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1: <?xml version='1.0' encoding='ISO-8859-1' standalone='no'?> 2: <!DOCTYPE spec SYSTEM "dtds/spec.dtd" [ 3: 4:  5: 6:  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 "--">  28: <!ENTITY com "--"> 29: <!ENTITY como "--"> 30: <!ENTITY comc "--"> 31: <!ENTITY hcro "&#x"> 32:  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:  41: <!ENTITY doc.audience "public review and discussion"> 42: <!ENTITY doc.distribution "may be distributed freely, as long as 43: all text and legal notices remain intact"> 44: 45: ]> 46: 47:  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;"> 60: http://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"> 62: http://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"> 64: http://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"> 66: http://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"> 68: http://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"> 72: http://www.w3.org/TR/REC-xml</loc> 73: </latestloc> 74: <prevlocs> 75: <loc href="http://www.w3.org/TR/PR-xml-971208"> 76: http://www.w3.org/TR/PR-xml-971208</loc> 77:  88: </prevlocs> 89: <authlist> 90: <author><name>Tim Bray</name> 91: <affiliation>Textuality and Netscape</affiliation> 92: <email 93: href="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: The Extensible Markup Language (XML) is a subset of 103: SGML that is completely described in this document. Its goal is to 104: enable generic SGML to be served, received, and processed on the Web 105: in the way that is now possible with HTML. XML has been designed for 106: ease of implementation and for interoperability with both SGML and 107: HTML. 108: </abstract> 109: <status> 110: This document has been reviewed by W3C Members and 111: other interested parties and has been endorsed by the 112: Director as a W3C Recommendation. It is a stable 113: document and may be used as reference material or cited 114: as a normative reference from another document. W3C's 115: role in making the Recommendation is to draw attention 116: to the specification and to promote its widespread 117: deployment. This enhances the functionality and 118: interoperability of the Web. 119: 120: This document specifies a syntax created by subsetting an existing, 121: widely used international text processing standard (Standard 122: Generalized Markup Language, ISO 8879:1986(E) as amended and 123: corrected) for use on the World Wide Web. It is a product of the W3C 124: XML Activity, details of which can be found at <loc 125: href='http://www.w3.org/XML'>http://www.w3.org/XML</loc>. A list of 126: current W3C Recommendations and other technical documents can be found 127: at <loc href='http://www.w3.org/TR'>http://www.w3.org/TR</loc>. 128: 129: This specification uses the term URI, which is defined by <bibref 130: ref="Berners-Lee"/>, a work in progress expected to update <bibref 131: ref="RFC1738"/> and <bibref ref="RFC1808"/>. 132: 133: The list of known errors in this specification is 134: available at 135: <loc href='http://www.w3.org/XML/xml-19980210-errata'>http://www.w3.org/XML/xml-19980210-errata</loc>. 136: Please report errors in this document to 137: <loc href='mailto:xml-editor@w3.org'>xml-editor@w3.org</loc>. 138: 139: </status> 140: 141: 142: <pubstmt> 143: Chicago, Vancouver, Mountain View, et al.: 144: World-Wide Web Consortium, XML Working Group, 1996, 1997. 145: </pubstmt> 146: <sourcedesc> 147: Created in electronic form. 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, 157: 2 December 1997)</sitem> 158: <sitem>1997-12-02 : CMSMcQ : deal with as many corrections and 159: comments from the proofreaders as possible: 160: entify hard-coded document date in pubdate element, 161: change expansion of entity WebSGML, 162: update status description as per Dan Connolly (am not sure 163: about refernece to Berners-Lee et al.), 164: add 'The' to abstract as per WG decision, 165: move Relationship to Existing Standards to back matter and 166: combine with References, 167: re-order back matter so normative appendices come first, 168: re-tag back matter so informative appendices are tagged informdiv1, 169: remove XXX XXX from list of 'normative' specs in prose, 170: move some references from Other References to Normative References, 171: add RFC 1738, 1808, and 2141 to Other References (they are not 172: normative since we do not require the processor to enforce any 173: rules based on them), 174: add reference to 'Fielding draft' (Berners-Lee et al.), 175: move notation section to end of body, 176: drop URIchar non-terminal and use SkipLit instead, 177: lose stray reference to defunct nonterminal 'markupdecls', 178: move reference to Aho et al. into appendix (Tim's right), 179: add prose note saying that hash marks and fragment identifiers are 180: NOT part of the URI formally speaking, and are NOT legal in 181: system identifiers (processor 'may' signal an error). 182: Work through: 183: Tim Bray reacting to James Clark, 184: Tim Bray on his own, 185: Eve Maler, 186: 187: NOT DONE YET: 188: change binary / text to unparsed / parsed. 189: handle James's suggestion about < in attriubte values 190: uppercase hex characters, 191: namechar 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 195: recent WG decisions and other corrections: 196: binding sources of character encoding info (27 Aug / 3 Sept), 197: correct wording of Faust quotation (restore dropped line), 198: drop SDD from EncodingDecl, 199: change text at version number 1.0, 200: drop misleading (wrong!) sentence about ignorables and extenders, 201: modify definition of PCData to make bar on msc grammatical, 202: change grammar's handling of internal subset (drop non-terminal markupdecls), 203: change definition of includeSect to allow conditional sections, 204: add integral-declaration constraint on internal subset, 205: drop misleading / dangerous sentence about relationship of 206: entities with system storage objects, 207: change table body tag to htbody as per EM change to DTD, 208: add rule about space normalization in public identifiers, 209: add description of how to generate our name-space rules from 210: Unicode character database (needs further work!). 211: </sitem> 212: <sitem>1997-10-08 : TB : Removed %-constructs again, new rules 213: for PE appearance.</sitem> 214: <sitem>1997-10-01 : TB : Case-sensitive markup; cleaned up 215: element-type defs, lotsa little edits for style</sitem> 216: <sitem>1997-09-25 : TB : Change to elm's new DTD, with 217: substantial detail cleanup as a side-effect</sitem> 218: <sitem>1997-07-24 : CMSMcQ : correct error (lost *) in definition 219: of ignoreSectContents (thanks to Makoto Murata)</sitem> 220: <sitem>Allow all empty elements to have end-tags, consistent with 221: SGML TC (as per JJC).</sitem> 222: <sitem>1997-07-23 : CMSMcQ : pre-emptive strike on pending corrections: 223: introduce the term 'empty-element tag', note that all empty elements 224: may use it, and elements declared EMPTY must use it. 225: Add WFC requiring encoding decl to come first in an entity. 226: Redefine notations to point to PIs as well as binary entities. 227: Change autodetection table by removing bytes 3 and 4 from 228: examples with Byte Order Mark. 229: Add content model as a term and clarify that it applies to both 230: mixed and element content. 231: </sitem> 232: <sitem>1997-06-30 : CMSMcQ : change date, some cosmetic changes, 233: changes to productions for choice, seq, Mixed, NotationType, 234: Enumeration. Follow James Clark's suggestion and prohibit 235: conditional sections in internal subset. TO DO: simplify 236: production for ignored sections as a result, since we don't 237: need to worry about parsers which don't expand PErefs finding 238: a conditional section.</sitem> 239: <sitem>1997-06-29 : TB : various edits</sitem> 240: <sitem>1997-06-29 : CMSMcQ : further changes: 241: Suppress old FINAL EDIT comments and some dead material. 242: Revise occurrences of % in grammar to exploit Henry Thompson's pun, 243: especially markupdecl and attdef. 244: Remove RMD requirement relating to element content (?). 245: </sitem> 246: <sitem>1997-06-28 : CMSMcQ : Various changes for 1 July draft: 247: Add text for draconian error handling (introduce 248: the term Fatal Error). 249: RE deleta est (changing wording from 250: original announcement to restrict the requirement to validating 251: parsers). 252: Tag definition of validating processor and link to it. 253: Add colon as name character. 254: Change def of %operator. 255: Change standard definitions of lt, gt, amp. 256: Strip leading zeros from #x00nn forms.</sitem> 257: <sitem>1997-04-02 : CMSMcQ : final corrections of editorial errors 258: found in last night's proofreading. Reverse course once more on 259: well-formed: Webster's Second hyphenates it, and that's enough 260: for 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), 264: some Charles Goldfarb, some ERB decisions (PE handling in miscellaneous 265: declarations. Changed Ident element to accept def attribute. 266: Allow normalization of Unicode characters. move def of systemliteral 267: into section on literals.</sitem> 268: <sitem>1997-03-28 : CMSMcQ : make as many corrections as possible, from 269: Terry Allen, Norbert Mikula, James Clark, Jon Bosak, Henry Thompson, 270: Paul Grosso, and self. Among other things: give in on "well formed" 271: (Terry is right), tentatively rename QuotedCData as AttValue 272: and Literal as EntityValue to be more informative, since attribute 273: values are the <emph>only</emph> place QuotedCData was used, and 274: vice versa for entity text and Literal. (I'd call it Entity Text, 275: but 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 277: my changes dated 03-20 and 03-21. Normalize old 'may not' to 'must not' 278: except 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 280: to 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 285: WWW conference April 1997: restore some of the internal entity 286: references (e.g. to docdate, etc.), change character xA0 to &nbsp; 287: and define nbsp as &#160;, and refill a lot of paragraphs for 288: legibility.</sitem> 289: <sitem>1996-11-12 : CMSMcQ : revise using Tim's edits: 290: Add list type of NUMBERED and change most lists either to 291: BULLETS or to NUMBERED. 292: Suppress QuotedNames, Names (not used). 293: Correct trivial-grammar doc type decl. 294: Rename 'marked section' as 'CDATA section' passim. 295: Also edits from James Clark: 296: Define the set of characters from which [^abc] subtracts. 297: Charref should use just [0-9] not Digit. 298: Location info needs cleaner treatment: remove? (ERB 299: question). 300: One example of a PI has wrong pic. 301: Clarify discussion of encoding names. 302: Encoding failure should lead to unspecified results; don't 303: prescribe error recovery. 304: Don't require exposure of entity boundaries. 305: Ignore white space in element content. 306: Reserve entity names of the form u-NNNN. 307: Clarify relative URLs. 308: And some of my own: 309: Correct productions for content model: model cannot 310: consist of a name, so "elements ::= cp" is no good. 311: </sitem> 312: <sitem>1996-11-11 : CMSMcQ : revise for style. 313: Add new rhs to entity declaration, for parameter entities.</sitem> 314: <sitem>1996-11-10 : CMSMcQ : revise for style. 315: Fix / complete section on names, characters. 316: Add sections on parameter entities, conditional sections. 317: Still to do: Add compatibility note on deterministic content models. 318: Finish 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 321: ERB decision re EMPTY.</sitem> 322: <sitem>1996-10-28 : TB : Change DTD. Implement some of Michael's 323: suggestions. Change comments back to //. Introduce language for 324: XML namespace reservation. Add section on white-space handling. 325: Lots more cleanup.</sitem> 326: <sitem>1996-10-24 : CMSMcQ : quick tweaks, implement some ERB 327: decisions. Characters are not integers. Comments are /* */ not //. 328: Add bibliographic refs to 10646, HyTime, Unicode. 329: Rename old Cdata as MsData since it's <emph>only</emph> seen 330: in marked sections. Call them attribute-value pairs not 331: name-value pairs, except once. Internal subset is optional, needs 332: '?'. Implied attributes should be signaled to the app, not 333: have values supplied by processor.</sitem> 334: <sitem>1996-10-16 : TB : track down & excise all DSD references; 335: introduce some EBNF for entity declarations.</sitem> 336: <sitem>1996-10-?? : TB : consistency check, fix up scraps so 337: they all parse, get formatter working, correct a few productions.</sitem> 338: <sitem>1996-10-10/11 : CMSMcQ : various maintenance, stylistic, and 339: organizational changes: 340: Replace a few literals with xmlpio and 341: pic entities, to make them consistent and ensure we can change pic 342: reliably when the ERB votes. 343: Drop paragraph on recognizers from notation section. 344: Add match, exact match to terminology. 345: Move old 2.2 XML Processors and Apps into intro. 346: Mention comments, PIs, and marked sections in discussion of 347: delimiter escaping. 348: Streamline discussion of doctype decl syntax. 349: Drop old section of 'PI syntax' for doctype decl, and add 350: section on partial-DTD summary PIs to end of Logical Structures 351: section. 352: Revise DSD syntax section to use Tim's subset-in-a-PI 353: mechanism.</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, 358: at 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 361: CDATA</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, 368: do some housekeeping</sitem> 369: </slist> 370: </revisiondesc> 371: </header> 372: <body> 373: <div1 id='sec-intro'> 374: <head>Introduction</head> 375: Extensible Markup Language, abbreviated XML, describes a class of 376: data objects called <termref def="dt-xml-doc">XML documents</termref> and 377: partially describes the behavior of 378: computer programs which process them. XML is an application profile or 379: restricted form of SGML, the Standard Generalized Markup 380: Language <bibref ref='ISO8879'/>. 381: By construction, XML documents 382: are conforming SGML documents. 383: 384: XML documents are made up of storage units called <termref 385: def="dt-entity">entities</termref>, which contain either parsed 386: or unparsed data. 387: Parsed data is made up of <termref def="dt-character">characters</termref>, 388: some 389: of which form <termref def="dt-chardata">character data</termref>, 390: and some of which form <termref def="dt-markup">markup</termref>. 391: Markup encodes a description of the document's storage layout and 392: logical structure. XML provides a mechanism to impose constraints on 393: the storage layout and logical structure. 394: <termdef id="dt-xml-proc" term="XML Processor">A software module 395: called an <term>XML processor</term> is used to read XML documents 396: and provide access to their content and structure.</termdef> <termdef 397: id="dt-app" term="Application">It is assumed that an XML processor is 398: doing its work on behalf of another module, called the 399: <term>application</term>.</termdef> This specification describes the 400: required behavior of an XML processor in terms of how it must read XML 401: data and the information it must provide to the application. 402: 403: <div2 id='sec-origin-goals'> 404: <head>Origin and Goals</head> 405: XML was developed by an XML Working Group (originally known as the 406: SGML Editorial Review Board) formed under the auspices of the World 407: Wide Web Consortium (W3C) in 1996. 408: It was chaired by Jon Bosak of Sun 409: Microsystems with the active participation of an XML Special 410: Interest Group (previously known as the SGML Working Group) also 411: organized by the W3C. The membership of the XML Working Group is given 412: in an appendix. Dan Connolly served as the WG's contact with the W3C. 413: 414: The design goals for XML are:<olist> 415: <item>XML shall be straightforwardly usable over the 416: Internet.