT-EncName'>EncName</nt> "'" ) 2721</rhs> 2722</prod> 2723<prod id='NT-EncName'><lhs>EncName</lhs> 2724<rhs>[A-Za-z] ([A-Za-z0-9._] | '-')*</rhs> 2725<com>Encoding name contains only Latin characters</com> 2726</prod> 2727</scrap> 2728In the <termref def='dt-docent'>document entity</termref>, the encoding 2729declaration is part of the <termref def="dt-xmldecl">XML declaration</termref>. 2730The <nt def="NT-EncName">EncName</nt> is the name of the encoding used. 2731</p> 2732<!-- FINAL EDIT: check name of IANA and charset names --> 2733<p>In an encoding declaration, the values 2734"<code>UTF-8</code>", 2735"<code>UTF-16</code>", 2736"<code>ISO-10646-UCS-2</code>", and 2737"<code>ISO-10646-UCS-4</code>" should be 2738used for the various encodings and transformations of Unicode / 2739ISO/IEC 10646, the values 2740"<code>ISO-8859-1</code>", 2741"<code>ISO-8859-2</code>", ... 2742"<code>ISO-8859-9</code>" should be used for the parts of ISO 8859, and 2743the values 2744"<code>ISO-2022-JP</code>", 2745"<code>Shift_JIS</code>", and 2746"<code>EUC-JP</code>" 2747should be used for the various encoded forms of JIS X-0208-1997. XML 2748processors may recognize other encodings; it is recommended that 2749character encodings registered (as <emph>charset</emph>s) 2750with the Internet Assigned Numbers 2751Authority <bibref ref='IANA'/>, other than those just listed, should be 2752referred to 2753using their registered names. 2754Note that these registered names are defined to be 2755case-insensitive, so processors wishing to match against them 2756should do so in a case-insensitive 2757way.</p> 2758<p>In the absence of information provided by an external 2759transport protocol (e.g. HTTP or MIME), 2760it is an <termref def="dt-error">error</termref> for an entity including 2761an encoding declaration to be presented to the XML processor 2762in an encoding other than that named in the declaration, 2763for an encoding declaration to occur other than at the beginning 2764of an external entity, or for 2765an entity which begins with neither a Byte Order Mark nor an encoding 2766declaration to use an encoding other than UTF-8. 2767Note that since ASCII 2768is a subset of UTF-8, ordinary ASCII entities do not strictly need 2769an encoding declaration.</p> 2770 2771<p>It is a <termref def='dt-fatal'>fatal error</termref> when an XML processor 2772encounters an entity with an encoding that it is unable to process.</p> 2773<p>Examples of encoding declarations: 2774<eg><?xml encoding='UTF-8'?> 2775<?xml encoding='EUC-JP'?></eg></p> 2776</div3> 2777</div2> 2778<div2 id='entproc'> 2779<head>XML Processor Treatment of Entities and References</head> 2780<p>The table below summarizes the contexts in which character references, 2781entity references, and invocations of unparsed entities might appear and the 2782required behavior of an <termref def='dt-xml-proc'>XML processor</termref> in 2783each case. 2784The labels in the leftmost column describe the recognition context: 2785<glist> 2786<gitem><label>Reference in Content</label> 2787<def><p>as a reference 2788anywhere after the <termref def='dt-stag'>start-tag</termref> and 2789before the <termref def='dt-etag'>end-tag</termref> of an element; corresponds 2790to the nonterminal <nt def='NT-content'>content</nt>.</p></def> 2791</gitem> 2792<gitem> 2793<label>Reference in Attribute Value</label> 2794<def><p>as a reference within either the value of an attribute in a 2795<termref def='dt-stag'>start-tag</termref>, or a default 2796value in an <termref def='dt-attdecl'>attribute declaration</termref>; 2797corresponds to the nonterminal 2798<nt def='NT-AttValue'>AttValue</nt>.</p></def></gitem> 2799<gitem> 2800<label>Occurs as Attribute Value</label> 2801<def><p>as a <nt def='NT-Name'>Name</nt>, not a reference, appearing either as 2802the value of an 2803attribute which has been declared as type <kw>ENTITY</kw>, or as one of 2804the space-separated tokens in the value of an attribute which has been 2805declared as type <kw>ENTITIES</kw>.</p> 2806</def></gitem> 2807<gitem><label>Reference in Entity Value</label> 2808<def><p>as a reference 2809within a parameter or internal entity's 2810<termref def='dt-litentval'>literal entity value</termref> in 2811the entity's declaration; corresponds to the nonterminal 2812<nt def='NT-EntityValue'>EntityValue</nt>.</p></def></gitem> 2813<gitem><label>Reference in DTD</label> 2814<def><p>as a reference within either the internal or external subsets of the 2815<termref def='dt-doctype'>DTD</termref>, but outside 2816of an <nt def='NT-EntityValue'>EntityValue</nt> or 2817<nt def="NT-AttValue">AttValue</nt>.</p></def> 2818</gitem> 2819</glist></p> 2820<htable border='1' cellpadding='7' align='center'> 2821<htbody> 2822<tr><td bgcolor='&cellback;' rowspan='2' colspan='1'></td> 2823<td bgcolor='&cellback;' align='center' valign='bottom' colspan='4'>Entity Type</td> 2824<td bgcolor='&cellback;' rowspan='2' align='center'>Character</td> 2825</tr> 2826<tr align='center' valign='bottom'> 2827<td bgcolor='&cellback;'>Parameter</td> 2828<td bgcolor='&cellback;'>Internal 2829General</td> 2830<td bgcolor='&cellback;'>External Parsed 2831General</td> 2832<td bgcolor='&cellback;'>Unparsed</td> 2833</tr> 2834<tr align='center' valign='middle'> 2835 2836<td bgcolor='&cellback;' align='right'>Reference 2837in Content</td> 2838<td bgcolor='&cellback;'><titleref href='not-recognized'>Not recognized</titleref></td> 2839<td bgcolor='&cellback;'><titleref href='included'>Included</titleref></td> 2840<td bgcolor='&cellback;'><titleref href='include-if-valid'>Included if validating</titleref></td> 2841<td bgcolor='&cellback;'><titleref href='forbidden'>Forbidden</titleref></td> 2842<td bgcolor='&cellback;'><titleref href='included'>Included</titleref></td> 2843</tr> 2844<tr align='center' valign='middle'> 2845<td bgcolor='&cellback;' align='right'>Reference 2846in Attribute Value</td> 2847<td bgcolor='&cellback;'><titleref href='not-recognized'>Not recognized</titleref></td> 2848<td bgcolor='&cellback;'><titleref href='inliteral'>Included in literal</titleref></td> 2849<td bgcolor='&cellback;'><titleref href='forbidden'>Forbidden</titleref></td> 2850<td bgcolor='&cellback;'><titleref href='forbidden'>Forbidden</titleref></td> 2851<td bgcolor='&cellback;'><titleref href='included'>Included</titleref></td> 2852</tr> 2853<tr align='center' valign='middle'> 2854<td bgcolor='&cellback;' align='right'>Occurs as 2855Attribute Value</td> 2856<td bgcolor='&cellback;'><titleref href='not-recognized'>Not recognized</titleref></td> 2857<td bgcolor='&cellback;'><titleref href='not-recognized'>Forbidden</titleref></td> 2858<td bgcolor='&cellback;'><titleref href='not-recognized'>Forbidden</titleref></td> 2859<td bgcolor='&cellback;'><titleref href='notify'>Notify</titleref></td> 2860<td bgcolor='&cellback;'><titleref href='not recognized'>Not recognized</titleref></td> 2861</tr> 2862<tr align='center' valign='middle'> 2863<td bgcolor='&cellback;' align='right'>Reference 2864in EntityValue</td> 2865<td bgcolor='&cellback;'><titleref href='inliteral'>Included