REC-xml-19980210.xml
1 <?xml version="1.0" encoding="ISO-8859-1" standalone="no"?> 2 <!DOCTYPE spec SYSTEM "dtds/spec.dtd" [ 3 <!-- LAST TOUCHED BY: Tim Bray, 8 February 1997 --><!-- The words 'FINAL EDIT' in comments mark places where changes 4 need to be made after approval of the document by the ERB, before 5 publication. --><!ENTITY XML.version "1.0"> 6 <!ENTITY doc.date "10 February 1998"> 7 <!ENTITY iso6.doc.date "19980210"> 8 <!ENTITY w3c.doc.date "02-Feb-1998"> 9 <!ENTITY draft.day "10"> 10 <!ENTITY draft.month "February"> 11 <!ENTITY draft.year "1998"> 12 <!ENTITY WebSGML "WebSGML Adaptations Annex to ISO 8879"> 13 <!ENTITY lt "<"> 14 <!ENTITY gt ">"> 15 <!ENTITY xmlpio "'<?xml'"> 16 <!ENTITY pic "'?>'"> 17 <!ENTITY br "\n"> 18 <!ENTITY cellback "#c0d9c0"> 19 <!ENTITY mdash "--"> 20 <!-- —, but nsgmls doesn't grok hex --><!ENTITY com "--"> 21 <!ENTITY como "--"> 22 <!ENTITY comc "--"> 23 <!ENTITY hcro "&#x"> 24 <!-- <!ENTITY nbsp "�"> --><!ENTITY nbsp " "> 25 <!ENTITY magicents "<code>amp</code>, 26 <code>lt</code>, 27 <code>gt</code>, 28 <code>apos</code>, 29 <code>quot</code>"> 30 <!-- audience and distribution status: for use at publication time --><!ENTITY doc.audience "public review and discussion"> 31 <!ENTITY doc.distribution "may be distributed freely, as long as 32 all text and legal notices remain intact"> 33 ]> 34 <!-- for Panorama *--> 35 <?VERBATIM "eg" ?> 36 <spec> 37 <header> 38 <title>Extensible Markup Language (XML) 1.0</title> 39 <version/> 40 <w3c-designation>REC-xml-&iso6.doc.date;</w3c-designation> 41 <w3c-doctype>W3C Recommendation</w3c-doctype> 42 <pubdate><day>&draft.day;</day><month>&draft.month;</month><year>&draft.year;</year></pubdate> 43 44 <publoc> 45 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;"> 46 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;</loc> 47 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.xml"> 48 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.xml</loc> 49 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.html"> 50 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.html</loc> 51 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.pdf"> 52 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.pdf</loc> 53 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.ps"> 54 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.ps</loc> 55 </publoc> 56 <latestloc> 57 <loc href="http://www.w3.org/TR/REC-xml"> 58 http://www.w3.org/TR/REC-xml</loc> 59 </latestloc> 60 <prevlocs> 61 <loc href="http://www.w3.org/TR/PR-xml-971208"> 62 http://www.w3.org/TR/PR-xml-971208</loc> 63 <!-- 64 <loc href='http://www.w3.org/TR/WD-xml-961114'> 65 http://www.w3.org/TR/WD-xml-961114</loc> 66 <loc href='http://www.w3.org/TR/WD-xml-lang-970331'> 67 http://www.w3.org/TR/WD-xml-lang-970331</loc> 68 <loc href='http://www.w3.org/TR/WD-xml-lang-970630'> 69 http://www.w3.org/TR/WD-xml-lang-970630</loc> 70 <loc href='http://www.w3.org/TR/WD-xml-970807'> 71 http://www.w3.org/TR/WD-xml-970807</loc> 72 <loc href='http://www.w3.org/TR/WD-xml-971117'> 73 http://www.w3.org/TR/WD-xml-971117</loc>--> 74 </prevlocs> 75 <authlist> 76 <author><name>Tim Bray</name> 77 <affiliation>Textuality and Netscape</affiliation> 78 <email href="mailto:tbray@textuality.com">tbray@textuality.com</email></author> 79 <author><name>Jean Paoli</name> 80 <affiliation>Microsoft</affiliation> 81 <email href="mailto:jeanpa@microsoft.com">jeanpa@microsoft.com</email></author> 82 <author><name>C. M. Sperberg-McQueen</name> 83 <affiliation>University of Illinois at Chicago</affiliation> 84 <email href="mailto:cmsmcq@uic.edu">cmsmcq@uic.edu</email></author> 85 </authlist> 86 <abstract> 87 <p>The Extensible Markup Language (XML) is a subset of 88 SGML that is completely described in this document. Its goal is to 89 enable generic SGML to be served, received, and processed on the Web 90 in the way that is now possible with HTML. XML has been designed for 91 ease of implementation and for interoperability with both SGML and 92 HTML.</p> 93 </abstract> 94 <status> 95 <p>This document has been reviewed by W3C Members and 96 other interested parties and has been endorsed by the 97 Director as a W3C Recommendation. It is a stable 98 document and may be used as reference material or cited 99 as a normative reference from another document. W3C's 100 role in making the Recommendation is to draw attention 101 to the specification and to promote its widespread 102 deployment. This enhances the functionality and 103 interoperability of the Web.</p> 104 <p> 105 This document specifies a syntax created by subsetting an existing, 106 widely used international text processing standard (Standard 107 Generalized Markup Language, ISO 8879:1986(E) as amended and 108 corrected) for use on the World Wide Web. It is a product of the W3C 109 XML Activity, details of which can be found at <loc href="http://www.w3.org/XML">http://www.w3.org/XML</loc>. A list of 110 current W3C Recommendations and other technical documents can be found 111 at <loc href="http://www.w3.org/TR">http://www.w3.org/TR</loc>. 112 </p> 113 <p>This specification uses the term URI, which is defined by <bibref ref="Berners-Lee"/>, a work in progress expected to update <bibref ref="RFC1738"/> and <bibref ref="RFC1808"/>. 114 </p> 115 <p>The list of known errors in this specification is 116 available at 117 <loc href="http://www.w3.org/XML/xml-19980210-errata">http://www.w3.org/XML/xml-19980210-errata</loc>.</p> 118 <p>Please report errors in this document to 119 <loc href="mailto:xml-editor@w3.org">xml-editor@w3.org</loc>. 120 </p> 121 </status> 122 123 124 <pubstmt> 125 <p>Chicago, Vancouver, Mountain View, et al.: 126 World-Wide Web Consortium, XML Working Group, 1996, 1997.</p> 127 </pubstmt> 128 <sourcedesc> 129 <p>Created in electronic form.</p> 130 </sourcedesc> 131 <langusage> 132 <language id="EN">English</language> 133 <language id="ebnf">Extended Backus-Naur Form (formal grammar)</language> 134 </langusage> 135 <revisiondesc> 136 <slist> 137 <sitem>1997-12-03 : CMSMcQ : yet further changes</sitem> 138 <sitem>1997-12-02 : TB : further changes (see TB to XML WG, 139 2 December 1997)</sitem> 140 <sitem>1997-12-02 : CMSMcQ : deal with as many corrections and 141 comments from the proofreaders as possible: 142 entify hard-coded document date in pubdate element, 143 change expansion of entity WebSGML, 144 update status description as per Dan Connolly (am not sure 145 about refernece to Berners-Lee et al.), 146 add 'The' to abstract as per WG decision, 147 move Relationship to Existing Standards to back matter and 148 combine with References, 149 re-order back matter so normative appendices come first, 150 re-tag back matter so informative appendices are tagged informdiv1, 151 remove XXX XXX from list of 'normative' specs in prose, 152 move some references from Other References to Normative References, 153 add RFC 1738, 1808, and 2141 to Other References (they are not 154 normative since we do not require the processor to enforce any 155 rules based on them), 156 add reference to 'Fielding draft' (Berners-Lee et al.), 157 move notation section to end of body, 158 drop URIchar non-terminal and use SkipLit instead, 159 lose stray reference to defunct nonterminal 'markupdecls', 160 move reference to Aho et al. into appendix (Tim's right), 161 add prose note saying that hash marks and fragment identifiers are 162 NOT part of the URI formally speaking, and are NOT legal in 163 system identifiers (processor 'may' signal an error). 164 Work through: 165 Tim Bray reacting to James Clark, 166 Tim Bray on his own, 167 Eve Maler, 168 169 NOT DONE YET: 170 change binary / text to unparsed / parsed. 171 handle James's suggestion about < in attriubte values 172 uppercase hex characters, 173 namechar list, 174 </sitem> 175 <sitem>1997-12-01 : JB : add some column-width parameters</sitem> 176 <sitem>1997-12-01 : CMSMcQ : begin round of changes to incorporate 177 recent WG decisions and other corrections: 178 binding sources of character encoding info (27 Aug / 3 Sept), 179 correct wording of Faust quotation (restore dropped line), 180 drop SDD from EncodingDecl, 181 change text at version number 1.0, 182 drop misleading (wrong!) sentence about ignorables and extenders, 183 modify definition of PCData to make bar on msc grammatical, 184 change grammar's handling of internal subset (drop non-terminal markupdecls), 185 change definition of includeSect to allow conditional sections, 186 add integral-declaration constraint on internal subset, 187 drop misleading / dangerous sentence about relationship of 188 entities with system storage objects, 189 change table body tag to htbody as per EM change to DTD, 190 add rule about space normalization in public identifiers, 191 add description of how to generate our name-space rules from 192 Unicode character database (needs further work!). 193 </sitem> 194 <sitem>1997-10-08 : TB : Removed %-constructs again, new rules 195 for PE appearance.</sitem> 196 <sitem>1997-10-01 : TB : Case-sensitive markup; cleaned up 197 element-type defs, lotsa little edits for style</sitem> 198 <sitem>1997-09-25 : TB : Change to elm's new DTD, with 199 substantial detail cleanup as a side-effect</sitem> 200 <sitem>1997-07-24 : CMSMcQ : correct error (lost *) in definition 201 of ignoreSectContents (thanks to Makoto Murata)</sitem> 202 <sitem>Allow all empty elements to have end-tags, consistent with 203 SGML TC (as per JJC).</sitem> 204 <sitem>1997-07-23 : CMSMcQ : pre-emptive strike on pending corrections: 205 introduce the term 'empty-element tag', note that all empty elements 206 may use it, and elements declared EMPTY must use it. 207 Add WFC requiring encoding decl to come first in an entity. 208 Redefine notations to point to PIs as well as binary entities. 209 Change autodetection table by removing bytes 3 and 4 from 210 examples with Byte Order Mark. 211 Add content model as a term and clarify that it applies to both 212 mixed and element content. 213 </sitem> 214 <sitem>1997-06-30 : CMSMcQ : change date, some cosmetic changes, 215 changes to productions for choice, seq, Mixed, NotationType, 216 Enumeration. Follow James Clark's suggestion and prohibit 217 conditional sections in internal subset. TO DO: simplify 218 production for ignored sections as a result, since we don't 219 need to worry about parsers which don't expand PErefs finding 220 a conditional section.</sitem> 221 <sitem>1997-06-29 : TB : various edits</sitem> 222 <sitem>1997-06-29 : CMSMcQ : further changes: 223 Suppress old FINAL EDIT comments and some dead material. 224 Revise occurrences of % in grammar to exploit Henry Thompson's pun, 225 especially markupdecl and attdef. 226 Remove RMD requirement relating to element content (?). 227 </sitem> 228 <sitem>1997-06-28 : CMSMcQ : Various changes for 1 July draft: 229 Add text for draconian error handling (introduce 230 the term Fatal Error). 231 RE deleta est (changing wording from 232 original announcement to restrict the requirement to validating 233 parsers). 234 Tag definition of validating processor and link to it. 235 Add colon as name character. 236 Change def of %operator. 237 Change standard definitions of lt, gt, amp. 238 Strip leading zeros from #x00nn forms.</sitem> 239 <sitem>1997-04-02 : CMSMcQ : final corrections of editorial errors 240 found in last night's proofreading. Reverse course once more on 241 well-formed: Webster's Second hyphenates it, and that's enough 242 for me.</sitem> 243 <sitem>1997-04-01 : CMSMcQ : corrections from JJC, EM, HT, and self</sitem> 244 <sitem>1997-03-31 : Tim Bray : many changes</sitem> 245 <sitem>1997-03-29 : CMSMcQ : some Henry Thompson (on entity handling), 246 some Charles Goldfarb, some ERB decisions (PE handling in miscellaneous 247 declarations. Changed Ident element to accept def attribute. 248 Allow normalization of Unicode characters. move def of systemliteral 249 into section on literals.</sitem> 250 <sitem>1997-03-28 : CMSMcQ : make as many corrections as possible, from 251 Terry Allen, Norbert Mikula, James Clark, Jon Bosak, Henry Thompson, 252 Paul Grosso, and self. Among other things: give in on "well formed" 253 (Terry is right), tentatively rename QuotedCData as AttValue 254 and Literal as EntityValue to be more informative, since attribute 255 values are the <emph>only</emph> place QuotedCData was used, and 256 vice versa for entity text and Literal. (I'd call it Entity Text, 257 but 8879 uses that name for both internal and external entities.)</sitem> 258 <sitem>1997-03-26 : CMSMcQ : resynch the two forks of this draft, reapply 259 my changes dated 03-20 and 03-21. Normalize old 'may not' to 'must not' 260 except in the one case where it meant 'may or may not'.</sitem> 261 <sitem>1997-03-21 : TB : massive changes on plane flight from Chicago 262 to Vancouver</sitem> 263 <sitem>1997-03-21 : CMSMcQ : correct as many reported errors as possible. 264 </sitem> 265 <sitem>1997-03-20 : CMSMcQ : correct typos listed in CMSMcQ hand copy of spec.</sitem> 266 <sitem>1997-03-20 : CMSMcQ : cosmetic changes preparatory to revision for 267 WWW conference April 1997: restore some of the internal entity 268 references (e.g. to docdate, etc.), change character xA0 to &nbsp; 269 and define nbsp as &#160;, and refill a lot of paragraphs for 270 legibility.</sitem> 271 <sitem>1996-11-12 : CMSMcQ : revise using Tim's edits: 272 Add list type of NUMBERED and change most lists either to 273 BULLETS or to NUMBERED. 274 Suppress QuotedNames, Names (not used). 275 Correct trivial-grammar doc type decl. 276 Rename 'marked section' as 'CDATA section' passim. 277 Also edits from James Clark: 278 Define the set of characters from which [^abc] subtracts. 279 Charref should use just [0-9] not Digit. 280 Location info needs cleaner treatment: remove? (ERB 281 question). 282 One example of a PI has wrong pic. 283 Clarify discussion of encoding names. 284 Encoding failure should lead to unspecified results; don't 285 prescribe error recovery. 286 Don't require exposure of entity boundaries. 287 Ignore white space in element content. 288 Reserve entity names of the form u-NNNN. 289 Clarify relative URLs. 290 And some of my own: 291 Correct productions for content model: model cannot 292 consist of a name, so "elements ::= cp" is no good. 293 </sitem> 294 <sitem>1996-11-11 : CMSMcQ : revise for style. 295 Add new rhs to entity declaration, for parameter entities.</sitem> 296 <sitem>1996-11-10 : CMSMcQ : revise for style. 297 Fix / complete section on names, characters. 298 Add sections on parameter entities, conditional sections. 299 Still to do: Add compatibility note on deterministic content models. 300 Finish stylistic revision.</sitem> 301 <sitem>1996-10-31 : TB : Add Entity Handling section</sitem> 302 <sitem>1996-10-30 : TB : Clean up term & termdef. Slip in 303 ERB decision re EMPTY.</sitem> 304 <sitem>1996-10-28 : TB : Change DTD. Implement some of Michael's 305 suggestions. Change comments back to //. Introduce language for 306 XML namespace reservation. Add section on white-space handling. 307 Lots more cleanup.</sitem> 308 <sitem>1996-10-24 : CMSMcQ : quick tweaks, implement some ERB 309 decisions. Characters are not integers. Comments are /* */ not //. 310 Add bibliographic refs to 10646, HyTime, Unicode. 311 Rename old Cdata as MsData since it's <emph>only</emph> seen 312 in marked sections. Call them attribute-value pairs not 313 name-value pairs, except once. Internal subset is optional, needs 314 '?'. Implied attributes should be signaled to the app, not 315 have values supplied by processor.</sitem> 316 <sitem>1996-10-16 : TB : track down & excise all DSD references; 317 introduce some EBNF for entity declarations.</sitem> 318 <sitem>1996-10-?? : TB : consistency check, fix up scraps so 319 they all parse, get formatter working, correct a few productions.</sitem> 320 <sitem>1996-10-10/11 : CMSMcQ : various maintenance, stylistic, and 321 organizational changes: 322 Replace a few literals with xmlpio and 323 pic entities, to make them consistent and ensure we can change pic 324 reliably when the ERB votes. 325 Drop paragraph on recognizers from notation section. 326 Add match, exact match to terminology. 327 Move old 2.2 XML Processors and Apps into intro. 328 Mention comments, PIs, and marked sections in discussion of 329 delimiter escaping. 330 Streamline discussion of doctype decl syntax. 331 Drop old section of 'PI syntax' for doctype decl, and add 332 section on partial-DTD summary PIs to end of Logical Structures 333 section. 334 Revise DSD syntax section to use Tim's subset-in-a-PI 335 mechanism.</sitem> 336 <sitem>1996-10-10 : TB : eliminate name recognizers (and more?)</sitem> 337 <sitem>1996-10-09 : CMSMcQ : revise for style, consistency through 2.3 338 (Characters)</sitem> 339 <sitem>1996-10-09 : CMSMcQ : re-unite everything for convenience, 340 at least temporarily, and revise quickly</sitem> 341 <sitem>1996-10-08 : TB : first major homogenization pass</sitem> 342 <sitem>1996-10-08 : TB : turn "current" attribute on div type into 343 CDATA</sitem> 344 <sitem>1996-10-02 : TB : remould into skeleton + entities</sitem> 345 <sitem>1996-09-30 : CMSMcQ : add a few more sections prior to exchange 346 with Tim.</sitem> 347 <sitem>1996-09-20 : CMSMcQ : finish transcribing notes.</sitem> 348 <sitem>1996-09-19 : CMSMcQ : begin transcribing notes for draft.</sitem> 349 <sitem>1996-09-13 : CMSMcQ : made outline from notes of 09-06, 350 do some housekeeping</sitem> 351 </slist> 352 </revisiondesc> 353 </header> 354 <body> 355 <div1 id="sec-intro"> 356 <head>Introduction</head> 357 <p>Extensible Markup Language, abbreviated XML, describes a class of 358 data objects called <termref def="dt-xml-doc">XML documents</termref> and 359 partially describes the behavior of 360 computer programs which process them. XML is an application profile or 361 restricted form of SGML, the Standard Generalized Markup 362 Language <bibref ref="ISO8879"/>. 363 By construction, XML documents 364 are conforming SGML documents. 365 </p> 366 <p>XML documents are made up of storage units called <termref def="dt-entity">entities</termref>, which contain either parsed 367 or unparsed data. 368 Parsed data is made up of <termref def="dt-character">characters</termref>, 369 some 370 of which form <termref def="dt-chardata">character data</termref>, 371 and some of which form <termref def="dt-markup">markup</termref>. 372 Markup encodes a description of the document's storage layout and 373 logical structure. XML provides a mechanism to impose constraints on 374 the storage layout and logical structure.</p> 375 <p><termdef id="dt-xml-proc" term="XML Processor">A software module 376 called an <term>XML processor</term> is used to read XML documents 377 and provide access to their content and structure.</termdef> <termdef id="dt-app" term="Application">It is assumed that an XML processor is 378 doing its work on behalf of another module, called the 379 <term>application</term>.</termdef> This specification describes the 380 required behavior of an XML processor in terms of how it must read XML 381 data and the information it must provide to the application.</p> 382 383 <div2 id="sec-origin-goals"> 384 <head>Origin and Goals</head> 385 <p>XML was developed by an XML Working Group (originally known as the 386 SGML Editorial Review Board) formed under the auspices of the World 387 Wide Web Consortium (W3C) in 1996. 388 It was chaired by Jon Bosak of Sun 389 Microsystems with the active participation of an XML Special 390 Interest Group (previously known as the SGML Working Group) also 391 organized by the W3C. The membership of the XML Working Group is given 392 in an appendix. Dan Connolly served as the WG's contact with the W3C. 393 </p> 394 <p>The design goals for XML are:<olist> 395 <item><p>XML shall be straightforwardly usable over the 396 Internet.</p></item> 397 <item><p>XML shall support a wide variety of applications.</p></item> 398 <item><p>XML shall be compatible with SGML.</p></item> 399 <item><p>It shall be easy to write programs which process XML 400 documents.</p></item> 401 <item><p>The number of optional features in XML is to be kept to the 402 absolute minimum, ideally zero.</p></item> 403 <item><p>XML documents should be human-legible and reasonably 404 clear.</p></item> 405 <item><p>The XML design should be prepared quickly.</p></item> 406 <item><p>The design of XML shall be formal and concise.</p></item> 407 <item><p>XML documents shall be easy to create.</p></item> 408 <item><p>Terseness in XML markup is of minimal importance.</p></item></olist> 409 </p> 410 <p>This specification, 411 together with associated standards 412 (Unicode and ISO/IEC 10646 for characters, 413 Internet RFC 1766 for language identification tags, 414 ISO 639 for language name codes, and 415 ISO 3166 for country name codes), 416 provides all the information necessary to understand 417 XML Version &XML.version; 418 and construct computer programs to process it.</p> 419 <p>This version of the XML specification 420 <!-- is for &doc.audience;.--> 421 &doc.distribution;.</p> 422 423 </div2> 424 425 426 427 428 <div2 id="sec-terminology"> 429 <head>Terminology</head> 430 431 <p>The terminology used to describe XML documents is defined in the body of 432 this specification. 433 The terms defined in the following list are used in building those 434 definitions and in describing the actions of an XML processor: 435 <glist> 436 <gitem> 437 <label>may</label> 438 <def><p><termdef id="dt-may" term="May">Conforming documents and XML 439 processors are permitted to but need not behave as 440 described.</termdef></p></def> 441 </gitem> 442 <gitem> 443 <label>must</label> 444 <def><p>Conforming documents and XML processors 445 are required to behave as described; otherwise they are in error. 446 <!