</item> 417: <item>XML shall support a wide variety of applications.</item> 418: <item>XML shall be compatible with SGML.</item> 419: <item>It shall be easy to write programs which process XML 420: documents.</item> 421: <item>The number of optional features in XML is to be kept to the 422: absolute minimum, ideally zero.</item> 423: <item>XML documents should be human-legible and reasonably 424: clear.</item> 425: <item>The XML design should be prepared quickly.</item> 426: <item>The design of XML shall be formal and concise.</item> 427: <item>XML documents shall be easy to create.</item> 428: <item>Terseness in XML markup is of minimal importance.</item></olist> 429: 430: This specification, 431: together with associated standards 432: (Unicode and ISO/IEC 10646 for characters, 433: Internet RFC 1766 for language identification tags, 434: ISO 639 for language name codes, and 435: ISO 3166 for country name codes), 436: provides all the information necessary to understand 437: XML Version &XML.version; 438: and construct computer programs to process it. 439: This version of the XML specification 440:  441: &doc.distribution;. 442: 443: </div2> 444: 445: 446: 447: 448: <div2 id='sec-terminology'> 449: <head>Terminology</head> 450: 451: The terminology used to describe XML documents is defined in the body of 452: this specification. 453: The terms defined in the following list are used in building those 454: definitions and in describing the actions of an XML processor: 455: <glist> 456: <gitem> 457: <label>may</label> 458: <def><termdef id="dt-may" term="May">Conforming documents and XML 459: processors are permitted to but need not behave as 460: described.</termdef></def> 461: </gitem> 462: <gitem> 463: <label>must</label> 464: <def>Conforming documents and XML processors 465: are required to behave as described; otherwise they are in error. 466:  468: </def> 469: </gitem> 470: <gitem> 471: <label>error</label> 472: <def><termdef id='dt-error' term='Error' 473: >A violation of the rules of this 474: specification; results are 475: undefined. Conforming software may detect and report an error and may 476: recover from it.</termdef></def> 477: </gitem> 478: <gitem> 479: <label>fatal error</label> 480: <def><termdef id="dt-fatal" term="Fatal Error">An error 481: which a conforming <termref def="dt-xml-proc">XML processor</termref> 482: must detect and report to the application. 483: After encountering a fatal error, the 484: processor may continue 485: processing the data to search for further errors and may report such 486: errors to the application. In order to support correction of errors, 487: the processor may make unprocessed data from the document (with 488: intermingled character data and markup) available to the application. 489: Once a fatal error is detected, however, the processor must not 490: continue normal processing (i.e., it must not 491: continue to pass character data and information about the document's 492: logical structure to the application in the normal way). 493: </termdef></def> 494: </gitem> 495: <gitem> 496: <label>at user option</label> 497: <def>Conforming software may or must (depending on the modal verb in the 498: sentence) behave as described; if it does, it must 499: provide users a means to enable or disable the behavior 500: described.</def> 501: </gitem> 502: <gitem> 503: <label>validity constraint</label> 504: <def>A rule which applies to all 505: <termref def="dt-valid">valid</termref> XML documents. 506: Violations of validity constraints are errors; they must, at user option, 507: be reported by 508: <termref def="dt-validating">validating XML processors</termref>.</def> 509: </gitem> 510: <gitem> 511: <label>well-formedness constraint</label> 512: <def>A rule which applies to all <termref 513: def="dt-wellformed">well-formed</termref> XML documents. 514: Violations of well-formedness constraints are 515: <termref def="dt-fatal">fatal errors</termref>.</def> 516: </gitem> 517: 518: <gitem> 519: <label>match</label> 520: <def><termdef id="dt-match" term="match">(Of strings or names:) 521: Two strings or names being compared must be identical. 522: Characters with multiple possible representations in ISO/IEC 10646 (e.g. 523: characters with 524: both precomposed and base+diacritic forms) match only if they have the 525: same representation in both strings. 526: At user option, processors may normalize such characters to 527: some canonical form. 528: No case folding is performed. 529: (Of strings and rules in the grammar:) 530: A string matches a grammatical production if it belongs to the 531: language generated by that production. 532: (Of content and content models:) 533: An element matches its declaration when it conforms 534: in the fashion described in the constraint 535: <specref ref='elementvalid'/>. 536: </termdef> 537: </def> 538: </gitem> 539: <gitem> 540: <label>for compatibility</label> 541: <def><termdef id="dt-compat" term="For Compatibility">A feature of 542: XML included solely to ensure that XML remains compatible with SGML. 543: </termdef></def> 544: </gitem> 545: <gitem> 546: <label>for interoperability</label> 547: <def><termdef id="dt-interop" term="For interoperability">A 548: non-binding recommendation included to increase the chances that XML 549: documents can be processed by the existing installed base of SGML 550: processors which predate the 551: &WebSGML;.</termdef></def> 552: </gitem> 553: </glist> 554: 555: </div2> 556: 557: 558: </div1> 559:  560: 561: <div1 id='sec-documents'> 562: <head>Documents</head> 563: 564: <termdef id="dt-xml-doc" term="XML Document"> 565: A data object is an 566: <term>XML document</term> if it is 567: <termref def="dt-wellformed">well-formed</termref>, as 568: defined in this specification. 569: A well-formed XML document may in addition be 570: <termref def="dt-valid">valid</termref> if it meets certain further 571: constraints.</termdef> 572: 573: Each XML document has both a logical and a physical structure. 574: Physically, the document is composed of units called <termref 575: def="dt-entity">entities</termref>. An entity may <termref 576: def="dt-entref">refer</termref> to other entities to cause their 577: inclusion in the document. A document begins in a "root" or <termref 578: def="dt-docent">document entity</termref>. 579: Logically, the document is composed of declarations, elements, 580: comments, 581: character references, and 582: processing 583: instructions, all of which are indicated in the document by explicit 584: markup. 585: The logical and physical structures must nest properly, as described 586: in <specref ref='wf-entities'/>. 587: 588: 589: <div2 id='sec-well-formed'> 590: <head>Well-Formed XML Documents</head> 591: 592: <termdef id="dt-wellformed" term="Well-Formed"> 593: A textual object is 594: a well-formed XML document if:</termdef> 595: <olist> 596: <item>Taken as a whole, it 597: matches the production labeled <nt def='NT-document'>document</nt>.</item> 598: <item>It 599: meets all the well-formedness constraints given in this specification. 600: </item> 601: <item>Each of the <termref def='dt-parsedent'>parsed entities</termref> 602: which is referenced directly or indirectly within the document is 603: <titleref href='wf-entities'>well-formed</titleref>.</item> 604: </olist> 605: 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: 614: Matching the <nt def="NT-document">document</nt> production 615: implies that: 616: <olist> 617: <item>It contains one or more 618: <termref def="dt-element">elements</termref>. 619: </item> 620:  628: <item><termdef id="dt-root" term="Root Element">There is exactly 629: one element, called the <term>root</term>, or document element, no 630: part of which appears in the <termref 631: def="dt-content">content</termref> of any other element.</termdef> 632: For all other elements, if the start-tag is in the content of another 633: element, the end-tag is in the content of the same element. More 634: simply stated, the elements, delimited by start- and end-tags, nest 635: properly within each other. 636: </item> 637: </olist> 638: 639: <termdef id="dt-parentchild" term="Parent/Child">As a consequence 640: of this, 641: for each non-root element 642: <code>C</code> in the document, there is one other element <code>P</code> 643: in the document such that 644: <code>C</code> is in the content of <code>P</code>, but is not in 645: the 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></div2> 650: 651: <div2 id="charsets"> 652: <head>Characters</head> 653: 654: <termdef id="dt-text" term="Text">A parsed entity contains 655: <term>text</term>, a sequence of 656: <termref def="dt-character">characters</termref>, 657: which may represent markup or character data.</termdef> 658: <termdef id="dt-character" term="Character">A <term>character</term> 659: is an atomic unit of text as specified by 660: ISO/IEC 10646 <bibref ref="ISO10646"/>. 661: Legal characters are tab, carriage return, line feed, and the legal 662: graphic characters of Unicode and ISO/IEC 10646. 663: The use of "compatibility characters", as defined in section 6.8 664: of <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 673: surrogate blocks, FFFE, and FFFF.</com> </prod> 674: </prodgroup> 675: </scrap> 676: 677: 678: The mechanism for encoding character code points into bit patterns may 679: vary from entity to entity. All XML processors must accept the UTF-8 680: and UTF-16 encodings of 10646; the mechanisms for signaling which of 681: the two is in use, or for bringing other encodings into play, are 682: discussed later, in <specref ref='charencoding'/>. 683: 684:  690: </div2> 691: 692: <div2 id='sec-common-syn'> 693: <head>Common Syntactic Constructs</head> 694: 695: This section defines some symbols used widely in the grammar. 696: <nt def="NT-S">S</nt> (white space) consists of one or more space (#x20) 697: characters, 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> 707: Characters are classified for convenience as letters, digits, or other 708: characters. Letters consist of an alphabetic or syllabic 709: base character possibly 710: followed by one or more combining characters, or of an ideographic 711: character. 712: Full definitions of the specific characters in each class 713: are given in <specref ref='CharClasses'/>. 714: <termdef id="dt-name" term="Name">A <term>Name</term> is a token 715: beginning with a letter or one of a few punctuation characters, and continuing 716: with letters, digits, hyphens, underscores, colons, or full stops, together 717: known as name characters.</termdef> 718: Names beginning with the string "<code>xml</code>", or any string 719: which would match <code>(('X'|'x') ('M'|'m') ('L'|'l'))</code>, are 720: reserved for standardization in this or future versions of this 721: specification. 722: 723: <note> 724: The colon character within XML names is reserved for experimentation with 725: name spaces. 726: Its meaning is expected to be 727: standardized at some future point, at which point those documents 728: using the colon for experimental purposes may need to be updated. 729: (There is no guarantee that any name-space mechanism 730: adopted for XML will in fact use the colon as a name-space delimiter.) 731: In practice, this means that authors should not use the colon in XML 732: names except as part of name-space experiments, but that XML processors 733: should accept the colon as a name character. 734: </note> 735: An 736: <nt def='NT-Nmtoken'>Nmtoken</nt> (name token) is any mixture of 737: name 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: 759: Literal data is any quoted string not containing 760: the quotation mark used as a delimiter for that string. 761: Literals are used 762: for specifying the content of internal entities 763: (<nt def='NT-EntityValue'>EntityValue</nt>), 764: the values of attributes (<nt def='NT-AttValue'>AttValue</nt>), 765: and external identifiers 766: (<nt def="NT-SystemLiteral">SystemLiteral</nt>). 767: Note that a <nt def='NT-SystemLiteral'>SystemLiteral</nt> 768: can 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: 813: 814: </div2> 815: 816: <div2 id='syntax'> 817: <head>Character Data and Markup</head> 818: 819: <termref def='dt-text'>Text</termref> consists of intermingled 820: <termref def="dt-chardata">character 821: data</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: 834: <termdef id="dt-chardata" term="Character Data">All text that is not markup 835: constitutes the <term>character data</term> of 836: the document.</termdef> 837: The ampersand character (&) and the left angle bracket (<) 838: may appear in their literal form <emph>only</emph> when used as markup 839: delimiters, or within a <termref def="dt-comment">comment</termref>, a 840: <termref def="dt-pi">processing instruction</termref>, 841: or a <termref def="dt-cdsection">CDATA section</termref>. 842: 843: They are also legal within the <termref def='dt-litentval'>literal entity 844: value</termref> of an internal entity declaration; see 845: <specref ref='wf-entities'/>. 846:  847: If they are needed elsewhere, 848: they must be <termref def="dt-escape">escaped</termref> 849: using either <termref def='dt-charref'>numeric character references</termref> 850: or the strings 851: "<code>&amp;</code>" and "<code>&lt;</code>" respectively. 852: The right angle 853: bracket (>) may be represented using the string 854: "<code>&gt;</code>", and must, <termref def='dt-compat'>for 855: compatibility</termref>, 856: be escaped using 857: "<code>&gt;</code>" or a character reference 858: when it appears in the string 859: "<code>]]></code>" 860: in content, 861: when that string is not marking the end of 862: a <termref def="dt-cdsection">CDATA section</termref>. 863: 864: 865: In the content of elements, character data 866: is any string of characters which does 867: not contain the start-delimiter of any markup. 868: In a CDATA section, character data 869: is any string of characters not including the CDATA-section-close 870: delimiter, "<code>]]></code>". 871: 872: To allow attribute values to contain both single and double quotes, the 873: apostrophe 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: 884: </div2> 885: 886: <div2 id='sec-comments'> 887: <head>Comments</head> 888: 889: <termdef id="dt-comment" term="Comment"><term>Comments</term> may 890: appear anywhere in a document outside other 891: <termref def='dt-markup'>markup</termref>; in addition, 892: they may appear within the document type declaration 893: at places allowed by the grammar. 894: They are not part of the document's <termref def="dt-chardata">character 895: data</termref>; an XML 896: processor may, but need not, make it possible for an application to 897: retrieve the text of comments. 898: <termref def="dt-compat">For compatibility</termref>, the string 899: "<code>--</code>" (double-hyphen) must not occur within 900: comments. 901: <scrap lang="ebnf"> 902: <head>Comments</head> 903: <prod id='NT-Comment'><lhs>Comment</lhs> 904: <rhs>''</rhs> 908: </prod> 909: </scrap> 910: </termdef> 911: An example of a comment: 912: <eg><!&como; declarations for <head> & <body> &comc;></eg> 913: 914: </div2> 915: 916: <div2 id='sec-pi'> 917: <head>Processing Instructions</head> 918: 919: <termdef id="dt-pi" term="Processing instruction"><term>Processing 920: instructions</term> (PIs) allow documents to contain instructions 921: for 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> 936: PIs are not part of the document's <termref def="dt-chardata">character 937: data</termref>, but must be passed through to the application. The 938: PI begins with a target (<nt def='NT-PITarget'>PITarget</nt>) used 939: to identify the application to which the instruction is directed. 940: The target names "<code>XML</code>", "<code>xml</code>", and so on are 941: reserved for standardization in this or future versions of this 942: specification. 943: The 944: XML <termref def='dt-notation'>Notation</termref> mechanism 945: may be used for 946: formal declaration of PI targets. 