in literal</titleref></td> 2866<td bgcolor='&cellback;'><titleref href='bypass'>Bypassed</titleref></td> 2867<td bgcolor='&cellback;'><titleref href='bypass'>Bypassed</titleref></td> 2868<td bgcolor='&cellback;'><titleref href='forbidden'>Forbidden</titleref></td> 2869<td bgcolor='&cellback;'><titleref href='included'>Included</titleref></td> 2870</tr> 2871<tr align='center' valign='middle'> 2872<td bgcolor='&cellback;' align='right'>Reference 2873in DTD</td> 2874<td bgcolor='&cellback;'><titleref href='as-PE'>Included as PE</titleref></td> 2875<td bgcolor='&cellback;'><titleref href='forbidden'>Forbidden</titleref></td> 2876<td bgcolor='&cellback;'><titleref href='forbidden'>Forbidden</titleref></td> 2877<td bgcolor='&cellback;'><titleref href='forbidden'>Forbidden</titleref></td> 2878<td bgcolor='&cellback;'><titleref href='forbidden'>Forbidden</titleref></td> 2879</tr> 2880</htbody> 2881</htable> 2882<div3 id='not-recognized'> 2883<head>Not Recognized</head> 2884<p>Outside the DTD, the <code>%</code> character has no 2885special significance; thus, what would be parameter entity references in the 2886DTD are not recognized as markup in <nt def='NT-content'>content</nt>. 2887Similarly, the names of unparsed entities are not recognized except 2888when they appear in the value of an appropriately declared attribute. 2889</p> 2890</div3> 2891<div3 id='included'> 2892<head>Included</head> 2893<p><termdef id="dt-include" term="Include">An entity is 2894<term>included</term> when its 2895<termref def='dt-repltext'>replacement text</termref> is retrieved 2896and processed, in place of the reference itself, 2897as though it were part of the document at the location the 2898reference was recognized. 2899The replacement text may contain both 2900<termref def='dt-chardata'>character data</termref> 2901and (except for parameter entities) <termref def="dt-markup">markup</termref>, 2902which must be recognized in 2903the usual way, except that the replacement text of entities used to escape 2904markup delimiters (the entities &magicents;) is always treated as 2905data. (The string "<code>AT&amp;T;</code>" expands to 2906"<code>AT&T;</code>" and the remaining ampersand is not recognized 2907as an entity-reference delimiter.) 2908A character reference is <term>included</term> when the indicated 2909character is processed in place of the reference itself. 2910</termdef></p> 2911</div3> 2912<div3 id='include-if-valid'> 2913<head>Included If Validating</head> 2914<p>When an XML processor recognizes a reference to a parsed entity, in order 2915to <termref def="dt-valid">validate</termref> 2916the document, the processor must 2917<termref def="dt-include">include</termref> its 2918replacement text. 2919If the entity is external, and the processor is not 2920attempting to validate the XML document, the 2921processor <termref def="dt-may">may</termref>, but need not, 2922include the entity's replacement text. 2923If a non-validating parser does not include the replacement text, 2924it must inform the application that it recognized, but did not 2925read, the entity.</p> 2926<p>This rule is based on the recognition that the automatic inclusion 2927provided by the SGML and XML entity mechanism, primarily designed 2928to support modularity in authoring, is not necessarily 2929appropriate for other applications, in particular document browsing. 2930Browsers, for example, when encountering an external parsed entity reference, 2931might choose to provide a visual indication of the entity's 2932presence and retrieve it for display only on demand. 2933</p> 2934</div3> 2935<div3 id='forbidden'> 2936<head>Forbidden</head> 2937<p>The following are forbidden, and constitute 2938<termref def='dt-fatal'>fatal</termref> errors: 2939<ulist> 2940<item><p>the appearance of a reference to an 2941<termref def='dt-unparsed'>unparsed entity</termref>. 2942</p></item> 2943<item><p>the appearance of any character or general-entity reference in the 2944DTD except within an <nt def='NT-EntityValue'>EntityValue</nt> or 2945<nt def="NT-AttValue">AttValue</nt>.</p></item> 2946<item><p>a reference to an external entity in an attribute value.</p> 2947</item> 2948</ulist> 2949</p> 2950</div3> 2951<div3 id='inliteral'> 2952<head>Included in Literal</head> 2953<p>When an <termref def='dt-entref'>entity reference</termref> appears in an 2954attribute value, or a parameter entity reference appears in a literal entity 2955value, its <termref def='dt-repltext'>replacement text</termref> is 2956processed in place of the reference itself as though it 2957were part of the document at the location the reference was recognized, 2958except that a single or double quote character in the replacement text 2959is always treated as a normal data character and will not terminate the 2960literal. 2961For example, this is well-formed: 2962<eg><![CDATA[<!ENTITY % YN '"Yes"' > 2963<!ENTITY WhatHeSaid "He said &YN;" >]]></eg> 2964while this is not: 2965<eg><!ENTITY EndAttr "27'" > 2966<element attribute='a-&EndAttr;></eg> 2967</p></div3> 2968<div3 id='notify'> 2969<head>Notify</head> 2970<p>When the name of an <termref def='dt-unparsed'>unparsed 2971entity</termref> appears as a token in the 2972value of an attribute of declared type <kw>ENTITY</kw> or <kw>ENTITIES</kw>, 2973a validating processor must inform the 2974application of the <termref def='dt-sysid'>system</termref> 2975and <termref def='dt-pubid'>public</termref> (if any) 2976identifiers for both the entity and its associated 2977<termref def="dt-notation">notation</termref>.</p> 2978</div3> 2979<div3 id='bypass'> 2980<head>Bypassed</head> 2981<p>When a general entity reference appears in the 2982<nt def='NT-EntityValue'>EntityValue</nt> in an entity declaration, 2983it is bypassed and left as is.</p> 2984</div3> 2985<div3 id='as-PE'> 2986<head>Included as PE</head> 2987<p>Just as with external parsed entities, parameter entities 2988need only be <titleref href='include-if-valid'>included if 2989validating</titleref>. 2990When a parameter-entity reference is recognized in the DTD 2991and included, its 2992<termref def='dt-repltext'>replacement 2993text</termref> is enlarged by the attachment of one leading and one following 2994space (#x20) character; the intent is to constrain the replacement 2995text of parameter 2996entities to contain an integral number of grammatical tokens in the DTD. 2997</p> 2998</div3> 2999 3000</div2> 3001<div2 id='intern-replacement'> 3002<head>Construction of Internal Entity Replacement Text</head> 3003<p>In discussing the treatment 3004of internal entities, it is 3005useful to distinguish two forms of the entity's value. 3006<termdef id="dt-litentval" term='Literal Entity Value'>The <term>literal 3007entity value</term> is the quoted string actually 3008present in the entity declaration, corresponding to the 3009non-terminal <nt def='NT-EntityValue'>EntityValue</nt>.</termdef> 3010<termdef id='dt-repltext' term='Replacement Text'>The <term>replacement 3011text</term> is the content of the entity, after 3012replacement of character references and parameter-entity 3013references. 