-- do NOT change this! this is what defines a violation of 447 a 'must' clause as 'an error'. -MSM --> 448 </p></def> 449 </gitem> 450 <gitem> 451 <label>error</label> 452 <def><p><termdef id="dt-error" term="Error">A violation of the rules of this 453 specification; results are 454 undefined. Conforming software may detect and report an error and may 455 recover from it.</termdef></p></def> 456 </gitem> 457 <gitem> 458 <label>fatal error</label> 459 <def><p><termdef id="dt-fatal" term="Fatal Error">An error 460 which a conforming <termref def="dt-xml-proc">XML processor</termref> 461 must detect and report to the application. 462 After encountering a fatal error, the 463 processor may continue 464 processing the data to search for further errors and may report such 465 errors to the application. In order to support correction of errors, 466 the processor may make unprocessed data from the document (with 467 intermingled character data and markup) available to the application. 468 Once a fatal error is detected, however, the processor must not 469 continue normal processing (i.e., it must not 470 continue to pass character data and information about the document's 471 logical structure to the application in the normal way). 472 </termdef></p></def> 473 </gitem> 474 <gitem> 475 <label>at user option</label> 476 <def><p>Conforming software may or must (depending on the modal verb in the 477 sentence) behave as described; if it does, it must 478 provide users a means to enable or disable the behavior 479 described.</p></def> 480 </gitem> 481 <gitem> 482 <label>validity constraint</label> 483 <def><p>A rule which applies to all 484 <termref def="dt-valid">valid</termref> XML documents. 485 Violations of validity constraints are errors; they must, at user option, 486 be reported by 487 <termref def="dt-validating">validating XML processors</termref>.</p></def> 488 </gitem> 489 <gitem> 490 <label>well-formedness constraint</label> 491 <def><p>A rule which applies to all <termref def="dt-wellformed">well-formed</termref> XML documents. 492 Violations of well-formedness constraints are 493 <termref def="dt-fatal">fatal errors</termref>.</p></def> 494 </gitem> 495 496 <gitem> 497 <label>match</label> 498 <def><p><termdef id="dt-match" term="match">(Of strings or names:) 499 Two strings or names being compared must be identical. 500 Characters with multiple possible representations in ISO/IEC 10646 (e.g. 501 characters with 502 both precomposed and base+diacritic forms) match only if they have the 503 same representation in both strings. 504 At user option, processors may normalize such characters to 505 some canonical form. 506 No case folding is performed. 507 (Of strings and rules in the grammar:) 508 A string matches a grammatical production if it belongs to the 509 language generated by that production. 510 (Of content and content models:) 511 An element matches its declaration when it conforms 512 in the fashion described in the constraint 513 <specref ref="elementvalid"/>. 514 </termdef> 515 </p></def> 516 </gitem> 517 <gitem> 518 <label>for compatibility</label> 519 <def><p><termdef id="dt-compat" term="For Compatibility">A feature of 520 XML included solely to ensure that XML remains compatible with SGML. 521 </termdef></p></def> 522 </gitem> 523 <gitem> 524 <label>for interoperability</label> 525 <def><p><termdef id="dt-interop" term="For interoperability">A 526 non-binding recommendation included to increase the chances that XML 527 documents can be processed by the existing installed base of SGML 528 processors which predate the 529 &WebSGML;.</termdef></p></def> 530 </gitem> 531 </glist> 532 </p> 533 </div2> 534 535 536 </div1> 537 <!-- &Docs; --> 538 539 <div1 id="sec-documents"> 540 <head>Documents</head> 541 542 <p><termdef id="dt-xml-doc" term="XML Document"> 543 A data object is an 544 <term>XML document</term> if it is 545 <termref def="dt-wellformed">well-formed</termref>, as 546 defined in this specification. 547 A well-formed XML document may in addition be 548 <termref def="dt-valid">valid</termref> if it meets certain further 549 constraints.</termdef></p> 550 551 <p>Each XML document has both a logical and a physical structure. 552 Physically, the document is composed of units called <termref def="dt-entity">entities</termref>. An entity may <termref def="dt-entref">refer</termref> to other entities to cause their 553 inclusion in the document. A document begins in a "root" or <termref def="dt-docent">document entity</termref>. 554 Logically, the document is composed of declarations, elements, 555 comments, 556 character references, and 557 processing 558 instructions, all of which are indicated in the document by explicit 559 markup. 560 The logical and physical structures must nest properly, as described 561 in <specref ref="wf-entities"/>. 562 </p> 563 564 <div2 id="sec-well-formed"> 565 <head>Well-Formed XML Documents</head> 566 567 <p><termdef id="dt-wellformed" term="Well-Formed"> 568 A textual object is 569 a well-formed XML document if:</termdef> 570 <olist> 571 <item><p>Taken as a whole, it 572 matches the production labeled <nt def="NT-document">document</nt>.</p></item> 573 <item><p>It 574 meets all the well-formedness constraints given in this specification.</p> 575 </item> 576 <item><p>Each of the <termref def="dt-parsedent">parsed entities</termref> 577 which is referenced directly or indirectly within the document is 578 <titleref href="wf-entities">well-formed</titleref>.</p></item> 579 </olist></p> 580 <p> 581 <scrap lang="ebnf" id="document"> 582 <head>Document</head> 583 <prod id="NT-document"><lhs>document</lhs> 584 <rhs><nt def="NT-prolog">prolog</nt> 585 <nt def="NT-element">element</nt> 586 <nt def="NT-Misc">Misc</nt>*</rhs></prod> 587 </scrap> 588 </p> 589 <p>Matching the <nt def="NT-document">document</nt> production 590 implies that: 591 <olist> 592 <item><p>It contains one or more 593 <termref def="dt-element">elements</termref>.</p> 594 </item> 595 <!--* N.B. some readers (notably JC) find the following 596 paragraph awkward and redundant. I agree it's logically redundant: 597 it *says* it is summarizing the logical implications of 598 matching the grammar, and that means by definition it's 599 logically redundant. I don't think it's rhetorically 600 redundant or unnecessary, though, so I'm keeping it. It 601 could however use some recasting when the editors are feeling 602 stronger. -MSM *--> 603 <item><p><termdef id="dt-root" term="Root Element">There is exactly 604 one element, called the <term>root</term>, or document element, no 605 part of which appears in the <termref def="dt-content">content</termref> of any other element.</termdef> 606 For all other elements, if the start-tag is in the content of another 607 element, the end-tag is in the content of the same element. More 608 simply stated, the elements, delimited by start- and end-tags, nest 609 properly within each other. 610 </p></item> 611 </olist> 612 </p> 613 <p><termdef id="dt-parentchild" term="Parent/Child">As a consequence 614 of this, 615 for each non-root element 616 <code>C</code> in the document, there is one other element <code>P</code> 617 in the document such that 618 <code>C</code> is in the content of <code>P</code>, but is not in 619 the content of any other element that is in the content of 620 <code>P</code>. 621 <code>P</code> is referred to as the 622 <term>parent</term> of <code>C</code>, and <code>C</code> as a 623 <term>child</term> of <code>P</code>.</termdef></p></div2> 624 625 <div2 id="charsets"> 626 <head>Characters</head> 627 628 <p><termdef id="dt-text" term="Text">A parsed entity contains 629 <term>text</term>, a sequence of 630 <termref def="dt-character">characters</termref>, 631 which may represent markup or character data.</termdef> 632 <termdef id="dt-character" term="Character">A <term>character</term> 633 is an atomic unit of text as specified by 634 ISO/IEC 10646 <bibref ref="ISO10646"/>. 635 Legal characters are tab, carriage return, line feed, and the legal 636 graphic characters of Unicode and ISO/IEC 10646. 637 The use of "compatibility characters", as defined in section 6.8 638 of <bibref ref="Unicode"/>, is discouraged. 639 </termdef> 640 <scrap lang="ebnf" id="char32"> 641 <head>Character Range</head> 642 <prodgroup pcw2="4" pcw4="17.5" pcw5="11"> 643 <prod id="NT-Char"><lhs>Char</lhs> 644 <rhs>#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] 645 | [#x10000-#x10FFFF]</rhs> 646 <com>any Unicode character, excluding the 647 surrogate blocks, FFFE, and FFFF.</com> </prod> 648 </prodgroup> 649 </scrap> 650 </p> 651 652 <p>The mechanism for encoding character code points into bit patterns may 653 vary from entity to entity. All XML processors must accept the UTF-8 654 and UTF-16 encodings of 10646; the mechanisms for signaling which of 655 the two is in use, or for bringing other encodings into play, are 656 discussed later, in <specref ref="charencoding"/>. 657 </p> 658 <!-- 659 <p>Regardless of the specific encoding used, any character in the ISO/IEC 660 10646 character set may be referred to by the decimal or hexadecimal 661 equivalent of its 662 UCS-4 code value. 663 </p>--> 664 </div2> 665 666 <div2 id="sec-common-syn"> 667 <head>Common Syntactic Constructs</head> 668 669 <p>This section defines some symbols used widely in the grammar.</p> 670 <p><nt def="NT-S">S</nt> (white space) consists of one or more space (#x20) 671 characters, carriage returns, line feeds, or tabs. 672 673 <scrap lang="ebnf" id="white"> 674 <head>White Space</head> 675 <prodgroup pcw2="4" pcw4="17.5" pcw5="11"> 676 <prod id="NT-S"><lhs>S</lhs> 677 <rhs>(#x20 | #x9 | #xD | #xA)+</rhs> 678 </prod> 679 </prodgroup> 680 </scrap></p> 681 <p>Characters are classified for convenience as letters, digits, or other 682 characters. Letters consist of an alphabetic or syllabic 683 base character possibly 684 followed by one or more combining characters, or of an ideographic 685 character. 686 Full definitions of the specific characters in each class 687 are given in <specref ref="CharClasses"/>.</p> 688 <p><termdef id="dt-name" term="Name">A <term>Name</term> is a token 689 beginning with a letter or one of a few punctuation characters, and continuing 690 with letters, digits, hyphens, underscores, colons, or full stops, together 691 known as name characters.</termdef> 692 Names beginning with the string "<code>xml</code>", or any string 693 which would match <code>(('X'|'x') ('M'|'m') ('L'|'l'))</code>, are 694 reserved for standardization in this or future versions of this 695 specification. 696 </p> 697 <note> 698 <p>The colon character within XML names is reserved for experimentation with 699 name spaces. 700 Its meaning is expected to be 701 standardized at some future point, at which point those documents 702 using the colon for experimental purposes may need to be updated. 703 (There is no guarantee that any name-space mechanism 704 adopted for XML will in fact use the colon as a name-space delimiter.) 705 In practice, this means that authors should not use the colon in XML 706 names except as part of name-space experiments, but that XML processors 707 should accept the colon as a name character.</p> 708 </note> 709 <p>An 710 <nt def="NT-Nmtoken">Nmtoken</nt> (name token) is any mixture of 711 name characters. 712 <scrap lang="ebnf"> 713 <head>Names and Tokens</head> 714 <prod id="NT-NameChar"><lhs>NameChar</lhs> 715 <rhs><nt def="NT-Letter">Letter</nt> 716 | <nt def="NT-Digit">Digit</nt> 717 | '.' | '-' | '_' | ':' 718 | <nt def="NT-CombiningChar">CombiningChar</nt> 719 | <nt def="NT-Extender">Extender</nt></rhs> 720 </prod> 721 <prod id="NT-Name"><lhs>Name</lhs> 722 <rhs>(<nt def="NT-Letter">Letter</nt> | '_' | ':') 723 (<nt def="NT-NameChar">NameChar</nt>)*</rhs></prod> 724 <prod id="NT-Names"><lhs>Names</lhs> 725 <rhs><nt def="NT-Name">Name</nt> 726 (<nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt>)*</rhs></prod> 727 <prod id="NT-Nmtoken"><lhs>Nmtoken</lhs> 728 <rhs>(<nt def="NT-NameChar">NameChar</nt>)+</rhs></prod> 729 <prod id="NT-Nmtokens"><lhs>Nmtokens</lhs> 730 <rhs><nt def="NT-Nmtoken">Nmtoken</nt> (<nt def="NT-S">S</nt> <nt def="NT-Nmtoken">Nmtoken</nt>)*</rhs></prod> 731 </scrap> 732 </p> 733 <p>Literal data is any quoted string not containing 734 the quotation mark used as a delimiter for that string. 735 Literals are used 736 for specifying the content of internal entities 737 (<nt def="NT-EntityValue">EntityValue</nt>), 738 the values of attributes (<nt def="NT-AttValue">AttValue</nt>), 739 and external identifiers 740 (<nt def="NT-SystemLiteral">SystemLiteral</nt>). 741 Note that a <nt def="NT-SystemLiteral">SystemLiteral</nt> 742 can be parsed without scanning for markup. 743 <scrap lang="ebnf"> 744 <head>Literals</head> 745 <prod id="NT-EntityValue"><lhs>EntityValue</lhs> 746 <rhs>'"' 747 ([^%&"] 748 | <nt def="NT-PEReference">PEReference</nt> 749 | <nt def="NT-Reference">Reference</nt>)* 750 '"' 751 </rhs> 752 <rhs>| 753 "'" 754 ([^%&'] 755 | <nt def="NT-PEReference">PEReference</nt> 756 | <nt def="NT-Reference">Reference</nt>)* 757 "'"</rhs> 758 </prod> 759 <prod id="NT-AttValue"><lhs>AttValue</lhs> 760 <rhs>'"' 761 ([^<&"] 762 | <nt def="NT-Reference">Reference</nt>)* 763 '"' 764 </rhs> 765 <rhs>| 766 "'" 767 ([^<&'] 768 | <nt def="NT-Reference">Reference</nt>)* 769 "'"</rhs> 770 </prod> 771 <prod id="NT-SystemLiteral"><lhs>SystemLiteral</lhs> 772 <rhs>('"' [^"]* '"') | ("'" [^']* "'") 773 </rhs> 774 </prod> 775 <prod id="NT-PubidLiteral"><lhs>PubidLiteral</lhs> 776 <rhs>'"' <nt def="NT-PubidChar">PubidChar</nt>* 777 '"' 778 | "'" (<nt def="NT-PubidChar">PubidChar</nt> - "'")* "'"</rhs> 779 </prod> 780 <prod id="NT-PubidChar"><lhs>PubidChar</lhs> 781 <rhs>#x20 | #xD | #xA 782 | [a-zA-Z0-9] 783 | [-'()+,./:=?;!*#@$_%]</rhs> 784 </prod> 785 </scrap> 786 </p> 787 788 </div2> 789 790 <div2 id="syntax"> 791 <head>Character Data and Markup</head> 792 793 <p><termref def="dt-text">Text</termref> consists of intermingled 794 <termref def="dt-chardata">character 795 data</termref> and markup. 796 <termdef id="dt-markup" term="Markup"><term>Markup</term> takes the form of 797 <termref def="dt-stag">start-tags</termref>, 798 <termref def="dt-etag">end-tags</termref>, 799 <termref def="dt-empty">empty-element tags</termref>, 800 <termref def="dt-entref">entity references</termref>, 801 <termref def="dt-charref">character references</termref>, 802 <termref def="dt-comment">comments</termref>, 803 <termref def="dt-cdsection">CDATA section</termref> delimiters, 804 <termref def="dt-doctype">document type declarations</termref>, and 805 <termref def="dt-pi">processing instructions</termref>. 806 </termdef> 807 </p> 808 <p><termdef id="dt-chardata" term="Character Data">All text that is not markup 809 constitutes the <term>character data</term> of 810 the document.</termdef></p> 811 <p>The ampersand character (&) and the left angle bracket (<) 812 may appear in their literal form <emph>only</emph> when used as markup 813 delimiters, or within a <termref def="dt-comment">comment</termref>, a 814 <termref def="dt-pi">processing instruction</termref>, 815 or a <termref def="dt-cdsection">CDATA section</termref>. 816 817 They are also legal within the <termref def="dt-litentval">literal entity 818 value</termref> of an internal entity declaration; see 819 <specref ref="wf-entities"/>. 820 <!-- FINAL EDIT: restore internal entity decl or leave it out. --> 821 If they are needed elsewhere, 822 they must be <termref def="dt-escape">escaped</termref> 823 using either <termref def="dt-charref">numeric character references</termref> 824 or the strings 825 "<code>&amp;</code>" and "<code>&lt;</code>" respectively. 826 The right angle 827 bracket (>) may be represented using the string 828 "<code>&gt;</code>", and must, <termref def="dt-compat">for 829 compatibility</termref>, 830 be escaped using 831 "<code>&gt;</code>" or a character reference 832 when it appears in the string 833 "<code>]]></code>" 834 in content, 835 when that string is not marking the end of 836 a <termref def="dt-cdsection">CDATA section</termref>. 837 </p> 838 <p> 839 In the content of elements, character data 840 is any string of characters which does 841 not contain the start-delimiter of any markup. 842 In a CDATA section, character data 843 is any string of characters not including the CDATA-section-close 844 delimiter, "<code>]]></code>".</p> 845 <p> 846 To allow attribute values to contain both single and double quotes, the 847 apostrophe or single-quote character (') may be represented as 848 "<code>&apos;</code>", and the double-quote character (") as 849 "<code>&quot;</code>". 850 <scrap lang="ebnf"> 851 <head>Character Data</head> 852 <prod id="NT-CharData"> 853 <lhs>CharData</lhs> 854 <rhs>[^<&]* - ([^<&]* ']]>' [^<&]*)</rhs> 855 </prod> 856 </scrap> 857 </p> 858 </div2> 859 860 <div2 id="sec-comments"> 861 <head>Comments</head> 862 863 <p><termdef id="dt-comment" term="Comment"><term>Comments</term> may 864 appear anywhere in a document outside other 865 <termref def="dt-markup">markup</termref>; in addition, 866 they may appear within the document type declaration 867 at places allowed by the grammar. 868 They are not part of the document's <termref def="dt-chardata">character 869 data</termref>; an XML 870 processor may, but need not, make it possible for an application to 871 retrieve the text of comments. 872 <termref def="dt-compat">For compatibility</termref>, the string 873 "<code>--</code>" (double-hyphen) must not occur within 874 comments. 875 <scrap lang="ebnf"> 876 <head>Comments</head> 877 <prod id="NT-Comment"><lhs>Comment</lhs> 878 <rhs>'<!--' 879 ((<nt def="NT-Char">Char</nt> - '-') 880 | ('-' (<nt def="NT-Char">Char</nt> - '-')))* 881 '-->'</rhs> 882 </prod> 883 </scrap> 884 </termdef></p> 885 <p>An example of a comment: 886 <eg><!&como; declarations for <head> & <body> &comc;></eg> 887 </p> 888 </div2> 889 890 <div2 id="sec-pi"> 891 <head>Processing Instructions</head> 892 893 <p><termdef id="dt-pi" term="Processing instruction"><term>Processing 894 instructions</term> (PIs) allow documents to contain instructions 895 for applications. 896 897 <scrap lang="ebnf"> 898 <head>Processing Instructions</head> 899 <prod id="NT-PI"><lhs>PI</lhs> 900 <rhs>'<?' <nt def="NT-PITarget">PITarget</nt> 901 (<nt def="NT-S">S</nt> 902 (<nt def="NT-Char">Char</nt>* - 903 (<nt def="NT-Char">Char</nt>* &pic; <nt def="NT-Char">Char</nt>*)))? 904 &pic;</rhs></prod> 905 <prod id="NT-PITarget"><lhs>PITarget</lhs> 906 <rhs><nt def="NT-Name">Name</nt> - 907 (('X' | 'x') ('M' | 'm') ('L' | 'l'))</rhs> 908 </prod> 909 </scrap></termdef> 910 PIs are not part of the document's <termref def="dt-chardata">character 911 data</termref>, but must be passed through to the application. The 912 PI begins with a target (<nt def="NT-PITarget">PITarget</nt>) used 913 to identify the application to which the instruction is directed. 914 The target names "<code>XML</code>", "<code>xml</code>", and so on are 915 reserved for standardization in this or future versions of this 916 specification. 917 The 918 XML <termref def="dt-notation">Notation</termref> mechanism 919 may be used for 920 formal declaration of PI targets. 921 </p> 922 </div2> 923 924 <div2 id="sec-cdata-sect"> 925 <head>CDATA Sections</head> 926 927 <p><termdef id="dt-cdsection" term="CDATA Section"><term>CDATA sections</term> 928 may occur 929 anywhere character data may occur; they are 930 used to escape blocks of text containing characters which would 931 otherwise be recognized as markup. CDATA sections begin with the 932 string "<code><![CDATA[</code>" and end with the string 933 "<code>]]></code>": 934 <scrap lang="ebnf"> 935 <head>CDATA Sections</head> 936 <prod id="NT-CDSect"><lhs>CDSect</lhs> 937 <rhs><nt def="NT-CDStart">CDStart</nt> 938 <nt def="NT-CData">CData</nt> 939 <nt def="NT-CDEnd">CDEnd</nt></rhs></prod> 940 <prod id="NT-CDStart"><lhs>CDStart</lhs> 941 <rhs>'<![CDATA['</rhs> 942 </prod> 943 <prod id="NT-CData"><lhs>CData</lhs> 944 <rhs>(<nt def="NT-Char">Char</nt>* - 945 (<nt def="NT-Char">Char</nt>* ']]>' <nt def="NT-Char">Char</nt>*)) 946 </rhs> 947 </prod> 948 <prod id="NT-CDEnd"><lhs>CDEnd</lhs> 949 <rhs>']]>'</rhs> 950 </prod> 951 </scrap> 952 953 Within a CDATA section, only the <nt def="NT-CDEnd">CDEnd</nt> string is 954 recognized as markup, so that left angle brackets and ampersands may occur in 955 their literal form; they need not (and cannot) be escaped using 956 "<code>&lt;</code>" and "<code>&amp;</code>". CDATA sections 957 cannot nest.</termdef> 958 </p> 959 960 <p>An example of a CDATA section, in which "<code><greeting></code>" and 961 "<code></greeting></code>" 962 are recognized as <termref def="dt-chardata">character data</termref>, not 963 <termref def="dt-markup">markup</termref>: 964 <eg><![CDATA[<greeting>Hello, world!</greeting>]]></eg> 965 </p> 966 </div2> 967 968 <div2 id="sec-prolog-dtd"> 969 <head>Prolog and Document Type Declaration</head> 970 971 <p><termdef id="dt-xmldecl" term="XML Declaration">XML documents 972 may, and should, 973 begin with an <term>XML declaration</term> which specifies 974 the version of 975 XML being used.</termdef> 976 For example, the following is a complete XML document, <termref def="dt-wellformed">well-formed</termref> but not 977 <termref def="dt-valid">valid</termref>: 978 <eg><![CDATA[<?xml version="1.0"?> 979 <greeting>Hello, world!</greeting> 980 ]]></eg> 981 and so is this: 982 <eg><![CDATA[<greeting>Hello, world!</greeting> 983 ]]></eg> 984 </p> 985 986 <p>The version number "<code>1.0</code>" should be used to indicate 987 conformance to this version of this specification; it is an error 988 for a document to use the value "<code>1.0</code>" 989 if it does not conform to this version of this specification. 