947: 948: </div2> 949: 950: <div2 id='sec-cdata-sect'> 951: <head>CDATA Sections</head> 952: 953: <termdef id="dt-cdsection" term="CDATA Section"><term>CDATA sections</term> 954: may occur 955: anywhere character data may occur; they are 956: used to escape blocks of text containing characters which would 957: otherwise be recognized as markup. CDATA sections begin with the 958: string "<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: 979: Within a CDATA section, only the <nt def='NT-CDEnd'>CDEnd</nt> string is 980: recognized as markup, so that left angle brackets and ampersands may occur in 981: their literal form; they need not (and cannot) be escaped using 982: "<code>&lt;</code>" and "<code>&amp;</code>". CDATA sections 983: cannot nest.</termdef> 984: 985: 986: An example of a CDATA section, in which "<code><greeting></code>" and 987: "<code></greeting></code>" 988: are 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: 992: </div2> 993: 994: <div2 id='sec-prolog-dtd'> 995: <head>Prolog and Document Type Declaration</head> 996: 997: <termdef id='dt-xmldecl' term='XML Declaration'>XML documents 998: may, and should, 999: begin with an <term>XML declaration</term> which specifies 1000: the version of 1001: XML being used.</termdef> 1002: For example, the following is a complete XML document, <termref 1003: def="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> 1008: and so is this: 1009: <eg><![CDATA[<greeting>Hello, world!</greeting> 1010: ]]></eg> 1011: 1012: 1013: The version number "<code>1.0</code>" should be used to indicate 1014: conformance to this version of this specification; it is an error 1015: for a document to use the value "<code>1.0</code>" 1016: if it does not conform to this version of this specification. 1017: It is the intent 1018: of the XML working group to give later versions of this specification 1019: numbers other than "<code>1.0</code>", but this intent does not 1020: indicate a 1021: commitment to produce any future versions of XML, nor if any are produced, to 1022: use any particular numbering scheme. 1023: Since future versions are not ruled out, this construct is provided 1024: as a means to allow the possibility of automatic version recognition, should 1025: it become necessary. 1026: Processors may signal an error if they receive documents labeled with 1027: versions they do not support. 1028: 1029: The function of the markup in an XML document is to describe its 1030: storage and logical structure and to associate attribute-value pairs 1031: with its logical structures. XML provides a mechanism, the <termref 1032: def="dt-doctype">document type declaration</termref>, to define 1033: constraints on the logical structure and to support the use of 1034: predefined 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 1038: declaration and if the document 1039: complies with the constraints expressed in it.</termdef> 1040: The document type declaration must appear before 1041: the 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> 1074: 1075: <termdef id="dt-doctype" term="Document Type Declaration">The XML 1076: <term>document type declaration</term> 1077: contains or points to 1078: <termref def='dt-markupdecl'>markup declarations</termref> 1079: that provide a grammar for a 1080: class of documents. 1081: This grammar is known as a document type definition, 1082: or <term>DTD</term>. 1083: The document type declaration can point to an external subset (a 1084: special kind of 1085: <termref def='dt-extent'>external entity</termref>) containing markup 1086: declarations, or can 1087: contain the markup declarations directly in an internal subset, or can do 1088: both. 1089: The DTD for a document consists of both subsets taken 1090: together.</termdef> 1091: 1092: <termdef id="dt-markupdecl" term="markup declaration"> 1093: A <term>markup declaration</term> is 1094: an <termref def="dt-eldecl">element type declaration</termref>, 1095: an <termref def="dt-attdecl">attribute-list declaration</termref>, 1096: an <termref def="dt-entdecl">entity declaration</termref>, or 1097: a <termref def="dt-notdecl">notation declaration</termref>. 1098: </termdef> 1099: These declarations may be contained in whole or in part 1100: within <termref def='dt-PE'>parameter entities</termref>, 1101: as described in the well-formedness and validity constraints below. 1102: For fuller information, see 1103: <specref ref="sec-physical-struct"/>. 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: The markup declarations may be made up in whole or in part of 1135: the <termref def='dt-repltext'>replacement text</termref> of 1136: <termref def='dt-PE'>parameter entities</termref>. 1137: The productions later in this specification for 1138: individual nonterminals (<nt def='NT-elementdecl'>elementdecl</nt>, 1139: <nt def='NT-AttlistDecl'>AttlistDecl</nt>, and so on) describe 1140: the declarations <emph>after</emph> all the parameter entities have been 1141: <termref def='dt-include'>included</termref>. 1142: 1143: <vcnote id="vc-roottype"> 1144: <head>Root Element Type</head> 1145: 1146: The <nt def='NT-Name'>Name</nt> in the document type declaration must 1147: match the element type of the <termref def='dt-root'>root element</termref>. 1148: 1149: </vcnote> 1150: 1151: <vcnote id='vc-PEinMarkupDecl'> 1152: <head>Proper Declaration/PE Nesting</head> 1153: Parameter-entity 1154: <termref def='dt-repltext'>replacement text</termref> must be properly nested 1155: with markup declarations. 1156: That is to say, if either the first character 1157: or the last character of a markup 1158: declaration (<nt def='NT-markupdecl'>markupdecl</nt> above) 1159: is contained in the replacement text for a 1160: <termref def='dt-PERef'>parameter-entity reference</termref>, 1161: both must be contained in the same replacement text. 1162: </vcnote> 1163: <wfcnote id="wfc-PEinInternalSubset"> 1164: <head>PEs in Internal Subset</head> 1165: In the internal DTD subset, 1166: <termref def='dt-PERef'>parameter-entity references</termref> 1167: can occur only where markup declarations can occur, not 1168: within markup declarations. (This does not apply to 1169: references that occur in 1170: external parameter entities or to the external subset.) 1171: 1172: </wfcnote> 1173: 1174: Like the internal subset, the external subset and 1175: any external parameter entities referred to in the DTD 1176: must consist of a series of complete markup declarations of the types 1177: allowed by the non-terminal symbol 1178: <nt def="NT-markupdecl">markupdecl</nt>, interspersed with white space 1179: or <termref def="dt-PERef">parameter-entity references</termref>. 1180: However, portions of the contents 1181: of the 1182: external subset or of external parameter entities may conditionally be ignored 1183: by using 1184: the <termref def="dt-cond-section">conditional section</termref> 1185: construct; 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> 1203: The external subset and external parameter entities also differ 1204: from the internal subset in that in them, 1205: <termref def="dt-PERef">parameter-entity references</termref> 1206: are permitted <emph>within</emph> markup declarations, 1207: not only <emph>between</emph> markup declarations. 1208: 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> 1213: The <termref def="dt-sysid">system identifier</termref> 1214: "<code>hello.dtd</code>" gives the URI of a DTD for the document. 1215: The declarations can also be given locally, as in this 1216: example: 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> 1223: If both the external and internal subsets are used, the 1224: internal subset is considered to occur before the external subset. 1225:  1226: This has the effect that entity and attribute-list declarations in the 1227: internal subset take precedence over those in the external subset. 1228: 1229: </div2> 1230: 1231: <div2 id='sec-rmd'> 1232: <head>Standalone Document Declaration</head> 1233: Markup declarations can affect the content of the document, 1234: as passed from an <termref def="dt-xml-proc">XML processor</termref> 1235: to an application; examples are attribute defaults and entity 1236: declarations. 1237: The standalone document declaration, 1238: which may appear as a component of the XML declaration, signals 1239: whether or not there are such declarations which appear external to 1240: the <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> 1253: 1254: In a standalone document declaration, the value "<code>yes</code>" indicates 1255: that there 1256: are no markup declarations external to the <termref def='dt-docent'>document 1257: entity</termref> (either in the DTD external subset, or in an 1258: external parameter entity referenced from the internal subset) 1259: which affect the information passed from the XML processor to 1260: the application. 1261: The value "<code>no</code>" indicates that there are or may be such 1262: external markup declarations. 1263: Note that the standalone document declaration only 1264: denotes the presence of external <emph>declarations</emph>; the presence, in a 1265: document, of 1266: references to external <emph>entities</emph>, when those entities are 1267: internally declared, 1268: does not change its standalone status. 1269: If there are no external markup declarations, the standalone document 1270: declaration has no meaning. 1271: If there are external markup declarations but there is no standalone 1272: document declaration, the value "<code>no</code>" is assumed. 1273: Any XML document for which <code>standalone="no"</code> holds can 1274: be converted algorithmically to a standalone document, 1275: which may be desirable for some network delivery applications. 1276: <vcnote id='vc-check-rmd'> 1277: <head>Standalone Document Declaration</head> 1278: The standalone document declaration must have 1279: the value "<code>no</code>" if any external markup declarations 1280: contain declarations of:<ulist> 1281: <item>attributes with <termref def="dt-default">default</termref> values, if 1282: elements to which 1283: these attributes apply appear in the document without 1284: specifications of values for these attributes, or</item> 1285: <item>entities (other than &magicents;), 1286: if <termref def="dt-entref">references</termref> to those 1287: entities appear in the document, or 1288: </item> 1289: <item>attributes with values subject to 1290: <titleref href='AVNormalize'>normalization</titleref>, where the 1291: attribute appears in the document with a value which will 1292: change as a result of normalization, or 1293: </item> 1294: <item> 1295: element types with <termref def="dt-elemcontent">element content</termref>, 1296: if white space occurs 1297: directly within any instance of those types. 1298: </item> 1299: </ulist> 1300: 1301: </vcnote> 1302: An example XML declaration with a standalone document declaration:<eg 1303: ><?xml version="&XML.version;" standalone='yes'?></eg> 1304: </div2> 1305: <div2 id='sec-white-space'> 1306: <head>White Space Handling</head> 1307: 1308: 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 1311: set apart the markup for greater readability. Such white space is typically 1312: not intended for inclusion in the delivered version of the document. 1313: On the other hand, "significant" white space that should be preserved in the 1314: delivered version is common, for example in poetry and 1315: source code. 1316: An <termref def='dt-xml-proc'>XML processor</termref> 1317: must always pass all characters in a document that are not 1318: markup through to the application. A <termref def='dt-validating'> 1319: validating XML processor</termref> must also inform the application 1320: which of these characters constitute white space appearing 1321: in <termref def="dt-elemcontent">element content</termref>. 1322: 1323: A special <termref def='dt-attr'>attribute</termref> 1324: named <kw>xml:space</kw> may be attached to an element 1325: to signal an intention that in that element, 1326: white space should be preserved by applications. 1327: In valid documents, this attribute, like any other, must be 1328: <termref def="dt-attdecl">declared</termref> if it is used. 1329: When declared, it must be given as an 1330: <termref def='dt-enumerated'>enumerated type</termref> whose only 1331: possible values are "<code>default</code>" and "<code>preserve</code>". 1332: For example:<eg><![CDATA[ <!ATTLIST poem xml:space (default|preserve) 'preserve'>]]></eg> 1333: The value "<code>default</code>" signals that applications' 1334: default white-space processing modes are acceptable for this element; the 1335: value "<code>preserve</code>" indicates the intent that applications preserve 1336: all the white space. 1337: This declared intent is considered to apply to all elements within the content 1338: of the element where it is specified, unless overriden with another instance 1339: of the <kw>xml:space</kw> attribute. 1340: 1341: The <termref def='dt-root'>root element</termref> of any document 1342: is considered to have signaled no intentions as regards application space 1343: handling, unless it provides a value for 1344: this attribute or the attribute is declared with a default value. 1345: 1346: 1347: </div2> 1348: <div2 id='sec-line-ends'> 1349: <head>End-of-Line Handling</head> 1350: XML <termref def='dt-parsedent'>parsed entities</termref> are often stored in 1351: computer files which, for editing convenience, are organized into lines. 1352: These lines are typically separated by some combination of the characters 1353: carriage-return (#xD) and line-feed (#xA). 1354: To simplify the tasks of <termref def='dt-app'>applications</termref>, 1355: wherever an external parsed entity or the literal entity value 1356: of an internal parsed entity contains either the literal 1357: two-character sequence "#xD#xA" or a standalone literal 1358: #xD, an <termref def='dt-xml-proc'>XML processor</termref> must 1359: pass to the application the single character #xA. 1360: (This behavior can 1361: conveniently be produced by normalizing all 1362: line breaks to #xA on input, before parsing.) 1363: 1364: </div2> 1365: <div2 id='sec-lang-tag'> 1366: <head>Language Identification</head> 1367: In document processing, it is often useful to 1368: identify the natural or formal language 1369: in which the content is 1370: written. 1371: A special <termref def="dt-attr">attribute</termref> named 1372: <kw>xml:lang</kw> may be inserted in 1373: documents to specify the 1374: language used in the contents and attribute values 1375: of any element in an XML document. 1376: In valid documents, this attribute, like any other, must be 1377: <termref def="dt-attdecl">declared</termref> if it is used. 1378: The values of the attribute are language identifiers as defined 1379: by <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> 1399: The <nt def='NT-Langcode'>Langcode</nt> may be any of the following: 1400: <ulist> 1401: <item>a two-letter language code as defined by 1402: <bibref ref="ISO639"/>, "Codes 1403: for the representation of names of languages"</item> 1404: <item>a language identifier registered with the Internet 1405: Assigned Numbers Authority <bibref ref='IANA'/>; these begin with the 1406: prefix "<code>i-</code>" (or "<code>I-</code>")</item> 1407: <item>a language identifier assigned by the user, or agreed on 1408: between parties in private use; these must begin with the 1409: prefix "<code>x-</code>" or "<code>X-</code>" in order to ensure that they do not conflict 1410: with names later standardized or registered with IANA</item> 1411: </ulist> 1412: There may be any number of <nt def='NT-Subcode'>Subcode</nt> segments; if 1413: the first 1414: subcode segment exists and the Subcode consists of two 1415: letters, then it must be a country code from 1416: <bibref ref="ISO3166"/>, "Codes 1417: for the representation of names of countries." 1418: If the first 1419: subcode consists of more than two letters, it must be 1420: a subcode for the language in question registered with IANA, 1421: unless the <nt def='NT-Langcode'>Langcode</nt> begins with the prefix 1422: "<code>x-</code>" or 1423: "<code>X-</code>". 