3014</termdef></p> 3015 3016<p>The literal entity value 3017as given in an internal entity declaration 3018(<nt def='NT-EntityValue'>EntityValue</nt>) may contain character, 3019parameter-entity, and general-entity references. 3020Such references must be contained entirely within the 3021literal entity value. 3022The actual replacement text that is 3023<termref def='dt-include'>included</termref> as described above 3024must contain the <emph>replacement text</emph> of any 3025parameter entities referred to, and must contain the character 3026referred to, in place of any character references in the 3027literal entity value; however, 3028general-entity references must be left as-is, unexpanded. 3029For example, given the following declarations: 3030 3031<eg><![CDATA[<!ENTITY % pub "Éditions Gallimard" > 3032<!ENTITY rights "All rights reserved" > 3033<!ENTITY book "La Peste: Albert Camus, 3034© 1947 %pub;. &rights;" >]]></eg> 3035then the replacement text for the entity "<code>book</code>" is: 3036<eg>La Peste: Albert Camus, 3037© 1947 Éditions Gallimard. &rights;</eg> 3038The general-entity reference "<code>&rights;</code>" would be expanded 3039should the reference "<code>&book;</code>" appear in the document's 3040content or an attribute value.</p> 3041<p>These simple rules may have complex interactions; for a detailed 3042discussion of a difficult example, see 3043<specref ref='sec-entexpand'/>. 3044</p> 3045 3046</div2> 3047<div2 id='sec-predefined-ent'> 3048<head>Predefined Entities</head> 3049<p><termdef id="dt-escape" term="escape">Entity and character 3050references can both be used to <term>escape</term> the left angle bracket, 3051ampersand, and other delimiters. A set of general entities 3052(&magicents;) is specified for this purpose. 3053Numeric character references may also be used; they are 3054expanded immediately when recognized and must be treated as 3055character data, so the numeric character references 3056"<code>&#60;</code>" and "<code>&#38;</code>" may be used to 3057escape <code><</code> and <code>&</code> when they occur 3058in character data.</termdef></p> 3059<p>All XML processors must recognize these entities whether they 3060are declared or not. 3061<termref def='dt-interop'>For interoperability</termref>, 3062valid XML documents should declare these 3063entities, like any others, before using them. 3064If the entities in question are declared, they must be declared 3065as internal entities whose replacement text is the single 3066character being escaped or a character reference to 3067that character, as shown below. 3068<eg><![CDATA[<!ENTITY lt "&#60;"> 3069<!ENTITY gt ">"> 3070<!ENTITY amp "&#38;"> 3071<!ENTITY apos "'"> 3072<!ENTITY quot """> 3073]]></eg> 3074Note that the <code><</code> and <code>&</code> characters 3075in the declarations of "<code>lt</code>" and "<code>amp</code>" 3076are doubly escaped to meet the requirement that entity replacement 3077be well-formed. 3078</p> 3079</div2> 3080 3081<div2 id='Notations'> 3082<head>Notation Declarations</head> 3083 3084<p><termdef id="dt-notation" term="Notation"><term>Notations</term> identify by 3085name the format of <termref def="dt-extent">unparsed 3086entities</termref>, the 3087format of elements which bear a notation attribute, 3088or the application to which 3089a <termref def="dt-pi">processing instruction</termref> is 3090addressed.</termdef></p> 3091<p><termdef id="dt-notdecl" term="Notation Declaration"> 3092<term>Notation declarations</term> 3093provide a name for the notation, for use in 3094entity and attribute-list declarations and in attribute specifications, 3095and an external identifier for the notation which may allow an XML 3096processor or its client application to locate a helper application 3097capable of processing data in the given notation. 3098<scrap lang='ebnf'> 3099<head>Notation Declarations</head> 3100<prod id='NT-NotationDecl'><lhs>NotationDecl</lhs> 3101<rhs>'<!NOTATION' <nt def='NT-S'>S</nt> <nt def='NT-Name'>Name</nt> 3102<nt def='NT-S'>S</nt> 3103(<nt def='NT-ExternalID'>ExternalID</nt> | 3104<nt def='NT-PublicID'>PublicID</nt>) 3105<nt def='NT-S'>S</nt>? '>'</rhs></prod> 3106<prod id='NT-PublicID'><lhs>PublicID</lhs> 3107<rhs>'PUBLIC' <nt def='NT-S'>S</nt> 3108<nt def='NT-PubidLiteral'>PubidLiteral</nt> 3109</rhs></prod> 3110</scrap> 3111</termdef></p> 3112<p>XML processors must provide applications with the name and external 3113identifier(s) of any notation declared and referred to in an attribute 3114value, attribute definition, or entity declaration. They may 3115additionally resolve the external identifier into the 3116<termref def="dt-sysid">system identifier</termref>, 3117file name, or other information needed to allow the 3118application to call a processor for data in the notation described. (It 3119is not an error, however, for XML documents to declare and refer to 3120notations for which notation-specific applications are not available on 3121the system where the XML processor or application is running.)</p> 3122</div2> 3123 3124 3125<div2 id='sec-doc-entity'> 3126<head>Document Entity</head> 3127 3128<p><termdef id="dt-docent" term="Document Entity">The <term>document 3129entity</term> serves as the root of the entity 3130tree and a starting-point for an <termref def="dt-xml-proc">XML 3131processor</termref>.</termdef> 3132This specification does 3133not specify how the document entity is to be located by an XML 3134processor; unlike other entities, the document entity has no name and might 3135well appear on a processor input stream 3136without any identification at all.</p> 3137</div2> 3138 3139 3140</div1> 3141<!-- &Conformance; --> 3142 3143<div1 id='sec-conformance'> 3144<head>Conformance</head> 3145 3146<div2 id='proc-types'> 3147<head>Validating and Non-Validating Processors</head> 3148<p>Conforming <termref def="dt-xml-proc">XML processors</termref> fall into two 3149classes: validating and non-validating.</p> 3150<p>Validating and non-validating processors alike must report 3151violations of this specification's well-formedness constraints 3152in the content of the 3153<termref def='dt-docent'>document entity</termref> and any 3154other <termref def='dt-parsedent'>parsed entities</termref> that 3155they read.</p> 3156<p><termdef id="dt-validating" term="Validating Processor"> 3157<term>Validating processors</term> must report 3158violations of the constraints expressed by the declarations in the 3159<termref def="dt-doctype">DTD</termref>, and 3160failures to fulfill the validity constraints given 3161in this specification. 3162</termdef> 3163To accomplish this, validating XML processors must read and process the entire 3164DTD and all external parsed entities referenced in the document. 3165</p> 3166<p>Non-validating processors are required to check only the 3167<termref def='dt-docent'>document entity</termref>, including 3168the entire internal DTD subset, for well-formedness. 