990 It is the intent 991 of the XML working group to give later versions of this specification 992 numbers other than "<code>1.0</code>", but this intent does not 993 indicate a 994 commitment to produce any future versions of XML, nor if any are produced, to 995 use any particular numbering scheme. 996 Since future versions are not ruled out, this construct is provided 997 as a means to allow the possibility of automatic version recognition, should 998 it become necessary. 999 Processors may signal an error if they receive documents labeled with 1000 versions they do not support. 1001 </p> 1002 <p>The function of the markup in an XML document is to describe its 1003 storage and logical structure and to associate attribute-value pairs 1004 with its logical structures. XML provides a mechanism, the <termref def="dt-doctype">document type declaration</termref>, to define 1005 constraints on the logical structure and to support the use of 1006 predefined storage units. 1007 1008 <termdef id="dt-valid" term="Validity">An XML document is 1009 <term>valid</term> if it has an associated document type 1010 declaration and if the document 1011 complies with the constraints expressed in it.</termdef></p> 1012 <p>The document type declaration must appear before 1013 the first <termref def="dt-element">element</termref> in the document. 1014 <scrap lang="ebnf" id="xmldoc"> 1015 <head>Prolog</head> 1016 <prodgroup pcw2="6" pcw4="17.5" pcw5="9"> 1017 <prod id="NT-prolog"><lhs>prolog</lhs> 1018 <rhs><nt def="NT-XMLDecl">XMLDecl</nt>? 1019 <nt def="NT-Misc">Misc</nt>* 1020 (<nt def="NT-doctypedecl">doctypedecl</nt> 1021 <nt def="NT-Misc">Misc</nt>*)?</rhs></prod> 1022 <prod id="NT-XMLDecl"><lhs>XMLDecl</lhs> 1023 <rhs>&xmlpio; 1024 <nt def="NT-VersionInfo">VersionInfo</nt> 1025 <nt def="NT-EncodingDecl">EncodingDecl</nt>? 1026 <nt def="NT-SDDecl">SDDecl</nt>? 1027 <nt def="NT-S">S</nt>? 1028 &pic;</rhs> 1029 </prod> 1030 <prod id="NT-VersionInfo"><lhs>VersionInfo</lhs> 1031 <rhs><nt def="NT-S">S</nt> 'version' <nt def="NT-Eq">Eq</nt> 1032 (' <nt def="NT-VersionNum">VersionNum</nt> ' 1033 | " <nt def="NT-VersionNum">VersionNum</nt> ")</rhs> 1034 </prod> 1035 <prod id="NT-Eq"><lhs>Eq</lhs> 1036 <rhs><nt def="NT-S">S</nt>? '=' <nt def="NT-S">S</nt>?</rhs></prod> 1037 <prod id="NT-VersionNum"> 1038 <lhs>VersionNum</lhs> 1039 <rhs>([a-zA-Z0-9_.:] | '-')+</rhs> 1040 </prod> 1041 <prod id="NT-Misc"><lhs>Misc</lhs> 1042 <rhs><nt def="NT-Comment">Comment</nt> | <nt def="NT-PI">PI</nt> | 1043 <nt def="NT-S">S</nt></rhs></prod> 1044 </prodgroup> 1045 </scrap></p> 1046 1047 <p><termdef id="dt-doctype" term="Document Type Declaration">The XML 1048 <term>document type declaration</term> 1049 contains or points to 1050 <termref def="dt-markupdecl">markup declarations</termref> 1051 that provide a grammar for a 1052 class of documents. 1053 This grammar is known as a document type definition, 1054 or <term>DTD</term>. 1055 The document type declaration can point to an external subset (a 1056 special kind of 1057 <termref def="dt-extent">external entity</termref>) containing markup 1058 declarations, or can 1059 contain the markup declarations directly in an internal subset, or can do 1060 both. 1061 The DTD for a document consists of both subsets taken 1062 together.</termdef> 1063 </p> 1064 <p><termdef id="dt-markupdecl" term="markup declaration"> 1065 A <term>markup declaration</term> is 1066 an <termref def="dt-eldecl">element type declaration</termref>, 1067 an <termref def="dt-attdecl">attribute-list declaration</termref>, 1068 an <termref def="dt-entdecl">entity declaration</termref>, or 1069 a <termref def="dt-notdecl">notation declaration</termref>. 1070 </termdef> 1071 These declarations may be contained in whole or in part 1072 within <termref def="dt-PE">parameter entities</termref>, 1073 as described in the well-formedness and validity constraints below. 1074 For fuller information, see 1075 <specref ref="sec-physical-struct"/>.</p> 1076 <scrap lang="ebnf" id="dtd"> 1077 <head>Document Type Definition</head> 1078 <prodgroup pcw2="6" pcw4="17.5" pcw5="9"> 1079 <prod id="NT-doctypedecl"><lhs>doctypedecl</lhs> 1080 <rhs>'<!DOCTYPE' <nt def="NT-S">S</nt> 1081 <nt def="NT-Name">Name</nt> (<nt def="NT-S">S</nt> 1082 <nt def="NT-ExternalID">ExternalID</nt>)? 1083 <nt def="NT-S">S</nt>? ('[' 1084 (<nt def="NT-markupdecl">markupdecl</nt> 1085 | <nt def="NT-PEReference">PEReference</nt> 1086 | <nt def="NT-S">S</nt>)* 1087 ']' 1088 <nt def="NT-S">S</nt>?)? '>'</rhs> 1089 <vc def="vc-roottype"/> 1090 </prod> 1091 <prod id="NT-markupdecl"><lhs>markupdecl</lhs> 1092 <rhs><nt def="NT-elementdecl">elementdecl</nt> 1093 | <nt def="NT-AttlistDecl">AttlistDecl</nt> 1094 | <nt def="NT-EntityDecl">EntityDecl</nt> 1095 | <nt def="NT-NotationDecl">NotationDecl</nt> 1096 | <nt def="NT-PI">PI</nt> 1097 | <nt def="NT-Comment">Comment</nt> 1098 </rhs> 1099 <vc def="vc-PEinMarkupDecl"/> 1100 <wfc def="wfc-PEinInternalSubset"/> 1101 </prod> 1102 1103 </prodgroup> 1104 </scrap> 1105 1106 <p>The markup declarations may be made up in whole or in part of 1107 the <termref def="dt-repltext">replacement text</termref> of 1108 <termref def="dt-PE">parameter entities</termref>. 1109 The productions later in this specification for 1110 individual nonterminals (<nt def="NT-elementdecl">elementdecl</nt>, 1111 <nt def="NT-AttlistDecl">AttlistDecl</nt>, and so on) describe 1112 the declarations <emph>after</emph> all the parameter entities have been 1113 <termref def="dt-include">included</termref>.</p> 1114 1115 <vcnote id="vc-roottype"> 1116 <head>Root Element Type</head> 1117 <p> 1118 The <nt def="NT-Name">Name</nt> in the document type declaration must 1119 match the element type of the <termref def="dt-root">root element</termref>. 1120 </p> 1121 </vcnote> 1122 1123 <vcnote id="vc-PEinMarkupDecl"> 1124 <head>Proper Declaration/PE Nesting</head> 1125 <p>Parameter-entity 1126 <termref def="dt-repltext">replacement text</termref> must be properly nested 1127 with markup declarations. 1128 That is to say, if either the first character 1129 or the last character of a markup 1130 declaration (<nt def="NT-markupdecl">markupdecl</nt> above) 1131 is contained in the replacement text for a 1132 <termref def="dt-PERef">parameter-entity reference</termref>, 1133 both must be contained in the same replacement text.</p> 1134 </vcnote> 1135 <wfcnote id="wfc-PEinInternalSubset"> 1136 <head>PEs in Internal Subset</head> 1137 <p>In the internal DTD subset, 1138 <termref def="dt-PERef">parameter-entity references</termref> 1139 can occur only where markup declarations can occur, not 1140 within markup declarations. (This does not apply to 1141 references that occur in 1142 external parameter entities or to the external subset.) 1143 </p> 1144 </wfcnote> 1145 <p> 1146 Like the internal subset, the external subset and 1147 any external parameter entities referred to in the DTD 1148 must consist of a series of complete markup declarations of the types 1149 allowed by the non-terminal symbol 1150 <nt def="NT-markupdecl">markupdecl</nt>, interspersed with white space 1151 or <termref def="dt-PERef">parameter-entity references</termref>. 1152 However, portions of the contents 1153 of the 1154 external subset or of external parameter entities may conditionally be ignored 1155 by using 1156 the <termref def="dt-cond-section">conditional section</termref> 1157 construct; this is not allowed in the internal subset. 1158 1159 <scrap id="ext-Subset"> 1160 <head>External Subset</head> 1161 <prodgroup pcw2="6" pcw4="17.5" pcw5="9"> 1162 <prod id="NT-extSubset"><lhs>extSubset</lhs> 1163 <rhs><nt def="NT-TextDecl">TextDecl</nt>? 1164 <nt def="NT-extSubsetDecl">extSubsetDecl</nt></rhs></prod> 1165 <prod id="NT-extSubsetDecl"><lhs>extSubsetDecl</lhs> 1166 <rhs>( 1167 <nt def="NT-markupdecl">markupdecl</nt> 1168 | <nt def="NT-conditionalSect">conditionalSect</nt> 1169 | <nt def="NT-PEReference">PEReference</nt> 1170 | <nt def="NT-S">S</nt> 1171 )*</rhs> 1172 </prod> 1173 </prodgroup> 1174 </scrap></p> 1175 <p>The external subset and external parameter entities also differ 1176 from the internal subset in that in them, 1177 <termref def="dt-PERef">parameter-entity references</termref> 1178 are permitted <emph>within</emph> markup declarations, 1179 not only <emph>between</emph> markup declarations.</p> 1180 <p>An example of an XML document with a document type declaration: 1181 <eg><![CDATA[<?xml version="1.0"?> 1182 <!DOCTYPE greeting SYSTEM "hello.dtd"> 1183 <greeting>Hello, world!</greeting> 1184 ]]></eg> 1185 The <termref def="dt-sysid">system identifier</termref> 1186 "<code>hello.dtd</code>" gives the URI of a DTD for the document.</p> 1187 <p>The declarations can also be given locally, as in this 1188 example: 1189 <eg><![CDATA[<?xml version="1.0" encoding="UTF-8" ?> 1190 <!DOCTYPE greeting [ 1191 <!ELEMENT greeting (#PCDATA)> 1192 ]> 1193 <greeting>Hello, world!</greeting> 1194 ]]></eg> 1195 If both the external and internal subsets are used, the 1196 internal subset is considered to occur before the external subset. 1197 <!-- 'is considered to'? boo. whazzat mean? --> 1198 This has the effect that entity and attribute-list declarations in the 1199 internal subset take precedence over those in the external subset. 1200 </p> 1201 </div2> 1202 1203 <div2 id="sec-rmd"> 1204 <head>Standalone Document Declaration</head> 1205 <p>Markup declarations can affect the content of the document, 1206 as passed from an <termref def="dt-xml-proc">XML processor</termref> 1207 to an application; examples are attribute defaults and entity 1208 declarations. 1209 The standalone document declaration, 1210 which may appear as a component of the XML declaration, signals 1211 whether or not there are such declarations which appear external to 1212 the <termref def="dt-docent">document entity</termref>. 1213 <scrap lang="ebnf" id="fulldtd"> 1214 <head>Standalone Document Declaration</head> 1215 <prodgroup pcw2="4" pcw4="19.5" pcw5="9"> 1216 <prod id="NT-SDDecl"><lhs>SDDecl</lhs> 1217 <rhs> 1218 <nt def="NT-S">S</nt> 1219 'standalone' <nt def="NT-Eq">Eq</nt> 1220 (("'" ('yes' | 'no') "'") | ('"' ('yes' | 'no') '"')) 1221 </rhs> 1222 <vc def="vc-check-rmd"/></prod> 1223 </prodgroup> 1224 </scrap></p> 1225 <p> 1226 In a standalone document declaration, the value "<code>yes</code>" indicates 1227 that there 1228 are no markup declarations external to the <termref def="dt-docent">document 1229 entity</termref> (either in the DTD external subset, or in an 1230 external parameter entity referenced from the internal subset) 1231 which affect the information passed from the XML processor to 1232 the application. 1233 The value "<code>no</code>" indicates that there are or may be such 1234 external markup declarations. 1235 Note that the standalone document declaration only 1236 denotes the presence of external <emph>declarations</emph>; the presence, in a 1237 document, of 1238 references to external <emph>entities</emph>, when those entities are 1239 internally declared, 1240 does not change its standalone status.</p> 1241 <p>If there are no external markup declarations, the standalone document 1242 declaration has no meaning. 1243 If there are external markup declarations but there is no standalone 1244 document declaration, the value "<code>no</code>" is assumed.</p> 1245 <p>Any XML document for which <code>standalone="no"</code> holds can 1246 be converted algorithmically to a standalone document, 1247 which may be desirable for some network delivery applications.</p> 1248 <vcnote id="vc-check-rmd"> 1249 <head>Standalone Document Declaration</head> 1250 <p>The standalone document declaration must have 1251 the value "<code>no</code>" if any external markup declarations 1252 contain declarations of:</p><ulist> 1253 <item><p>attributes with <termref def="dt-default">default</termref> values, if 1254 elements to which 1255 these attributes apply appear in the document without 1256 specifications of values for these attributes, or</p></item> 1257 <item><p>entities (other than &magicents;), 1258 if <termref def="dt-entref">references</termref> to those 1259 entities appear in the document, or</p> 1260 </item> 1261 <item><p>attributes with values subject to 1262 <titleref href="AVNormalize">normalization</titleref>, where the 1263 attribute appears in the document with a value which will 1264 change as a result of normalization, or</p> 1265 </item> 1266 <item> 1267 <p>element types with <termref def="dt-elemcontent">element content</termref>, 1268 if white space occurs 1269 directly within any instance of those types. 1270 </p></item> 1271 </ulist> 1272 1273 </vcnote> 1274 <p>An example XML declaration with a standalone document declaration:<eg><?xml version="&XML.version;" standalone='yes'?></eg></p> 1275 </div2> 1276 <div2 id="sec-white-space"> 1277 <head>White Space Handling</head> 1278 1279 <p>In editing XML documents, it is often convenient to use "white space" 1280 (spaces, tabs, and blank lines, denoted by the nonterminal 1281 <nt def="NT-S">S</nt> in this specification) to 1282 set apart the markup for greater readability. Such white space is typically 1283 not intended for inclusion in the delivered version of the document. 1284 On the other hand, "significant" white space that should be preserved in the 1285 delivered version is common, for example in poetry and 1286 source code.</p> 1287 <p>An <termref def="dt-xml-proc">XML processor</termref> 1288 must always pass all characters in a document that are not 1289 markup through to the application. A <termref def="dt-validating"> 1290 validating XML processor</termref> must also inform the application 1291 which of these characters constitute white space appearing 1292 in <termref def="dt-elemcontent">element content</termref>. 1293 </p> 1294 <p>A special <termref def="dt-attr">attribute</termref> 1295 named <kw>xml:space</kw> may be attached to an element 1296 to signal an intention that in that element, 1297 white space should be preserved by applications. 1298 In valid documents, this attribute, like any other, must be 1299 <termref def="dt-attdecl">declared</termref> if it is used. 1300 When declared, it must be given as an 1301 <termref def="dt-enumerated">enumerated type</termref> whose only 1302 possible values are "<code>default</code>" and "<code>preserve</code>". 1303 For example:<eg><![CDATA[ <!ATTLIST poem xml:space (default|preserve) 'preserve'>]]></eg></p> 1304 <p>The value "<code>default</code>" signals that applications' 1305 default white-space processing modes are acceptable for this element; the 1306 value "<code>preserve</code>" indicates the intent that applications preserve 1307 all the white space. 1308 This declared intent is considered to apply to all elements within the content 1309 of the element where it is specified, unless overriden with another instance 1310 of the <kw>xml:space</kw> attribute. 1311 </p> 1312 <p>The <termref def="dt-root">root element</termref> of any document 1313 is considered to have signaled no intentions as regards application space 1314 handling, unless it provides a value for 1315 this attribute or the attribute is declared with a default value. 1316 </p> 1317 1318 </div2> 1319 <div2 id="sec-line-ends"> 1320 <head>End-of-Line Handling</head> 1321 <p>XML <termref def="dt-parsedent">parsed entities</termref> are often stored in 1322 computer files which, for editing convenience, are organized into lines. 1323 These lines are typically separated by some combination of the characters 1324 carriage-return (#xD) and line-feed (#xA).</p> 1325 <p>To simplify the tasks of <termref def="dt-app">applications</termref>, 1326 wherever an external parsed entity or the literal entity value 1327 of an internal parsed entity contains either the literal 1328 two-character sequence "#xD#xA" or a standalone literal 1329 #xD, an <termref def="dt-xml-proc">XML processor</termref> must 1330 pass to the application the single character #xA. 1331 (This behavior can 1332 conveniently be produced by normalizing all 1333 line breaks to #xA on input, before parsing.) 1334 </p> 1335 </div2> 1336 <div2 id="sec-lang-tag"> 1337 <head>Language Identification</head> 1338 <p>In document processing, it is often useful to 1339 identify the natural or formal language 1340 in which the content is 1341 written. 1342 A special <termref def="dt-attr">attribute</termref> named 1343 <kw>xml:lang</kw> may be inserted in 1344 documents to specify the 1345 language used in the contents and attribute values 1346 of any element in an XML document. 1347 In valid documents, this attribute, like any other, must be 1348 <termref def="dt-attdecl">declared</termref> if it is used. 1349 The values of the attribute are language identifiers as defined 1350 by <bibref ref="RFC1766"/>, "Tags for the Identification of Languages": 1351 <scrap lang="ebnf"> 1352 <head>Language Identification</head> 1353 <prod id="NT-LanguageID"><lhs>LanguageID</lhs> 1354 <rhs><nt def="NT-Langcode">Langcode</nt> 1355 ('-' <nt def="NT-Subcode">Subcode</nt>)*</rhs></prod> 1356 <prod id="NT-Langcode"><lhs>Langcode</lhs> 1357 <rhs><nt def="NT-ISO639Code">ISO639Code</nt> | 1358 <nt def="NT-IanaCode">IanaCode</nt> | 1359 <nt def="NT-UserCode">UserCode</nt></rhs> 1360 </prod> 1361 <prod id="NT-ISO639Code"><lhs>ISO639Code</lhs> 1362 <rhs>([a-z] | [A-Z]) ([a-z] | [A-Z])</rhs></prod> 1363 <prod id="NT-IanaCode"><lhs>IanaCode</lhs> 1364 <rhs>('i' | 'I') '-' ([a-z] | [A-Z])+</rhs></prod> 1365 <prod id="NT-UserCode"><lhs>UserCode</lhs> 1366 <rhs>('x' | 'X') '-' ([a-z] | [A-Z])+</rhs></prod> 1367 <prod id="NT-Subcode"><lhs>Subcode</lhs> 1368 <rhs>([a-z] | [A-Z])+</rhs></prod> 1369 </scrap> 1370 The <nt def="NT-Langcode">Langcode</nt> may be any of the following: 1371 <ulist> 1372 <item><p>a two-letter language code as defined by 1373 <bibref ref="ISO639"/>, "Codes 1374 for the representation of names of languages"</p></item> 1375 <item><p>a language identifier registered with the Internet 1376 Assigned Numbers Authority <bibref ref="IANA"/>; these begin with the 1377 prefix "<code>i-</code>" (or "<code>I-</code>")</p></item> 1378 <item><p>a language identifier assigned by the user, or agreed on 1379 between parties in private use; these must begin with the 1380 prefix "<code>x-</code>" or "<code>X-</code>" in order to ensure that they do not conflict 1381 with names later standardized or registered with IANA</p></item> 1382 </ulist></p> 1383 <p>There may be any number of <nt def="NT-Subcode">Subcode</nt> segments; if 1384 the first 1385 subcode segment exists and the Subcode consists of two 1386 letters, then it must be a country code from 1387 <bibref ref="ISO3166"/>, "Codes 1388 for the representation of names of countries." 1389 If the first 1390 subcode consists of more than two letters, it must be 1391 a subcode for the language in question registered with IANA, 1392 unless the <nt def="NT-Langcode">Langcode</nt> begins with the prefix 1393 "<code>x-</code>" or 1394 "<code>X-</code>". </p> 1395 <p>It is customary to give the language code in lower case, and 1396 the country code (if any) in upper case. 1397 Note that these values, unlike other names in XML documents, 1398 are case insensitive.</p> 1399 <p>For example: 1400 <eg><![CDATA[<p xml:lang="en">The quick brown fox jumps over the lazy dog.</p> 1401 <p xml:lang="en-GB">What colour is it?</p> 1402 <p xml:lang="en-US">What color is it?</p> 1403 <sp who="Faust" desc='leise' xml:lang="de"> 1404 <l>Habe nun, ach! Philosophie,</l> 1405 <l>Juristerei, und Medizin</l> 1406 <l>und leider auch Theologie</l> 1407 <l>durchaus studiert mit hei�em Bem�h'n.</l> 1408 </sp>]]></eg></p> 1409 <!--<p>The xml:lang value is considered to apply both to the contents of an 1410 element and 1411 (unless otherwise via attribute default values) to the 1412 values of all of its attributes with free-text (CDATA) values. --> 1413 <p>The intent declared with <kw>xml:lang</kw> is considered to apply to 1414 all attributes and content of the element where it is specified, 1415 unless overridden with an instance of <kw>xml:lang</kw> 1416 on another element within that content.</p> 1417 <!-- 1418 If no 1419 value is specified for xml:lang on an element, and no default value is 1420 defined for it in the DTD, then the xml:lang attribute of any element 1421 takes the same value it has in the parent element, if any. The two 1422 technical terms in the following example both have the same effective 1423 value for xml:lang: 1424 1425 <p xml:lang="en">Here the keywords are 1426 <term xml:lang="en">shift</term> and 1427 <term>reduce</term>. ...</p> 1428 1429 The application, not the XML processor, is responsible for this ' 1430 inheritance' of attribute values. 1431 --> 1432 <p>A simple declaration for <kw>xml:lang</kw> might take 1433 the form 1434 <eg>xml:lang NMTOKEN #IMPLIED</eg> 1435 but specific default values may also be given, if appropriate. In a 1436 collection of French poems for English students, with glosses and 1437 notes in English, the xml:lang attribute might be declared this way: 1438 <eg><![CDATA[ <!ATTLIST poem xml:lang NMTOKEN 'fr'> 1439 <!ATTLIST gloss xml:lang NMTOKEN 'en'> 1440 <!ATTLIST note xml:lang NMTOKEN 'en'>]]></eg> 1441 </p> 1442 1443 </div2> 1444 </div1> 1445 <!-- &Elements; --> 1446 1447 <div1 id="sec-logical-struct"> 1448 <head>Logical Structures</head> 1449 1450 <p><termdef id="dt-element" term="Element">Each <termref def="dt-xml-doc">XML document</termref> contains one or more 1451 <term>elements</term>, the boundaries of which are 1452 either delimited by <termref def="dt-stag">start-tags</termref> 1453 and <termref def="dt-etag">end-tags</termref>, or, for <termref def="dt-empty">empty</termref> elements, by an <termref def="dt-eetag">empty-element tag</termref>. Each element has a type, 1454 identified by name, sometimes called its "generic 1455 identifier" (GI), and may have a set of 1456 attribute specifications.