1424: It is customary to give the language code in lower case, and 1425: the country code (if any) in upper case. 1426: Note that these values, unlike other names in XML documents, 1427: are case insensitive. 1428: For example: 1429: <eg><![CDATA[The quick brown fox jumps over the lazy dog. 1430: What colour is it? 1431: What color is it? 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 heißem Bemüh'n.</l> 1437: </sp>]]></eg> 1438:  1442: The intent declared with <kw>xml:lang</kw> is considered to apply to 1443: all attributes and content of the element where it is specified, 1444: unless overridden with an instance of <kw>xml:lang</kw> 1445: on another element within that content. 1446:  1461: A simple declaration for <kw>xml:lang</kw> might take 1462: the form 1463: <eg>xml:lang NMTOKEN #IMPLIED</eg> 1464: but specific default values may also be given, if appropriate. In a 1465: collection of French poems for English students, with glosses and 1466: notes 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: 1471: 1472: </div2> 1473: </div1> 1474:  1475: 1476: <div1 id='sec-logical-struct'> 1477: <head>Logical Structures</head> 1478: 1479: <termdef id="dt-element" term="Element">Each <termref 1480: def="dt-xml-doc">XML document</termref> contains one or more 1481: <term>elements</term>, the boundaries of which are 1482: either delimited by <termref def="dt-stag">start-tags</termref> 1483: and <termref def="dt-etag">end-tags</termref>, or, for <termref 1484: def="dt-empty">empty</termref> elements, by an <termref 1485: def="dt-eetag">empty-element tag</termref>. Each element has a type, 1486: identified by name, sometimes called its "generic 1487: identifier" (GI), and may have a set of 1488: attribute specifications.</termdef> Each attribute specification 1489: has a <termref 1490: def="dt-attrname">name</termref> and a <termref 1491: def="dt-attrval">value</termref>. 1492: 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: This specification does not constrain the semantics, use, or (beyond 1503: syntax) names of the element types and attributes, except that names 1504: beginning with a match to <code>(('X'|'x')('M'|'m')('L'|'l'))</code> 1505: are reserved for standardization in this or future versions of this 1506: specification. 1507: 1508: <wfcnote id='GIMatch'> 1509: <head>Element Type Match</head> 1510: 1511: The <nt def='NT-Name'>Name</nt> in an element's end-tag must match 1512: the element type in 1513: the start-tag. 1514: 1515: </wfcnote> 1516: <vcnote id='elementvalid'> 1517: <head>Element Valid</head> 1518: An element is 1519: valid if 1520: there 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 1523: one of the following holds: 1524: <olist> 1525: <item>The declaration matches <kw>EMPTY</kw> and the element has no 1526: <termref def='dt-content'>content</termref>.</item> 1527: <item>The declaration matches <nt def='NT-children'>children</nt> and 1528: the sequence of 1529: <termref def="dt-parentchild">child elements</termref> 1530: belongs to the language generated by the regular expression in 1531: the content model, with optional white space (characters 1532: matching the nonterminal <nt def='NT-S'>S</nt>) between each pair 1533: of child elements.</item> 1534: <item>The declaration matches <nt def='NT-Mixed'>Mixed</nt> and 1535: the content consists of <termref def='dt-chardata'>character 1536: data</termref> and <termref def='dt-parentchild'>child elements</termref> 1537: whose types match names in the content model.</item> 1538: <item>The declaration matches <kw>ANY</kw>, and the types 1539: of any <termref def='dt-parentchild'>child elements</termref> have 1540: been declared.</item> 1541: </olist> 1542: </vcnote> 1543: 1544: <div2 id='sec-starttags'> 1545: <head>Start-Tags, End-Tags, and Empty-Element Tags</head> 1546: 1547: <termdef id="dt-stag" term="Start-Tag">The beginning of every 1548: non-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> 1566: The <nt def='NT-Name'>Name</nt> in 1567: the start- and end-tags gives the 1568: element's <term>type</term>.</termdef> 1569: <termdef id="dt-attr" term="Attribute"> 1570: The <nt def='NT-Name'>Name</nt>-<nt def='NT-AttValue'>AttValue</nt> pairs are 1571: referred to as 1572: the <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 1575: referred 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) 1579: as the <term>attribute value</term>.</termdef> 1580: 1581: <wfcnote id='uniqattspec'> 1582: <head>Unique Att Spec</head> 1583: 1584: No attribute name may appear more than once in the same start-tag 1585: or empty-element tag. 1586: 1587: </wfcnote> 1588: <vcnote id='ValueType'> 1589: <head>Attribute Value Type</head> 1590: 1591: The attribute must have been declared; the value must be of the type 1592: declared for it. 1593: (For attribute types, see <specref ref='attdecls'/>.) 1594: 1595: </vcnote> 1596: <wfcnote id='NoExternalRefs'> 1597: <head>No External Entity References</head> 1598: 1599: Attribute values cannot contain direct or indirect entity references 1600: to external entities. 1601: 1602: </wfcnote> 1603: <wfcnote id='CleanAttrVals'> 1604: <head>No <code><</code> in Attribute Values</head> 1605: The <termref def='dt-repltext'>replacement text</termref> of any entity 1606: referred to directly or indirectly in an attribute 1607: value (other than "<code>&lt;</code>") must not contain 1608: a <code><</code>. 1609: </wfcnote> 1610: An example of a start-tag: 1611: <eg><termdef id="dt-dog" term="dog"></eg> 1612: <termdef id="dt-etag" term="End Tag">The end of every element 1613: that begins with a start-tag must 1614: be marked by an <term>end-tag</term> 1615: containing a name that echoes the element's type as given in the 1616: start-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> 1626: An example of an end-tag:<eg></termdef></eg> 1627: <termdef id="dt-content" term="Content">The 1628: <termref def='dt-text'>text</termref> between the start-tag and 1629: end-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> 1642: <termdef id="dt-empty" term="Empty">If an element is <term>empty</term>, 1643: it must be represented either by a start-tag immediately followed 1644: by 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> 1659: Empty-element tags may be used for any element which has no 1660: content, whether or not it is declared using the keyword 1661: <kw>EMPTY</kw>. 1662: <termref def='dt-interop'>For interoperability</termref>, the empty-element 1663: tag must be used, and can only be used, for elements which are 1664: <termref def='dt-eldecl'>declared</termref> <kw>EMPTY</kw>. 1665: Examples of empty elements: 1666: <eg><IMG align="left" 1667: src="http://www.w3.org/Icons/WWW/w3c_home" /> 1668: 1669: </eg> 1670: </div2> 1671: 1672: <div2 id='elemdecls'> 1673: <head>Element Type Declarations</head> 1674: 1675: 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, 1678: be constrained 1679: using element type and attribute-list declarations. 1680: An element type declaration constrains the element's 1681: <termref def="dt-content">content</termref>. 1682: 1683: 1684: Element type declarations often constrain which element types can 1685: appear as <termref def="dt-parentchild">children</termref> of the element. 1686: At user option, an XML processor may issue a warning 1687: when a declaration mentions an element type for which no declaration 1688: is provided, but this is not an error. 1689: <termdef id="dt-eldecl" term="Element Type declaration">An <term>element 1690: type 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> 1710: where the <nt def='NT-Name'>Name</nt> gives the element type 1711: being declared.</termdef> 1712: 1713: 1714: <vcnote id='EDUnique'> 1715: <head>Unique Element Type Declaration</head> 1716: 1717: No element type may be declared more than once. 1718: 1719: </vcnote> 1720: 1721: 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> 1726: 1727: <div3 id='sec-element-content'> 1728: <head>Element Content</head> 1729: 1730: <termdef id='dt-elemcontent' term='Element content'>An element <termref 1731: def="dt-stag">type</termref> has 1732: <term>element content</term> when elements of that 1733: type must contain only <termref def='dt-parentchild'>child</termref> 1734: elements (no character data), optionally separated by 1735: white space (characters matching the nonterminal 1736: <nt def='NT-S'>S</nt>). 1737: </termdef> 1738: In this case, the 1739: constraint includes a content model, a simple grammar governing 1740: the allowed types of the child 1741: elements and the order in which they are allowed to appear. 1742: The grammar is built on 1743: content particles (<nt def='NT-cp'>cp</nt>s), which consist of names, 1744: choice lists of content particles, or 1745: sequence 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> 1771: where each <nt def='NT-Name'>Name</nt> is the type of an element which may 1772: appear as a <termref def="dt-parentchild">child</termref>. 1773: Any content 1774: particle in a choice list may appear in the <termref 1775: def="dt-elemcontent">element content</termref> at the location where 1776: the choice list appears in the grammar; 1777: content particles occurring in a sequence list must each 1778: appear in the <termref def="dt-elemcontent">element content</termref> in the 1779: order given in the list. 1780: The optional character following a name or list governs 1781: whether the element or the content particles in the list may occur one 1782: or more (<code>+</code>), zero or more (<code>*</code>), or zero or 1783: one times (<code>?</code>). 1784: The absence of such an operator means that the element or content particle 1785: must appear exactly once. 1786: This syntax 1787: and meaning are identical to those used in the productions in this 1788: specification. 1789: 1790: The content of an element matches a content model if and only if it is 1791: possible to trace out a path through the content model, obeying the 1792: sequence, choice, and repetition operators and matching each element in 1793: the content against an element type in the content model. <termref 1794: def='dt-compat'>For compatibility</termref>, it is an error 1795: if an element in the document can 1796: match more than one occurrence of an element type in the content model. 1797: For more information, see <specref ref="determinism"/>. 1798:  1799:  1800: 1801: <vcnote id='vc-PEinGroup'> 1802: <head>Proper Group/PE Nesting</head> 1803: Parameter-entity 1804: <termref def='dt-repltext'>replacement text</termref> must be properly nested 1805: with parenthetized groups. 1806: That is to say, if either of the opening or closing parentheses 1807: in a <nt def='NT-choice'>choice</nt>, <nt def='NT-seq'>seq</nt>, or 1808: <nt def='NT-Mixed'>Mixed</nt> construct 1809: is contained in the replacement text for a 1810: <termref def='dt-PERef'>parameter entity</termref>, 1811: both must be contained in the same replacement text. 1812: <termref def='dt-interop'>For interoperability</termref>, 1813: if 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 1816: should not be empty, and 1817: neither the first nor last non-blank 1818: character of the replacement text should be a connector 1819: (<code>|</code> or <code>,</code>). 1820: 1821: </vcnote> 1822: 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> 1826: </div3> 1827: 1828: <div3 id='sec-mixed-content'> 1829: <head>Mixed Content</head> 1830: 1831: <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 1834: character data, optionally interspersed with 1835: <termref def="dt-parentchild">child</termref> elements.</termdef> 1836: In this case, the types of the child elements 1837: may 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> 1857: where the <nt def='NT-Name'>Name</nt>s give the types of elements 1858: that may appear as children. 1859: 1860: <vcnote id='vc-MixedChildrenUnique'> 1861: <head>No Duplicate Types</head> 1862: The same name must not appear more than once in a single mixed-content 1863: declaration. 1864: </vcnote> 1865: 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> 1869: </div3> 1870: </div2> 1871: 1872: <div2 id='attdecls'> 1873: <head>Attribute-List Declarations</head> 1874: 1875: <termref def="dt-attr">Attributes</termref> are used to associate 1876: name-value pairs with <termref def="dt-element">elements</termref>. 1877: Attribute specifications may appear only within <termref 1878: def="dt-stag">start-tags</termref> 1879: and <termref def="dt-eetag">empty-element tags</termref>; 1880: thus, the productions used to 1881: recognize them appear in <specref ref='sec-starttags'/>. 1882: Attribute-list 1883: declarations may be used: 1884: <ulist> 1885: <item>To define the set of attributes pertaining to a given 1886: element type.</item> 1887: <item>To establish type constraints for these 1888: attributes.</item> 1889: <item>To provide <termref def="dt-default">default values</termref> 1890: for attributes.</item> 1891: </ulist> 1892: 1893: <termdef id="dt-attdecl" term="Attribute-List Declaration"> 1894: <term>Attribute-list declarations</term> specify the name, data type, and default 1895: value (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> 1910: The <nt def="NT-Name">Name</nt> in the 1911: <nt def='NT-AttlistDecl'>AttlistDecl</nt> rule is the type of an element. At 1912: user option, an XML processor may issue a warning if attributes are 1913: declared for an element type not itself declared, but this is not an 1914: error. The <nt def='NT-Name'>Name</nt> in the 1915: <nt def='NT-AttDef'>AttDef</nt> rule is 1916: the name of the attribute.</termdef> 1917: 1918: When more than one <nt def='NT-AttlistDecl'>AttlistDecl</nt> is provided for a 1919: given element type, the contents of all those provided are merged. When 1920: more than one definition is provided for the same attribute of a 1921: given element type, the first declaration is binding and later 1922: declarations are ignored. 1923: <termref def='dt-interop'>For interoperability,</termref> writers of DTDs 1924: may choose to provide at most one attribute-list declaration 1925: for a given element type, at most one attribute definition 1926: for a given attribute name, and at least one attribute definition 1927: in each attribute-list declaration. 1928: For interoperability, an XML processor may at user option 1929: issue a warning when more than one attribute-list declaration is 1930: provided for a given element type, or more than one attribute definition 1931: is provided 1932: for a given attribute, but this is not an error. 1933: 1934: 1935: <div3 id='sec-attribute-types'> 1936: <head>Attribute Types</head> 1937: 1938: XML attribute types are of three kinds: a string type, a 1939: set of tokenized types, and enumerated types. The string type may take 1940: any literal string as a value; the tokenized types have varying lexical 1941: and 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: 1974: <vcnote id='id' > 1975: <head>ID</head> 1976: 1977: Values of type <kw>ID</kw> must match the 1978: <nt def='NT-Name'>Name</nt> production. 1979: A name must not appear more than once in 1980: an XML document as a value of this type; i.e., ID values must uniquely 1981: identify the elements which bear them. 1982: 1983: </vcnote> 1984: <vcnote id='one-id-per-el'> 1985: <head>One ID per Element Type</head> 1986: No element type may have more than one ID attribute specified. 1987: </vcnote> 1988: <vcnote id='id-default'> 1989: <head>ID Attribute Default</head> 1990: An ID attribute must have a declared default of <kw>#IMPLIED</kw> or 1991: <kw>#REQUIRED</kw>. 1992: </vcnote> 1993: <vcnote id='idref'> 1994: <head>IDREF</head> 1995: 1996: Values of type <kw>IDREF</kw> must match 1997: the <nt def="NT-Name">Name</nt> production, and 1998: values of type <kw>IDREFS</kw> must match 1999: <nt def="NT-Names">Names</nt>; 2000: each <nt def='NT-Name'>Name</nt> must match the value of an ID attribute on 2001: some element in the XML document; i.e. <kw>IDREF</kw> values must 2002: match the value of some ID attribute. 