3169<termdef id='dt-use-mdecl' term='Process Declarations'> 3170While they are not required to check the document for validity, 3171they are required to 3172<term>process</term> all the declarations they read in the 3173internal DTD subset and in any parameter entity that they 3174read, up to the first reference 3175to a parameter entity that they do <emph>not</emph> read; that is to 3176say, they must 3177use the information in those declarations to 3178<titleref href='AVNormalize'>normalize</titleref> attribute values, 3179<titleref href='included'>include</titleref> the replacement text of 3180internal entities, and supply 3181<titleref href='sec-attr-defaults'>default attribute values</titleref>. 3182</termdef> 3183They must not <termref def='dt-use-mdecl'>process</termref> 3184<termref def='dt-entdecl'>entity declarations</termref> or 3185<termref def='dt-attdecl'>attribute-list declarations</termref> 3186encountered after a reference to a parameter entity that is not 3187read, since the entity may have contained overriding declarations. 3188</p> 3189</div2> 3190<div2 id='safe-behavior'> 3191<head>Using XML Processors</head> 3192<p>The behavior of a validating XML processor is highly predictable; it 3193must read every piece of a document and report all well-formedness and 3194validity violations. 3195Less is required of a non-validating processor; it need not read any 3196part of the document other than the document entity. 3197This has two effects that may be important to users of XML processors: 3198<ulist> 3199<item><p>Certain well-formedness errors, specifically those that require 3200reading external entities, may not be detected by a non-validating processor. 3201Examples include the constraints entitled 3202<titleref href='wf-entdeclared'>Entity Declared</titleref>, 3203<titleref href='wf-textent'>Parsed Entity</titleref>, and 3204<titleref href='wf-norecursion'>No Recursion</titleref>, as well 3205as some of the cases described as 3206<titleref href='forbidden'>forbidden</titleref> in 3207<specref ref='entproc'/>.</p></item> 3208<item><p>The information passed from the processor to the application may 3209vary, depending on whether the processor reads 3210parameter and external entities. 3211For example, a non-validating processor may not 3212<titleref href='AVNormalize'>normalize</titleref> attribute values, 3213<titleref href='included'>include</titleref> the replacement text of 3214internal entities, or supply 3215<titleref href='sec-attr-defaults'>default attribute values</titleref>, 3216where doing so depends on having read declarations in 3217external or parameter entities.</p></item> 3218</ulist> 3219</p> 3220<p>For maximum reliability in interoperating between different XML 3221processors, applications which use non-validating processors should not 3222rely on any behaviors not required of such processors. 3223Applications which require facilities such as the use of default 3224attributes or internal entities which are declared in external 3225entities should use validating XML processors.</p> 3226</div2> 3227</div1> 3228 3229<div1 id='sec-notation'> 3230<head>Notation</head> 3231 3232<p>The formal grammar of XML is given in this specification using a simple 3233Extended Backus-Naur Form (EBNF) notation. Each rule in the grammar defines 3234one symbol, in the form 3235<eg>symbol ::= expression</eg></p> 3236<p>Symbols are written with an initial capital letter if they are 3237defined by a regular expression, or with an initial lower case letter 3238otherwise. 3239Literal strings are quoted. 3240 3241</p> 3242 3243<p>Within the expression on the right-hand side of a rule, the following 3244expressions are used to match strings of one or more characters: 3245<glist> 3246<gitem> 3247<label><code>#xN</code></label> 3248<def><p>where <code>N</code> is a hexadecimal integer, the 3249expression matches the character in ISO/IEC 10646 whose canonical 3250(UCS-4) 3251code value, when interpreted as an unsigned binary number, has 3252the value indicated. The number of leading zeros in the 3253<code>#xN</code> form is insignificant; the number of leading 3254zeros in the corresponding code value 3255is governed by the character 3256encoding in use and is not significant for XML.</p></def> 3257</gitem> 3258<gitem> 3259<label><code>[a-zA-Z]</code>, <code>[#xN-#xN]</code></label> 3260<def><p>matches any <termref def='dt-character'>character</termref> 3261with a value in the range(s) indicated (inclusive).</p></def> 3262</gitem> 3263<gitem> 3264<label><code>[^a-z]</code>, <code>[^#xN-#xN]</code></label> 3265<def><p>matches any <termref def='dt-character'>character</termref> 3266with a value <emph>outside</emph> the 3267range indicated.</p></def> 3268</gitem> 3269<gitem> 3270<label><code>[^abc]</code>, <code>[^#xN#xN#xN]</code></label> 3271<def><p>matches any <termref def='dt-character'>character</termref> 3272with a value not among the characters given.</p></def> 3273</gitem> 3274<gitem> 3275<label><code>"string"</code></label> 3276<def><p>matches a literal string <termref def="dt-match">matching</termref> 3277that given inside the double quotes.</p></def> 3278</gitem> 3279<gitem> 3280<label><code>'string'</code></label> 3281<def><p>matches a literal string <termref def="dt-match">matching</termref> 3282that given inside the single quotes.</p></def> 3283</gitem> 3284</glist> 3285These symbols may be combined to match more complex patterns as follows, 3286where <code>A</code> and <code>B</code> represent simple expressions: 3287<glist> 3288<gitem> 3289<label>(<code>expression</code>)</label> 3290<def><p><code>expression</code> is treated as a unit 3291and may be combined as described in this list.</p></def> 3292</gitem> 3293<gitem> 3294<label><code>A?</code></label> 3295<def><p>matches <code>A</code> or nothing; optional <code>A</code>.</p></def> 3296</gitem> 3297<gitem> 3298<label><code>A B</code></label> 3299<def><p>matches <code>A</code> followed by <code>B</code>.</p></def> 3300</gitem> 3301<gitem> 3302<label><code>A | B</code></label> 3303<def><p>matches <code>A</code> or <code>B</code> but not both.</p></def> 3304</gitem> 3305<gitem> 3306<label><code>A - B</code></label> 3307<def><p>matches any string that matches <code>A</code> but does not match 3308<code>B</code>. 3309</p></def> 3310</gitem> 3311<gitem> 3312<label><code>A+</code></label> 3313<def><p>matches one or more occurrences of <code>A</code>.</p></def> 3314</gitem> 3315<gitem> 3316<label><code>A*</code></label> 3317<def><p>matches zero or more occurrences of <code>A</code>.</p></def> 3318</gitem> 3319 3320</glist> 3321Other notations used in the productions are: 3322<glist> 3323<gitem> 3324<label><code>/* ... */</code></label> 3325<def><p>comment.</p></def> 3326</gitem> 3327<gitem> 3328<label><code>[ wfc: ... ]</code></label> 3329<def><p>well-formedness constraint; this identifies by name a 3330constraint on 3331<termref def="dt-wellformed">well-formed</termref> documents 3332associated with a production.</p></def> 3333</gitem> 3334<gitem> 3335<label><code>[ vc: ... ]</code></label> 3336<def><p>validity constraint; this identifies by name a constraint on 3337<termref def="dt-valid">valid</termref> documents associated with 3338a production.