</termdef> Each attribute specification 1457 has a <termref def="dt-attrname">name</termref> and a <termref def="dt-attrval">value</termref>. 1458 </p> 1459 <scrap lang="ebnf"><head>Element</head> 1460 <prod id="NT-element"><lhs>element</lhs> 1461 <rhs><nt def="NT-EmptyElemTag">EmptyElemTag</nt></rhs> 1462 <rhs>| <nt def="NT-STag">STag</nt> <nt def="NT-content">content</nt> 1463 <nt def="NT-ETag">ETag</nt></rhs> 1464 <wfc def="GIMatch"/> 1465 <vc def="elementvalid"/> 1466 </prod> 1467 </scrap> 1468 <p>This specification does not constrain the semantics, use, or (beyond 1469 syntax) names of the element types and attributes, except that names 1470 beginning with a match to <code>(('X'|'x')('M'|'m')('L'|'l'))</code> 1471 are reserved for standardization in this or future versions of this 1472 specification. 1473 </p> 1474 <wfcnote id="GIMatch"> 1475 <head>Element Type Match</head> 1476 <p> 1477 The <nt def="NT-Name">Name</nt> in an element's end-tag must match 1478 the element type in 1479 the start-tag. 1480 </p> 1481 </wfcnote> 1482 <vcnote id="elementvalid"> 1483 <head>Element Valid</head> 1484 <p>An element is 1485 valid if 1486 there is a declaration matching 1487 <nt def="NT-elementdecl">elementdecl</nt> where the 1488 <nt def="NT-Name">Name</nt> matches the element type, and 1489 one of the following holds:</p> 1490 <olist> 1491 <item><p>The declaration matches <kw>EMPTY</kw> and the element has no 1492 <termref def="dt-content">content</termref>.</p></item> 1493 <item><p>The declaration matches <nt def="NT-children">children</nt> and 1494 the sequence of 1495 <termref def="dt-parentchild">child elements</termref> 1496 belongs to the language generated by the regular expression in 1497 the content model, with optional white space (characters 1498 matching the nonterminal <nt def="NT-S">S</nt>) between each pair 1499 of child elements.</p></item> 1500 <item><p>The declaration matches <nt def="NT-Mixed">Mixed</nt> and 1501 the content consists of <termref def="dt-chardata">character 1502 data</termref> and <termref def="dt-parentchild">child elements</termref> 1503 whose types match names in the content model.</p></item> 1504 <item><p>The declaration matches <kw>ANY</kw>, and the types 1505 of any <termref def="dt-parentchild">child elements</termref> have 1506 been declared.</p></item> 1507 </olist> 1508 </vcnote> 1509 1510 <div2 id="sec-starttags"> 1511 <head>Start-Tags, End-Tags, and Empty-Element Tags</head> 1512 1513 <p><termdef id="dt-stag" term="Start-Tag">The beginning of every 1514 non-empty XML element is marked by a <term>start-tag</term>. 1515 <scrap lang="ebnf"> 1516 <head>Start-tag</head> 1517 <prodgroup pcw2="6" pcw4="15" pcw5="11.5"> 1518 <prod id="NT-STag"><lhs>STag</lhs> 1519 <rhs>'<' <nt def="NT-Name">Name</nt> 1520 (<nt def="NT-S">S</nt> <nt def="NT-Attribute">Attribute</nt>)* 1521 <nt def="NT-S">S</nt>? '>'</rhs> 1522 <wfc def="uniqattspec"/> 1523 </prod> 1524 <prod id="NT-Attribute"><lhs>Attribute</lhs> 1525 <rhs><nt def="NT-Name">Name</nt> <nt def="NT-Eq">Eq</nt> 1526 <nt def="NT-AttValue">AttValue</nt></rhs> 1527 <vc def="ValueType"/> 1528 <wfc def="NoExternalRefs"/> 1529 <wfc def="CleanAttrVals"/></prod> 1530 </prodgroup> 1531 </scrap> 1532 The <nt def="NT-Name">Name</nt> in 1533 the start- and end-tags gives the 1534 element's <term>type</term>.</termdef> 1535 <termdef id="dt-attr" term="Attribute"> 1536 The <nt def="NT-Name">Name</nt>-<nt def="NT-AttValue">AttValue</nt> pairs are 1537 referred to as 1538 the <term>attribute specifications</term> of the element</termdef>, 1539 <termdef id="dt-attrname" term="Attribute Name">with the 1540 <nt def="NT-Name">Name</nt> in each pair 1541 referred to as the <term>attribute name</term></termdef> and 1542 <termdef id="dt-attrval" term="Attribute Value">the content of the 1543 <nt def="NT-AttValue">AttValue</nt> (the text between the 1544 <code>'</code> or <code>"</code> delimiters) 1545 as the <term>attribute value</term>.</termdef> 1546 </p> 1547 <wfcnote id="uniqattspec"> 1548 <head>Unique Att Spec</head> 1549 <p> 1550 No attribute name may appear more than once in the same start-tag 1551 or empty-element tag. 1552 </p> 1553 </wfcnote> 1554 <vcnote id="ValueType"> 1555 <head>Attribute Value Type</head> 1556 <p> 1557 The attribute must have been declared; the value must be of the type 1558 declared for it. 1559 (For attribute types, see <specref ref="attdecls"/>.) 1560 </p> 1561 </vcnote> 1562 <wfcnote id="NoExternalRefs"> 1563 <head>No External Entity References</head> 1564 <p> 1565 Attribute values cannot contain direct or indirect entity references 1566 to external entities. 1567 </p> 1568 </wfcnote> 1569 <wfcnote id="CleanAttrVals"> 1570 <head>No <code><</code> in Attribute Values</head> 1571 <p>The <termref def="dt-repltext">replacement text</termref> of any entity 1572 referred to directly or indirectly in an attribute 1573 value (other than "<code>&lt;</code>") must not contain 1574 a <code><</code>. 1575 </p></wfcnote> 1576 <p>An example of a start-tag: 1577 <eg><termdef id="dt-dog" term="dog"></eg></p> 1578 <p><termdef id="dt-etag" term="End Tag">The end of every element 1579 that begins with a start-tag must 1580 be marked by an <term>end-tag</term> 1581 containing a name that echoes the element's type as given in the 1582 start-tag: 1583 <scrap lang="ebnf"> 1584 <head>End-tag</head> 1585 <prodgroup pcw2="6" pcw4="15" pcw5="11.5"> 1586 <prod id="NT-ETag"><lhs>ETag</lhs> 1587 <rhs>'</' <nt def="NT-Name">Name</nt> 1588 <nt def="NT-S">S</nt>? '>'</rhs></prod> 1589 </prodgroup> 1590 </scrap> 1591 </termdef></p> 1592 <p>An example of an end-tag:<eg></termdef></eg></p> 1593 <p><termdef id="dt-content" term="Content">The 1594 <termref def="dt-text">text</termref> between the start-tag and 1595 end-tag is called the element's 1596 <term>content</term>: 1597 <scrap lang="ebnf"> 1598 <head>Content of Elements</head> 1599 <prodgroup pcw2="6" pcw4="15" pcw5="11.5"> 1600 <prod id="NT-content"><lhs>content</lhs> 1601 <rhs>(<nt def="NT-element">element</nt> | <nt def="NT-CharData">CharData</nt> 1602 | <nt def="NT-Reference">Reference</nt> | <nt def="NT-CDSect">CDSect</nt> 1603 | <nt def="NT-PI">PI</nt> | <nt def="NT-Comment">Comment</nt>)*</rhs> 1604 </prod> 1605 </prodgroup> 1606 </scrap> 1607 </termdef></p> 1608 <p><termdef id="dt-empty" term="Empty">If an element is <term>empty</term>, 1609 it must be represented either by a start-tag immediately followed 1610 by an end-tag or by an empty-element tag.</termdef> 1611 <termdef id="dt-eetag" term="empty-element tag">An 1612 <term>empty-element tag</term> takes a special form: 1613 <scrap lang="ebnf"> 1614 <head>Tags for Empty Elements</head> 1615 <prodgroup pcw2="6" pcw4="15" pcw5="11.5"> 1616 <prod id="NT-EmptyElemTag"><lhs>EmptyElemTag</lhs> 1617 <rhs>'<' <nt def="NT-Name">Name</nt> (<nt def="NT-S">S</nt> 1618 <nt def="NT-Attribute">Attribute</nt>)* <nt def="NT-S">S</nt>? 1619 '/>'</rhs> 1620 <wfc def="uniqattspec"/> 1621 </prod> 1622 </prodgroup> 1623 </scrap> 1624 </termdef></p> 1625 <p>Empty-element tags may be used for any element which has no 1626 content, whether or not it is declared using the keyword 1627 <kw>EMPTY</kw>. 1628 <termref def="dt-interop">For interoperability</termref>, the empty-element 1629 tag must be used, and can only be used, for elements which are 1630 <termref def="dt-eldecl">declared</termref> <kw>EMPTY</kw>.</p> 1631 <p>Examples of empty elements: 1632 <eg><IMG align="left" 1633 src="http://www.w3.org/Icons/WWW/w3c_home" /> 1634 <br></br> 1635 <br/></eg></p> 1636 </div2> 1637 1638 <div2 id="elemdecls"> 1639 <head>Element Type Declarations</head> 1640 1641 <p>The <termref def="dt-element">element</termref> structure of an 1642 <termref def="dt-xml-doc">XML document</termref> may, for 1643 <termref def="dt-valid">validation</termref> purposes, 1644 be constrained 1645 using element type and attribute-list declarations. 1646 An element type declaration constrains the element's 1647 <termref def="dt-content">content</termref>. 1648 </p> 1649 1650 <p>Element type declarations often constrain which element types can 1651 appear as <termref def="dt-parentchild">children</termref> of the element. 1652 At user option, an XML processor may issue a warning 1653 when a declaration mentions an element type for which no declaration 1654 is provided, but this is not an error.</p> 1655 <p><termdef id="dt-eldecl" term="Element Type declaration">An <term>element 1656 type declaration</term> takes the form: 1657 <scrap lang="ebnf"> 1658 <head>Element Type Declaration</head> 1659 <prodgroup pcw2="5.5" pcw4="18" pcw5="9"> 1660 <prod id="NT-elementdecl"><lhs>elementdecl</lhs> 1661 <rhs>'<!ELEMENT' <nt def="NT-S">S</nt> 1662 <nt def="NT-Name">Name</nt> 1663 <nt def="NT-S">S</nt> 1664 <nt def="NT-contentspec">contentspec</nt> 1665 <nt def="NT-S">S</nt>? '>'</rhs> 1666 <vc def="EDUnique"/></prod> 1667 <prod id="NT-contentspec"><lhs>contentspec</lhs> 1668 <rhs>'EMPTY' 1669 | 'ANY' 1670 | <nt def="NT-Mixed">Mixed</nt> 1671 | <nt def="NT-children">children</nt> 1672 </rhs> 1673 </prod> 1674 </prodgroup> 1675 </scrap> 1676 where the <nt def="NT-Name">Name</nt> gives the element type 1677 being declared.</termdef> 1678 </p> 1679 1680 <vcnote id="EDUnique"> 1681 <head>Unique Element Type Declaration</head> 1682 <p> 1683 No element type may be declared more than once. 1684 </p> 1685 </vcnote> 1686 1687 <p>Examples of element type declarations: 1688 <eg><!ELEMENT br EMPTY> 1689 <!ELEMENT p (#PCDATA|emph)* > 1690 <!ELEMENT %name.para; %content.para; > 1691 <!ELEMENT container ANY></eg></p> 1692 1693 <div3 id="sec-element-content"> 1694 <head>Element Content</head> 1695 1696 <p><termdef id="dt-elemcontent" term="Element content">An element <termref def="dt-stag">type</termref> has 1697 <term>element content</term> when elements of that 1698 type must contain only <termref def="dt-parentchild">child</termref> 1699 elements (no character data), optionally separated by 1700 white space (characters matching the nonterminal 1701 <nt def="NT-S">S</nt>). 1702 </termdef> 1703 In this case, the 1704 constraint includes a content model, a simple grammar governing 1705 the allowed types of the child 1706 elements and the order in which they are allowed to appear. 1707 The grammar is built on 1708 content particles (<nt def="NT-cp">cp</nt>s), which consist of names, 1709 choice lists of content particles, or 1710 sequence lists of content particles: 1711 <scrap lang="ebnf"> 1712 <head>Element-content Models</head> 1713 <prodgroup pcw2="5.5" pcw4="16" pcw5="11"> 1714 <prod id="NT-children"><lhs>children</lhs> 1715 <rhs>(<nt def="NT-choice">choice</nt> 1716 | <nt def="NT-seq">seq</nt>) 1717 ('?' | '*' | '+')?</rhs></prod> 1718 <prod id="NT-cp"><lhs>cp</lhs> 1719 <rhs>(<nt def="NT-Name">Name</nt> 1720 | <nt def="NT-choice">choice</nt> 1721 | <nt def="NT-seq">seq</nt>) 1722 ('?' | '*' | '+')?</rhs></prod> 1723 <prod id="NT-choice"><lhs>choice</lhs> 1724 <rhs>'(' <nt def="NT-S">S</nt>? cp 1725 ( <nt def="NT-S">S</nt>? '|' <nt def="NT-S">S</nt>? <nt def="NT-cp">cp</nt> )* 1726 <nt def="NT-S">S</nt>? ')'</rhs> 1727 <vc def="vc-PEinGroup"/></prod> 1728 <prod id="NT-seq"><lhs>seq</lhs> 1729 <rhs>'(' <nt def="NT-S">S</nt>? cp 1730 ( <nt def="NT-S">S</nt>? ',' <nt def="NT-S">S</nt>? <nt def="NT-cp">cp</nt> )* 1731 <nt def="NT-S">S</nt>? ')'</rhs> 1732 <vc def="vc-PEinGroup"/></prod> 1733 1734 </prodgroup> 1735 </scrap> 1736 where each <nt def="NT-Name">Name</nt> is the type of an element which may 1737 appear as a <termref def="dt-parentchild">child</termref>. 1738 Any content 1739 particle in a choice list may appear in the <termref def="dt-elemcontent">element content</termref> at the location where 1740 the choice list appears in the grammar; 1741 content particles occurring in a sequence list must each 1742 appear in the <termref def="dt-elemcontent">element content</termref> in the 1743 order given in the list. 1744 The optional character following a name or list governs 1745 whether the element or the content particles in the list may occur one 1746 or more (<code>+</code>), zero or more (<code>*</code>), or zero or 1747 one times (<code>?</code>). 1748 The absence of such an operator means that the element or content particle 1749 must appear exactly once. 1750 This syntax 1751 and meaning are identical to those used in the productions in this 1752 specification.</p> 1753 <p> 1754 The content of an element matches a content model if and only if it is 1755 possible to trace out a path through the content model, obeying the 1756 sequence, choice, and repetition operators and matching each element in 1757 the content against an element type in the content model. <termref def="dt-compat">For compatibility</termref>, it is an error 1758 if an element in the document can 1759 match more than one occurrence of an element type in the content model. 1760 For more information, see <specref ref="determinism"/>. 1761 <!-- appendix <specref ref="determinism"/>. --> 1762 <!-- appendix on deterministic content models. --> 1763 </p> 1764 <vcnote id="vc-PEinGroup"> 1765 <head>Proper Group/PE Nesting</head> 1766 <p>Parameter-entity 1767 <termref def="dt-repltext">replacement text</termref> must be properly nested 1768 with parenthetized groups. 1769 That is to say, if either of the opening or closing parentheses 1770 in a <nt def="NT-choice">choice</nt>, <nt def="NT-seq">seq</nt>, or 1771 <nt def="NT-Mixed">Mixed</nt> construct 1772 is contained in the replacement text for a 1773 <termref def="dt-PERef">parameter entity</termref>, 1774 both must be contained in the same replacement text.</p> 1775 <p><termref def="dt-interop">For interoperability</termref>, 1776 if a parameter-entity reference appears in a 1777 <nt def="NT-choice">choice</nt>, <nt def="NT-seq">seq</nt>, or 1778 <nt def="NT-Mixed">Mixed</nt> construct, its replacement text 1779 should not be empty, and 1780 neither the first nor last non-blank 1781 character of the replacement text should be a connector 1782 (<code>|</code> or <code>,</code>). 1783 </p> 1784 </vcnote> 1785 <p>Examples of element-content models: 1786 <eg><!ELEMENT spec (front, body, back?)> 1787 <!ELEMENT div1 (head, (p | list | note)*, div2*)> 1788 <!ELEMENT dictionary-body (%div.mix; | %dict.mix;)*></eg></p> 1789 </div3> 1790 1791 <div3 id="sec-mixed-content"> 1792 <head>Mixed Content</head> 1793 1794 <p><termdef id="dt-mixed" term="Mixed Content">An element 1795 <termref def="dt-stag">type</termref> has 1796 <term>mixed content</term> when elements of that type may contain 1797 character data, optionally interspersed with 1798 <termref def="dt-parentchild">child</termref> elements.</termdef> 1799 In this case, the types of the child elements 1800 may be constrained, but not their order or their number of occurrences: 1801 <scrap lang="ebnf"> 1802 <head>Mixed-content Declaration</head> 1803 <prodgroup pcw2="5.5" pcw4="16" pcw5="11"> 1804 <prod id="NT-Mixed"><lhs>Mixed</lhs> 1805 <rhs>'(' <nt def="NT-S">S</nt>? 1806 '#PCDATA' 1807 (<nt def="NT-S">S</nt>? 1808 '|' 1809 <nt def="NT-S">S</nt>? 1810 <nt def="NT-Name">Name</nt>)* 1811 <nt def="NT-S">S</nt>? 1812 ')*' </rhs> 1813 <rhs>| '(' <nt def="NT-S">S</nt>? '#PCDATA' <nt def="NT-S">S</nt>? ')' 1814 </rhs><vc def="vc-PEinGroup"/> 1815 <vc def="vc-MixedChildrenUnique"/> 1816 </prod> 1817 1818 </prodgroup> 1819 </scrap> 1820 where the <nt def="NT-Name">Name</nt>s give the types of elements 1821 that may appear as children. 1822 </p> 1823 <vcnote id="vc-MixedChildrenUnique"> 1824 <head>No Duplicate Types</head> 1825 <p>The same name must not appear more than once in a single mixed-content 1826 declaration. 1827 </p></vcnote> 1828 <p>Examples of mixed content declarations: 1829 <eg><!ELEMENT p (#PCDATA|a|ul|b|i|em)*> 1830 <!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* > 1831 <!ELEMENT b (#PCDATA)></eg></p> 1832 </div3> 1833 </div2> 1834 1835 <div2 id="attdecls"> 1836 <head>Attribute-List Declarations</head> 1837 1838 <p><termref def="dt-attr">Attributes</termref> are used to associate 1839 name-value pairs with <termref def="dt-element">elements</termref>. 1840 Attribute specifications may appear only within <termref def="dt-stag">start-tags</termref> 1841 and <termref def="dt-eetag">empty-element tags</termref>; 1842 thus, the productions used to 1843 recognize them appear in <specref ref="sec-starttags"/>. 1844 Attribute-list 1845 declarations may be used: 1846 <ulist> 1847 <item><p>To define the set of attributes pertaining to a given 1848 element type.</p></item> 1849 <item><p>To establish type constraints for these 1850 attributes.</p></item> 1851 <item><p>To provide <termref def="dt-default">default values</termref> 1852 for attributes.</p></item> 1853 </ulist> 1854 </p> 1855 <p><termdef id="dt-attdecl" term="Attribute-List Declaration"> 1856 <term>Attribute-list declarations</term> specify the name, data type, and default 1857 value (if any) of each attribute associated with a given element type: 1858 <scrap lang="ebnf"> 1859 <head>Attribute-list Declaration</head> 1860 <prod id="NT-AttlistDecl"><lhs>AttlistDecl</lhs> 1861 <rhs>'<!ATTLIST' <nt def="NT-S">S</nt> 1862 <nt def="NT-Name">Name</nt> 1863 <nt def="NT-AttDef">AttDef</nt>* 1864 <nt def="NT-S">S</nt>? '>'</rhs> 1865 </prod> 1866 <prod id="NT-AttDef"><lhs>AttDef</lhs> 1867 <rhs><nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt> 1868 <nt def="NT-S">S</nt> <nt def="NT-AttType">AttType</nt> 1869 <nt def="NT-S">S</nt> <nt def="NT-DefaultDecl">DefaultDecl</nt></rhs> 1870 </prod> 1871 </scrap> 1872 The <nt def="NT-Name">Name</nt> in the 1873 <nt def="NT-AttlistDecl">AttlistDecl</nt> rule is the type of an element. At 1874 user option, an XML processor may issue a warning if attributes are 1875 declared for an element type not itself declared, but this is not an 1876 error. The <nt def="NT-Name">Name</nt> in the 1877 <nt def="NT-AttDef">AttDef</nt> rule is 1878 the name of the attribute.</termdef></p> 1879 <p> 1880 When more than one <nt def="NT-AttlistDecl">AttlistDecl</nt> is provided for a 1881 given element type, the contents of all those provided are merged. When 1882 more than one definition is provided for the same attribute of a 1883 given element type, the first declaration is binding and later 1884 declarations are ignored. 1885 <termref def="dt-interop">For interoperability,</termref> writers of DTDs 1886 may choose to provide at most one attribute-list declaration 1887 for a given element type, at most one attribute definition 1888 for a given attribute name, and at least one attribute definition 1889 in each attribute-list declaration. 1890 For interoperability, an XML processor may at user option 1891 issue a warning when more than one attribute-list declaration is 1892 provided for a given element type, or more than one attribute definition 1893 is provided 1894 for a given attribute, but this is not an error. 1895 </p> 1896 1897 <div3 id="sec-attribute-types"> 1898 <head>Attribute Types</head> 1899 1900 <p>XML attribute types are of three kinds: a string type, a 1901 set of tokenized types, and enumerated types. The string type may take 1902 any literal string as a value; the tokenized types have varying lexical 1903 and semantic constraints, as noted: 1904 <scrap lang="ebnf"> 1905 <head>Attribute Types</head> 1906 <prodgroup pcw4="14" pcw5="11.5"> 1907 <prod id="NT-AttType"><lhs>AttType</lhs> 1908 <rhs><nt def="NT-StringType">StringType</nt> 1909 | <nt def="NT-TokenizedType">TokenizedType</nt> 1910 | <nt def="NT-EnumeratedType">EnumeratedType</nt> 1911 </rhs> 1912 </prod> 1913 <prod id="NT-StringType"><lhs>StringType</lhs> 1914 <rhs>'CDATA'</rhs> 1915 </prod> 1916 <prod id="NT-TokenizedType"><lhs>TokenizedType</lhs> 1917 <rhs>'ID'</rhs> 1918 <vc def="id"/> 1919 <vc def="one-id-per-el"/> 1920 <vc def="id-default"/> 1921 <rhs>| 'IDREF'</rhs> 1922 <vc def="idref"/> 1923 <rhs>| 'IDREFS'</rhs> 1924 <vc def="idref"/> 1925 <rhs>| 'ENTITY'</rhs> 1926 <vc def="entname"/> 1927 <rhs>| 'ENTITIES'</rhs> 1928 <vc def="entname"/> 1929 <rhs>| 'NMTOKEN'</rhs> 1930 <vc def="nmtok"/> 1931 <rhs>| 'NMTOKENS'</rhs> 1932 <vc def="nmtok"/></prod> 1933 </prodgroup> 1934 </scrap> 1935 </p> 1936 <vcnote id="id"> 1937 <head>ID</head> 1938 <p> 1939 Values of type <kw>ID</kw> must match the 1940 <nt def="NT-Name">Name</nt> production. 1941 A name must not appear more than once in 1942 an XML document as a value of this type; i.e., ID values must uniquely 1943 identify the elements which bear them. 1944 </p> 1945 </vcnote> 1946 <vcnote id="one-id-per-el"> 1947 <head>One ID per Element Type</head> 1948 <p>No element type may have more than one ID attribute specified.</p> 1949 </vcnote> 1950 <vcnote id="id-default"> 1951 <head>ID Attribute Default</head> 1952 <p>An ID attribute must have a declared default of <kw>#IMPLIED</kw> or 1953 <kw>#REQUIRED</kw>.</p> 1954 </vcnote> 1955 <vcnote id="idref"> 1956 <head>IDREF</head> 1957 <p> 1958 Values of type <kw>IDREF</kw> must match 1959 the <nt def="NT-Name">Name</nt> production, and 1960 values of type <kw>IDREFS</kw> must match 1961 <nt def="NT-Names">Names</nt>; 1962 each <nt def="NT-Name">Name</nt> must match the value of an ID attribute on 1963 some element in the XML document; i.e. <kw>IDREF</kw> values must 1964 match the value of some ID attribute. 1965 </p> 1966 </vcnote> 1967 <vcnote id="entname"> 1968 <head>Entity Name</head> 1969 <p> 1970 Values of type <kw>ENTITY</kw> 1971 must match the <nt def="NT-Name">Name</nt> production, 1972 values of type <kw>ENTITIES</kw> must match 1973 <nt def="NT-Names">Names</nt>; 1974 each <nt def="NT-Name">Name</nt> must 1975 match the 1976 name of an <termref def="dt-unparsed">unparsed entity</termref> declared in the 1977 <termref def="dt-doctype">DTD</termref>. 1978 </p> 1979 </vcnote> 1980 <vcnote id="nmtok"> 1981 <head>Name Token</head> 1982 <p> 1983 Values of type <kw>NMTOKEN</kw> must match the 1984 <nt def="NT-Nmtoken">Nmtoken</nt> production; 1985 values of type <kw>NMTOKENS</kw> must 1986 match <termref def="NT-Nmtokens">Nmtokens</termref>. 