2003: 2004: </vcnote> 2005: <vcnote id='entname'> 2006: <head>Entity Name</head> 2007: 2008: Values of type <kw>ENTITY</kw> 2009: must match the <nt def="NT-Name">Name</nt> production, 2010: values of type <kw>ENTITIES</kw> must match 2011: <nt def="NT-Names">Names</nt>; 2012: each <nt def="NT-Name">Name</nt> must 2013: match the 2014: name of an <termref def="dt-unparsed">unparsed entity</termref> declared in the 2015: <termref def="dt-doctype">DTD</termref>. 2016: 2017: </vcnote> 2018: <vcnote id='nmtok'> 2019: <head>Name Token</head> 2020: 2021: Values of type <kw>NMTOKEN</kw> must match the 2022: <nt def="NT-Nmtoken">Nmtoken</nt> production; 2023: values of type <kw>NMTOKENS</kw> must 2024: match <termref def="NT-Nmtokens">Nmtokens</termref>. 2025: 2026: </vcnote> 2027:  2031: <termdef id='dt-enumerated' term='Enumerated Attribute 2032: Values'><term>Enumerated attributes</term> can take one 2033: of a list of values provided in the declaration</termdef>. There are two 2034: kinds 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> 2062: A <kw>NOTATION</kw> attribute identifies a 2063: <termref def='dt-notation'>notation</termref>, declared in the 2064: DTD with associated system and/or public identifiers, to 2065: be used in interpreting the element to which the attribute 2066: is attached. 2067: 2068: 2069: <vcnote id='notatn'> 2070: <head>Notation Attributes</head> 2071: 2072: Values of this type must match 2073: one of the <titleref href='Notations'>notation</titleref> names included in 2074: the declaration; all notation names in the declaration must 2075: be declared. 2076: 2077: </vcnote> 2078: <vcnote id='enum'> 2079: <head>Enumeration</head> 2080: 2081: Values of this type 2082: must match one of the <nt def='NT-Nmtoken'>Nmtoken</nt> tokens in the 2083: declaration. 2084: 2085: </vcnote> 2086: <termref def='dt-interop'>For interoperability,</termref> the same 2087: <nt def='NT-Nmtoken'>Nmtoken</nt> should not occur more than once in the 2088: enumerated attribute types of a single element type. 2089: 2090: </div3> 2091: 2092: <div3 id='sec-attr-defaults'> 2093: <head>Attribute Defaults</head> 2094: 2095: An <termref def="dt-attdecl">attribute declaration</termref> provides 2096: information on whether 2097: the attribute's presence is required, and if not, how an XML processor should 2098: react 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: 2115: In an attribute declaration, <kw>#REQUIRED</kw> means that the 2116: attribute must always be provided, <kw>#IMPLIED</kw> that no default 2117: value is provided. 2118:  2124: <termdef id="dt-default" term="Attribute Default">If the 2125: declaration 2126: is 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 2129: the attribute must always have the default value. 2130: If a default value 2131: is declared, when an XML processor encounters an omitted attribute, it 2132: is to behave as though the attribute were present with 2133: the declared default value.</termdef> 2134: <vcnote id='RequiredAttr'> 2135: <head>Required Attribute</head> 2136: If the default declaration is the keyword <kw>#REQUIRED</kw>, then 2137: the attribute must be specified for 2138: all elements of the type in the attribute-list declaration. 2139: </vcnote> 2140: <vcnote id='defattrvalid'> 2141: <head>Attribute Default Legal</head> 2142: 2143: The declared 2144: default value must meet the lexical constraints of the declared attribute type. 2145: 2146: </vcnote> 2147: <vcnote id='FixedAttr'> 2148: <head>Fixed Attribute Default</head> 2149: If an attribute has a default value declared with the 2150: <kw>#FIXED</kw> keyword, instances of that attribute must 2151: match the default value. 2152: </vcnote> 2153: 2154: 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> 2162: </div3> 2163: <div3 id='AVNormalize'> 2164: <head>Attribute-Value Normalization</head> 2165: Before the value of an attribute is passed to the application 2166: or checked for validity, the 2167: XML processor must normalize it as follows: 2168: <ulist> 2169: <item>a character reference is processed by appending the referenced 2170: character to the attribute value</item> 2171: <item>an entity reference is processed by recursively processing the 2172: replacement text of the entity</item> 2173: <item>a whitespace character (#x20, #xD, #xA, #x9) is processed by 2174: appending #x20 to the normalized value, except that only a single #x20 2175: is appended for a "#xD#xA" sequence that is part of an external 2176: parsed entity or the literal entity value of an internal parsed 2177: entity</item> 2178: <item>other characters are processed by appending them to the normalized 2179: value 2180: </item></ulist> 2181: 2182: If the declared value is not CDATA, then the XML processor must 2183: further process the normalized attribute value by discarding any 2184: leading and trailing space (#x20) characters, and by replacing 2185: sequences of space (#x20) characters by a single space (#x20) 2186: character. 2187: 2188: All attributes for which no declaration has been read should be treated 2189: by a non-validating parser as if declared 2190: <kw>CDATA</kw>. 2191: 2192: </div3> 2193: </div2> 2194: <div2 id='sec-condition-sect'> 2195: <head>Conditional Sections</head> 2196: <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> 2199: which are 2200: included in, or excluded from, the logical structure of the DTD based on 2201: the 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: 2236: Like the internal and external DTD subsets, a conditional section 2237: may contain one or more complete declarations, 2238: comments, processing instructions, 2239: or nested conditional sections, intermingled with white space. 2240: 2241: If the keyword of the 2242: conditional section is <kw>INCLUDE</kw>, then the contents of the conditional 2243: section are part of the DTD. 2244: If the keyword of the conditional 2245: section is <kw>IGNORE</kw>, then the contents of the conditional section are 2246: not logically part of the DTD. 2247: Note that for reliable parsing, the contents of even ignored 2248: conditional sections must be read in order to 2249: detect nested conditional sections and ensure that the end of the 2250: outermost (ignored) conditional section is properly detected. 2251: If a conditional section with a 2252: keyword of <kw>INCLUDE</kw> occurs within a larger conditional 2253: section with a keyword of <kw>IGNORE</kw>, both the outer and the 2254: inner conditional sections are ignored. 2255: If the keyword of the conditional section is a 2256: parameter-entity reference, the parameter entity must be replaced by its 2257: content before the processor decides whether to 2258: include or ignore the conditional section. 2259: 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: 2271: </div2> 2272: 2273: 2274:  2295: 2296: </div1> 2297:  2298: 2299: <div1 id='sec-physical-struct'> 2300: <head>Physical Structures</head> 2301: 2302: <termdef id="dt-entity" term="Entity">An XML document may consist 2303: of 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 2306: the <termref def='dt-doctype'>external DTD subset</termref>) 2307: identified by <term>name</term>. 2308: </termdef> 2309: Each XML document has one entity 2310: called the <termref def="dt-docent">document entity</termref>, which serves 2311: as the starting point for the <termref def="dt-xml-proc">XML 2312: processor</termref> and may contain the whole document. 2313: Entities may be either parsed or unparsed. 2314: <termdef id="dt-parsedent" term="Text Entity">A <term>parsed entity's</term> 2315: contents are referred to as its 2316: <termref def='dt-repltext'>replacement text</termref>; 2317: this <termref def="dt-text">text</termref> is considered an 2318: integral part of the document.</termdef> 2319: 2320: <termdef id="dt-unparsed" term="Unparsed Entity">An 2321: <term>unparsed entity</term> 2322: is a resource whose contents may or may not be 2323: <termref def='dt-text'>text</termref>, and if text, may not be XML. 2324: Each unparsed entity 2325: has an associated <termref 2326: def="dt-notation">notation</termref>, identified by name. 2327: Beyond a requirement 2328: that an XML processor make the identifiers for the entity and 2329: notation available to the application, 2330: XML places no constraints on the contents of unparsed entities.</termdef> 2331: 2332: 2333: Parsed entities are invoked by name using entity references; 2334: unparsed entities by name, given in the value of <kw>ENTITY</kw> 2335: or <kw>ENTITIES</kw> 2336: attributes. 2337: <termdef id='gen-entity' term='general entity' 2338: ><term>General entities</term> 2339: are entities for use within the document content. 2340: In this specification, general entities are sometimes referred 2341: to with the unqualified term <emph>entity</emph> when this leads 2342: to no ambiguity.</termdef> 2343: <termdef id='dt-PE' term='Parameter entity'>Parameter entities 2344: are parsed entities for use within the DTD.</termdef> 2345: These two types of entities use different forms of reference and 2346: are recognized in different contexts. 2347: Furthermore, they occupy different namespaces; a parameter entity and 2348: a general entity with the same name are two distinct entities. 2349: 2350: 2351: <div2 id='sec-references'> 2352: <head>Character and Entity References</head> 2353: <termdef id="dt-charref" term="Character Reference"> 2354: A <term>character reference</term> refers to a specific character in the 2355: ISO/IEC 10646 character set, for example one not directly accessible from 2356: available 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: Characters referred to using character references must 2368: match the production for 2369: <termref def="NT-Char">Char</termref>. 2370: </wfcnote> 2371: If the character reference begins with "<code>&#x</code>", the digits and 2372: letters up to the terminating <code>;</code> provide a hexadecimal 2373: representation of the character's code point in ISO/IEC 10646. 2374: If it begins just with "<code>&#</code>", the digits up to the terminating 2375: <code>;</code> provide a decimal representation of the character's 2376: code point. 2377: </termdef> 2378: 2379: <termdef id="dt-entref" term="Entity Reference">An <term>entity 2380: reference</term> refers to the content of a named entity.</termdef> 2381: <termdef id='dt-GERef' term='General Entity Reference'>References to 2382: parsed general entities 2383: use ampersand (<code>&</code>) and semicolon (<code>;</code>) as 2384: delimiters.</termdef> 2385: <termdef id='dt-PERef' term='Parameter-entity reference'> 2386: <term>Parameter-entity references</term> use percent-sign (<code>%</code>) and 2387: semicolon 2388: (<code>;</code>) as delimiters.</termdef> 2389: 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: In a document without any DTD, a document with only an internal 2413: DTD subset which contains no parameter entity references, or a document with 2414: "<code>standalone='yes'</code>", 2415: the <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 2418: well-formed documents need not declare 2419: any of the following entities: &magicents;. 2420: The declaration of a parameter entity must precede any reference to it. 2421: Similarly, the declaration of a general entity must precede any 2422: reference to it which appears in a default value in an attribute-list 2423: declaration. 2424: Note that if entities are declared in the external subset or in 2425: external parameter entities, a non-validating processor is 2426: <titleref href='include-if-valid'>not obligated to</titleref> read 2427: and process their declarations; for such documents, the rule that 2428: an entity must be declared is a well-formedness constraint only 2429: if <titleref href='sec-rmd'>standalone='yes'</titleref>. 2430: </wfcnote> 2431: <vcnote id="vc-entdeclared"> 2432: <head>Entity Declared</head> 2433: In a document with an external subset or external parameter 2434: entities with "<code>standalone='no'</code>", 2435: the <nt def='NT-Name'>Name</nt> given in the entity reference must <termref 2436: def="dt-match">match</termref> that in an 2437: <titleref href='sec-entity-decl'>entity declaration</titleref>. 2438: For interoperability, valid documents should declare the entities 2439: &magicents;, in the form 2440: specified in <specref ref="sec-predefined-ent"/>. 2441: The declaration of a parameter entity must precede any reference to it. 2442: Similarly, the declaration of a general entity must precede any 2443: reference to it which appears in a default value in an attribute-list 2444: declaration. 2445: </vcnote> 2446:  2447: <wfcnote id='textent'> 2448: <head>Parsed Entity</head> 2449: 2450: An entity reference must not contain the name of an <termref 2451: def="dt-unparsed">unparsed entity</termref>. Unparsed entities may be referred 2452: to only in <termref def="dt-attrval">attribute values</termref> declared to 2453: be of type <kw>ENTITY</kw> or <kw>ENTITIES</kw>. 2454: 2455: </wfcnote> 2456: <wfcnote id='norecursion'> 2457: <head>No Recursion</head> 2458: 2459: A parsed entity must not contain a recursive reference to itself, 2460: either directly or indirectly. 2461: 2462: </wfcnote> 2463: <wfcnote id='indtd'> 2464: <head>In DTD</head> 2465: 2466: Parameter-entity references may only appear in the 2467: <termref def='dt-doctype'>DTD</termref>. 2468: 2469: </wfcnote> 2470: Examples of character and entity references: 2471: <eg>Type <key>less-than</key> (&hcro;3C;) to save options. 2472: This document was prepared on &docdate; and 2473: is classified &security-level;.</eg> 2474: Example of a parameter-entity reference: 2475: <eg><![CDATA[ 2476: <!ENTITY % ISOLat2 2477: SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" > 2478:  2479: %ISOLat2;]]></eg> 2480: </div2> 2481: 2482: <div2 id='sec-entity-decl'> 2483: <head>Entity Declarations</head> 2484: 2485: <termdef id="dt-entdecl" term="entity declaration"> 2486: Entities 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> | <nt def="NT-PEDecl">PEDecl</nt></rhs> 2493:  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:  2505: </prod> 2506: <prod id='NT-EntityDef'><lhs>EntityDef</lhs> 2507: <rhs><nt def='NT-EntityValue'>EntityValue</nt> 2508: | (<nt def='NT-ExternalID'>ExternalID</nt> 2510: <nt def='NT-NDataDecl'>NDataDecl</nt>?)</rhs> 2511:  2512: </prod> 2513:  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> 2519: The <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 2521: unparsed entity, in the value of an <kw>ENTITY</kw> or <kw>ENTITIES</kw> 2522: attribute. 2523: If the same entity is declared more than once, the first declaration 2524: encountered is binding; at user option, an XML processor may issue a 2525: warning if entities are declared multiple times.</termdef> 2526: 2527: 2528: <div3 id='sec-internal-ent'> 2529: <head>Internal Entities</head> 2530: 2531: <termdef id='dt-internent' term="Internal Entity Replacement Text">If 2532: the entity definition is an 2533: <nt def='NT-EntityValue'>EntityValue</nt>, 2534: the defined entity is called an <term>internal entity</term>. 2535: There is no separate physical 2536: storage object, and the content of the entity is given in the 2537: declaration. </termdef> 2538: Note that some processing of entity and character references in the 2539: <termref def='dt-litentval'>literal entity value</termref> may be required to 2540: produce the correct <termref def='dt-repltext'>replacement 2541: text</termref>: see <specref ref='intern-replacement'/>. 2542: 2543: An internal entity is a <termref def="dt-parsedent">parsed 2544: entity</termref>. 2545: Example of an internal entity declaration: 2546: <eg><!ENTITY Pub-Status "This is a pre-release of the 2547: specification."