</p></def> 3339</gitem> 3340</glist> 3341</p></div1> 3342 3343</body> 3344<back> 3345<!-- &SGML; --> 3346 3347 3348<!-- &Biblio; --> 3349<div1 id='sec-bibliography'> 3350 3351<head>References</head> 3352<div2 id='sec-existing-stds'> 3353<head>Normative References</head> 3354 3355<blist> 3356<bibl id='IANA' key='IANA'> 3357(Internet Assigned Numbers Authority) <emph>Official Names for 3358Character Sets</emph>, 3359ed. Keld Simonsen et al. 3360See <loc href='ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets'>ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets</loc>. 3361</bibl> 3362 3363<bibl id='RFC1766' key='IETF RFC 1766'> 3364IETF (Internet Engineering Task Force). 3365<emph>RFC 1766: Tags for the Identification of Languages</emph>, 3366ed. H. Alvestrand. 33671995. 3368</bibl> 3369 3370<bibl id='ISO639' key='ISO 639'> 3371(International Organization for Standardization). 3372<emph>ISO 639:1988 (E). 3373Code for the representation of names of languages.</emph> 3374[Geneva]: International Organization for 3375Standardization, 1988.</bibl> 3376 3377<bibl id='ISO3166' key='ISO 3166'> 3378(International Organization for Standardization). 3379<emph>ISO 3166-1:1997 (E). 3380Codes for the representation of names of countries and their subdivisions 3381— Part 1: Country codes</emph> 3382[Geneva]: International Organization for 3383Standardization, 1997.</bibl> 3384 3385<bibl id='ISO10646' key='ISO/IEC 10646'>ISO 3386(International Organization for Standardization). 3387<emph>ISO/IEC 10646-1993 (E). Information technology — Universal 3388Multiple-Octet Coded Character Set (UCS) — Part 1: 3389Architecture and Basic Multilingual Plane.</emph> 3390[Geneva]: International Organization for 3391Standardization, 1993 (plus amendments AM 1 through AM 7). 3392</bibl> 3393 3394<bibl id='Unicode' key='Unicode'>The Unicode Consortium. 3395<emph>The Unicode Standard, Version 2.0.</emph> 3396Reading, Mass.: Addison-Wesley Developers Press, 1996.</bibl> 3397 3398</blist> 3399 3400</div2> 3401 3402<div2><head>Other References</head> 3403 3404<blist> 3405 3406<bibl id='Aho' key='Aho/Ullman'>Aho, Alfred V., 3407Ravi Sethi, and Jeffrey D. Ullman. 3408<emph>Compilers: Principles, Techniques, and Tools</emph>. 3409Reading: Addison-Wesley, 1986, rpt. corr. 1988.</bibl> 3410 3411<bibl id="Berners-Lee" xml-link="simple" key="Berners-Lee et al."> 3412Berners-Lee, T., R. Fielding, and L. Masinter. 3413<emph>Uniform Resource Identifiers (URI): Generic Syntax and 3414Semantics</emph>. 34151997. 3416(Work in progress; see updates to RFC1738.)</bibl> 3417 3418<bibl id='ABK' key='Br�ggemann-Klein'>Br�ggemann-Klein, Anne. 3419<emph>Regular Expressions into Finite Automata</emph>. 3420Extended abstract in I. Simon, Hrsg., LATIN 1992, 3421S. 97-98. Springer-Verlag, Berlin 1992. 3422Full Version in Theoretical Computer Science 120: 197-213, 1993. 3423 3424</bibl> 3425 3426<bibl id='ABKDW' key='Br�ggemann-Klein and Wood'>Br�ggemann-Klein, Anne, 3427and Derick Wood. 3428<emph>Deterministic Regular Languages</emph>. 3429Universit�t Freiburg, Institut f�r Informatik, 3430Bericht 38, Oktober 1991. 3431</bibl> 3432 3433<bibl id='Clark' key='Clark'>James Clark. 3434Comparison of SGML and XML. See 3435<loc href='http://www.w3.org/TR/NOTE-sgml-xml-971215'>http://www.w3.org/TR/NOTE-sgml-xml-971215</loc>. 3436</bibl> 3437<bibl id="RFC1738" xml-link="simple" key="IETF RFC1738"> 3438IETF (Internet Engineering Task Force). 3439<emph>RFC 1738: Uniform Resource Locators (URL)</emph>, 3440ed. T. Berners-Lee, L. Masinter, M. McCahill. 34411994. 3442</bibl> 3443 3444<bibl id="RFC1808" xml-link="simple" key="IETF RFC1808"> 3445IETF (Internet Engineering Task Force). 3446<emph>RFC 1808: Relative Uniform Resource Locators</emph>, 3447ed. R. Fielding. 34481995. 3449</bibl> 3450 3451<bibl id="RFC2141" xml-link="simple" key="IETF RFC2141"> 3452IETF (Internet Engineering Task Force). 3453<emph>RFC 2141: URN Syntax</emph>, 3454ed. R. Moats. 34551997. 3456</bibl> 3457 3458<bibl id='ISO8879' key='ISO 8879'>ISO 3459(International Organization for Standardization). 3460<emph>ISO 8879:1986(E). Information processing — Text and Office 3461Systems — Standard Generalized Markup Language (SGML).</emph> First 3462edition — 1986-10-15. [Geneva]: International Organization for 3463Standardization, 1986. 3464</bibl> 3465 3466 3467<bibl id='ISO10744' key='ISO/IEC 10744'>ISO 3468(International Organization for Standardization). 3469<emph>ISO/IEC 10744-1992 (E). Information technology — 3470Hypermedia/Time-based Structuring Language (HyTime). 3471</emph> 3472[Geneva]: International Organization for 3473Standardization, 1992. 3474<emph>Extended Facilities Annexe.</emph> 3475[Geneva]: International Organization for 3476Standardization, 1996. 3477</bibl> 3478 3479 3480 3481</blist> 3482</div2> 3483</div1> 3484<div1 id='CharClasses'> 3485<head>Character Classes</head> 3486<p>Following the characteristics defined in the Unicode standard, 3487characters are classed as base characters (among others, these 3488contain the alphabetic characters of the Latin alphabet, without 3489diacritics), ideographic characters, and combining characters (among 3490others, this class contains most diacritics); these classes combine 3491to form the class of letters. Digits and extenders are 3492also distinguished. 3493<scrap lang="ebnf" id="CHARACTERS"> 3494<head>Characters</head> 3495<prodgroup pcw3="3" pcw4="15"> 3496<prod id="NT-Letter"><lhs>Letter</lhs> 3497<rhs><nt def="NT-BaseChar">BaseChar</nt> 3498| <nt def="NT-Ideographic">Ideographic</nt></rhs> </prod> 3499<prod id='NT-BaseChar'><lhs>BaseChar</lhs> 3500<rhs>[#x0041-#x005A] 3501| [#x0061-#x007A] 3502| [#x00C0-#x00D6] 3503| [#x00D8-#x00F6] 3504| [#x00F8-#x00FF] 3505| [#x0100-#x0131] 3506| [#x0134-#x013E] 3507| [#x0141-#x0148] 3508| [#x014A-#x017E] 3509| [#x0180-#x01C3] 3510| [#x01CD-#x01F0] 3511| [#x01F4-#x01F5] 3512| [#x01FA-#x0217] 3513| [#x0250-#x02A8] 3514| [#x02BB-#x02C1] 3515| #x0386 3516| [#x0388-#x038A] 3517| #x038C 3518| [#x038E-#x03A1] 3519| [#x03A3-#x03CE] 3520| [#x03D0-#x03D6] 3521| #x03DA 3522| #x03DC 3523| #x03DE 3524| #x03E0 3525| [#x03E2-#x03F3] 3526| [#x0401-#x040C] 3527| [#x040E-#x044F] 3528| [#x0451-#x045C] 3529| [#x045E-#x0481] 3530| [#x0490-#x04C4] 3531| [#x04C7-#x04C8] 3532| [#x04CB-#x04CC] 3533| [#x04D0-#x04EB] 3534| [#x04EE-#x04F5] 3535| [#x04F8-#x04F9] 3536| [#x0531-#x0556] 3537| #x0559 3538| [#x0561-#x0586] 3539| [#x05D0-#x05EA] 3540| [#x05F0-#x05F2] 3541| [#x0621-#x063A] 3542| [#x0641-#x064A] 3543| [#x0671-#x06B7] 3544| [#x06BA-#x06BE] 3545| [#x06C0-#x06CE] 3546| [#x06D0-#x06D3] 3547| #x06D5 3548| [#x06E5-#x06E6] 3549| [#x0905-#x0939] 3550| #x093D 3551| [#x0958-#x0961] 3552| [#x0985-#x098C] 3553| [#x098F-#x0990] 3554| [#x0993-#x09A8] 3555| [#x09AA-#x09B0] 3556| #x09B2 3557| [#x09B6-#x09B9] 3558| [#x09DC-#x09DD] 3559| [#x09DF-#x09E1] 3560| [#x09F0-#x09F1] 3561| [#x0A05-#x0A0A] 3562| [#x0A0F-#x0A10] 3563| [#x0A13-#x0A28] 3564| [#x0A2A-#x0A30] 3565| [#x0A32-#x0A33] 3566| [#x0A35-#x0A36] 3567| [#x0A38-#x0A39] 3568| [#x0A59-#x0A5C] 