1987 </p> 1988 </vcnote> 1989 <!-- why? 1990 <p>The XML processor must normalize attribute values before 1991 passing them to the application, as described in 1992 <specref ref="AVNormalize"/>.</p>--> 1993 <p><termdef id="dt-enumerated" term="Enumerated Attribute Values"><term>Enumerated attributes</term> can take one 1994 of a list of values provided in the declaration</termdef>. There are two 1995 kinds of enumerated types: 1996 <scrap lang="ebnf"> 1997 <head>Enumerated Attribute Types</head> 1998 <prod id="NT-EnumeratedType"><lhs>EnumeratedType</lhs> 1999 <rhs><nt def="NT-NotationType">NotationType</nt> 2000 | <nt def="NT-Enumeration">Enumeration</nt> 2001 </rhs></prod> 2002 <prod id="NT-NotationType"><lhs>NotationType</lhs> 2003 <rhs>'NOTATION' 2004 <nt def="NT-S">S</nt> 2005 '(' 2006 <nt def="NT-S">S</nt>? 2007 <nt def="NT-Name">Name</nt> 2008 (<nt def="NT-S">S</nt>? '|' <nt def="NT-S">S</nt>? 2009 <nt def="NT-Name">Name</nt>)* 2010 <nt def="NT-S">S</nt>? ')' 2011 </rhs> 2012 <vc def="notatn"/></prod> 2013 <prod id="NT-Enumeration"><lhs>Enumeration</lhs> 2014 <rhs>'(' <nt def="NT-S">S</nt>? 2015 <nt def="NT-Nmtoken">Nmtoken</nt> 2016 (<nt def="NT-S">S</nt>? '|' 2017 <nt def="NT-S">S</nt>? 2018 <nt def="NT-Nmtoken">Nmtoken</nt>)* 2019 <nt def="NT-S">S</nt>? 2020 ')'</rhs> 2021 <vc def="enum"/></prod> 2022 </scrap> 2023 A <kw>NOTATION</kw> attribute identifies a 2024 <termref def="dt-notation">notation</termref>, declared in the 2025 DTD with associated system and/or public identifiers, to 2026 be used in interpreting the element to which the attribute 2027 is attached. 2028 </p> 2029 2030 <vcnote id="notatn"> 2031 <head>Notation Attributes</head> 2032 <p> 2033 Values of this type must match 2034 one of the <titleref href="Notations">notation</titleref> names included in 2035 the declaration; all notation names in the declaration must 2036 be declared. 2037 </p> 2038 </vcnote> 2039 <vcnote id="enum"> 2040 <head>Enumeration</head> 2041 <p> 2042 Values of this type 2043 must match one of the <nt def="NT-Nmtoken">Nmtoken</nt> tokens in the 2044 declaration. 2045 </p> 2046 </vcnote> 2047 <p><termref def="dt-interop">For interoperability,</termref> the same 2048 <nt def="NT-Nmtoken">Nmtoken</nt> should not occur more than once in the 2049 enumerated attribute types of a single element type. 2050 </p> 2051 </div3> 2052 2053 <div3 id="sec-attr-defaults"> 2054 <head>Attribute Defaults</head> 2055 2056 <p>An <termref def="dt-attdecl">attribute declaration</termref> provides 2057 information on whether 2058 the attribute's presence is required, and if not, how an XML processor should 2059 react if a declared attribute is absent in a document. 2060 <scrap lang="ebnf"> 2061 <head>Attribute Defaults</head> 2062 <prodgroup pcw4="14" pcw5="11.5"> 2063 <prod id="NT-DefaultDecl"><lhs>DefaultDecl</lhs> 2064 <rhs>'#REQUIRED' 2065 | '#IMPLIED' </rhs> 2066 <rhs>| (('#FIXED' S)? <nt def="NT-AttValue">AttValue</nt>)</rhs> 2067 <vc def="RequiredAttr"/> 2068 <vc def="defattrvalid"/> 2069 <wfc def="CleanAttrVals"/> 2070 <vc def="FixedAttr"/> 2071 </prod> 2072 </prodgroup> 2073 </scrap> 2074 2075 </p> 2076 <p>In an attribute declaration, <kw>#REQUIRED</kw> means that the 2077 attribute must always be provided, <kw>#IMPLIED</kw> that no default 2078 value is provided. 2079 <!-- not any more!! 2080 <kw>#IMPLIED</kw> means that if the attribute is omitted 2081 from an element of this type, 2082 the XML processor must inform the application 2083 that no value was specified; no constraint is placed on the behavior 2084 of the application. --> 2085 <termdef id="dt-default" term="Attribute Default">If the 2086 declaration 2087 is neither <kw>#REQUIRED</kw> nor <kw>#IMPLIED</kw>, then the 2088 <nt def="NT-AttValue">AttValue</nt> value contains the declared 2089 <term>default</term> value; the <kw>#FIXED</kw> keyword states that 2090 the attribute must always have the default value. 2091 If a default value 2092 is declared, when an XML processor encounters an omitted attribute, it 2093 is to behave as though the attribute were present with 2094 the declared default value.</termdef></p> 2095 <vcnote id="RequiredAttr"> 2096 <head>Required Attribute</head> 2097 <p>If the default declaration is the keyword <kw>#REQUIRED</kw>, then 2098 the attribute must be specified for 2099 all elements of the type in the attribute-list declaration. 2100 </p></vcnote> 2101 <vcnote id="defattrvalid"> 2102 <head>Attribute Default Legal</head> 2103 <p> 2104 The declared 2105 default value must meet the lexical constraints of the declared attribute type. 2106 </p> 2107 </vcnote> 2108 <vcnote id="FixedAttr"> 2109 <head>Fixed Attribute Default</head> 2110 <p>If an attribute has a default value declared with the 2111 <kw>#FIXED</kw> keyword, instances of that attribute must 2112 match the default value. 2113 </p></vcnote> 2114 2115 <p>Examples of attribute-list declarations: 2116 <eg><!ATTLIST termdef 2117 id ID #REQUIRED 2118 name CDATA #IMPLIED> 2119 <!ATTLIST list 2120 type (bullets|ordered|glossary) "ordered"> 2121 <!ATTLIST form 2122 method CDATA #FIXED "POST"></eg></p> 2123 </div3> 2124 <div3 id="AVNormalize"> 2125 <head>Attribute-Value Normalization</head> 2126 <p>Before the value of an attribute is passed to the application 2127 or checked for validity, the 2128 XML processor must normalize it as follows: 2129 <ulist> 2130 <item><p>a character reference is processed by appending the referenced 2131 character to the attribute value</p></item> 2132 <item><p>an entity reference is processed by recursively processing the 2133 replacement text of the entity</p></item> 2134 <item><p>a whitespace character (#x20, #xD, #xA, #x9) is processed by 2135 appending #x20 to the normalized value, except that only a single #x20 2136 is appended for a "#xD#xA" sequence that is part of an external 2137 parsed entity or the literal entity value of an internal parsed 2138 entity</p></item> 2139 <item><p>other characters are processed by appending them to the normalized 2140 value</p> 2141 </item></ulist> 2142 </p> 2143 <p>If the declared value is not CDATA, then the XML processor must 2144 further process the normalized attribute value by discarding any 2145 leading and trailing space (#x20) characters, and by replacing 2146 sequences of space (#x20) characters by a single space (#x20) 2147 character.</p> 2148 <p> 2149 All attributes for which no declaration has been read should be treated 2150 by a non-validating parser as if declared 2151 <kw>CDATA</kw>. 2152 </p> 2153 </div3> 2154 </div2> 2155 <div2 id="sec-condition-sect"> 2156 <head>Conditional Sections</head> 2157 <p><termdef id="dt-cond-section" term="conditional section"> 2158 <term>Conditional sections</term> are portions of the 2159 <termref def="dt-doctype">document type declaration external subset</termref> 2160 which are 2161 included in, or excluded from, the logical structure of the DTD based on 2162 the keyword which governs them.</termdef> 2163 <scrap lang="ebnf"> 2164 <head>Conditional Section</head> 2165 <prodgroup pcw2="9" pcw4="14.5"> 2166 <prod id="NT-conditionalSect"><lhs>conditionalSect</lhs> 2167 <rhs><nt def="NT-includeSect">includeSect</nt> 2168 | <nt def="NT-ignoreSect">ignoreSect</nt> 2169 </rhs> 2170 </prod> 2171 <prod id="NT-includeSect"><lhs>includeSect</lhs> 2172 <rhs>'<![' S? 'INCLUDE' S? '[' 2173 2174 <nt def="NT-extSubsetDecl">extSubsetDecl</nt> 2175 ']]>' 2176 </rhs> 2177 </prod> 2178 <prod id="NT-ignoreSect"><lhs>ignoreSect</lhs> 2179 <rhs>'<![' S? 'IGNORE' S? '[' 2180 <nt def="NT-ignoreSectContents">ignoreSectContents</nt>* 2181 ']]>'</rhs> 2182 </prod> 2183 2184 <prod id="NT-ignoreSectContents"><lhs>ignoreSectContents</lhs> 2185 <rhs><nt def="NT-Ignore">Ignore</nt> 2186 ('<![' <nt def="NT-ignoreSectContents">ignoreSectContents</nt> ']]>' 2187 <nt def="NT-Ignore">Ignore</nt>)*</rhs></prod> 2188 <prod id="NT-Ignore"><lhs>Ignore</lhs> 2189 <rhs><nt def="NT-Char">Char</nt>* - 2190 (<nt def="NT-Char">Char</nt>* ('<![' | ']]>') 2191 <nt def="NT-Char">Char</nt>*) 2192 </rhs></prod> 2193 2194 </prodgroup> 2195 </scrap> 2196 </p> 2197 <p>Like the internal and external DTD subsets, a conditional section 2198 may contain one or more complete declarations, 2199 comments, processing instructions, 2200 or nested conditional sections, intermingled with white space. 2201 </p> 2202 <p>If the keyword of the 2203 conditional section is <kw>INCLUDE</kw>, then the contents of the conditional 2204 section are part of the DTD. 2205 If the keyword of the conditional 2206 section is <kw>IGNORE</kw>, then the contents of the conditional section are 2207 not logically part of the DTD. 2208 Note that for reliable parsing, the contents of even ignored 2209 conditional sections must be read in order to 2210 detect nested conditional sections and ensure that the end of the 2211 outermost (ignored) conditional section is properly detected. 2212 If a conditional section with a 2213 keyword of <kw>INCLUDE</kw> occurs within a larger conditional 2214 section with a keyword of <kw>IGNORE</kw>, both the outer and the 2215 inner conditional sections are ignored.</p> 2216 <p>If the keyword of the conditional section is a 2217 parameter-entity reference, the parameter entity must be replaced by its 2218 content before the processor decides whether to 2219 include or ignore the conditional section.</p> 2220 <p>An example: 2221 <eg><!ENTITY % draft 'INCLUDE' > 2222 <!ENTITY % final 'IGNORE' > 2223 2224 <![%draft;[ 2225 <!ELEMENT book (comments*, title, body, supplements?)> 2226 ]]> 2227 <![%final;[ 2228 <!ELEMENT book (title, body, supplements?)> 2229 ]]> 2230 </eg> 2231 </p> 2232 </div2> 2233 2234 2235 <!-- 2236 <div2 id='sec-pass-to-app'> 2237 <head>XML Processor Treatment of Logical Structure</head> 2238 <p>When an XML processor encounters a start-tag, it must make 2239 at least the following information available to the application: 2240 <ulist> 2241 <item> 2242 <p>the element type's generic identifier</p> 2243 </item> 2244 <item> 2245 <p>the names of attributes known to apply to this element type 2246 (validating processors must make available names of all attributes 2247 declared for the element type; non-validating processors must 2248 make available at least the names of the attributes for which 2249 values are specified. 2250 </p> 2251 </item> 2252 </ulist> 2253 </p> 2254 </div2> 2255 --> 2256 2257 </div1> 2258 <!-- &Entities; --> 2259 2260 <div1 id="sec-physical-struct"> 2261 <head>Physical Structures</head> 2262 2263 <p><termdef id="dt-entity" term="Entity">An XML document may consist 2264 of one or many storage units. These are called 2265 <term>entities</term>; they all have <term>content</term> and are all 2266 (except for the document entity, see below, and 2267 the <termref def="dt-doctype">external DTD subset</termref>) 2268 identified by <term>name</term>. 2269 </termdef> 2270 Each XML document has one entity 2271 called the <termref def="dt-docent">document entity</termref>, which serves 2272 as the starting point for the <termref def="dt-xml-proc">XML 2273 processor</termref> and may contain the whole document.</p> 2274 <p>Entities may be either parsed or unparsed. 2275 <termdef id="dt-parsedent" term="Text Entity">A <term>parsed entity's</term> 2276 contents are referred to as its 2277 <termref def="dt-repltext">replacement text</termref>; 2278 this <termref def="dt-text">text</termref> is considered an 2279 integral part of the document.</termdef></p> 2280 2281 <p><termdef id="dt-unparsed" term="Unparsed Entity">An 2282 <term>unparsed entity</term> 2283 is a resource whose contents may or may not be 2284 <termref def="dt-text">text</termref>, and if text, may not be XML. 2285 Each unparsed entity 2286 has an associated <termref def="dt-notation">notation</termref>, identified by name. 2287 Beyond a requirement 2288 that an XML processor make the identifiers for the entity and 2289 notation available to the application, 2290 XML places no constraints on the contents of unparsed entities.</termdef> 2291 </p> 2292 <p> 2293 Parsed entities are invoked by name using entity references; 2294 unparsed entities by name, given in the value of <kw>ENTITY</kw> 2295 or <kw>ENTITIES</kw> 2296 attributes.</p> 2297 <p><termdef id="gen-entity" term="general entity"><term>General entities</term> 2298 are entities for use within the document content. 2299 In this specification, general entities are sometimes referred 2300 to with the unqualified term <emph>entity</emph> when this leads 2301 to no ambiguity.</termdef> 2302 <termdef id="dt-PE" term="Parameter entity">Parameter entities 2303 are parsed entities for use within the DTD.</termdef> 2304 These two types of entities use different forms of reference and 2305 are recognized in different contexts. 2306 Furthermore, they occupy different namespaces; a parameter entity and 2307 a general entity with the same name are two distinct entities. 2308 </p> 2309 2310 <div2 id="sec-references"> 2311 <head>Character and Entity References</head> 2312 <p><termdef id="dt-charref" term="Character Reference"> 2313 A <term>character reference</term> refers to a specific character in the 2314 ISO/IEC 10646 character set, for example one not directly accessible from 2315 available input devices. 2316 <scrap lang="ebnf"> 2317 <head>Character Reference</head> 2318 <prod id="NT-CharRef"><lhs>CharRef</lhs> 2319 <rhs>'&#' [0-9]+ ';' </rhs> 2320 <rhs>| '&hcro;' [0-9a-fA-F]+ ';'</rhs> 2321 <wfc def="wf-Legalchar"/> 2322 </prod> 2323 </scrap> 2324 <wfcnote id="wf-Legalchar"> 2325 <head>Legal Character</head> 2326 <p>Characters referred to using character references must 2327 match the production for 2328 <termref def="NT-Char">Char</termref>.</p> 2329 </wfcnote> 2330 If the character reference begins with "<code>&#x</code>", the digits and 2331 letters up to the terminating <code>;</code> provide a hexadecimal 2332 representation of the character's code point in ISO/IEC 10646. 2333 If it begins just with "<code>&#</code>", the digits up to the terminating 2334 <code>;</code> provide a decimal representation of the character's 2335 code point. 2336 </termdef> 2337 </p> 2338 <p><termdef id="dt-entref" term="Entity Reference">An <term>entity 2339 reference</term> refers to the content of a named entity.</termdef> 2340 <termdef id="dt-GERef" term="General Entity Reference">References to 2341 parsed general entities 2342 use ampersand (<code>&</code>) and semicolon (<code>;</code>) as 2343 delimiters.</termdef> 2344 <termdef id="dt-PERef" term="Parameter-entity reference"> 2345 <term>Parameter-entity references</term> use percent-sign (<code>%</code>) and 2346 semicolon 2347 (<code>;</code>) as delimiters.</termdef> 2348 </p> 2349 <scrap lang="ebnf"> 2350 <head>Entity Reference</head> 2351 <prod id="NT-Reference"><lhs>Reference</lhs> 2352 <rhs><nt def="NT-EntityRef">EntityRef</nt> 2353 | <nt def="NT-CharRef">CharRef</nt></rhs></prod> 2354 <prod id="NT-EntityRef"><lhs>EntityRef</lhs> 2355 <rhs>'&' <nt def="NT-Name">Name</nt> ';'</rhs> 2356 <wfc def="wf-entdeclared"/> 2357 <vc def="vc-entdeclared"/> 2358 <wfc def="textent"/> 2359 <wfc def="norecursion"/> 2360 </prod> 2361 <prod id="NT-PEReference"><lhs>PEReference</lhs> 2362 <rhs>'%' <nt def="NT-Name">Name</nt> ';'</rhs> 2363 <vc def="vc-entdeclared"/> 2364 <wfc def="norecursion"/> 2365 <wfc def="indtd"/> 2366 </prod> 2367 </scrap> 2368 2369 <wfcnote id="wf-entdeclared"> 2370 <head>Entity Declared</head> 2371 <p>In a document without any DTD, a document with only an internal 2372 DTD subset which contains no parameter entity references, or a document with 2373 "<code>standalone='yes'</code>", 2374 the <nt def="NT-Name">Name</nt> given in the entity reference must 2375 <termref def="dt-match">match</termref> that in an 2376 <titleref href="sec-entity-decl">entity declaration</titleref>, except that 2377 well-formed documents need not declare 2378 any of the following entities: &magicents;. 2379 The declaration of a parameter entity must precede any reference to it. 2380 Similarly, the declaration of a general entity must precede any 2381 reference to it which appears in a default value in an attribute-list 2382 declaration.</p> 2383 <p>Note that if entities are declared in the external subset or in 2384 external parameter entities, a non-validating processor is 2385 <titleref href="include-if-valid">not obligated to</titleref> read 2386 and process their declarations; for such documents, the rule that 2387 an entity must be declared is a well-formedness constraint only 2388 if <titleref href="sec-rmd">standalone='yes'</titleref>.</p> 2389 </wfcnote> 2390 <vcnote id="vc-entdeclared"> 2391 <head>Entity Declared</head> 2392 <p>In a document with an external subset or external parameter 2393 entities with "<code>standalone='no'</code>", 2394 the <nt def="NT-Name">Name</nt> given in the entity reference must <termref def="dt-match">match</termref> that in an 2395 <titleref href="sec-entity-decl">entity declaration</titleref>. 2396 For interoperability, valid documents should declare the entities 2397 &magicents;, in the form 2398 specified in <specref ref="sec-predefined-ent"/>. 2399 The declaration of a parameter entity must precede any reference to it. 2400 Similarly, the declaration of a general entity must precede any 2401 reference to it which appears in a default value in an attribute-list 2402 declaration.</p> 2403 </vcnote> 2404 <!-- FINAL EDIT: is this duplication too clumsy? --> 2405 <wfcnote id="textent"> 2406 <head>Parsed Entity</head> 2407 <p> 2408 An entity reference must not contain the name of an <termref def="dt-unparsed">unparsed entity</termref>. Unparsed entities may be referred 2409 to only in <termref def="dt-attrval">attribute values</termref> declared to 2410 be of type <kw>ENTITY</kw> or <kw>ENTITIES</kw>. 2411 </p> 2412 </wfcnote> 2413 <wfcnote id="norecursion"> 2414 <head>No Recursion</head> 2415 <p> 2416 A parsed entity must not contain a recursive reference to itself, 2417 either directly or indirectly. 2418 </p> 2419 </wfcnote> 2420 <wfcnote id="indtd"> 2421 <head>In DTD</head> 2422 <p> 2423 Parameter-entity references may only appear in the 2424 <termref def="dt-doctype">DTD</termref>. 2425 </p> 2426 </wfcnote> 2427 <p>Examples of character and entity references: 2428 <eg>Type <key>less-than</key> (&hcro;3C;) to save options. 2429 This document was prepared on &docdate; and 2430 is classified &security-level;.</eg></p> 2431 <p>Example of a parameter-entity reference: 2432 <eg><![CDATA[<!-- declare the parameter entity "ISOLat2"... --> 2433 <!ENTITY % ISOLat2 2434 SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" > 2435 <!-- ... now reference it. --> 2436 %ISOLat2;]]></eg></p> 2437 </div2> 2438 2439 <div2 id="sec-entity-decl"> 2440 <head>Entity Declarations</head> 2441 2442 <p><termdef id="dt-entdecl" term="entity declaration"> 2443 Entities are declared thus: 2444 <scrap lang="ebnf"> 2445 <head>Entity Declaration</head> 2446 <prodgroup pcw2="5" pcw4="18.5"> 2447 <prod id="NT-EntityDecl"><lhs>EntityDecl</lhs> 2448 <rhs><nt def="NT-GEDecl">GEDecl</nt><!--</rhs><com>General entities</com> 2449 <rhs>--> | <nt def="NT-PEDecl">PEDecl</nt></rhs> 2450 <!--<com>Parameter entities</com>--> 2451 </prod> 2452 <prod id="NT-GEDecl"><lhs>GEDecl</lhs> 2453 <rhs>'<!ENTITY' <nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt> 2454 <nt def="NT-S">S</nt> <nt def="NT-EntityDef">EntityDef</nt> 2455 <nt def="NT-S">S</nt>? '>'</rhs> 2456 </prod> 2457 <prod id="NT-PEDecl"><lhs>PEDecl</lhs> 2458 <rhs>'<!ENTITY' <nt def="NT-S">S</nt> '%' <nt def="NT-S">S</nt> 2459 <nt def="NT-Name">Name</nt> <nt def="NT-S">S</nt> 2460 <nt def="NT-PEDef">PEDef</nt> <nt def="NT-S">S</nt>? '>'</rhs> 2461 <!--<com>Parameter entities</com>--> 2462 </prod> 2463 <prod id="NT-EntityDef"><lhs>EntityDef</lhs> 2464 <rhs><nt def="NT-EntityValue">EntityValue</nt> 2465 <!--</rhs> 2466 <rhs>-->| (<nt def="NT-ExternalID">ExternalID</nt> 2467 <nt def="NT-NDataDecl">NDataDecl</nt>?)</rhs> 2468 <!-- <nt def='NT-ExternalDef'>ExternalDef</nt></rhs> --> 2469 </prod> 2470 <!-- FINAL EDIT: what happened to WFs here? --> 2471 <prod id="NT-PEDef"><lhs>PEDef</lhs> 2472 <rhs><nt def="NT-EntityValue">EntityValue</nt> 2473 | <nt def="NT-ExternalID">ExternalID</nt></rhs></prod> 2474 </prodgroup> 2475 </scrap> 2476 The <nt def="NT-Name">Name</nt> identifies the entity in an 2477 <termref def="dt-entref">entity reference</termref> or, in the case of an 2478 unparsed entity, in the value of an <kw>ENTITY</kw> or <kw>ENTITIES</kw> 2479 attribute. 2480 If the same entity is declared more than once, the first declaration 2481 encountered is binding; at user option, an XML processor may issue a 2482 warning if entities are declared multiple times.</termdef> 2483 </p> 2484 2485 <div3 id="sec-internal-ent"> 2486 <head>Internal Entities</head> 2487 2488 <p><termdef id="dt-internent" term="Internal Entity Replacement Text">If 2489 the entity definition is an 2490 <nt def="NT-EntityValue">EntityValue</nt>, 2491 the defined entity is called an <term>internal entity</term>. 2492 There is no separate physical 2493 storage object, and the content of the entity is given in the 2494 declaration. </termdef> 2495 Note that some processing of entity and character references in the 2496 <termref def="dt-litentval">literal entity value</termref> may be required to 2497 produce the correct <termref def="dt-repltext">replacement 2498 text</termref>: see <specref ref="intern-replacement"/>. 2499 </p> 2500 <p>An internal entity is a <termref def="dt-parsedent">parsed 2501 entity</termref>.</p> 2502 <p>Example of an internal entity declaration: 2503 <eg><!ENTITY Pub-Status "This is a pre-release of the 2504 specification."