></eg> 2548: </div3> 2549: 2550: <div3 id='sec-external-ent'> 2551: <head>External Entities</head> 2552: 2553: <termdef id="dt-extent" term="External Entity">If the entity is not 2554: internal, it is an <term>external 2555: entity</term>, declared as follows: 2556: <scrap lang='ebnf'> 2557: <head>External Entity Declaration</head> 2558:  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> 2575: If the <nt def='NT-NDataDecl'>NDataDecl</nt> is present, this is a 2576: general <termref def="dt-unparsed">unparsed 2577: entity</termref>; otherwise it is a parsed entity.</termdef> 2578: <vcnote id='not-declared'> 2579: <head>Notation Declared</head> 2580: 2581: The <nt def='NT-Name'>Name</nt> must match the declared name of a 2582: <termref def="dt-notation">notation</termref>. 2583: 2584: </vcnote> 2585: <termdef id="dt-sysid" term="System Identifier">The 2586: <nt def='NT-SystemLiteral'>SystemLiteral</nt> 2587: is called the entity's <term>system identifier</term>. It is a URI, 2588: which may be used to retrieve the entity.</termdef> 2589: Note that the hash mark (<code>#</code>) and fragment identifier 2590: frequently used with URIs are not, formally, part of the URI itself; 2591: an XML processor may signal an error if a fragment identifier is 2592: given as part of a system identifier. 2593: Unless otherwise provided by information outside the scope of this 2594: specification (e.g. a special XML element type defined by a particular 2595: DTD, or a processing instruction defined by a particular application 2596: specification), relative URIs are relative to the location of the 2597: resource within which the entity declaration occurs. 2598: A URI might thus be relative to the 2599: <termref def='dt-docent'>document entity</termref>, to the entity 2600: containing the <termref def='dt-doctype'>external DTD subset</termref>, 2601: or to some other <termref def='dt-extent'>external parameter entity</termref>. 2602: 2603: An XML processor should handle a non-ASCII character in a URI by 2604: representing the character in UTF-8 as one or more bytes, and then 2605: escaping these bytes with the URI escaping mechanism (i.e., by 2606: converting each byte to %HH, where HH is the hexadecimal notation of the 2607: byte value). 2608: <termdef id="dt-pubid" term="Public identifier"> 2609: In addition to a system identifier, an external identifier may 2610: include a <term>public identifier</term>.</termdef> 2611: An XML processor attempting to retrieve the entity's content may use the public 2612: identifier to try to generate an alternative URI. If the processor 2613: is unable to do so, it must use the URI specified in the system 2614: literal. Before a match is attempted, all strings 2615: of white space in the public identifier must be normalized to single space characters (#x20), 2616: and leading and trailing white space must be removed. 2617: 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> 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: External parsed entities may each begin with a <term>text 2635: declaration</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: 2648: The text declaration must be provided literally, not 2649: by reference to a parsed entity. 2650: No text declaration may appear at any position other than the beginning of 2651: an external parsed entity. 2652: </div3> 2653: <div3 id='wf-entities'> 2654: <head>Well-Formed Parsed Entities</head> 2655: The document entity is well-formed if it matches the production labeled 2656: <nt def='NT-document'>document</nt>. 2657: An external general 2658: parsed entity is well-formed if it matches the production labeled 2659: <nt def='NT-extParsedEnt'>extParsedEnt</nt>. 2660: An external parameter 2661: entity 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> 2674: An internal general parsed entity is well-formed if its replacement text 2675: matches the production labeled 2676: <nt def='NT-content'>content</nt>. 2677: All internal parameter entities are well-formed by definition. 2678: 2679: A consequence of well-formedness in entities is that the logical 2680: and 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 2688: reference</termref>, or 2689: <termref def='dt-entref'>entity reference</termref> 2690: can begin in one entity and end in another. 2691: </div3> 2692: <div3 id='charencoding'> 2693: <head>Character Encoding in Entities</head> 2694: 2695: Each external parsed entity in an XML document may use a different 2696: encoding for its characters. All XML processors must be able to read 2697: entities in either UTF-8 or UTF-16. 2698: 2699: 2700: Entities encoded in UTF-16 must 2701: begin with the Byte Order Mark described by ISO/IEC 10646 Annex E and 2702: Unicode Appendix B (the ZERO WIDTH NO-BREAK SPACE character, #xFEFF). 2703: This is an encoding signature, not part of either the markup or the 2704: character data of the XML document. 2705: XML processors must be able to use this character to 2706: differentiate between UTF-8 and UTF-16 encoded documents. 2707: Although an XML processor is required to read only entities in 2708: the UTF-8 and UTF-16 encodings, it is recognized that other encodings are 2709: used around the world, and it may be desired for XML processors 2710: to read entities that use them. 2711: Parsed entities which are stored in an encoding other than 2712: UTF-8 or UTF-16 must begin with a <titleref href='TextDecl'>text 2713: declaration</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> 2728: In the <termref def='dt-docent'>document entity</termref>, the encoding 2729: declaration is part of the <termref def="dt-xmldecl">XML declaration</termref>. 2730: The <nt def="NT-EncName">EncName</nt> is the name of the encoding used. 2731: 2732:  2733: 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 2738: used for the various encodings and transformations of Unicode / 2739: ISO/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 2743: the values 2744: "<code>ISO-2022-JP</code>", 2745: "<code>Shift_JIS</code>", and 2746: "<code>EUC-JP</code>" 2747: should be used for the various encoded forms of JIS X-0208-1997. XML 2748: processors may recognize other encodings; it is recommended that 2749: character encodings registered (as <emph>charset</emph>s) 2750: with the Internet Assigned Numbers 2751: Authority <bibref ref='IANA'/>, other than those just listed, should be 2752: referred to 2753: using their registered names. 2754: Note that these registered names are defined to be 2755: case-insensitive, so processors wishing to match against them 2756: should do so in a case-insensitive 2757: way. 2758: In the absence of information provided by an external 2759: transport protocol (e.g. HTTP or MIME), 2760: it is an <termref def="dt-error">error</termref> for an entity including 2761: an encoding declaration to be presented to the XML processor 2762: in an encoding other than that named in the declaration, 2763: for an encoding declaration to occur other than at the beginning 2764: of an external entity, or for 2765: an entity which begins with neither a Byte Order Mark nor an encoding 2766: declaration to use an encoding other than UTF-8. 2767: Note that since ASCII 2768: is a subset of UTF-8, ordinary ASCII entities do not strictly need 2769: an encoding declaration. 2770: 2771: It is a <termref def='dt-fatal'>fatal error</termref> when an XML processor 2772: encounters an entity with an encoding that it is unable to process. 2773: Examples of encoding declarations: 2774: <eg><?xml encoding='UTF-8'?> 2775: <?xml encoding='EUC-JP'?></eg> 2776: </div3> 2777: </div2> 2778: <div2 id='entproc'> 2779: <head>XML Processor Treatment of Entities and References</head> 2780: The table below summarizes the contexts in which character references, 2781: entity references, and invocations of unparsed entities might appear and the 2782: required behavior of an <termref def='dt-xml-proc'>XML processor</termref> in 2783: each case. 2784: The labels in the leftmost column describe the recognition context: 2785: <glist> 2786: <gitem><label>Reference in Content</label> 2787: <def>as a reference 2788: anywhere after the <termref def='dt-stag'>start-tag</termref> and 2789: before the <termref def='dt-etag'>end-tag</termref> of an element; corresponds 2790: to the nonterminal <nt def='NT-content'>content</nt>.</def> 2791: </gitem> 2792: <gitem> 2793: <label>Reference in Attribute Value</label> 2794: <def>as a reference within either the value of an attribute in a 2795: <termref def='dt-stag'>start-tag</termref>, or a default 2796: value in an <termref def='dt-attdecl'>attribute declaration</termref>; 2797: corresponds to the nonterminal 2798: <nt def='NT-AttValue'>AttValue</nt>.</def></gitem> 2799: <gitem> 2800: <label>Occurs as Attribute Value</label> 2801: <def>as a <nt def='NT-Name'>Name</nt>, not a reference, appearing either as 2802: the value of an 2803: attribute which has been declared as type <kw>ENTITY</kw>, or as one of 2804: the space-separated tokens in the value of an attribute which has been 2805: declared as type <kw>ENTITIES</kw>. 2806: </def></gitem> 2807: <gitem><label>Reference in Entity Value</label> 2808: <def>as a reference 2809: within a parameter or internal entity's 2810: <termref def='dt-litentval'>literal entity value</termref> in 2811: the entity's declaration; corresponds to the nonterminal 2812: <nt def='NT-EntityValue'>EntityValue</nt>.</def></gitem> 2813: <gitem><label>Reference in DTD</label> 2814: <def>as a reference within either the internal or external subsets of the 2815: <termref def='dt-doctype'>DTD</termref>, but outside 2816: of an <nt def='NT-EntityValue'>EntityValue</nt> or 2817: <nt def="NT-AttValue">AttValue</nt>.</def> 2818: </gitem> 2819: </glist> 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 2829: General</td> 2830: <td bgcolor='&cellback;'>External Parsed 2831: General</td> 2832: <td bgcolor='&cellback;'>Unparsed</td> 2833: </tr> 2834: <tr align='center' valign='middle'> 2835: 2836: <td bgcolor='&cellback;' align='right'>Reference 2837: in 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 2846: in 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 2855: Attribute 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 2864: in 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 2873: in 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: Outside the DTD, the <code>%</code> character has no 2885: special significance; thus, what would be parameter entity references in the 2886: DTD are not recognized as markup in <nt def='NT-content'>content</nt>. 2887: Similarly, the names of unparsed entities are not recognized except 2888: when they appear in the value of an appropriately declared attribute. 2889: 2890: </div3> 2891: <div3 id='included'> 2892: <head>Included</head> 2893: <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 2896: and processed, in place of the reference itself, 2897: as though it were part of the document at the location the 2898: reference was recognized. 2899: The replacement text may contain both 2900: <termref def='dt-chardata'>character data</termref> 2901: and (except for parameter entities) <termref def="dt-markup">markup</termref>, 2902: which must be recognized in 2903: the usual way, except that the replacement text of entities used to escape 2904: markup delimiters (the entities &magicents;) is always treated as 2905: data. (The string "<code>AT&amp;T;</code>" expands to 2906: "<code>AT&T;</code>" and the remaining ampersand is not recognized 2907: as an entity-reference delimiter.) 2908: A character reference is <term>included</term> when the indicated 2909: character is processed in place of the reference itself. 2910: </termdef> 2911: </div3> 2912: <div3 id='include-if-valid'> 2913: <head>Included If Validating</head> 2914: When an XML processor recognizes a reference to a parsed entity, in order 2915: to <termref def="dt-valid">validate</termref> 2916: the document, the processor must 2917: <termref def="dt-include">include</termref> its 2918: replacement text. 2919: If the entity is external, and the processor is not 2920: attempting to validate the XML document, the 2921: processor <termref def="dt-may">may</termref>, but need not, 2922: include the entity's replacement text. 2923: If a non-validating parser does not include the replacement text, 2924: it must inform the application that it recognized, but did not 2925: read, the entity. 2926: This rule is based on the recognition that the automatic inclusion 2927: provided by the SGML and XML entity mechanism, primarily designed 2928: to support modularity in authoring, is not necessarily 2929: appropriate for other applications, in particular document browsing. 2930: Browsers, for example, when encountering an external parsed entity reference, 2931: might choose to provide a visual indication of the entity's 2932: presence and retrieve it for display only on demand. 2933: 2934: </div3> 2935: <div3 id='forbidden'> 2936: <head>Forbidden</head> 2937: The following are forbidden, and constitute 2938: <termref def='dt-fatal'>fatal</termref> errors: 2939: <ulist> 2940: <item>the appearance of a reference to an 2941: <termref def='dt-unparsed'>unparsed entity</termref>. 2942: </item> 2943: <item>the appearance of any character or general-entity reference in the 2944: DTD except within an <nt def='NT-EntityValue'>EntityValue</nt> or 2945: <nt def="NT-AttValue">AttValue</nt>.</item> 2946: <item>a reference to an external entity in an attribute value. 2947: </item> 2948: </ulist> 2949: 2950: </div3> 2951: <div3 id='inliteral'> 2952: <head>Included in Literal</head> 2953: When an <termref def='dt-entref'>entity reference</termref> appears in an 2954: attribute value, or a parameter entity reference appears in a literal entity 2955: value, its <termref def='dt-repltext'>replacement text</termref> is 2956: processed in place of the reference itself as though it 2957: were part of the document at the location the reference was recognized, 2958: except that a single or double quote character in the replacement text 2959: is always treated as a normal data character and will not terminate the 2960: literal. 2961: For example, this is well-formed: 2962: <eg><![CDATA[<!ENTITY % YN '"Yes"' > 2963: <!ENTITY WhatHeSaid "He said &YN;" >]]></eg> 2964: while this is not: 2965: <eg><!ENTITY EndAttr "27'" > 2966: <element attribute='a-&EndAttr;></eg> 2967: </div3> 2968: <div3 id='notify'> 2969: <head>Notify</head> 2970: When the name of an <termref def='dt-unparsed'>unparsed 2971: entity</termref> appears as a token in the 2972: value of an attribute of declared type <kw>ENTITY</kw> or <kw>ENTITIES</kw>, 2973: a validating processor must inform the 2974: application of the <termref def='dt-sysid'>system</termref> 2975: and <termref def='dt-pubid'>public</termref> (if any) 2976: identifiers for both the entity and its associated 2977: <termref def="dt-notation">notation</termref>. 2978: </div3> 2979: <div3 id='bypass'> 2980: <head>Bypassed</head> 2981: When a general entity reference appears in the 2982: <nt def='NT-EntityValue'>EntityValue</nt> in an entity declaration, 2983: it is bypassed and left as is. 2984: </div3> 2985: <div3 id='as-PE'> 2986: <head>Included as PE</head> 2987: Just as with external parsed entities, parameter entities 2988: need only be <titleref href='include-if-valid'>included if 2989: validating</titleref>. 2990: When a parameter-entity reference is recognized in the DTD 2991: and included, its 2992: <termref def='dt-repltext'>replacement 2993: text</termref> is enlarged by the attachment of one leading and one following 2994: space (#x20) character; the intent is to constrain the replacement 2995: text of parameter 2996: entities to contain an integral number of grammatical tokens in the DTD. 2997: 2998: </div3> 2999: 3000: </div2> 3001: <div2 id='intern-replacement'> 3002: <head>Construction of Internal Entity Replacement Text</head> 3003: In discussing the treatment 3004: of internal entities, it is 3005: useful to distinguish two forms of the entity's value. 3006: <termdef id="dt-litentval" term='Literal Entity Value'>The <term>literal 3007: entity value</term> is the quoted string actually 3008: present in the entity declaration, corresponding to the 3009: non-terminal <nt def='NT-EntityValue'>EntityValue</nt>.