3569| #x0A5E 3570| [#x0A72-#x0A74] 3571| [#x0A85-#x0A8B] 3572| #x0A8D 3573| [#x0A8F-#x0A91] 3574| [#x0A93-#x0AA8] 3575| [#x0AAA-#x0AB0] 3576| [#x0AB2-#x0AB3] 3577| [#x0AB5-#x0AB9] 3578| #x0ABD 3579| #x0AE0 3580| [#x0B05-#x0B0C] 3581| [#x0B0F-#x0B10] 3582| [#x0B13-#x0B28] 3583| [#x0B2A-#x0B30] 3584| [#x0B32-#x0B33] 3585| [#x0B36-#x0B39] 3586| #x0B3D 3587| [#x0B5C-#x0B5D] 3588| [#x0B5F-#x0B61] 3589| [#x0B85-#x0B8A] 3590| [#x0B8E-#x0B90] 3591| [#x0B92-#x0B95] 3592| [#x0B99-#x0B9A] 3593| #x0B9C 3594| [#x0B9E-#x0B9F] 3595| [#x0BA3-#x0BA4] 3596| [#x0BA8-#x0BAA] 3597| [#x0BAE-#x0BB5] 3598| [#x0BB7-#x0BB9] 3599| [#x0C05-#x0C0C] 3600| [#x0C0E-#x0C10] 3601| [#x0C12-#x0C28] 3602| [#x0C2A-#x0C33] 3603| [#x0C35-#x0C39] 3604| [#x0C60-#x0C61] 3605| [#x0C85-#x0C8C] 3606| [#x0C8E-#x0C90] 3607| [#x0C92-#x0CA8] 3608| [#x0CAA-#x0CB3] 3609| [#x0CB5-#x0CB9] 3610| #x0CDE 3611| [#x0CE0-#x0CE1] 3612| [#x0D05-#x0D0C] 3613| [#x0D0E-#x0D10] 3614| [#x0D12-#x0D28] 3615| [#x0D2A-#x0D39] 3616| [#x0D60-#x0D61] 3617| [#x0E01-#x0E2E] 3618| #x0E30 3619| [#x0E32-#x0E33] 3620| [#x0E40-#x0E45] 3621| [#x0E81-#x0E82] 3622| #x0E84 3623| [#x0E87-#x0E88] 3624| #x0E8A 3625| #x0E8D 3626| [#x0E94-#x0E97] 3627| [#x0E99-#x0E9F] 3628| [#x0EA1-#x0EA3] 3629| #x0EA5 3630| #x0EA7 3631| [#x0EAA-#x0EAB] 3632| [#x0EAD-#x0EAE] 3633| #x0EB0 3634| [#x0EB2-#x0EB3] 3635| #x0EBD 3636| [#x0EC0-#x0EC4] 3637| [#x0F40-#x0F47] 3638| [#x0F49-#x0F69] 3639| [#x10A0-#x10C5] 3640| [#x10D0-#x10F6] 3641| #x1100 3642| [#x1102-#x1103] 3643| [#x1105-#x1107] 3644| #x1109 3645| [#x110B-#x110C] 3646| [#x110E-#x1112] 3647| #x113C 3648| #x113E 3649| #x1140 3650| #x114C 3651| #x114E 3652| #x1150 3653| [#x1154-#x1155] 3654| #x1159 3655| [#x115F-#x1161] 3656| #x1163 3657| #x1165 3658| #x1167 3659| #x1169 3660| [#x116D-#x116E] 3661| [#x1172-#x1173] 3662| #x1175 3663| #x119E 3664| #x11A8 3665| #x11AB 3666| [#x11AE-#x11AF] 3667| [#x11B7-#x11B8] 3668| #x11BA 3669| [#x11BC-#x11C2] 3670| #x11EB 3671| #x11F0 3672| #x11F9 3673| [#x1E00-#x1E9B] 3674| [#x1EA0-#x1EF9] 3675| [#x1F00-#x1F15] 3676| [#x1F18-#x1F1D] 3677| [#x1F20-#x1F45] 3678| [#x1F48-#x1F4D] 3679| [#x1F50-#x1F57] 3680| #x1F59 3681| #x1F5B 3682| #x1F5D 3683| [#x1F5F-#x1F7D] 3684| [#x1F80-#x1FB4] 3685| [#x1FB6-#x1FBC] 3686| #x1FBE 3687| [#x1FC2-#x1FC4] 3688| [#x1FC6-#x1FCC] 3689| [#x1FD0-#x1FD3] 3690| [#x1FD6-#x1FDB] 3691| [#x1FE0-#x1FEC] 3692| [#x1FF2-#x1FF4] 3693| [#x1FF6-#x1FFC] 3694| #x2126 3695| [#x212A-#x212B] 3696| #x212E 3697| [#x2180-#x2182] 3698| [#x3041-#x3094] 3699| [#x30A1-#x30FA] 3700| [#x3105-#x312C] 3701| [#xAC00-#xD7A3] 3702</rhs></prod> 3703<prod id='NT-Ideographic'><lhs>Ideographic</lhs> 3704<rhs>[#x4E00-#x9FA5] 3705| #x3007 3706| [#x3021-#x3029] 3707</rhs></prod> 3708<prod id='NT-CombiningChar'><lhs>CombiningChar</lhs> 3709<rhs>[#x0300-#x0345] 3710| [#x0360-#x0361] 3711| [#x0483-#x0486] 3712| [#x0591-#x05A1] 3713| [#x05A3-#x05B9] 3714| [#x05BB-#x05BD] 3715| #x05BF 3716| [#x05C1-#x05C2] 3717| #x05C4 3718| [#x064B-#x0652] 3719| #x0670 3720| [#x06D6-#x06DC] 3721| [#x06DD-#x06DF] 3722| [#x06E0-#x06E4] 3723| [#x06E7-#x06E8] 3724| [#x06EA-#x06ED] 3725| [#x0901-#x0903] 3726| #x093C 3727| [#x093E-#x094C] 3728| #x094D 3729| [#x0951-#x0954] 3730| [#x0962-#x0963] 3731| [#x0981-#x0983] 3732| #x09BC 3733| #x09BE 3734| #x09BF 3735| [#x09C0-#x09C4] 3736| [#x09C7-#x09C8] 3737| [#x09CB-#x09CD] 3738| #x09D7 3739| [#x09E2-#x09E3] 3740| #x0A02 3741| #x0A3C 3742| #x0A3E 3743| #x0A3F 3744| [#x0A40-#x0A42] 3745| [#x0A47-#x0A48] 3746| [#x0A4B-#x0A4D] 3747| [#x0A70-#x0A71] 3748| [#x0A81-#x0A83] 3749| #x0ABC 3750| [#x0ABE-#x0AC5] 3751| [#x0AC7-#x0AC9] 3752| [#x0ACB-#x0ACD] 3753| [#x0B01-#x0B03] 3754| #x0B3C 3755| [#x0B3E-#x0B43] 3756| [#x0B47-#x0B48] 3757| [#x0B4B-#x0B4D] 3758| [#x0B56-#x0B57] 3759| [#x0B82-#x0B83] 3760| [#x0BBE-#x0BC2] 3761| [#x0BC6-#x0BC8] 3762| [#x0BCA-#x0BCD] 3763| #x0BD7 3764| [#x0C01-#x0C03] 3765| [#x0C3E-#x0C44] 3766| [#x0C46-#x0C48] 3767| [#x0C4A-#x0C4D] 3768| [#x0C55-#x0C56] 3769| [#x0C82-#x0C83] 3770| [#x0CBE-#x0CC4] 3771| [#x0CC6-#x0CC8] 3772| [#x0CCA-#x0CCD] 3773| [#x0CD5-#x0CD6] 3774| [#x0D02-#x0D03] 3775| [#x0D3E-#x0D43] 3776| [#x0D46-#x0D48] 3777| [#x0D4A-#x0D4D] 3778| #x0D57 3779| #x0E31 3780| [#x0E34-#x0E3A] 3781| [#x0E47-#x0E4E] 3782| #x0EB1 3783| [#x0EB4-#x0EB9] 3784| [#x0EBB-#x0EBC] 3785| [#x0EC8-#x0ECD] 3786| [#x0F18-#x0F19] 3787| #x0F35 3788| #x0F37 3789| #x0F39 3790| #x0F3E 3791| #x0F3F 3792| [#x0F71-#x0F84] 3793| [#x0F86-#x0F8B] 3794| [#x0F90-#x0F95] 3795| #x0F97 3796| [#x0F99-#x0FAD] 3797| [#x0FB1-#x0FB7] 3798| #x0FB9 3799| [#x20D0-#x20DC] 3800| #x20E1 3801| [#x302A-#x302F] 3802| #x3099 3803| #x309A 3804</rhs></prod> 3805<prod id='NT-Digit'><lhs>Digit</lhs> 3806<rhs>[#x0030-#x0039] 3807| [#x0660-#x0669] 3808| [#x06F0-#x06F9] 3809| [#x0966-#x096F] 3810| [#x09E6-#x09EF] 3811| [#x0A66-#x0A6F] 3812| [#x0AE6-#x0AEF] 3813| [#x0B66-#x0B6F] 3814| [#x0BE7-#x0BEF] 3815| [#x0C66-#x0C6F] 3816| [#x0CE6-#x0CEF] 3817| [#x0D66-#x0D6F] 3818| [#x0E50-#x0E59] 3819| [#x0ED0-#x0ED9] 3820| [#x0F20-#x0F29] 3821</rhs></prod> 3822<prod id='NT-Extender'><lhs>Extender</lhs> 3823<rhs>#x00B7 3824| #x02D0 3825| #x02D1 3826| #x0387 3827| #x0640 3828| #x0E46 3829| #x0EC6 3830| #x3005 3831| [#x3031-#x3035] 3832| [#x309D-#x309E] 3833| [#x30FC-#x30FE] 3834</rhs></prod> 3835 3836</prodgroup> 3837</scrap> 3838</p> 3839<p>The character classes defined here can be derived from the 3840Unicode character database as follows: 3841<ulist> 3842<item> 3843<p>Name start characters must have one of the categories Ll, Lu, 3844Lo, Lt, Nl.</p> 3845</item> 3846<item> 3847<p>Name characters other than Name-start characters 3848must have one of the categories Mc, Me, Mn, Lm, or Nd.</p> 3849</item> 3850<item> 3851<p>Characters in the compatibility area (i.e. with character code 3852greater than #xF900 and less than #xFFFE) are not allowed in XML 3853names.</p> 3854</item> 3855<item> 3856<p>Characters which have a font or compatibility decomposition (i.e. those 3857with a "compatibility formatting tag" in field 5 of the database -- 3858marked by field 5 beginning with a "<") are not allowed.</p> 3859</item> 3860<item> 3861<p>The following characters are treated as name-start characters 3862rather than name characters, because the property file classifies 3863them as Alphabetic: [#x02BB-#x02C1], #x0559, #x06E5, #x06E6.</p> 3864</item> 3865<item> 3866<p>Characters #x20DD-#x20E0 are excluded (in accordance with 3867Unicode, section 5.14).</p> 3868</item> 3869<item> 3870<p>Character #x00B7 is classified as an extender, because the 3871property list so identifies it.</p> 3872</item> 3873<item> 3874<p>Character #x0387 is added as a name character, because #x00B7 3875is its canonical equivalent.</p> 3876</item> 3877<item> 3878<p>Characters ':' and '_' are allowed as name-start characters.</p> 3879</item> 3880<item> 3881<p>Characters '-' and '.' are allowed as name characters.</p> 3882</item> 3883</ulist> 3884</p> 3885</div1> 3886<inform-div1 id="sec-xml-and-sgml"> 3887<head>XML and SGML</head> 3888 3889<p>XML is designed to be a subset of SGML, in that every 3890<termref def="dt-valid">valid</termref> XML document should also be a 3891conformant SGML document. 