></eg></p> 2505 </div3> 2506 2507 <div3 id="sec-external-ent"> 2508 <head>External Entities</head> 2509 2510 <p><termdef id="dt-extent" term="External Entity">If the entity is not 2511 internal, it is an <term>external 2512 entity</term>, declared as follows: 2513 <scrap lang="ebnf"> 2514 <head>External Entity Declaration</head> 2515 <!-- 2516 <prod id='NT-ExternalDef'><lhs>ExternalDef</lhs> 2517 <rhs></prod> --> 2518 <prod id="NT-ExternalID"><lhs>ExternalID</lhs> 2519 <rhs>'SYSTEM' <nt def="NT-S">S</nt> 2520 <nt def="NT-SystemLiteral">SystemLiteral</nt></rhs> 2521 <rhs>| 'PUBLIC' <nt def="NT-S">S</nt> 2522 <nt def="NT-PubidLiteral">PubidLiteral</nt> 2523 <nt def="NT-S">S</nt> 2524 <nt def="NT-SystemLiteral">SystemLiteral</nt> 2525 </rhs> 2526 </prod> 2527 <prod id="NT-NDataDecl"><lhs>NDataDecl</lhs> 2528 <rhs><nt def="NT-S">S</nt> 'NDATA' <nt def="NT-S">S</nt> 2529 <nt def="NT-Name">Name</nt></rhs> 2530 <vc def="not-declared"/></prod> 2531 </scrap> 2532 If the <nt def="NT-NDataDecl">NDataDecl</nt> is present, this is a 2533 general <termref def="dt-unparsed">unparsed 2534 entity</termref>; otherwise it is a parsed entity.</termdef></p> 2535 <vcnote id="not-declared"> 2536 <head>Notation Declared</head> 2537 <p> 2538 The <nt def="NT-Name">Name</nt> must match the declared name of a 2539 <termref def="dt-notation">notation</termref>. 2540 </p> 2541 </vcnote> 2542 <p><termdef id="dt-sysid" term="System Identifier">The 2543 <nt def="NT-SystemLiteral">SystemLiteral</nt> 2544 is called the entity's <term>system identifier</term>. It is a URI, 2545 which may be used to retrieve the entity.</termdef> 2546 Note that the hash mark (<code>#</code>) and fragment identifier 2547 frequently used with URIs are not, formally, part of the URI itself; 2548 an XML processor may signal an error if a fragment identifier is 2549 given as part of a system identifier. 2550 Unless otherwise provided by information outside the scope of this 2551 specification (e.g. a special XML element type defined by a particular 2552 DTD, or a processing instruction defined by a particular application 2553 specification), relative URIs are relative to the location of the 2554 resource within which the entity declaration occurs. 2555 A URI might thus be relative to the 2556 <termref def="dt-docent">document entity</termref>, to the entity 2557 containing the <termref def="dt-doctype">external DTD subset</termref>, 2558 or to some other <termref def="dt-extent">external parameter entity</termref>. 2559 </p> 2560 <p>An XML processor should handle a non-ASCII character in a URI by 2561 representing the character in UTF-8 as one or more bytes, and then 2562 escaping these bytes with the URI escaping mechanism (i.e., by 2563 converting each byte to %HH, where HH is the hexadecimal notation of the 2564 byte value).</p> 2565 <p><termdef id="dt-pubid" term="Public identifier"> 2566 In addition to a system identifier, an external identifier may 2567 include a <term>public identifier</term>.</termdef> 2568 An XML processor attempting to retrieve the entity's content may use the public 2569 identifier to try to generate an alternative URI. If the processor 2570 is unable to do so, it must use the URI specified in the system 2571 literal. Before a match is attempted, all strings 2572 of white space in the public identifier must be normalized to single space characters (#x20), 2573 and leading and trailing white space must be removed.</p> 2574 <p>Examples of external entity declarations: 2575 <eg><!ENTITY open-hatch 2576 SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml"> 2577 <!ENTITY open-hatch 2578 PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN" 2579 "http://www.textuality.com/boilerplate/OpenHatch.xml"> 2580 <!ENTITY hatch-pic 2581 SYSTEM "../grafix/OpenHatch.gif" 2582 NDATA gif ></eg></p> 2583 </div3> 2584 2585 </div2> 2586 2587 <div2 id="TextEntities"> 2588 <head>Parsed Entities</head> 2589 <div3 id="sec-TextDecl"> 2590 <head>The Text Declaration</head> 2591 <p>External parsed entities may each begin with a <term>text 2592 declaration</term>. 2593 <scrap lang="ebnf"> 2594 <head>Text Declaration</head> 2595 <prodgroup pcw4="12.5" pcw5="13"> 2596 <prod id="NT-TextDecl"><lhs>TextDecl</lhs> 2597 <rhs>&xmlpio; 2598 <nt def="NT-VersionInfo">VersionInfo</nt>? 2599 <nt def="NT-EncodingDecl">EncodingDecl</nt> 2600 <nt def="NT-S">S</nt>? &pic;</rhs> 2601 </prod> 2602 </prodgroup> 2603 </scrap> 2604 </p> 2605 <p>The text declaration must be provided literally, not 2606 by reference to a parsed entity. 2607 No text declaration may appear at any position other than the beginning of 2608 an external parsed entity.</p> 2609 </div3> 2610 <div3 id="wf-entities"> 2611 <head>Well-Formed Parsed Entities</head> 2612 <p>The document entity is well-formed if it matches the production labeled 2613 <nt def="NT-document">document</nt>. 2614 An external general 2615 parsed entity is well-formed if it matches the production labeled 2616 <nt def="NT-extParsedEnt">extParsedEnt</nt>. 2617 An external parameter 2618 entity is well-formed if it matches the production labeled 2619 <nt def="NT-extPE">extPE</nt>. 2620 <scrap lang="ebnf"> 2621 <head>Well-Formed External Parsed Entity</head> 2622 <prod id="NT-extParsedEnt"><lhs>extParsedEnt</lhs> 2623 <rhs><nt def="NT-TextDecl">TextDecl</nt>? 2624 <nt def="NT-content">content</nt></rhs> 2625 </prod> 2626 <prod id="NT-extPE"><lhs>extPE</lhs> 2627 <rhs><nt def="NT-TextDecl">TextDecl</nt>? 2628 <nt def="NT-extSubsetDecl">extSubsetDecl</nt></rhs> 2629 </prod> 2630 </scrap> 2631 An internal general parsed entity is well-formed if its replacement text 2632 matches the production labeled 2633 <nt def="NT-content">content</nt>. 2634 All internal parameter entities are well-formed by definition. 2635 </p> 2636 <p>A consequence of well-formedness in entities is that the logical 2637 and physical structures in an XML document are properly nested; no 2638 <termref def="dt-stag">start-tag</termref>, 2639 <termref def="dt-etag">end-tag</termref>, 2640 <termref def="dt-empty">empty-element tag</termref>, 2641 <termref def="dt-element">element</termref>, 2642 <termref def="dt-comment">comment</termref>, 2643 <termref def="dt-pi">processing instruction</termref>, 2644 <termref def="dt-charref">character 2645 reference</termref>, or 2646 <termref def="dt-entref">entity reference</termref> 2647 can begin in one entity and end in another.</p> 2648 </div3> 2649 <div3 id="charencoding"> 2650 <head>Character Encoding in Entities</head> 2651 2652 <p>Each external parsed entity in an XML document may use a different 2653 encoding for its characters. All XML processors must be able to read 2654 entities in either UTF-8 or UTF-16. 2655 2656 </p> 2657 <p>Entities encoded in UTF-16 must 2658 begin with the Byte Order Mark described by ISO/IEC 10646 Annex E and 2659 Unicode Appendix B (the ZERO WIDTH NO-BREAK SPACE character, #xFEFF). 2660 This is an encoding signature, not part of either the markup or the 2661 character data of the XML document. 2662 XML processors must be able to use this character to 2663 differentiate between UTF-8 and UTF-16 encoded documents.</p> 2664 <p>Although an XML processor is required to read only entities in 2665 the UTF-8 and UTF-16 encodings, it is recognized that other encodings are 2666 used around the world, and it may be desired for XML processors 2667 to read entities that use them. 2668 Parsed entities which are stored in an encoding other than 2669 UTF-8 or UTF-16 must begin with a <titleref href="TextDecl">text 2670 declaration</titleref> containing an encoding declaration: 2671 <scrap lang="ebnf"> 2672 <head>Encoding Declaration</head> 2673 <prod id="NT-EncodingDecl"><lhs>EncodingDecl</lhs> 2674 <rhs><nt def="NT-S">S</nt> 2675 'encoding' <nt def="NT-Eq">Eq</nt> 2676 ('"' <nt def="NT-EncName">EncName</nt> '"' | 2677 "'" <nt def="NT-EncName">EncName</nt> "'" ) 2678 </rhs> 2679 </prod> 2680 <prod id="NT-EncName"><lhs>EncName</lhs> 2681 <rhs>[A-Za-z] ([A-Za-z0-9._] | '-')*</rhs> 2682 <com>Encoding name contains only Latin characters</com> 2683 </prod> 2684 </scrap> 2685 In the <termref def="dt-docent">document entity</termref>, the encoding 2686 declaration is part of the <termref def="dt-xmldecl">XML declaration</termref>. 2687 The <nt def="NT-EncName">EncName</nt> is the name of the encoding used. 2688 </p> 2689 <!-- FINAL EDIT: check name of IANA and charset names --> 2690 <p>In an encoding declaration, the values 2691 "<code>UTF-8</code>", 2692 "<code>UTF-16</code>", 2693 "<code>ISO-10646-UCS-2</code>", and 2694 "<code>ISO-10646-UCS-4</code>" should be 2695 used for the various encodings and transformations of Unicode / 2696 ISO/IEC 10646, the values 2697 "<code>ISO-8859-1</code>", 2698 "<code>ISO-8859-2</code>", ... 2699 "<code>ISO-8859-9</code>" should be used for the parts of ISO 8859, and 2700 the values 2701 "<code>ISO-2022-JP</code>", 2702 "<code>Shift_JIS</code>", and 2703 "<code>EUC-JP</code>" 2704 should be used for the various encoded forms of JIS X-0208-1997. XML 2705 processors may recognize other encodings; it is recommended that 2706 character encodings registered (as <emph>charset</emph>s) 2707 with the Internet Assigned Numbers 2708 Authority <bibref ref="IANA"/>, other than those just listed, should be 2709 referred to 2710 using their registered names. 2711 Note that these registered names are defined to be 2712 case-insensitive, so processors wishing to match against them 2713 should do so in a case-insensitive 2714 way.</p> 2715 <p>In the absence of information provided by an external 2716 transport protocol (e.g. HTTP or MIME), 2717 it is an <termref def="dt-error">error</termref> for an entity including 2718 an encoding declaration to be presented to the XML processor 2719 in an encoding other than that named in the declaration, 2720 for an encoding declaration to occur other than at the beginning 2721 of an external entity, or for 2722 an entity which begins with neither a Byte Order Mark nor an encoding 2723 declaration to use an encoding other than UTF-8. 2724 Note that since ASCII 2725 is a subset of UTF-8, ordinary ASCII entities do not strictly need 2726 an encoding declaration.</p> 2727 2728 <p>It is a <termref def="dt-fatal">fatal error</termref> when an XML processor 2729 encounters an entity with an encoding that it is unable to process.</p> 2730 <p>Examples of encoding declarations: 2731 <eg><?xml encoding='UTF-8'?> 2732 <?xml encoding='EUC-JP'?></eg></p> 2733 </div3> 2734 </div2> 2735 <div2 id="entproc"> 2736 <head>XML Processor Treatment of Entities and References</head> 2737 <p>The table below summarizes the contexts in which character references, 2738 entity references, and invocations of unparsed entities might appear and the 2739 required behavior of an <termref def="dt-xml-proc">XML processor</termref> in 2740 each case. 2741 The labels in the leftmost column describe the recognition context: 2742 <glist> 2743 <gitem><label>Reference in Content</label> 2744 <def><p>as a reference 2745 anywhere after the <termref def="dt-stag">start-tag</termref> and 2746 before the <termref def="dt-etag">end-tag</termref> of an element; corresponds 2747 to the nonterminal <nt def="NT-content">content</nt>.</p></def> 2748 </gitem> 2749 <gitem> 2750 <label>Reference in Attribute Value</label> 2751 <def><p>as a reference within either the value of an attribute in a 2752 <termref def="dt-stag">start-tag</termref>, or a default 2753 value in an <termref def="dt-attdecl">attribute declaration</termref>; 2754 corresponds to the nonterminal 2755 <nt def="NT-AttValue">AttValue</nt>.</p></def></gitem> 2756 <gitem> 2757 <label>Occurs as Attribute Value</label> 2758 <def><p>as a <nt def="NT-Name">Name</nt>, not a reference, appearing either as 2759 the value of an 2760 attribute which has been declared as type <kw>ENTITY</kw>, or as one of 2761 the space-separated tokens in the value of an attribute which has been 2762 declared as type <kw>ENTITIES</kw>.</p> 2763 </def></gitem> 2764 <gitem><label>Reference in Entity Value</label> 2765 <def><p>as a reference 2766 within a parameter or internal entity's 2767 <termref def="dt-litentval">literal entity value</termref> in 2768 the entity's declaration; corresponds to the nonterminal 2769 <nt def="NT-EntityValue">EntityValue</nt>.</p></def></gitem> 2770 <gitem><label>Reference in DTD</label> 2771 <def><p>as a reference within either the internal or external subsets of the 2772 <termref def="dt-doctype">DTD</termref>, but outside 2773 of an <nt def="NT-EntityValue">EntityValue</nt> or 2774 <nt def="NT-AttValue">AttValue</nt>.</p></def> 2775 </gitem> 2776 </glist></p> 2777 <htable border="1" cellpadding="7" align="center"> 2778 <htbody> 2779 <tr><td bgcolor="&cellback;" rowspan="2" colspan="1"/> 2780 <td bgcolor="&cellback;" align="center" valign="bottom" colspan="4">Entity Type</td> 2781 <td bgcolor="&cellback;" rowspan="2" align="center">Character</td> 2782 </tr> 2783 <tr align="center" valign="bottom"> 2784 <td bgcolor="&cellback;">Parameter</td> 2785 <td bgcolor="&cellback;">Internal 2786 General</td> 2787 <td bgcolor="&cellback;">External Parsed 2788 General</td> 2789 <td bgcolor="&cellback;">Unparsed</td> 2790 </tr> 2791 <tr align="center" valign="middle"> 2792 2793 <td bgcolor="&cellback;" align="right">Reference 2794 in Content</td> 2795 <td bgcolor="&cellback;"><titleref href="not-recognized">Not recognized</titleref></td> 2796 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td> 2797 <td bgcolor="&cellback;"><titleref href="include-if-valid">Included if validating</titleref></td> 2798 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td> 2799 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td> 2800 </tr> 2801 <tr align="center" valign="middle"> 2802 <td bgcolor="&cellback;" align="right">Reference 2803 in Attribute Value</td> 2804 <td bgcolor="&cellback;"><titleref href="not-recognized">Not recognized</titleref></td> 2805 <td bgcolor="&cellback;"><titleref href="inliteral">Included in literal</titleref></td> 2806 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td> 2807 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td> 2808 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td> 2809 </tr> 2810 <tr align="center" valign="middle"> 2811 <td bgcolor="&cellback;" align="right">Occurs as 2812 Attribute Value</td> 2813 <td bgcolor="&cellback;"><titleref href="not-recognized">Not recognized</titleref></td> 2814 <td bgcolor="&cellback;"><titleref href="not-recognized">Forbidden</titleref></td> 2815 <td bgcolor="&cellback;"><titleref href="not-recognized">Forbidden</titleref></td> 2816 <td bgcolor="&cellback;"><titleref href="notify">Notify</titleref></td> 2817 <td bgcolor="&cellback;"><titleref href="not recognized">Not recognized</titleref></td> 2818 </tr> 2819 <tr align="center" valign="middle"> 2820 <td bgcolor="&cellback;" align="right">Reference 2821 in EntityValue</td> 2822 <td bgcolor="&cellback;"><titleref href="inliteral">Included in literal</titleref></td> 2823 <td bgcolor="&cellback;"><titleref href="bypass">Bypassed</titleref></td> 2824 <td bgcolor="&cellback;"><titleref href="bypass">Bypassed</titleref></td> 2825 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td> 2826 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td> 2827 </tr> 2828 <tr align="center" valign="middle"> 2829 <td bgcolor="&cellback;" align="right">Reference 2830 in DTD</td> 2831 <td bgcolor="&cellback;"><titleref href="as-PE">Included as PE</titleref></td> 2832 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td> 2833 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td> 2834 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td> 2835 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td> 2836 </tr> 2837 </htbody> 2838 </htable> 2839 <div3 id="not-recognized"> 2840 <head>Not Recognized</head> 2841 <p>Outside the DTD, the <code>%</code> character has no 2842 special significance; thus, what would be parameter entity references in the 2843 DTD are not recognized as markup in <nt def="NT-content">content</nt>. 2844 Similarly, the names of unparsed entities are not recognized except 2845 when they appear in the value of an appropriately declared attribute. 2846 </p> 2847 </div3> 2848 <div3 id="included"> 2849 <head>Included</head> 2850 <p><termdef id="dt-include" term="Include">An entity is 2851 <term>included</term> when its 2852 <termref def="dt-repltext">replacement text</termref> is retrieved 2853 and processed, in place of the reference itself, 2854 as though it were part of the document at the location the 2855 reference was recognized. 2856 The replacement text may contain both 2857 <termref def="dt-chardata">character data</termref> 2858 and (except for parameter entities) <termref def="dt-markup">markup</termref>, 2859 which must be recognized in 2860 the usual way, except that the replacement text of entities used to escape 2861 markup delimiters (the entities &magicents;) is always treated as 2862 data. (The string "<code>AT&amp;T;</code>" expands to 2863 "<code>AT&T;</code>" and the remaining ampersand is not recognized 2864 as an entity-reference delimiter.) 2865 A character reference is <term>included</term> when the indicated 2866 character is processed in place of the reference itself. 2867 </termdef></p> 2868 </div3> 2869 <div3 id="include-if-valid"> 2870 <head>Included If Validating</head> 2871 <p>When an XML processor recognizes a reference to a parsed entity, in order 2872 to <termref def="dt-valid">validate</termref> 2873 the document, the processor must 2874 <termref def="dt-include">include</termref> its 2875 replacement text. 2876 If the entity is external, and the processor is not 2877 attempting to validate the XML document, the 2878 processor <termref def="dt-may">may</termref>, but need not, 2879 include the entity's replacement text. 2880 If a non-validating parser does not include the replacement text, 2881 it must inform the application that it recognized, but did not 2882 read, the entity.</p> 2883 <p>This rule is based on the recognition that the automatic inclusion 2884 provided by the SGML and XML entity mechanism, primarily designed 2885 to support modularity in authoring, is not necessarily 2886 appropriate for other applications, in particular document browsing. 2887 Browsers, for example, when encountering an external parsed entity reference, 2888 might choose to provide a visual indication of the entity's 2889 presence and retrieve it for display only on demand. 2890 </p> 2891 </div3> 2892 <div3 id="forbidden"> 2893 <head>Forbidden</head> 2894 <p>The following are forbidden, and constitute 2895 <termref def="dt-fatal">fatal</termref> errors: 2896 <ulist> 2897 <item><p>the appearance of a reference to an 2898 <termref def="dt-unparsed">unparsed entity</termref>. 2899 </p></item> 2900 <item><p>the appearance of any character or general-entity reference in the 2901 DTD except within an <nt def="NT-EntityValue">EntityValue</nt> or 2902 <nt def="NT-AttValue">AttValue</nt>.</p></item> 2903 <item><p>a reference to an external entity in an attribute value.</p> 2904 </item> 2905 </ulist> 2906 </p> 2907 </div3> 2908 <div3 id="inliteral"> 2909 <head>Included in Literal</head> 2910 <p>When an <termref def="dt-entref">entity reference</termref> appears in an 2911 attribute value, or a parameter entity reference appears in a literal entity 2912 value, its <termref def="dt-repltext">replacement text</termref> is 2913 processed in place of the reference itself as though it 2914 were part of the document at the location the reference was recognized, 2915 except that a single or double quote character in the replacement text 2916 is always treated as a normal data character and will not terminate the 2917 literal. 2918 For example, this is well-formed: 2919 <eg><![CDATA[<!ENTITY % YN '"Yes"' > 2920 <!ENTITY WhatHeSaid "He said &YN;" >]]></eg> 2921 while this is not: 2922 <eg><!ENTITY EndAttr "27'" > 2923 <element attribute='a-&EndAttr;></eg> 2924 </p></div3> 2925 <div3 id="notify"> 2926 <head>Notify</head> 2927 <p>When the name of an <termref def="dt-unparsed">unparsed 2928 entity</termref> appears as a token in the 2929 value of an attribute of declared type <kw>ENTITY</kw> or <kw>ENTITIES</kw>, 2930 a validating processor must inform the 2931 application of the <termref def="dt-sysid">system</termref> 2932 and <termref def="dt-pubid">public</termref> (if any) 2933 identifiers for both the entity and its associated 2934 <termref def="dt-notation">notation</termref>.</p> 2935 </div3> 2936 <div3 id="bypass"> 2937 <head>Bypassed</head> 2938 <p>When a general entity reference appears in the 2939 <nt def="NT-EntityValue">EntityValue</nt> in an entity declaration, 2940 it is bypassed and left as is.</p> 2941 </div3> 2942 <div3 id="as-PE"> 2943 <head>Included as PE</head> 2944 <p>Just as with external parsed entities, parameter entities 2945 need only be <titleref href="include-if-valid">included if 2946 validating</titleref>. 2947 When a parameter-entity reference is recognized in the DTD 2948 and included, its 2949 <termref def="dt-repltext">replacement 2950 text</termref> is enlarged by the attachment of one leading and one following 2951 space (#x20) character; the intent is to constrain the replacement 2952 text of parameter 2953 entities to contain an integral number of grammatical tokens in the DTD. 2954 </p> 2955 </div3> 2956 2957 </div2> 2958 <div2 id="intern-replacement"> 2959 <head>Construction of Internal Entity Replacement Text</head> 2960 <p>In discussing the treatment 2961 of internal entities, it is 2962 useful to distinguish two forms of the entity's value. 2963 <termdef id="dt-litentval" term="Literal Entity Value">The <term>literal 2964 entity value</term> is the quoted string actually 2965 present in the entity declaration, corresponding to the 2966 non-terminal <nt def="NT-EntityValue">EntityValue</nt>.