</termdef> 3010: <termdef id='dt-repltext' term='Replacement Text'>The <term>replacement 3011: text</term> is the content of the entity, after 3012: replacement of character references and parameter-entity 3013: references. 3014: </termdef> 3015: 3016: The literal entity value 3017: as given in an internal entity declaration 3018: (<nt def='NT-EntityValue'>EntityValue</nt>) may contain character, 3019: parameter-entity, and general-entity references. 3020: Such references must be contained entirely within the 3021: literal entity value. 3022: The actual replacement text that is 3023: <termref def='dt-include'>included</termref> as described above 3024: must contain the <emph>replacement text</emph> of any 3025: parameter entities referred to, and must contain the character 3026: referred to, in place of any character references in the 3027: literal entity value; however, 3028: general-entity references must be left as-is, unexpanded. 3029: For 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> 3035: then the replacement text for the entity "<code>book</code>" is: 3036: <eg>La Peste: Albert Camus, 3037: © 1947 Éditions Gallimard. &rights;</eg> 3038: The general-entity reference "<code>&rights;</code>" would be expanded 3039: should the reference "<code>&book;</code>" appear in the document's 3040: content or an attribute value. 3041: These simple rules may have complex interactions; for a detailed 3042: discussion of a difficult example, see 3043: <specref ref='sec-entexpand'/>. 3044: 3045: 3046: </div2> 3047: <div2 id='sec-predefined-ent'> 3048: <head>Predefined Entities</head> 3049: <termdef id="dt-escape" term="escape">Entity and character 3050: references can both be used to <term>escape</term> the left angle bracket, 3051: ampersand, and other delimiters. A set of general entities 3052: (&magicents;) is specified for this purpose. 3053: Numeric character references may also be used; they are 3054: expanded immediately when recognized and must be treated as 3055: character data, so the numeric character references 3056: "<code>&#60;</code>" and "<code>&#38;</code>" may be used to 3057: escape <code><</code> and <code>&</code> when they occur 3058: in character data.</termdef> 3059: All XML processors must recognize these entities whether they 3060: are declared or not. 3061: <termref def='dt-interop'>For interoperability</termref>, 3062: valid XML documents should declare these 3063: entities, like any others, before using them. 3064: If the entities in question are declared, they must be declared 3065: as internal entities whose replacement text is the single 3066: character being escaped or a character reference to 3067: that 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> 3074: Note that the <code><</code> and <code>&</code> characters 3075: in the declarations of "<code>lt</code>" and "<code>amp</code>" 3076: are doubly escaped to meet the requirement that entity replacement 3077: be well-formed. 3078: 3079: </div2> 3080: 3081: <div2 id='Notations'> 3082: <head>Notation Declarations</head> 3083: 3084: <termdef id="dt-notation" term="Notation"><term>Notations</term> identify by 3085: name the format of <termref def="dt-extent">unparsed 3086: entities</termref>, the 3087: format of elements which bear a notation attribute, 3088: or the application to which 3089: a <termref def="dt-pi">processing instruction</termref> is 3090: addressed.</termdef> 3091: <termdef id="dt-notdecl" term="Notation Declaration"> 3092: <term>Notation declarations</term> 3093: provide a name for the notation, for use in 3094: entity and attribute-list declarations and in attribute specifications, 3095: and an external identifier for the notation which may allow an XML 3096: processor or its client application to locate a helper application 3097: capable 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> 3112: XML processors must provide applications with the name and external 3113: identifier(s) of any notation declared and referred to in an attribute 3114: value, attribute definition, or entity declaration. They may 3115: additionally resolve the external identifier into the 3116: <termref def="dt-sysid">system identifier</termref>, 3117: file name, or other information needed to allow the 3118: application to call a processor for data in the notation described. (It 3119: is not an error, however, for XML documents to declare and refer to 3120: notations for which notation-specific applications are not available on 3121: the system where the XML processor or application is running.) 3122: </div2> 3123: 3124: 3125: <div2 id='sec-doc-entity'> 3126: <head>Document Entity</head> 3127: 3128: <termdef id="dt-docent" term="Document Entity">The <term>document 3129: entity</term> serves as the root of the entity 3130: tree and a starting-point for an <termref def="dt-xml-proc">XML 3131: processor</termref>.</termdef> 3132: This specification does 3133: not specify how the document entity is to be located by an XML 3134: processor; unlike other entities, the document entity has no name and might 3135: well appear on a processor input stream 3136: without any identification at all. 3137: </div2> 3138: 3139: 3140: </div1> 3141:  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: Conforming <termref def="dt-xml-proc">XML processors</termref> fall into two 3149: classes: validating and non-validating. 3150: Validating and non-validating processors alike must report 3151: violations of this specification's well-formedness constraints 3152: in the content of the 3153: <termref def='dt-docent'>document entity</termref> and any 3154: other <termref def='dt-parsedent'>parsed entities</termref> that 3155: they read. 3156: <termdef id="dt-validating" term="Validating Processor"> 3157: <term>Validating processors</term> must report 3158: violations of the constraints expressed by the declarations in the 3159: <termref def="dt-doctype">DTD</termref>, and 3160: failures to fulfill the validity constraints given 3161: in this specification. 3162: </termdef> 3163: To accomplish this, validating XML processors must read and process the entire 3164: DTD and all external parsed entities referenced in the document. 3165: 3166: Non-validating processors are required to check only the 3167: <termref def='dt-docent'>document entity</termref>, including 3168: the entire internal DTD subset, for well-formedness. 3169: <termdef id='dt-use-mdecl' term='Process Declarations'> 3170: While they are not required to check the document for validity, 3171: they are required to 3172: <term>process</term> all the declarations they read in the 3173: internal DTD subset and in any parameter entity that they 3174: read, up to the first reference 3175: to a parameter entity that they do <emph>not</emph> read; that is to 3176: say, they must 3177: use the information in those declarations to 3178: <titleref href='AVNormalize'>normalize</titleref> attribute values, 3179: <titleref href='included'>include</titleref> the replacement text of 3180: internal entities, and supply 3181: <titleref href='sec-attr-defaults'>default attribute values</titleref>. 3182: </termdef> 3183: They 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> 3186: encountered after a reference to a parameter entity that is not 3187: read, since the entity may have contained overriding declarations. 3188: 3189: </div2> 3190: <div2 id='safe-behavior'> 3191: <head>Using XML Processors</head> 3192: The behavior of a validating XML processor is highly predictable; it 3193: must read every piece of a document and report all well-formedness and 3194: validity violations. 3195: Less is required of a non-validating processor; it need not read any 3196: part of the document other than the document entity. 3197: This has two effects that may be important to users of XML processors: 3198: <ulist> 3199: <item>Certain well-formedness errors, specifically those that require 3200: reading external entities, may not be detected by a non-validating processor. 3201: Examples 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 3205: as some of the cases described as 3206: <titleref href='forbidden'>forbidden</titleref> in 3207: <specref ref='entproc'/>.</item> 3208: <item>The information passed from the processor to the application may 3209: vary, depending on whether the processor reads 3210: parameter and external entities. 3211: For 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 3214: internal entities, or supply 3215: <titleref href='sec-attr-defaults'>default attribute values</titleref>, 3216: where doing so depends on having read declarations in 3217: external or parameter entities.</item> 3218: </ulist> 3219: 3220: For maximum reliability in interoperating between different XML 3221: processors, applications which use non-validating processors should not 3222: rely on any behaviors not required of such processors. 3223: Applications which require facilities such as the use of default 3224: attributes or internal entities which are declared in external 3225: entities should use validating XML processors. 3226: </div2> 3227: </div1> 3228: 3229: <div1 id='sec-notation'> 3230: <head>Notation</head> 3231: 3232: The formal grammar of XML is given in this specification using a simple 3233: Extended Backus-Naur Form (EBNF) notation. Each rule in the grammar defines 3234: one symbol, in the form 3235: <eg>symbol ::= expression</eg> 3236: Symbols are written with an initial capital letter if they are 3237: defined by a regular expression, or with an initial lower case letter 3238: otherwise. 3239: Literal strings are quoted. 3240: 3241: 3242: 3243: Within the expression on the right-hand side of a rule, the following 3244: expressions are used to match strings of one or more characters: 3245: <glist> 3246: <gitem> 3247: <label><code>#xN</code></label> 3248: <def>where <code>N</code> is a hexadecimal integer, the 3249: expression matches the character in ISO/IEC 10646 whose canonical 3250: (UCS-4) 3251: code value, when interpreted as an unsigned binary number, has 3252: the value indicated. The number of leading zeros in the 3253: <code>#xN</code> form is insignificant; the number of leading 3254: zeros in the corresponding code value 3255: is governed by the character 3256: encoding in use and is not significant for XML.</def> 3257: </gitem> 3258: <gitem> 3259: <label><code>[a-zA-Z]</code>, <code>[#xN-#xN]</code></label> 3260: <def>matches any <termref def='dt-character'>character</termref> 3261: with a value in the range(s) indicated (inclusive).</def> 3262: </gitem> 3263: <gitem> 3264: <label><code>[^a-z]</code>, <code>[^#xN-#xN]</code></label> 3265: <def>matches any <termref def='dt-character'>character</termref> 3266: with a value <emph>outside</emph> the 3267: range indicated.</def> 3268: </gitem> 3269: <gitem> 3270: <label><code>[^abc]</code>, <code>[^#xN#xN#xN]</code></label> 3271: <def>matches any <termref def='dt-character'>character</termref> 3272: with a value not among the characters given.</def> 3273: </gitem> 3274: <gitem> 3275: <label><code>"string"</code></label> 3276: <def>matches a literal string <termref def="dt-match">matching</termref> 3277: that given inside the double quotes.</def> 3278: </gitem> 3279: <gitem> 3280: <label><code>'string'</code></label> 3281: <def>matches a literal string <termref def="dt-match">matching</termref> 3282: that given inside the single quotes.</def> 3283: </gitem> 3284: </glist> 3285: These symbols may be combined to match more complex patterns as follows, 3286: where <code>A</code> and <code>B</code> represent simple expressions: 3287: <glist> 3288: <gitem> 3289: <label>(<code>expression</code>)</label> 3290: <def><code>expression</code> is treated as a unit 3291: and may be combined as described in this list.</def> 3292: </gitem> 3293: <gitem> 3294: <label><code>A?</code></label> 3295: <def>matches <code>A</code> or nothing; optional <code>A</code>.</def> 3296: </gitem> 3297: <gitem> 3298: <label><code>A B</code></label> 3299: <def>matches <code>A</code> followed by <code>B</code>.</def> 3300: </gitem> 3301: <gitem> 3302: <label><code>A | B</code></label> 3303: <def>matches <code>A</code> or <code>B</code> but not both.</def> 3304: </gitem> 3305: <gitem> 3306: <label><code>A - B</code></label> 3307: <def>matches any string that matches <code>A</code> but does not match 3308: <code>B</code>. 3309: </def> 3310: </gitem> 3311: <gitem> 3312: <label><code>A+</code></label> 3313: <def>matches one or more occurrences of <code>A</code>.</def> 3314: </gitem> 3315: <gitem> 3316: <label><code>A*</code></label> 3317: <def>matches zero or more occurrences of <code>A</code>.</def> 3318: </gitem> 3319: 3320: </glist> 3321: Other notations used in the productions are: 3322: <glist> 3323: <gitem> 3324: <label><code>/* ... */</code></label> 3325: <def>comment.</def> 3326: </gitem> 3327: <gitem> 3328: <label><code>[ wfc: ... ]</code></label> 3329: <def>well-formedness constraint; this identifies by name a 3330: constraint on 3331: <termref def="dt-wellformed">well-formed</termref> documents 3332: associated with a production.</def> 3333: </gitem> 3334: <gitem> 3335: <label><code>[ vc: ... ]</code></label> 3336: <def>validity constraint; this identifies by name a constraint on 3337: <termref def="dt-valid">valid</termref> documents associated with 3338: a production.</def> 3339: </gitem> 3340: </glist> 3341: </div1> 3342: 3343: </body> 3344: <back> 3345:  3346: 3347: 3348:  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 3358: Character Sets</emph>, 3359: ed. Keld Simonsen et al. 3360: See <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'> 3364: IETF (Internet Engineering Task Force). 3365: <emph>RFC 1766: Tags for the Identification of Languages</emph>, 3366: ed. H. Alvestrand. 3367: 1995. 3368: </bibl> 3369: 3370: <bibl id='ISO639' key='ISO 639'> 3371: (International Organization for Standardization). 3372: <emph>ISO 639:1988 (E). 3373: Code for the representation of names of languages.</emph> 3374: [Geneva]: International Organization for 3375: Standardization, 1988.</bibl> 3376: 3377: <bibl id='ISO3166' key='ISO 3166'> 3378: (International Organization for Standardization). 3379: <emph>ISO 3166-1:1997 (E). 3380: Codes for the representation of names of countries and their subdivisions 3381: — Part 1: Country codes</emph> 3382: [Geneva]: International Organization for 3383: Standardization, 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 3388: Multiple-Octet Coded Character Set (UCS) — Part 1: 3389: Architecture and Basic Multilingual Plane.</emph> 3390: [Geneva]: International Organization for 3391: Standardization, 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> 3396: Reading, 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., 3407: Ravi Sethi, and Jeffrey D. Ullman. 3408: <emph>Compilers: Principles, Techniques, and Tools</emph>. 3409: Reading: Addison-Wesley, 1986, rpt. corr. 1988.</bibl> 3410: 3411: <bibl id="Berners-Lee" xml-link="simple" key="Berners-Lee et al."> 3412: Berners-Lee, T., R. Fielding, and L. Masinter. 3413: <emph>Uniform Resource Identifiers (URI): Generic Syntax and 3414: Semantics</emph>. 3415: 1997. 3416: (Work in progress; see updates to RFC1738.)</bibl> 3417: 3418: <bibl id='ABK' key='Brüggemann-Klein'>Brüggemann-Klein, Anne. 3419: <emph>Regular Expressions into Finite Automata</emph>. 3420: Extended abstract in I. Simon, Hrsg., LATIN 1992, 3421: S. 97-98. Springer-Verlag, Berlin 1992. 3422: Full Version in Theoretical Computer Science 120: 197-213, 1993. 3423: 3424: </bibl> 3425: 3426: <bibl id='ABKDW' key='Brüggemann-Klein and Wood'>Brüggemann-Klein, Anne, 3427: and Derick Wood. 3428: <emph>Deterministic Regular Languages</emph>. 3429: Universität Freiburg, Institut für Informatik, 3430: Bericht 38, Oktober 1991. 3431: </bibl> 3432: 3433: <bibl id='Clark' key='Clark'>James Clark. 3434: Comparison 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"> 3438: IETF (Internet Engineering Task Force). 3439: <emph>RFC 1738: Uniform Resource Locators (URL)</emph>, 3440: ed. T. Berners-Lee, L. Masinter, M. McCahill. 