3892For a detailed comparison of the additional restrictions that XML places on 3893documents beyond those of SGML, see <bibref ref='Clark'/>. 3894</p> 3895</inform-div1> 3896<inform-div1 id="sec-entexpand"> 3897<head>Expansion of Entity and Character References</head> 3898<p>This appendix contains some examples illustrating the 3899sequence of entity- and character-reference recognition and 3900expansion, as specified in <specref ref='entproc'/>.</p> 3901<p> 3902If the DTD contains the declaration 3903<eg><![CDATA[<!ENTITY example "<p>An ampersand (&#38;) may be escaped 3904numerically (&#38;#38;) or with a general entity 3905(&amp;).</p>" > 3906]]></eg> 3907then the XML processor will recognize the character references 3908when it parses the entity declaration, and resolve them before 3909storing the following string as the 3910value of the entity "<code>example</code>": 3911<eg><![CDATA[<p>An ampersand (&) may be escaped 3912numerically (&#38;) or with a general entity 3913(&amp;).</p> 3914]]></eg> 3915A reference in the document to "<code>&example;</code>" 3916will cause the text to be reparsed, at which time the 3917start- and end-tags of the "<code>p</code>" element will be recognized 3918and the three references will be recognized and expanded, 3919resulting in a "<code>p</code>" element with the following content 3920(all data, no delimiters or markup): 3921<eg><![CDATA[An ampersand (&) may be escaped 3922numerically (&) or with a general entity 3923(&). 3924]]></eg> 3925</p> 3926<p>A more complex example will illustrate the rules and their 3927effects fully. In the following example, the line numbers are 3928solely for reference. 3929<eg><![CDATA[1 <?xml version='1.0'?> 39302 <!DOCTYPE test [ 39313 <!ELEMENT test (#PCDATA) > 39324 <!ENTITY % xx '%zz;'> 39335 <!ENTITY % zz '<!ENTITY tricky "error-prone" >' > 39346 %xx; 39357 ]> 39368 <test>This sample shows a &tricky; method.</test> 3937]]></eg> 3938This produces the following: 3939<ulist spacing="compact"> 3940<item><p>in line 4, the reference to character 37 is expanded immediately, 3941and the parameter entity "<code>xx</code>" is stored in the symbol 3942table with the value "<code>%zz;</code>". Since the replacement text 3943is not rescanned, the reference to parameter entity "<code>zz</code>" 3944is not recognized. (And it would be an error if it were, since 3945"<code>zz</code>" is not yet declared.)</p></item> 3946<item><p>in line 5, the character reference "<code>&#60;</code>" is 3947expanded immediately and the parameter entity "<code>zz</code>" is 3948stored with the replacement text 3949"<code><!ENTITY tricky "error-prone" ></code>", 3950which is a well-formed entity declaration.</p></item> 3951<item><p>in line 6, the reference to "<code>xx</code>" is recognized, 3952and the replacement text of "<code>xx</code>" (namely 3953"<code>%zz;</code>") is parsed. The reference to "<code>zz</code>" 3954is recognized in its turn, and its replacement text 3955("<code><!ENTITY tricky "error-prone" ></code>") is parsed. 3956The general entity "<code>tricky</code>" has now been 3957declared, with the replacement text "<code>error-prone</code>".</p></item> 3958<item><p> 3959in line 8, the reference to the general entity "<code>tricky</code>" is 3960recognized, and it is expanded, so the full content of the 3961"<code>test</code>" element is the self-describing (and ungrammatical) string 3962<emph>This sample shows a error-prone method.</emph> 3963</p></item> 3964</ulist> 3965</p> 3966</inform-div1> 3967<inform-div1 id="determinism"> 3968<head>Deterministic Content Models</head> 3969<p><termref def='dt-compat'>For compatibility</termref>, it is 3970required 3971that content models in element type declarations be deterministic. 3972</p> 3973<!-- FINAL EDIT: WebSGML allows ambiguity? --> 3974<p>SGML 3975requires deterministic content models (it calls them 3976"unambiguous"); XML processors built using SGML systems may 3977flag non-deterministic content models as errors.</p> 3978<p>For example, the content model <code>((b, c) | (b, d))</code> is 3979non-deterministic, because given an initial <code>b</code> the parser 3980cannot know which <code>b</code> in the model is being matched without 3981looking ahead to see which element follows the <code>b</code>. 3982In this case, the two references to 3983<code>b</code> can be collapsed 3984into a single reference, making the model read 3985<code>(b, (c | d))</code>. An initial <code>b</code> now clearly 3986matches only a single name in the content model. The parser doesn't 3987need to look ahead to see what follows; either <code>c</code> or 3988<code>d</code> would be accepted.</p> 3989<p>More formally: a finite state automaton may be constructed from the 3990content model using the standard algorithms, e.g. algorithm 3.5 3991in section 3.9 3992of Aho, Sethi, and Ullman <bibref ref='Aho'/>. 3993In many such algorithms, a follow set is constructed for each 3994position in the regular expression (i.e., each leaf 3995node in the 3996syntax tree for the regular expression); 3997if any position has a follow set in which 3998more than one following position is 3999labeled with the same element type name, 4000then the content model is in error 4001and may be reported as an error. 4002</p> 4003<p>Algorithms exist which allow many but not all non-deterministic 4004content models to be reduced automatically to equivalent deterministic 4005models; see Br�ggemann-Klein 1991 <bibref ref='ABK'/>.</p> 4006</inform-div1> 4007<inform-div1 id="sec-guessing"> 4008<head>Autodetection of Character Encodings</head> 4009<p>The XML encoding declaration functions as an internal label on each 4010entity, indicating which character encoding is in use. Before an XML 4011processor can read the internal label, however, it apparently has to 4012know what character encoding is in use—which is what the internal label 4013is trying to indicate. In the general case, this is a hopeless 4014situation. It is not entirely hopeless in XML, however, because XML 4015limits the general case in two ways: each implementation is assumed 4016to support only a finite set of character encodings, and the XML 4017encoding declaration is restricted in position and content in order to 4018make it feasible to autodetect the character encoding in use in each 4019entity in normal cases. Also, in many cases other sources of information 4020are available in addition to the XML data stream itself. 4021Two cases may be distinguished, 4022depending on whether the XML entity is presented to the 4023processor without, or with, any accompanying 4024(external) information. We consider the first case first. 4025</p> 4026<p> 4027Because each XML entity not in UTF-8 or UTF-16 format <emph>must</emph> 4028begin with an XML encoding declaration, in which the first characters 4029must be '<code><?xml</code>', any conforming processor can detect, 4030after two to four octets of input, which of the following cases apply. 4031In reading this list, it may help to know that in UCS-4, '<' is 4032"<code>#x0000003C</code>" and '?' is "<code>#x0000003F</code>", and the Byte 4033Order Mark required of UTF-16 data streams is "<code>#xFEFF</code>".</p> 4034<p> 4035<ulist> 4036<item> 4037<p><code>00 00 00 3C</code>: UCS-4, big-endian machine (1234 order)</p> 4038</item> 4039<item> 4040<p><code>3C 00 00 00</code>: UCS-4, little-endian machine (4321 order)</p> 4041</item> 4042<item> 4043<p><code>00 00 3C 00</code>: UCS-4, unusual octet order (2143)</p> 4044</item> 4045<item> 4046<p><code>00 3C 00 00</code>: UCS-4, unusual octet order (3412)</p> 4047</item> 4048<item> 4049<p><code>FE FF</code>: UTF-16, big-endian</p> 4050</item> 4051<item> 4052<p><code>FF FE</code>: UTF-16, little-endian</p> 4053</item> 4054<item> 4055<p><code>00 3C 00 3F</code>: UTF-16, big-endian, no Byte Order Mark 4056(and thus, strictly speaking, in error)</p> 4057</item> 4058<item> 4059<p><code>3C 00 3F 00</code>: UTF-16, little-endian, no Byte Order Mark 4060(and thus, strictly speaking, in error)</p> 4061</item> 4062<item> 4063<p><code>3C 3F 78 6D</code>: UTF-8, ISO 646, ASCII, some part of ISO 8859, 4064Shift-JIS, EUC, or any other 7-bit, 8-bit, or mixed-width encoding 4065which ensures that the characters of ASCII have their normal positions, 4066width, 4067and values; the actual encoding declaration must be read to 4068detect which of these applies, but since all of these encodings 4069use the same bit patterns for the ASCII characters, the encoding 4070declaration itself may be read reliably 4071</p> 4072</item> 4073<item> 4074<p><code>4C 6F A7 94</code>: EBCDIC (in some flavor; the full 4075encoding declaration must be read to tell which code page is in 4076use)</p> 4077</item> 4078<item> 4079<p>other: UTF-8 without an encoding declaration, or else 4080the data stream is corrupt, fragmentary, or enclosed in 4081a wrapper of some kind</p> 4082</item> 4083</ulist> 4084</p> 4085<p> 4086This level of autodetection is enough to read the XML encoding 4087declaration and parse the character-encoding identifier, which is 4088still necessary to distinguish the individual members of each family 4089of encodings (e.g. to tell UTF-8 from 8859, and the parts of 8859 4090from each other, or to distinguish the specific EBCDIC code page in 4091use, and so on). 4092</p> 4093<p> 4094Because the contents of the encoding declaration are restricted to 4095ASCII characters, a processor can reliably read the entire encoding 4096declaration as soon as it has detected which family of encodings is in 4097use. Since in practice, all widely used character encodings fall into 4098one of the categories above, the XML encoding declaration allows 4099reasonably reliable in-band labeling of character encodings, even when 4100external sources of information at the operating-system or 4101transport-protocol level are unreliable. 4102</p> 4103<p> 4104Once the processor has detected the character encoding in use, it can 4105act appropriately, whether by invoking a separate input routine for 4106each case, or by calling the proper conversion function on each 4107character of input. 4108</p> 4109<p> 4110Like any self-labeling system, the XML encoding declaration will not 4111work if any software changes the entity's character set or encoding 4112without updating the encoding declaration. Implementors of 4113character-encoding routines should be careful to ensure the accuracy 4114of the internal and external information used to label the entity. 4115</p> 4116<p>The second possible case occurs when the XML entity is accompanied 4117by encoding information, as in some file systems and some network 4118protocols. 4119When multiple sources of information are available, 4120 4121their relative 4122priority and the preferred method of handling conflict should be 4123specified as part of the higher-level protocol used to deliver XML. 4124Rules for the relative priority of the internal label and the 4125MIME-type label in an external header, for example, should be part of the 4126RFC document defining the text/xml and application/xml MIME types. In 4127the interests of interoperability, however, the following rules 4128are recommended. 4129<ulist> 4130<item><p>If an XML entity is in a file, the Byte-Order Mark 4131and encoding-declaration PI are used (if present) to determine the 4132character encoding. All other heuristics and sources of information 4133are solely for error recovery. 4134</p></item> 4135<item><p>If an XML entity is delivered with a 4136MIME type of text/xml, then the <code>charset</code> parameter 4137on the MIME type determines the 4138character encoding method; all other heuristics and sources of 4139information are solely for error recovery. 4140</p></item> 4141<item><p>If an XML entity is delivered 4142with a 4143MIME type of application/xml, then the Byte-Order Mark and 4144encoding-declaration PI are used (if present) to determine the 4145character encoding. All other heuristics and sources of 4146information are solely for error recovery. 4147</p></item> 4148</ulist> 4149These rules apply only in the absence of protocol-level documentation; 4150in particular, when the MIME types text/xml and application/xml are 4151defined, the recommendations of the relevant RFC will supersede 4152these rules. 4153</p> 4154 4155</inform-div1> 4156 4157<inform-div1 id="sec-xml-wg"> 4158<head>W3C XML Working Group</head> 4159 4160<p>This specification was prepared and approved for publication by the 4161W3C XML Working Group (WG). WG approval of this specification does 4162not necessarily imply that all WG members voted for its approval. 4163The current and former members of the XML WG are:</p> 4164 4165<orglist> 4166<member><name>Jon Bosak, Sun</name><role>Chair</role></member> 4167<member><name>James Clark</name><role>Technical Lead</role></member> 4168<member><name>Tim Bray, Textuality and Netscape</name><role>XML Co-editor</role></member> 4169<member><name>Jean Paoli, Microsoft</name><role>XML Co-editor</role></member> 4170<member><name>C. M. Sperberg-McQueen, U. of Ill.</name><role>XML 4171Co-editor</role></member> 4172<member><name>Dan Connolly, W3C</name><role>W3C Liaison</role></member> 4173<member><name>Paula Angerstein, Texcel</name></member> 4174<member><name>Steve DeRose, INSO</name></member> 4175<member><name>Dave Hollander, HP</name></member> 4176<member><name>Eliot Kimber, ISOGEN</name></member> 4177<member><name>Eve Maler, ArborText</name></member> 4178<member><name>Tom Magliery, NCSA</name></member> 4179<member><name>Murray Maloney, Muzmo and Grif</name></member> 4180<member><name>Makoto Murata, Fuji Xerox Information Systems</name></member> 4181<member><name>Joel Nava, Adobe</name></member> 4182<member><name>Conleth O'Connell, Vignette</name></member> 4183<member><name>Peter Sharpe, SoftQuad</name></member> 4184<member><name>John Tigue, DataChannel</name></member> 4185</orglist> 4186 4187</inform-div1> 4188</back> 4189</spec> 4190<!-- Keep this comment at the end of the file 4191Local variables: 4192mode: sgml 4193sgml-default-dtd-file:"~/sgml/spec.ced" 4194sgml-omittag:t 4195sgml-shorttag:t 4196End: 4197--> 4198