</termdef> 2967 <termdef id="dt-repltext" term="Replacement Text">The <term>replacement 2968 text</term> is the content of the entity, after 2969 replacement of character references and parameter-entity 2970 references. 2971 </termdef></p> 2972 2973 <p>The literal entity value 2974 as given in an internal entity declaration 2975 (<nt def="NT-EntityValue">EntityValue</nt>) may contain character, 2976 parameter-entity, and general-entity references. 2977 Such references must be contained entirely within the 2978 literal entity value. 2979 The actual replacement text that is 2980 <termref def="dt-include">included</termref> as described above 2981 must contain the <emph>replacement text</emph> of any 2982 parameter entities referred to, and must contain the character 2983 referred to, in place of any character references in the 2984 literal entity value; however, 2985 general-entity references must be left as-is, unexpanded. 2986 For example, given the following declarations: 2987 2988 <eg><![CDATA[<!ENTITY % pub "Éditions Gallimard" > 2989 <!ENTITY rights "All rights reserved" > 2990 <!ENTITY book "La Peste: Albert Camus, 2991 © 1947 %pub;. &rights;" >]]></eg> 2992 then the replacement text for the entity "<code>book</code>" is: 2993 <eg>La Peste: Albert Camus, 2994 � 1947 �ditions Gallimard. &rights;</eg> 2995 The general-entity reference "<code>&rights;</code>" would be expanded 2996 should the reference "<code>&book;</code>" appear in the document's 2997 content or an attribute value.</p> 2998 <p>These simple rules may have complex interactions; for a detailed 2999 discussion of a difficult example, see 3000 <specref ref="sec-entexpand"/>. 3001 </p> 3002 3003 </div2> 3004 <div2 id="sec-predefined-ent"> 3005 <head>Predefined Entities</head> 3006 <p><termdef id="dt-escape" term="escape">Entity and character 3007 references can both be used to <term>escape</term> the left angle bracket, 3008 ampersand, and other delimiters. A set of general entities 3009 (&magicents;) is specified for this purpose. 3010 Numeric character references may also be used; they are 3011 expanded immediately when recognized and must be treated as 3012 character data, so the numeric character references 3013 "<code>&#60;</code>" and "<code>&#38;</code>" may be used to 3014 escape <code><</code> and <code>&</code> when they occur 3015 in character data.</termdef></p> 3016 <p>All XML processors must recognize these entities whether they 3017 are declared or not. 3018 <termref def="dt-interop">For interoperability</termref>, 3019 valid XML documents should declare these 3020 entities, like any others, before using them. 3021 If the entities in question are declared, they must be declared 3022 as internal entities whose replacement text is the single 3023 character being escaped or a character reference to 3024 that character, as shown below. 3025 <eg><![CDATA[<!ENTITY lt "&#60;"> 3026 <!ENTITY gt ">"> 3027 <!ENTITY amp "&#38;"> 3028 <!ENTITY apos "'"> 3029 <!ENTITY quot """> 3030 ]]></eg> 3031 Note that the <code><</code> and <code>&</code> characters 3032 in the declarations of "<code>lt</code>" and "<code>amp</code>" 3033 are doubly escaped to meet the requirement that entity replacement 3034 be well-formed. 3035 </p> 3036 </div2> 3037 3038 <div2 id="Notations"> 3039 <head>Notation Declarations</head> 3040 3041 <p><termdef id="dt-notation" term="Notation"><term>Notations</term> identify by 3042 name the format of <termref def="dt-extent">unparsed 3043 entities</termref>, the 3044 format of elements which bear a notation attribute, 3045 or the application to which 3046 a <termref def="dt-pi">processing instruction</termref> is 3047 addressed.</termdef></p> 3048 <p><termdef id="dt-notdecl" term="Notation Declaration"> 3049 <term>Notation declarations</term> 3050 provide a name for the notation, for use in 3051 entity and attribute-list declarations and in attribute specifications, 3052 and an external identifier for the notation which may allow an XML 3053 processor or its client application to locate a helper application 3054 capable of processing data in the given notation. 3055 <scrap lang="ebnf"> 3056 <head>Notation Declarations</head> 3057 <prod id="NT-NotationDecl"><lhs>NotationDecl</lhs> 3058 <rhs>'<!NOTATION' <nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt> 3059 <nt def="NT-S">S</nt> 3060 (<nt def="NT-ExternalID">ExternalID</nt> | 3061 <nt def="NT-PublicID">PublicID</nt>) 3062 <nt def="NT-S">S</nt>? '>'</rhs></prod> 3063 <prod id="NT-PublicID"><lhs>PublicID</lhs> 3064 <rhs>'PUBLIC' <nt def="NT-S">S</nt> 3065 <nt def="NT-PubidLiteral">PubidLiteral</nt> 3066 </rhs></prod> 3067 </scrap> 3068 </termdef></p> 3069 <p>XML processors must provide applications with the name and external 3070 identifier(s) of any notation declared and referred to in an attribute 3071 value, attribute definition, or entity declaration. They may 3072 additionally resolve the external identifier into the 3073 <termref def="dt-sysid">system identifier</termref>, 3074 file name, or other information needed to allow the 3075 application to call a processor for data in the notation described. (It 3076 is not an error, however, for XML documents to declare and refer to 3077 notations for which notation-specific applications are not available on 3078 the system where the XML processor or application is running.)</p> 3079 </div2> 3080 3081 3082 <div2 id="sec-doc-entity"> 3083 <head>Document Entity</head> 3084 3085 <p><termdef id="dt-docent" term="Document Entity">The <term>document 3086 entity</term> serves as the root of the entity 3087 tree and a starting-point for an <termref def="dt-xml-proc">XML 3088 processor</termref>.</termdef> 3089 This specification does 3090 not specify how the document entity is to be located by an XML 3091 processor; unlike other entities, the document entity has no name and might 3092 well appear on a processor input stream 3093 without any identification at all.</p> 3094 </div2> 3095 3096 3097 </div1> 3098 <!-- &Conformance; --> 3099 3100 <div1 id="sec-conformance"> 3101 <head>Conformance</head> 3102 3103 <div2 id="proc-types"> 3104 <head>Validating and Non-Validating Processors</head> 3105 <p>Conforming <termref def="dt-xml-proc">XML processors</termref> fall into two 3106 classes: validating and non-validating.</p> 3107 <p>Validating and non-validating processors alike must report 3108 violations of this specification's well-formedness constraints 3109 in the content of the 3110 <termref def="dt-docent">document entity</termref> and any 3111 other <termref def="dt-parsedent">parsed entities</termref> that 3112 they read.</p> 3113 <p><termdef id="dt-validating" term="Validating Processor"> 3114 <term>Validating processors</term> must report 3115 violations of the constraints expressed by the declarations in the 3116 <termref def="dt-doctype">DTD</termref>, and 3117 failures to fulfill the validity constraints given 3118 in this specification. 3119 </termdef> 3120 To accomplish this, validating XML processors must read and process the entire 3121 DTD and all external parsed entities referenced in the document. 3122 </p> 3123 <p>Non-validating processors are required to check only the 3124 <termref def="dt-docent">document entity</termref>, including 3125 the entire internal DTD subset, for well-formedness. 3126 <termdef id="dt-use-mdecl" term="Process Declarations"> 3127 While they are not required to check the document for validity, 3128 they are required to 3129 <term>process</term> all the declarations they read in the 3130 internal DTD subset and in any parameter entity that they 3131 read, up to the first reference 3132 to a parameter entity that they do <emph>not</emph> read; that is to 3133 say, they must 3134 use the information in those declarations to 3135 <titleref href="AVNormalize">normalize</titleref> attribute values, 3136 <titleref href="included">include</titleref> the replacement text of 3137 internal entities, and supply 3138 <titleref href="sec-attr-defaults">default attribute values</titleref>. 3139 </termdef> 3140 They must not <termref def="dt-use-mdecl">process</termref> 3141 <termref def="dt-entdecl">entity declarations</termref> or 3142 <termref def="dt-attdecl">attribute-list declarations</termref> 3143 encountered after a reference to a parameter entity that is not 3144 read, since the entity may have contained overriding declarations. 3145 </p> 3146 </div2> 3147 <div2 id="safe-behavior"> 3148 <head>Using XML Processors</head> 3149 <p>The behavior of a validating XML processor is highly predictable; it 3150 must read every piece of a document and report all well-formedness and 3151 validity violations. 3152 Less is required of a non-validating processor; it need not read any 3153 part of the document other than the document entity. 3154 This has two effects that may be important to users of XML processors: 3155 <ulist> 3156 <item><p>Certain well-formedness errors, specifically those that require 3157 reading external entities, may not be detected by a non-validating processor. 3158 Examples include the constraints entitled 3159 <titleref href="wf-entdeclared">Entity Declared</titleref>, 3160 <titleref href="wf-textent">Parsed Entity</titleref>, and 3161 <titleref href="wf-norecursion">No Recursion</titleref>, as well 3162 as some of the cases described as 3163 <titleref href="forbidden">forbidden</titleref> in 3164 <specref ref="entproc"/>.</p></item> 3165 <item><p>The information passed from the processor to the application may 3166 vary, depending on whether the processor reads 3167 parameter and external entities. 3168 For example, a non-validating processor may not 3169 <titleref href="AVNormalize">normalize</titleref> attribute values, 3170 <titleref href="included">include</titleref> the replacement text of 3171 internal entities, or supply 3172 <titleref href="sec-attr-defaults">default attribute values</titleref>, 3173 where doing so depends on having read declarations in 3174 external or parameter entities.</p></item> 3175 </ulist> 3176 </p> 3177 <p>For maximum reliability in interoperating between different XML 3178 processors, applications which use non-validating processors should not 3179 rely on any behaviors not required of such processors. 3180 Applications which require facilities such as the use of default 3181 attributes or internal entities which are declared in external 3182 entities should use validating XML processors.</p> 3183 </div2> 3184 </div1> 3185 3186 <div1 id="sec-notation"> 3187 <head>Notation</head> 3188 3189 <p>The formal grammar of XML is given in this specification using a simple 3190 Extended Backus-Naur Form (EBNF) notation. Each rule in the grammar defines 3191 one symbol, in the form 3192 <eg>symbol ::= expression</eg></p> 3193 <p>Symbols are written with an initial capital letter if they are 3194 defined by a regular expression, or with an initial lower case letter 3195 otherwise. 3196 Literal strings are quoted. 3197 3198 </p> 3199 3200 <p>Within the expression on the right-hand side of a rule, the following 3201 expressions are used to match strings of one or more characters: 3202 <glist> 3203 <gitem> 3204 <label><code>#xN</code></label> 3205 <def><p>where <code>N</code> is a hexadecimal integer, the 3206 expression matches the character in ISO/IEC 10646 whose canonical 3207 (UCS-4) 3208 code value, when interpreted as an unsigned binary number, has 3209 the value indicated. The number of leading zeros in the 3210 <code>#xN</code> form is insignificant; the number of leading 3211 zeros in the corresponding code value 3212 is governed by the character 3213 encoding in use and is not significant for XML.</p></def> 3214 </gitem> 3215 <gitem> 3216 <label><code>[a-zA-Z]</code>, <code>[#xN-#xN]</code></label> 3217 <def><p>matches any <termref def="dt-character">character</termref> 3218 with a value in the range(s) indicated (inclusive).</p></def> 3219 </gitem> 3220 <gitem> 3221 <label><code>[^a-z]</code>, <code>[^#xN-#xN]</code></label> 3222 <def><p>matches any <termref def="dt-character">character</termref> 3223 with a value <emph>outside</emph> the 3224 range indicated.</p></def> 3225 </gitem> 3226 <gitem> 3227 <label><code>[^abc]</code>, <code>[^#xN#xN#xN]</code></label> 3228 <def><p>matches any <termref def="dt-character">character</termref> 3229 with a value not among the characters given.</p></def> 3230 </gitem> 3231 <gitem> 3232 <label><code>"string"</code></label> 3233 <def><p>matches a literal string <termref def="dt-match">matching</termref> 3234 that given inside the double quotes.</p></def> 3235 </gitem> 3236 <gitem> 3237 <label><code>'string'</code></label> 3238 <def><p>matches a literal string <termref def="dt-match">matching</termref> 3239 that given inside the single quotes.</p></def> 3240 </gitem> 3241 </glist> 3242 These symbols may be combined to match more complex patterns as follows, 3243 where <code>A</code> and <code>B</code> represent simple expressions: 3244 <glist> 3245 <gitem> 3246 <label>(<code>expression</code>)</label> 3247 <def><p><code>expression</code> is treated as a unit 3248 and may be combined as described in this list.</p></def> 3249 </gitem> 3250 <gitem> 3251 <label><code>A?</code></label> 3252 <def><p>matches <code>A</code> or nothing; optional <code>A</code>.</p></def> 3253 </gitem> 3254 <gitem> 3255 <label><code>A B</code></label> 3256 <def><p>matches <code>A</code> followed by <code>B</code>.</p></def> 3257 </gitem> 3258 <gitem> 3259 <label><code>A | B</code></label> 3260 <def><p>matches <code>A</code> or <code>B</code> but not both.</p></def> 3261 </gitem> 3262 <gitem> 3263 <label><code>A - B</code></label> 3264 <def><p>matches any string that matches <code>A</code> but does not match 3265 <code>B</code>. 3266 </p></def> 3267 </gitem> 3268 <gitem> 3269 <label><code>A+</code></label> 3270 <def><p>matches one or more occurrences of <code>A</code>.</p></def> 3271 </gitem> 3272 <gitem> 3273 <label><code>A*</code></label> 3274 <def><p>matches zero or more occurrences of <code>A</code>.</p></def> 3275 </gitem> 3276 3277 </glist> 3278 Other notations used in the productions are: 3279 <glist> 3280 <gitem> 3281 <label><code>/* ... */</code></label> 3282 <def><p>comment.</p></def> 3283 </gitem> 3284 <gitem> 3285 <label><code>[ wfc: ... ]</code></label> 3286 <def><p>well-formedness constraint; this identifies by name a 3287 constraint on 3288 <termref def="dt-wellformed">well-formed</termref> documents 3289 associated with a production.</p></def> 3290 </gitem> 3291 <gitem> 3292 <label><code>[ vc: ... ]</code></label> 3293 <def><p>validity constraint; this identifies by name a constraint on 3294 <termref def="dt-valid">valid</termref> documents associated with 3295 a production.</p></def> 3296 </gitem> 3297 </glist> 3298 </p></div1> 3299 3300 </body> 3301 <back> 3302 <!-- &SGML; --> 3303 3304 3305 <!-- &Biblio; --> 3306 <div1 id="sec-bibliography"> 3307 3308 <head>References</head> 3309 <div2 id="sec-existing-stds"> 3310 <head>Normative References</head> 3311 3312 <blist> 3313 <bibl id="IANA" key="IANA"> 3314 (Internet Assigned Numbers Authority) <emph>Official Names for 3315 Character Sets</emph>, 3316 ed. Keld Simonsen et al. 3317 See <loc href="ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets">ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets</loc>. 3318 </bibl> 3319 3320 <bibl id="RFC1766" key="IETF RFC 1766"> 3321 IETF (Internet Engineering Task Force). 3322 <emph>RFC 1766: Tags for the Identification of Languages</emph>, 3323 ed. H. Alvestrand. 3324 1995. 3325 </bibl> 3326 3327 <bibl id="ISO639" key="ISO 639"> 3328 (International Organization for Standardization). 3329 <emph>ISO 639:1988 (E). 3330 Code for the representation of names of languages.</emph> 3331 [Geneva]: International Organization for 3332 Standardization, 1988.</bibl> 3333 3334 <bibl id="ISO3166" key="ISO 3166"> 3335 (International Organization for Standardization). 3336 <emph>ISO 3166-1:1997 (E). 3337 Codes for the representation of names of countries and their subdivisions 3338 — Part 1: Country codes</emph> 3339 [Geneva]: International Organization for 3340 Standardization, 1997.</bibl> 3341 3342 <bibl id="ISO10646" key="ISO/IEC 10646">ISO 3343 (International Organization for Standardization). 3344 <emph>ISO/IEC 10646-1993 (E). Information technology — Universal 3345 Multiple-Octet Coded Character Set (UCS) — Part 1: 3346 Architecture and Basic Multilingual Plane.</emph> 3347 [Geneva]: International Organization for 3348 Standardization, 1993 (plus amendments AM 1 through AM 7). 3349 </bibl> 3350 3351 <bibl id="Unicode" key="Unicode">The Unicode Consortium. 3352 <emph>The Unicode Standard, Version 2.0.</emph> 3353 Reading, Mass.: Addison-Wesley Developers Press, 1996.</bibl> 3354 3355 </blist> 3356 3357 </div2> 3358 3359 <div2><head>Other References</head> 3360 3361 <blist> 3362 3363 <bibl id="Aho" key="Aho/Ullman">Aho, Alfred V., 3364 Ravi Sethi, and Jeffrey D. Ullman. 3365 <emph>Compilers: Principles, Techniques, and Tools</emph>. 3366 Reading: Addison-Wesley, 1986, rpt. corr. 1988.</bibl> 3367 3368 <bibl id="Berners-Lee" xml-link="simple" key="Berners-Lee et al."> 3369 Berners-Lee, T., R. Fielding, and L. Masinter. 3370 <emph>Uniform Resource Identifiers (URI): Generic Syntax and 3371 Semantics</emph>. 3372 1997. 3373 (Work in progress; see updates to RFC1738.)</bibl> 3374 3375 <bibl id="ABK" key="Br�ggemann-Klein">Br�ggemann-Klein, Anne. 3376 <emph>Regular Expressions into Finite Automata</emph>. 3377 Extended abstract in I. Simon, Hrsg., LATIN 1992, 3378 S. 97-98. Springer-Verlag, Berlin 1992. 3379 Full Version in Theoretical Computer Science 120: 197-213, 1993. 3380 3381 </bibl> 3382 3383 <bibl id="ABKDW" key="Br�ggemann-Klein and Wood">Br�ggemann-Klein, Anne, 3384 and Derick Wood. 3385 <emph>Deterministic Regular Languages</emph>. 3386 Universit�t Freiburg, Institut f�r Informatik, 3387 Bericht 38, Oktober 1991. 3388 </bibl> 3389 3390 <bibl id="Clark" key="Clark">James Clark. 3391 Comparison of SGML and XML. See 3392 <loc href="http://www.w3.org/TR/NOTE-sgml-xml-971215">http://www.w3.org/TR/NOTE-sgml-xml-971215</loc>. 3393 </bibl> 3394 <bibl id="RFC1738" xml-link="simple" key="IETF RFC1738"> 3395 IETF (Internet Engineering Task Force). 3396 <emph>RFC 1738: Uniform Resource Locators (URL)</emph>, 3397 ed. T. Berners-Lee, L. Masinter, M. McCahill. 3398 1994. 3399 </bibl> 3400 3401 <bibl id="RFC1808" xml-link="simple" key="IETF RFC1808"> 3402 IETF (Internet Engineering Task Force). 3403 <emph>RFC 1808: Relative Uniform Resource Locators</emph>, 3404 ed. R. Fielding. 3405 1995. 3406 </bibl> 3407 3408 <bibl id="RFC2141" xml-link="simple" key="IETF RFC2141"> 3409 IETF (Internet Engineering Task Force). 3410 <emph>RFC 2141: URN Syntax</emph>, 3411 ed. R. Moats. 3412 1997. 3413 </bibl> 3414 3415 <bibl id="ISO8879" key="ISO 8879">ISO 3416 (International Organization for Standardization). 3417 <emph>ISO 8879:1986(E). Information processing — Text and Office 3418 Systems — Standard Generalized Markup Language (SGML).</emph> First 3419 edition — 1986-10-15. [Geneva]: International Organization for 3420 Standardization, 1986. 3421 </bibl> 3422 3423 3424 <bibl id="ISO10744" key="ISO/IEC 10744">ISO 3425 (International Organization for Standardization). 3426 <emph>ISO/IEC 10744-1992 (E). Information technology — 3427 Hypermedia/Time-based Structuring Language (HyTime). 3428 </emph> 3429 [Geneva]: International Organization for 3430 Standardization, 1992. 3431 <emph>Extended Facilities Annexe.</emph> 3432 [Geneva]: International Organization for 3433 Standardization, 1996. 3434 </bibl> 3435 3436 3437 3438 </blist> 3439 </div2> 3440 </div1> 3441 <div1 id="CharClasses"> 3442 <head>Character Classes</head> 3443 <p>Following the characteristics defined in the Unicode standard, 3444 characters are classed as base characters (among others, these 3445 contain the alphabetic characters of the Latin alphabet, without 3446 diacritics), ideographic characters, and combining characters (among 3447 others, this class contains most diacritics); these classes combine 3448 to form the class of letters. Digits and extenders are 3449 also distinguished. 3450 <scrap lang="ebnf" id="CHARACTERS"> 3451 <head>Characters</head> 3452 <prodgroup pcw3="3" pcw4="15"> 3453 <prod id="NT-Letter"><lhs>Letter</lhs> 3454 <rhs><nt def="NT-BaseChar">BaseChar</nt> 3455 | <nt def="NT-Ideographic">Ideographic</nt></rhs> </prod> 3456 <prod id="NT-BaseChar"><lhs>BaseChar</lhs> 3457 <rhs>[#x0041-#x005A] 3458 | [#x0061-#x007A] 3459 | [#x00C0-#x00D6] 3460 | [#x00D8-#x00F6] 3461 | [#x00F8-#x00FF] 3462 | [#x0100-#x0131] 3463 | [#x0134-#x013E] 3464 | [#x0141-#x0148] 3465 | [#x014A-#x017E] 3466 | [#x0180-#x01C3] 3467 | [#x01CD-#x01F0] 3468 | [#x01F4-#x01F5] 3469 | [#x01FA-#x0217] 3470 | [#x0250-#x02A8] 3471 | [#x02BB-#x02C1] 3472 | #x0386 3473 | [#x0388-#x038A] 3474 | #x038C 3475 | [#x038E-#x03A1] 3476 | [#x03A3-#x03CE] 3477 | [#x03D0-#x03D6] 3478 | #x03DA 3479 | #x03DC 3480 | #x03DE 3481 | #x03E0 3482 | [#x03E2-#x03F3] 3483 | [#x0401-#x040C] 3484 | [#x040E-#x044F] 3485 | [#x0451-#x045C] 3486 | [#x045E-#x0481] 3487 | [#x0490-#x04C4] 3488 | [#x04C7-#x04C8] 3489 | [#x04CB-#x04CC] 3490 | [#x04D0-#x04EB] 3491 | [#x04EE-#x04F5] 3492 | [#x04F8-#x04F9] 3493 | [#x0531-#x0556] 3494 | #x0559 3495 | [#x0561-#x0586] 3496 | [#x05D0-#x05EA] 3497 | [#x05F0-#x05F2] 3498 | [#x0621-#x063A] 3499 | [#x0641-#x064A] 3500 | [#x0671-#x06B7] 3501 | [#x06BA-#x06BE] 3502 | [#x06C0-#x06CE] 3503 | [#x06D0-#x06D3] 3504 | #x06D5 3505 | [#x06E5-#x06E6] 3506 | [#x0905-#x0939] 3507 | #x093D 3508 | [#x0958-#x0961] 3509 | [#x0985-#x098C] 3510 | [#x098F-#x0990] 3511 | [#x0993-#x09A8] 3512 | [#x09AA-#x09B0] 3513 | #x09B2 3514 | [#x09B6-#x09B9] 3515 | [#x09DC-#x09DD] 3516 | [#x09DF-#x09E1] 3517 | [#x09F0-#x09F1] 3518 | [#x0A05-#x0A0A] 3519 | [#x0A0F-#x0A10] 3520 | [#x0A13-#x0A28] 3521 | [#x0A2A-#x0A30] 3522 | [#x0A32-#x0A33] 3523 | [#x0A35-#x0A36] 3524 | [#x0A38-#x0A39] 3525 | [#x0A59-#x0A5C] 3526 | #x0A5E 3527 | [#x0A72-#x0A74] 3528 | [#x0A85-#x0A8B] 3529 | #x0A8D 3530 | [#x0A8F-#x0A91] 3531 | [#x0A93-#x0AA8] 3532 | [#x0AAA-#x0AB0] 3533 | [#x0AB2-#x0AB3] 3534 | [#x0AB5-#x0AB9] 3535 | #x0ABD 3536 | #x0AE0 3537 | [#x0B05-#x0B0C] 3538 | [#x0B0F-#x0B10] 3539 | [#x0B13-#x0B28] 3540 | [#x0B2A-#x0B30] 3541 | [#x0B32-#x0B33] 3542 | [#x0B36-#x0B39] 3543 | #x0B3D 3544 | [#x0B5C-#x0B5D] 3545 | [#x0B5F-#x0B61] 3546 | [#x0B85-#x0B8A] 3547 | [#x0B8E-#x0B90] 3548 | [#x0B92-#x0B95] 3549 | [#x0B99-#x0B9A] 3550 | #x0B9C 3551 | [#x0B9E-#x0B9F] 3552 | [#x0BA3-#x0BA4] 3553 | [#x0BA8-#x0BAA] 3554 | [#x0BAE-#x0BB5] 3555 | [#x0BB7-#x0BB9] 3556 | [#x0C05-#x0C0C] 3557 | [#x0C0E-#x0C10] 3558 | [#x0C12-#x0C28] 3559 | [#x0C2A-#x0C33] 3560 | [#x0C35-#x0C39] 3561 | [#x0C60-#x0C61] 3562 | [#x0C85-#x0C8C] 3563 | [#x0C8E-#x0C90] 3564 | [#x0C92-#x0CA8] 3565 | [#x0CAA-#x0CB3] 3566 | [#x0CB5-#x0CB9] 3567 | #x0CDE 3568 | [#x0CE0-#x0CE1] 3569 | [#x0D05-#x0D0C] 3570 | [#x0D0E-#x0D10] 3571 | [#x0D12-#x0D28] 3572 | [#x0D2A-#x0D39] 3573 | [#x0D60-#x0D61] 3574 | [#x0E01-#x0E2E] 3575 | #x0E30 3576 | [#x0E32-#x0E33] 3577 | [#x0E40-#x0E45] 3578 | [#x0E81-#x0E82] 3579 | #x0E84 3580 | [#x0E87-#x0E88] 3581 | #x0E8A 3582 | #x0E8D 3583 | [#x0E94-#x0E97] 3584 | [#x0E99-#x0E9F] 3585 | [#x0EA1-#x0EA3] 3586 | #x0EA5 3587 | #x0EA7 3588 | [#x0EAA-#x0EAB] 3589 | [#x0EAD-#x0EAE] 3590 | #x0EB0 3591 | [#x0EB2-#x0EB3] 3592 | #x0EBD 3593 | [#x0EC0-#x0EC4] 3594 | [#x0F40-#x0F47] 3595 | [#x0F49-#x0F69] 3596 | [#x10A0-#x10C5] 3597 | [#x10D0-#x10F6] 3598 | #x1100 3599 | [#x1102-#x1103] 3600 | [#x1105-#x1107] 3601 | #x1109 3602 | [#x110B-#x110C] 3603 | [#x110E-#x1112] 3604 | #x113C 3605 | #x113E 3606 | #x1140 3607 | #x114C 3608 | #x114E 3609 | #x1150 3610 | [#x1154-#x1155] 3611 | #x1159 3612 | [#x115F-#x1161] 3613 | #x1163 3614 | #x1165 3615 | #x1167 3616 | #x1169 3617 | [#x116D-#x116E] 3618 | [#x1172-#x1173] 3619 | #x1175 3620 | #x119E 3621 | #x11A8 3622 | #x11AB 3623 | [#x11AE-#x11AF] 3624 | [#x11B7-#x11B8] 3625 | #x11BA 3626 | [#x11BC-#x11C2] 3627 | #x11EB 3628 | #x11F0 3629 | #x11F9 3630 | [#x1E00-#x1E9B] 3631 | [#x1EA0-#x1EF9] 3632 | [#x1F00-#x1F15] 3633 | [#x1F18-#x1F1D] 3634 | [#x1F20-#x1F45] 3635 | [#x1F48-#x1F4D] 3636 | [#x1F50-#x1F57] 3637 | #x1F59 3638 | #x1F5B 3639 | #x1F5D 3640 | [#x1F5F-#x1F7D] 3641 | [#x1F80-#x1FB4] 3642 | [#x1FB6-#x1FBC] 3643 | #x1FBE 3644 | [#x1FC2-#x1FC4] 3645 | [#x1FC6-#x1FCC] 3646 | [#x1FD0-#x1FD3] 3647 | [#x1FD6-#x1FDB] 3648 | [#x1FE0-#x1FEC] 3649 | [#x1FF2-#x1FF4] 3650 | [#x1FF6-#x1FFC] 3651 | #x2126 3652 | [#x212A-#x212B] 3653 | #x212E 3654 | [#x2180-#x2182] 3655 | [#x3041-#x3094] 3656 | [#x30A1-#x30FA] 3657 | [#x3105-#x312C] 3658 | [#xAC00-#xD7A3] 3659 </rhs></prod> 3660 <prod id="NT-Ideographic"><lhs>Ideographic</lhs> 3661 <rhs>[#x4E00-#x9FA5] 3662 | #x3007 3663 | [#x3021-#x3029] 3664 </rhs></prod> 3665 <prod id="NT-CombiningChar"><lhs>CombiningChar</lhs> 3666 <rhs>[#x0300-#x0345] 3667 | [#x0360-#x0361] 3668 | [#x0483-#x0486] 3669 | [#x0591-#x05A1] 3670 | [#x05A3-#x05B9] 3671 | [#x05BB-#x05BD] 3672 | #x05BF 3673 | [#x05C1-#x05C2] 3674 | #x05C4 3675 | [#x064B-#x0652] 3676 | #x0670 3677 | [#x06D6-#x06DC] 3678 | [#x06DD-#x06DF] 3679 | [#x06E0-#x06E4] 3680 | [#x06E7-#x06E8] 3681 | [#x06EA-#x06ED] 3682 | [#x0901-#x0903] 3683 | #x093C 3684 | [#x093E-#x094C] 3685 | #x094D 3686 | [#x0951-#x0954] 3687 | [#x0962-#x0963] 3688 | [#x0981-#x0983] 3689 | #x09BC 3690 | #x09BE 3691 | #x09BF 3692 | [#x09C0-#x09C4] 3693 | [#x09C7-#x09C8] 3694 | [#x09CB-#x09CD] 3695 | #x09D7 3696 | [#x09E2-#x09E3] 3697 | #x0A02 3698 | #x0A3C 3699 | #x0A3E 3700 | #x0A3F 3701 | [#x0A40-#x0A42] 3702 | [#x0A47-#x0A48] 3703 | [#x0A4B-#x0A4D] 3704 | [#x0A70-#x0A71] 3705 | [#x0A81-#x0A83] 3706 | #x0ABC 3707 | [#x0ABE-#x0AC5] 3708 | [#x0AC7-#x0AC9] 3709 | [#x0ACB-#x0ACD] 3710 | [#x0B01-#x0B03] 3711 | #x0B3C 3712 | [#x0B3E-#x0B43] 3713 | [#x0B47-#x0B48] 3714 | [#x0B4B-#x0B4D] 3715 | [#x0B56-#x0B57] 3716 | [#x0B82-#x0B83] 3717 | [#x0BBE-#x0BC2] 3718 | [#x0BC6-#x0BC8] 3719 | [#x0BCA-#x0BCD] 3720 | #x0BD7 3721 | [#x0C01-#x0C03] 3722 | [#x0C3E-#x0C44] 3723 | [#x0C46-#x0C48] 3724 | [#x0C4A-#x0C4D] 3725 | [#x0C55-#x0C56] 3726 | [#x0C82-#x0C83] 3727 | [#x0CBE-#x0CC4] 3728 | [#x0CC6-#x0CC8] 3729 | [#x0CCA-#x0CCD] 3730 | [#x0CD5-#x0CD6] 3731 | [#x0D02-#x0D03] 3732 | [#x0D3E-#x0D43] 3733 | [#x0D46-#x0D48] 3734 | [#x0D4A-#x0D4D] 3735 | #x0D57 3736 | #x0E31 3737 | [#x0E34-#x0E3A] 3738 | [#x0E47-#x0E4E] 3739 | #x0EB1 3740 | [#x0EB4-#x0EB9] 3741 | [#x0EBB-#x0EBC] 3742 | [#x0EC8-#x0ECD] 3743 | [#x0F18-#x0F19] 3744 | #x0F35 3745 | #x0F37 3746 | #x0F39 3747 | #x0F3E 3748 | #x0F3F 3749 | [#x0F71-#x0F84] 3750 | [#x0F86-#x0F8B] 3751 | [#x0F90-#x0F95] 3752 | #x0F97 3753 | [#x0F99-#x0FAD] 3754 | [#x0FB1-#x0FB7] 3755 | #x0FB9 3756 | [#x20D0-#x20DC] 3757 | #x20E1 3758 | [#x302A-#x302F] 3759 | #x3099 3760 | #x309A 3761 </rhs></prod> 3762 <prod id="NT-Digit"><lhs>Digit</lhs> 3763 <rhs>[#x0030-#x0039] 3764 | [#x0660-#x0669] 3765 | [#x06F0-#x06F9] 3766 | [#x0966-#x096F] 3767 | [#x09E6-#x09EF] 3768 | [#x0A66-#x0A6F] 3769 | [#x0AE6-#x0AEF] 3770 | [#x0B66-#x0B6F] 3771 | [#x0BE7-#x0BEF] 3772 | [#x0C66-#x0C6F] 3773 | [#x0CE6-#x0CEF] 3774 | [#x0D66-#x0D6F] 3775 | [#x0E50-#x0E59] 3776 | [#x0ED0-#x0ED9] 3777 | [#x0F20-#x0F29] 3778 </rhs></prod> 3779 <prod id="NT-Extender"><lhs>Extender</lhs> 3780 <rhs>#x00B7 3781 | #x02D0 3782 | #x02D1 3783 | #x0387 3784 | #x0640 3785 | #x0E46 3786 | #x0EC6 3787 | #x3005 3788 | [#x3031-#x3035] 3789 | [#x309D-#x309E] 3790 | [#x30FC-#x30FE] 3791 </rhs></prod> 3792 3793 </prodgroup> 3794 </scrap> 3795 </p> 3796 <p>The character classes defined here can be derived from the 3797 Unicode character database as follows: 3798 <ulist> 3799 <item> 3800 <p>Name start characters must have one of the categories Ll, Lu, 3801 Lo, Lt, Nl.</p> 3802 </item> 3803 <item> 3804 <p>Name characters other than Name-start characters 3805 must have one of the categories Mc, Me, Mn, Lm, or Nd.</p> 3806 </item> 3807 <item> 3808 <p>Characters in the compatibility area (i.e. with character code 3809 greater than #xF900 and less than #xFFFE) are not allowed in XML 3810 names.</p> 3811 </item> 3812 <item> 3813 <p>Characters which have a font or compatibility decomposition (i.e. those 3814 with a "compatibility formatting tag" in field 5 of the database -- 3815 marked by field 5 beginning with a "<") are not allowed.</p> 3816 </item> 3817 <item> 3818 <p>The following characters are treated as name-start characters 3819 rather than name characters, because the property file classifies 3820 them as Alphabetic: [#x02BB-#x02C1], #x0559, #x06E5, #x06E6.</p> 3821 </item> 3822 <item> 3823 <p>Characters #x20DD-#x20E0 are excluded (in accordance with 3824 Unicode, section 5.14).</p> 3825 </item> 3826 <item> 3827 <p>Character #x00B7 is classified as an extender, because the 3828 property list so identifies it.</p> 3829 </item> 3830 <item> 3831 <p>Character #x0387 is added as a name character, because #x00B7 3832 is its canonical equivalent.</p> 3833 </item> 3834 <item> 3835 <p>Characters ':' and '_' are allowed as name-start characters.</p> 3836 </item> 3837 <item> 3838 <p>Characters '-' and '.' are allowed as name characters.</p> 3839 </item> 3840 </ulist> 3841 </p> 3842 </div1> 3843 <inform-div1 id="sec-xml-and-sgml"> 3844 <head>XML and SGML</head> 3845 3846 <p>XML is designed to be a subset of SGML, in that every 3847 <termref def="dt-valid">valid</termref> XML document should also be a 3848 conformant SGML document. 3849 For a detailed comparison of the additional restrictions that XML places on 3850 documents beyond those of SGML, see <bibref ref="Clark"/>. 3851 </p> 3852 </inform-div1> 3853 <inform-div1 id="sec-entexpand"> 3854 <head>Expansion of Entity and Character References</head> 3855 <p>This appendix contains some examples illustrating the 3856 sequence of entity- and character-reference recognition and 3857 expansion, as specified in <specref ref="entproc"/>.</p> 3858 <p> 3859 If the DTD contains the declaration 3860 <eg><![CDATA[<!ENTITY example "<p>An ampersand (&#38;) may be escaped 3861 numerically (&#38;#38;) or with a general entity 3862 (&amp;).</p>" > 3863 ]]></eg> 3864 then the XML processor will recognize the character references 3865 when it parses the entity declaration, and resolve them before 3866 storing the following string as the 3867 value of the entity "<code>example</code>": 3868 <eg><![CDATA[<p>An ampersand (&) may be escaped 3869 numerically (&#38;) or with a general entity 3870 (&amp;).</p> 3871 ]]></eg> 3872 A reference in the document to "<code>&example;</code>" 3873 will cause the text to be reparsed, at which time the 3874 start- and end-tags of the "<code>p</code>" element will be recognized 3875 and the three references will be recognized and expanded, 3876 resulting in a "<code>p</code>" element with the following content 3877 (all data, no delimiters or markup): 3878 <eg><![CDATA[An ampersand (&) may be escaped 3879 numerically (&) or with a general entity 3880 (&). 3881 ]]></eg> 3882 </p> 3883 <p>A more complex example will illustrate the rules and their 3884 effects fully. In the following example, the line numbers are 3885 solely for reference. 3886 <eg><![CDATA[1 <?xml version='1.0'?> 3887 2 <!DOCTYPE test [ 3888 3 <!ELEMENT test (#PCDATA) > 3889 4 <!ENTITY % xx '%zz;'> 3890 5 <!ENTITY % zz '<!ENTITY tricky "error-prone" >' > 3891 6 %xx; 3892 7 ]> 3893 8 <test>This sample shows a &tricky; method.</test> 3894 ]]></eg> 3895 This produces the following: 3896 <ulist spacing="compact"> 3897 <item><p>in line 4, the reference to character 37 is expanded immediately, 3898 and the parameter entity "<code>xx</code>" is stored in the symbol 3899 table with the value "<code>%zz;</code>". Since the replacement text 3900 is not rescanned, the reference to parameter entity "<code>zz</code>" 3901 is not recognized. (And it would be an error if it were, since 3902 "<code>zz</code>" is not yet declared.)</p></item> 3903 <item><p>in line 5, the character reference "<code>&#60;</code>" is 3904 expanded immediately and the parameter entity "<code>zz</code>" is 3905 stored with the replacement text 3906 "<code><!ENTITY tricky "error-prone" ></code>", 3907 which is a well-formed entity declaration.</p></item> 3908 <item><p>in line 6, the reference to "<code>xx</code>" is recognized, 3909 and the replacement text of "<code>xx</code>" (namely 3910 "<code>%zz;</code>") is parsed. The reference to "<code>zz</code>" 3911 is recognized in its turn, and its replacement text 3912 ("<code><!ENTITY tricky "error-prone" ></code>") is parsed. 3913 The general entity "<code>tricky</code>" has now been 3914 declared, with the replacement text "<code>error-prone</code>".</p></item> 3915 <item><p> 3916 in line 8, the reference to the general entity "<code>tricky</code>" is 3917 recognized, and it is expanded, so the full content of the 3918 "<code>test</code>" element is the self-describing (and ungrammatical) string 3919 <emph>This sample shows a error-prone method.</emph> 3920 </p></item> 3921 </ulist> 3922 </p> 3923 </inform-div1> 3924 <inform-div1 id="determinism"> 3925 <head>Deterministic Content Models</head> 3926 <p><termref def="dt-compat">For compatibility</termref>, it is 3927 required 3928 that content models in element type declarations be deterministic. 3929 </p> 3930 <!-- FINAL EDIT: WebSGML allows ambiguity? --> 3931 <p>SGML 3932 requires deterministic content models (it calls them 3933 "unambiguous"); XML processors built using SGML systems may 3934 flag non-deterministic content models as errors.</p> 3935 <p>For example, the content model <code>((b, c) | (b, d))</code> is 3936 non-deterministic, because given an initial <code>b</code> the parser 3937 cannot know which <code>b</code> in the model is being matched without 3938 looking ahead to see which element follows the <code>b</code>. 3939 In this case, the two references to 3940 <code>b</code> can be collapsed 3941 into a single reference, making the model read 3942 <code>(b, (c | d))</code>. An initial <code>b</code> now clearly 3943 matches only a single name in the content model. The parser doesn't 3944 need to look ahead to see what follows; either <code>c</code> or 3945 <code>d</code> would be accepted.</p> 3946 <p>More formally: a finite state automaton may be constructed from the 3947 content model using the standard algorithms, e.g. algorithm 3.5 3948 in section 3.9 3949 of Aho, Sethi, and Ullman <bibref ref="Aho"/>. 3950 In many such algorithms, a follow set is constructed for each 3951 position in the regular expression (i.e., each leaf 3952 node in the 3953 syntax tree for the regular expression); 3954 if any position has a follow set in which 3955 more than one following position is 3956 labeled with the same element type name, 3957 then the content model is in error 3958 and may be reported as an error. 3959 </p> 3960 <p>Algorithms exist which allow many but not all non-deterministic 3961 content models to be reduced automatically to equivalent deterministic 3962 models; see Br�ggemann-Klein 1991 <bibref ref="ABK"/>.</p> 3963 </inform-div1> 3964 <inform-div1 id="sec-guessing"> 3965 <head>Autodetection of Character Encodings</head> 3966 <p>The XML encoding declaration functions as an internal label on each 3967 entity, indicating which character encoding is in use. Before an XML 3968 processor can read the internal label, however, it apparently has to 3969 know what character encoding is in use—which is what the internal label 3970 is trying to indicate. In the general case, this is a hopeless 3971 situation. It is not entirely hopeless in XML, however, because XML 3972 limits the general case in two ways: each implementation is assumed 3973 to support only a finite set of character encodings, and the XML 3974 encoding declaration is restricted in position and content in order to 3975 make it feasible to autodetect the character encoding in use in each 3976 entity in normal cases. Also, in many cases other sources of information 3977 are available in addition to the XML data stream itself. 3978 Two cases may be distinguished, 3979 depending on whether the XML entity is presented to the 3980 processor without, or with, any accompanying 3981 (external) information. We consider the first case first. 3982 </p> 3983 <p> 3984 Because each XML entity not in UTF-8 or UTF-16 format <emph>must</emph> 3985 begin with an XML encoding declaration, in which the first characters 3986 must be '<code><?xml</code>', any conforming processor can detect, 3987 after two to four octets of input, which of the following cases apply. 3988 In reading this list, it may help to know that in UCS-4, '<' is 3989 "<code>#x0000003C</code>" and '?' is "<code>#x0000003F</code>", and the Byte 3990 Order Mark required of UTF-16 data streams is "<code>#xFEFF</code>".</p> 3991 <p> 3992 <ulist> 3993 <item> 3994 <p><code>00 00 00 3C</code>: UCS-4, big-endian machine (1234 order)</p> 3995 </item> 3996 <item> 3997 <p><code>3C 00 00 00</code>: UCS-4, little-endian machine (4321 order)</p> 3998 </item> 3999 <item> 4000 <p><code>00 00 3C 00</code>: UCS-4, unusual octet order (2143)</p> 4001 </item> 4002 <item> 4003 <p><code>00 3C 00 00</code>: UCS-4, unusual octet order (3412)</p> 4004 </item> 4005 <item> 4006 <p><code>FE FF</code>: UTF-16, big-endian</p> 4007 </item> 4008 <item> 4009 <p><code>FF FE</code>: UTF-16, little-endian</p> 4010 </item> 4011 <item> 4012 <p><code>00 3C 00 3F</code>: UTF-16, big-endian, no Byte Order Mark 4013 (and thus, strictly speaking, in error)</p> 4014 </item> 4015 <item> 4016 <p><code>3C 00 3F 00</code>: UTF-16, little-endian, no Byte Order Mark 4017 (and thus, strictly speaking, in error)</p> 4018 </item> 4019 <item> 4020 <p><code>3C 3F 78 6D</code>: UTF-8, ISO 646, ASCII, some part of ISO 8859, 4021 Shift-JIS, EUC, or any other 7-bit, 8-bit, or mixed-width encoding 4022 which ensures that the characters of ASCII have their normal positions, 4023 width, 4024 and values; the actual encoding declaration must be read to 4025 detect which of these applies, but since all of these encodings 4026 use the same bit patterns for the ASCII characters, the encoding 4027 declaration itself may be read reliably 4028 </p> 4029 </item> 4030 <item> 4031 <p><code>4C 6F A7 94</code>: EBCDIC (in some flavor; the full 4032 encoding declaration must be read to tell which code page is in 4033 use)</p> 4034 </item> 4035 <item> 4036 <p>other: UTF-8 without an encoding declaration, or else 4037 the data stream is corrupt, fragmentary, or enclosed in 4038 a wrapper of some kind</p> 4039 </item> 4040 </ulist> 4041 </p> 4042 <p> 4043 This level of autodetection is enough to read the XML encoding 4044 declaration and parse the character-encoding identifier, which is 4045 still necessary to distinguish the individual members of each family 4046 of encodings (e.g. to tell UTF-8 from 8859, and the parts of 8859 4047 from each other, or to distinguish the specific EBCDIC code page in 4048 use, and so on). 4049 </p> 4050 <p> 4051 Because the contents of the encoding declaration are restricted to 4052 ASCII characters, a processor can reliably read the entire encoding 4053 declaration as soon as it has detected which family of encodings is in 4054 use. Since in practice, all widely used character encodings fall into 4055 one of the categories above, the XML encoding declaration allows 4056 reasonably reliable in-band labeling of character encodings, even when 4057 external sources of information at the operating-system or 4058 transport-protocol level are unreliable. 4059 </p> 4060 <p> 4061 Once the processor has detected the character encoding in use, it can 4062 act appropriately, whether by invoking a separate input routine for 4063 each case, or by calling the proper conversion function on each 4064 character of input. 4065 </p> 4066 <p> 4067 Like any self-labeling system, the XML encoding declaration will not 4068 work if any software changes the entity's character set or encoding 4069 without updating the encoding declaration. Implementors of 4070 character-encoding routines should be careful to ensure the accuracy 4071 of the internal and external information used to label the entity. 4072 </p> 4073 <p>The second possible case occurs when the XML entity is accompanied 4074 by encoding information, as in some file systems and some network 4075 protocols. 4076 When multiple sources of information are available, 4077 4078 their relative 4079 priority and the preferred method of handling conflict should be 4080 specified as part of the higher-level protocol used to deliver XML. 4081 Rules for the relative priority of the internal label and the 4082 MIME-type label in an external header, for example, should be part of the 4083 RFC document defining the text/xml and application/xml MIME types. In 4084 the interests of interoperability, however, the following rules 4085 are recommended. 4086 <ulist> 4087 <item><p>If an XML entity is in a file, the Byte-Order Mark 4088 and encoding-declaration PI are used (if present) to determine the 4089 character encoding. All other heuristics and sources of information 4090 are solely for error recovery. 4091 </p></item> 4092 <item><p>If an XML entity is delivered with a 4093 MIME type of text/xml, then the <code>charset</code> parameter 4094 on the MIME type determines the 4095 character encoding method; all other heuristics and sources of 4096 information are solely for error recovery. 4097 </p></item> 4098 <item><p>If an XML entity is delivered 4099 with a 4100 MIME type of application/xml, then the Byte-Order Mark and 4101 encoding-declaration PI are used (if present) to determine the 4102 character encoding. All other heuristics and sources of 4103 information are solely for error recovery. 4104 </p></item> 4105 </ulist> 4106 These rules apply only in the absence of protocol-level documentation; 4107 in particular, when the MIME types text/xml and application/xml are 4108 defined, the recommendations of the relevant RFC will supersede 4109 these rules. 4110 </p> 4111 4112 </inform-div1> 4113 4114 <inform-div1 id="sec-xml-wg"> 4115 <head>W3C XML Working Group</head> 4116 4117 <p>This specification was prepared and approved for publication by the 4118 W3C XML Working Group (WG). WG approval of this specification does 4119 not necessarily imply that all WG members voted for its approval. 4120 The current and former members of the XML WG are:</p> 4121 4122 <orglist> 4123 <member><name>Jon Bosak, Sun</name><role>Chair</role></member> 4124 <member><name>James Clark</name><role>Technical Lead</role></member> 4125 <member><name>Tim Bray, Textuality and Netscape</name><role>XML Co-editor</role></member> 4126 <member><name>Jean Paoli, Microsoft</name><role>XML Co-editor</role></member> 4127 <member><name>C. M. Sperberg-McQueen, U. of Ill.</name><role>XML 4128 Co-editor</role></member> 4129 <member><name>Dan Connolly, W3C</name><role>W3C Liaison</role></member> 4130 <member><name>Paula Angerstein, Texcel</name></member> 4131 <member><name>Steve DeRose, INSO</name></member> 4132 <member><name>Dave Hollander, HP</name></member> 4133 <member><name>Eliot Kimber, ISOGEN</name></member> 4134 <member><name>Eve Maler, ArborText</name></member> 4135 <member><name>Tom Magliery, NCSA</name></member> 4136 <member><name>Murray Maloney, Muzmo and Grif</name></member> 4137 <member><name>Makoto Murata, Fuji Xerox Information Systems</name></member> 4138 <member><name>Joel Nava, Adobe</name></member> 4139 <member><name>Conleth O'Connell, Vignette</name></member> 4140 <member><name>Peter Sharpe, SoftQuad</name></member> 4141 <member><name>John Tigue, DataChannel</name></member> 4142 </orglist> 4143 4144 </inform-div1> 4145 </back> 4146 </spec> 4147 <!-- Keep this comment at the end of the file 4148 Local variables: 4149 mode: sgml 4150 sgml-default-dtd-file:"~/sgml/spec.ced" 4151 sgml-omittag:t 4152 sgml-shorttag:t 4153 End: 4154 -->