3441: 1994. 3442: </bibl> 3443: 3444: <bibl id="RFC1808" xml-link="simple" key="IETF RFC1808"> 3445: IETF (Internet Engineering Task Force). 3446: <emph>RFC 1808: Relative Uniform Resource Locators</emph>, 3447: ed. R. Fielding. 3448: 1995. 3449: </bibl> 3450: 3451: <bibl id="RFC2141" xml-link="simple" key="IETF RFC2141"> 3452: IETF (Internet Engineering Task Force). 3453: <emph>RFC 2141: URN Syntax</emph>, 3454: ed. R. Moats. 3455: 1997. 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 3461: Systems — Standard Generalized Markup Language (SGML).</emph> First 3462: edition — 1986-10-15. [Geneva]: International Organization for 3463: Standardization, 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 — 3470: Hypermedia/Time-based Structuring Language (HyTime). 3471: </emph> 3472: [Geneva]: International Organization for 3473: Standardization, 1992. 3474: <emph>Extended Facilities Annexe.</emph> 3475: [Geneva]: International Organization for 3476: Standardization, 1996. 3477: </bibl> 3478: 3479: 3480: 3481: </blist> 3482: </div2> 3483: </div1> 3484: <div1 id='CharClasses'> 3485: <head>Character Classes</head> 3486: Following the characteristics defined in the Unicode standard, 3487: characters are classed as base characters (among others, these 3488: contain the alphabetic characters of the Latin alphabet, without 3489: diacritics), ideographic characters, and combining characters (among 3490: others, this class contains most diacritics); these classes combine 3491: to form the class of letters. Digits and extenders are 3492: also 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: 3839: The character classes defined here can be derived from the 3840: Unicode character database as follows: 3841: <ulist> 3842: <item> 3843: Name start characters must have one of the categories Ll, Lu, 3844: Lo, Lt, Nl. 3845: </item> 3846: <item> 3847: Name characters other than Name-start characters 3848: must have one of the categories Mc, Me, Mn, Lm, or Nd. 3849: </item> 3850: <item> 3851: Characters in the compatibility area (i.e. with character code 3852: greater than #xF900 and less than #xFFFE) are not allowed in XML 3853: names. 3854: </item> 3855: <item> 3856: Characters which have a font or compatibility decomposition (i.e. those 3857: with a "compatibility formatting tag" in field 5 of the database -- 3858: marked by field 5 beginning with a "<") are not allowed. 3859: </item> 3860: <item> 3861: The following characters are treated as name-start characters 3862: rather than name characters, because the property file classifies 3863: them as Alphabetic: [#x02BB-#x02C1], #x0559, #x06E5, #x06E6. 3864: </item> 3865: <item> 3866: Characters #x20DD-#x20E0 are excluded (in accordance with 3867: Unicode, section 5.14). 3868: </item> 3869: <item> 3870: Character #x00B7 is classified as an extender, because the 3871: property list so identifies it. 3872: </item> 3873: <item> 3874: Character #x0387 is added as a name character, because #x00B7 3875: is its canonical equivalent. 3876: </item> 3877: <item> 3878: Characters ':' and '_' are allowed as name-start characters. 3879: </item> 3880: <item> 3881: Characters '-' and '.' are allowed as name characters. 3882: </item> 3883: </ulist> 3884: 3885: </div1> 3886: <inform-div1 id="sec-xml-and-sgml"> 3887: <head>XML and SGML</head> 3888: 3889: 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 3891: conformant SGML document. 3892: For a detailed comparison of the additional restrictions that XML places on 3893: documents beyond those of SGML, see <bibref ref='Clark'/>. 3894: 3895: </inform-div1> 3896: <inform-div1 id="sec-entexpand"> 3897: <head>Expansion of Entity and Character References</head> 3898: This appendix contains some examples illustrating the 3899: sequence of entity- and character-reference recognition and 3900: expansion, as specified in <specref ref='entproc'/>. 3901: 3902: If the DTD contains the declaration 3903: <eg><![CDATA[<!ENTITY example "An ampersand (&#38;) may be escaped 3904: numerically (&#38;#38;) or with a general entity 3905: (&amp;)." > 3906: ]]></eg> 3907: then the XML processor will recognize the character references 3908: when it parses the entity declaration, and resolve them before 3909: storing the following string as the 3910: value of the entity "<code>example</code>": 3911: <eg><![CDATA[An ampersand (&) may be escaped 3912: numerically (&#38;) or with a general entity 3913: (&amp;). 3914: ]]></eg> 3915: A reference in the document to "<code>&example;</code>" 3916: will cause the text to be reparsed, at which time the 3917: start- and end-tags of the "<code>p</code>" element will be recognized 3918: and the three references will be recognized and expanded, 3919: resulting 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 3922: numerically (&) or with a general entity 3923: (&). 3924: ]]></eg> 3925: 3926: A more complex example will illustrate the rules and their 3927: effects fully. In the following example, the line numbers are 3928: solely for reference. 3929: <eg><![CDATA[1 <?xml version='1.0'?> 3930: 2 <!DOCTYPE test [ 3931: 3 <!ELEMENT test (#PCDATA) > 3932: 4 <!ENTITY % xx '%zz;'> 3933: 5 <!ENTITY % zz '<!ENTITY tricky "error-prone" >' > 3934: 6 %xx; 3935: 7 ]> 3936: 8 <test>This sample shows a &tricky; method.</test> 3937: ]]></eg> 3938: This produces the following: 3939: <ulist spacing="compact"> 3940: <item>in line 4, the reference to character 37 is expanded immediately, 3941: and the parameter entity "<code>xx</code>" is stored in the symbol 3942: table with the value "<code>%zz;</code>". Since the replacement text 3943: is not rescanned, the reference to parameter entity "<code>zz</code>" 3944: is not recognized. (And it would be an error if it were, since 3945: "<code>zz</code>" is not yet declared.)</item> 3946: <item>in line 5, the character reference "<code>&#60;</code>" is 3947: expanded immediately and the parameter entity "<code>zz</code>" is 3948: stored with the replacement text 3949: "<code><!ENTITY tricky "error-prone" ></code>", 3950: which is a well-formed entity declaration.</item> 3951: <item>in line 6, the reference to "<code>xx</code>" is recognized, 3952: and the replacement text of "<code>xx</code>" (namely 3953: "<code>%zz;</code>") is parsed. The reference to "<code>zz</code>" 3954: is recognized in its turn, and its replacement text 3955: ("<code><!ENTITY tricky "error-prone" ></code>") is parsed. 3956: The general entity "<code>tricky</code>" has now been 3957: declared, with the replacement text "<code>error-prone</code>".</item> 3958: <item> 3959: in line 8, the reference to the general entity "<code>tricky</code>" is 3960: recognized, 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: </item> 3964: </ulist> 3965: 3966: </inform-div1> 3967: <inform-div1 id="determinism"> 3968: <head>Deterministic Content Models</head> 3969: <termref def='dt-compat'>For compatibility</termref>, it is 3970: required 3971: that content models in element type declarations be deterministic. 3972: 3973:  3974: SGML 3975: requires deterministic content models (it calls them 3976: "unambiguous"); XML processors built using SGML systems may 3977: flag non-deterministic content models as errors. 3978: For example, the content model <code>((b, c) | (b, d))</code> is 3979: non-deterministic, because given an initial <code>b</code> the parser 3980: cannot know which <code>b</code> in the model is being matched without 3981: looking ahead to see which element follows the <code>b</code>. 3982: In this case, the two references to 3983: <code>b</code> can be collapsed 3984: into a single reference, making the model read 3985: <code>(b, (c | d))</code>. An initial <code>b</code> now clearly 3986: matches only a single name in the content model. The parser doesn't 3987: need to look ahead to see what follows; either <code>c</code> or 3988: <code>d</code> would be accepted. 3989: More formally: a finite state automaton may be constructed from the 3990: content model using the standard algorithms, e.g. algorithm 3.5 3991: in section 3.9 3992: of Aho, Sethi, and Ullman <bibref ref='Aho'/>. 3993: In many such algorithms, a follow set is constructed for each 3994: position in the regular expression (i.e., each leaf 3995: node in the 3996: syntax tree for the regular expression); 3997: if any position has a follow set in which 3998: more than one following position is 3999: labeled with the same element type name, 4000: then the content model is in error 4001: and may be reported as an error. 4002: 4003: Algorithms exist which allow many but not all non-deterministic 4004: content models to be reduced automatically to equivalent deterministic 4005: models; see Brüggemann-Klein 1991 <bibref ref='ABK'/>. 4006: </inform-div1> 4007: <inform-div1 id="sec-guessing"> 4008: <head>Autodetection of Character Encodings</head> 4009: The XML encoding declaration functions as an internal label on each 4010: entity, indicating which character encoding is in use. Before an XML 4011: processor can read the internal label, however, it apparently has to 4012: know what character encoding is in use—which is what the internal label 4013: is trying to indicate. In the general case, this is a hopeless 4014: situation. It is not entirely hopeless in XML, however, because XML 4015: limits the general case in two ways: each implementation is assumed 4016: to support only a finite set of character encodings, and the XML 4017: encoding declaration is restricted in position and content in order to 4018: make it feasible to autodetect the character encoding in use in each 4019: entity in normal cases. Also, in many cases other sources of information 4020: are available in addition to the XML data stream itself. 4021: Two cases may be distinguished, 4022: depending on whether the XML entity is presented to the 4023: processor without, or with, any accompanying 4024: (external) information. We consider the first case first. 4025: 4026: 4027: Because each XML entity not in UTF-8 or UTF-16 format <emph>must</emph> 4028: begin with an XML encoding declaration, in which the first characters 4029: must be '<code><?xml</code>', any conforming processor can detect, 4030: after two to four octets of input, which of the following cases apply. 4031: In 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 4033: Order Mark required of UTF-16 data streams is "<code>#xFEFF</code>". 4034: 4035: <ulist> 4036: <item> 4037: <code>00 00 00 3C</code>: UCS-4, big-endian machine (1234 order) 4038: </item> 4039: <item> 4040: <code>3C 00 00 00</code>: UCS-4, little-endian machine (4321 order) 4041: </item> 4042: <item> 4043: <code>00 00 3C 00</code>: UCS-4, unusual octet order (2143) 4044: </item> 4045: <item> 4046: <code>00 3C 00 00</code>: UCS-4, unusual octet order (3412) 4047: </item> 4048: <item> 4049: <code>FE FF</code>: UTF-16, big-endian 4050: </item> 4051: <item> 4052: <code>FF FE</code>: UTF-16, little-endian 4053: </item> 4054: <item> 4055: <code>00 3C 00 3F</code>: UTF-16, big-endian, no Byte Order Mark 4056: (and thus, strictly speaking, in error) 4057: </item> 4058: <item> 4059: <code>3C 00 3F 00</code>: UTF-16, little-endian, no Byte Order Mark 4060: (and thus, strictly speaking, in error) 4061: </item> 4062: <item> 4063: <code>3C 3F 78 6D</code>: UTF-8, ISO 646, ASCII, some part of ISO 8859, 4064: Shift-JIS, EUC, or any other 7-bit, 8-bit, or mixed-width encoding 4065: which ensures that the characters of ASCII have their normal positions, 4066: width, 4067: and values; the actual encoding declaration must be read to 4068: detect which of these applies, but since all of these encodings 4069: use the same bit patterns for the ASCII characters, the encoding 4070: declaration itself may be read reliably 4071: 4072: </item> 4073: <item> 4074: <code>4C 6F A7 94</code>: EBCDIC (in some flavor; the full 4075: encoding declaration must be read to tell which code page is in 4076: use) 4077: </item> 4078: <item> 4079: other: UTF-8 without an encoding declaration, or else 4080: the data stream is corrupt, fragmentary, or enclosed in 4081: a wrapper of some kind 4082: </item> 4083: </ulist> 4084: 4085: 4086: This level of autodetection is enough to read the XML encoding 4087: declaration and parse the character-encoding identifier, which is 4088: still necessary to distinguish the individual members of each family 4089: of encodings (e.g. to tell UTF-8 from 8859, and the parts of 8859 4090: from each other, or to distinguish the specific EBCDIC code page in 4091: use, and so on). 4092: 4093: 4094: Because the contents of the encoding declaration are restricted to 4095: ASCII characters, a processor can reliably read the entire encoding 4096: declaration as soon as it has detected which family of encodings is in 4097: use. Since in practice, all widely used character encodings fall into 4098: one of the categories above, the XML encoding declaration allows 4099: reasonably reliable in-band labeling of character encodings, even when 4100: external sources of information at the operating-system or 4101: transport-protocol level are unreliable. 4102: 4103: 4104: Once the processor has detected the character encoding in use, it can 4105: act appropriately, whether by invoking a separate input routine for 4106: each case, or by calling the proper conversion function on each 4107: character of input. 4108: 4109: 4110: Like any self-labeling system, the XML encoding declaration will not 4111: work if any software changes the entity's character set or encoding 4112: without updating the encoding declaration. Implementors of 4113: character-encoding routines should be careful to ensure the accuracy 4114: of the internal and external information used to label the entity. 4115: 4116: The second possible case occurs when the XML entity is accompanied 4117: by encoding information, as in some file systems and some network 4118: protocols. 4119: When multiple sources of information are available, 4120: 4121: their relative 4122: priority and the preferred method of handling conflict should be 4123: specified as part of the higher-level protocol used to deliver XML. 4124: Rules for the relative priority of the internal label and the 4125: MIME-type label in an external header, for example, should be part of the 4126: RFC document defining the text/xml and application/xml MIME types. In 4127: the interests of interoperability, however, the following rules 4128: are recommended. 4129: <ulist> 4130: <item>If an XML entity is in a file, the Byte-Order Mark 4131: and encoding-declaration PI are used (if present) to determine the 4132: character encoding. All other heuristics and sources of information 4133: are solely for error recovery. 4134: </item> 4135: <item>If an XML entity is delivered with a 4136: MIME type of text/xml, then the <code>charset</code> parameter 4137: on the MIME type determines the 4138: character encoding method; all other heuristics and sources of 4139: information are solely for error recovery. 4140: </item> 4141: <item>If an XML entity is delivered 4142: with a 4143: MIME type of application/xml, then the Byte-Order Mark and 4144: encoding-declaration PI are used (if present) to determine the 4145: character encoding. All other heuristics and sources of 4146: information are solely for error recovery. 4147: </item> 4148: </ulist> 4149: These rules apply only in the absence of protocol-level documentation; 4150: in particular, when the MIME types text/xml and application/xml are 4151: defined, the recommendations of the relevant RFC will supersede 4152: these rules. 4153: 4154: 4155: </inform-div1> 4156: 4157: <inform-div1 id="sec-xml-wg"> 4158: <head>W3C XML Working Group</head> 4159: 4160: This specification was prepared and approved for publication by the 4161: W3C XML Working Group (WG). WG approval of this specification does 4162: not necessarily imply that all WG members voted for its approval. 4163: The current and former members of the XML WG are: 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 4171: Co-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: