1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<html lang="EN"><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Extensible Markup Language (XML) 1.0 (Second Edition) -- Review Version</title><style type="text/css"> 3code { font-family: monospace; } 4 5div.constraint, 6div.issue, 7div.note, 8div.notice { margin-left: 2em; } 9 10dt.label { display: run-in; } 11 12li p { margin-top: 0.3em; 13 margin-bottom: 0.3em; } 14 15div.diff-add { background-color: yellow } 16div.diff-del { text-decoration: line-through } 17div.diff-chg { background-color: lime } 18div.diff-off { } 19 20span.diff-add { background-color: yellow } 21span.diff-del { text-decoration: line-through } 22span.diff-chg { background-color: lime } 23span.diff-off { } 24 25td.diff-add { background-color: yellow } 26td.diff-del { text-decoration: line-through } 27td.diff-chg { background-color: lime } 28td.diff-off { } 29</style><link rel="stylesheet" type="text/css" href="W3C-REC.css"></head><body> 30 31<div class="head"><p><a href="http://www.w3.org/"><img src="http://www.w3.org/Icons/w3c_home" alt="W3C" height="48" width="72"></a></p> 32<h1>Extensible Markup Language (XML) 1.0 (Second Edition)</h1> 33<h2>W3C Recommendation 6 October 2000</h2><dl><dt>This version:</dt><dd><a href="http://www.w3.org/TR/2000/REC-xml-20001006">http://www.w3.org/TR/2000/REC-xml-20001006</a> 34(<a href="http://www.w3.org/TR/2000/REC-xml-20001006.html">XHTML</a>, <a href="http://www.w3.org/TR/2000/REC-xml-20001006.xml">XML</a>, <a href="http://www.w3.org/TR/2000/REC-xml-20001006.pdf">PDF</a>, <a href="http://www.w3.org/TR/2000/REC-xml-20001006-review.html">XHTML 35review version</a> with color-coded revision indicators)</dd><dt>Latest version:</dt><dd><a href="http://www.w3.org/TR/REC-xml">http://www.w3.org/TR/REC-xml</a></dd><dt>Previous versions:</dt><dd><a href="http://www.w3.org/TR/2000/WD-xml-2e-20000814"> http://www.w3.org/TR/2000/WD-xml-2e-20000814</a> 36<a href="http://www.w3.org/TR/1998/REC-xml-19980210"> http://www.w3.org/TR/1998/REC-xml-19980210</a> </dd><dt>Editors:</dt> 37<dd>Tim Bray, Textuality and Netscape <a href="mailto:tbray@textuality.com"><tbray@textuality.com></a></dd> 38<dd>Jean Paoli, Microsoft <a href="mailto:jeanpa@microsoft.com"><jeanpa@microsoft.com></a></dd> 39<dd><span class="diff-chg">C. M. Sperberg-McQueen, University 40of Illinois at Chicago and Text Encoding Initiative <a href="mailto:cmsmcq@uic.edu"><cmsmcq@uic.edu></a></span></dd> 41<dd><span class="diff-add">Eve Maler, Sun Microsystems, 42Inc. <a href="mailto:elm@east.sun.com"><eve.maler@east.sun.com></a> - Second Edition</span></dd> 43</dl><p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>���2000�<a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>�</sup> (<a href="http://www.lcs.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="http://www.inria.fr/"><abbr lang="fr" title="Institut National de Recherche en Informatique et Automatique">INRIA</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>, <a href="http://www.w3.org/Consortium/Legal/copyright-documents-19990405">document use</a>, and <a href="http://www.w3.org/Consortium/Legal/copyright-software-19980720">software licensing</a> rules apply.</p></div><hr><div id="abstract"> 44<h2><a name="abstract">Abstract</a></h2> 45<p>The Extensible Markup Language (XML) is a subset of SGML that is completely 46described in this document. Its goal is to enable generic SGML to be served, 47received, and processed on the Web in the way that is now possible with HTML. 48XML has been designed for ease of implementation and for interoperability 49with both SGML and HTML.</p> 50</div><div id="status"> 51<h2><a name="status">Status of this Document</a></h2> 52<p>This document has been reviewed by W3C Members and other interested parties 53and has been endorsed by the Director as a W3C Recommendation. It is a stable 54document and may be used as reference material or cited as a normative reference 55from another document. W3C's role in making the Recommendation is to draw 56attention to the specification and to promote its widespread deployment. This 57enhances the functionality and interoperability of the Web.</p> 58<p>This document specifies a syntax created by subsetting an existing, widely 59used international text processing standard (Standard Generalized Markup Language, 60ISO 8879:1986(E) as amended and corrected) for use on the World Wide Web. 61It is a product of the W3C XML Activity, details of which can be found at <a href="http://www.w3.org/XML/">http://www.w3.org/XML</a>. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E100">[E100]</a> 62The English version of this specification is the only normative version. However, 63for translations of this document, see <a href="http://www.w3.org/XML/#trans">http://www.w3.org/XML/#trans</a>. </span>A 64list of current W3C Recommendations and other technical documents can be found 65at <a href="http://www.w3.org/TR/">http://www.w3.org/TR</a>.</p> 66<div class="diff-del"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E66">[E66]</a>This 67specification uses the term URI, which is defined by <a href="#Berners-Lee">[Berners-Lee et al.]</a>, 68a work in progress expected to update <a href="#RFC1738">[IETF RFC1738]</a> and <a href="#RFC1808">[IETF RFC1808]</a>.</p></div> 69<div class="diff-add"><p>This second edition is <em>not</em> a new version of XML (first published 10 February 1998); 70it merely incorporates the changes dictated by the first-edition errata (available 71at <a href="http://www.w3.org/XML/xml-19980210-errata">http://www.w3.org/XML/xml-19980210-errata</a>) 72as a convenience to readers. The errata list for this second edition is available 73at <a href="http://www.w3.org/XML/xml-V10-2e-errata">http://www.w3.org/XML/xml-V10-2e-errata</a>.</p></div> 74<p>Please report errors in this document to <a href="mailto:xml-editor@w3.org">xml-editor@w3.org</a><span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E101">[E101]</a>; <a href="http://lists.w3.org/Archives/Public/xml-editor">archives</a> are available</span>.</p> 75<div class="diff-add"><div class="note"><p class="prefix"><b>Note:</b></p> 76<p>C. M. Sperberg-McQueen's affiliation has changed since the publication 77of the first edition. He is now at the World Wide Web Consortium, and can 78be contacted at <a href="mailto:cmsmcq@w3.org">cmsmcq@w3.org</a>.</p> 79</div></div> 80</div> 81<div class="toc"> 82<h2><a name="contents">Table of Contents</a></h2><p class="toc">1 <a href="#sec-intro">Introduction</a><br>����1.1 <a href="#sec-origin-goals">Origin and Goals</a><br>����1.2 <a href="#sec-terminology">Terminology</a><br>2 <a href="#sec-documents">Documents</a><br>����2.1 <a href="#sec-well-formed">Well-Formed XML Documents</a><br>����2.2 <a href="#charsets">Characters</a><br>����2.3 <a href="#sec-common-syn">Common Syntactic Constructs</a><br>����2.4 <a href="#syntax">Character Data and Markup</a><br>����2.5 <a href="#sec-comments">Comments</a><br>����2.6 <a href="#sec-pi">Processing Instructions</a><br>����2.7 <a href="#sec-cdata-sect">CDATA Sections</a><br>����2.8 <a href="#sec-prolog-dtd">Prolog and Document Type Declaration</a><br>����2.9 <a href="#sec-rmd">Standalone Document Declaration</a><br>����2.10 <a href="#sec-white-space">White Space Handling</a><br>����2.11 <a href="#sec-line-ends">End-of-Line Handling</a><br>����2.12 <a href="#sec-lang-tag">Language Identification</a><br>3 <a href="#sec-logical-struct">Logical Structures</a><br>����3.1 <a href="#sec-starttags">Start-Tags, End-Tags, and Empty-Element Tags</a><br>����3.2 <a href="#elemdecls">Element Type Declarations</a><br>��������3.2.1 <a href="#sec-element-content">Element Content</a><br>��������3.2.2 <a href="#sec-mixed-content">Mixed Content</a><br>����3.3 <a href="#attdecls">Attribute-List Declarations</a><br>��������3.3.1 <a href="#sec-attribute-types">Attribute Types</a><br>��������3.3.2 <a href="#sec-attr-defaults">Attribute Defaults</a><br>��������3.3.3 <a href="#AVNormalize">Attribute-Value 83Normalization</a><br>����3.4 <a href="#sec-condition-sect">Conditional Sections</a><br>4 <a href="#sec-physical-struct">Physical Structures</a><br>����4.1 <a href="#sec-references">Character and Entity References</a><br>����4.2 <a href="#sec-entity-decl">Entity Declarations</a><br>��������4.2.1 <a href="#sec-internal-ent">Internal Entities</a><br>��������4.2.2 <a href="#sec-external-ent">External Entities</a><br>����4.3 <a href="#TextEntities">Parsed Entities</a><br>��������4.3.1 <a href="#sec-TextDecl">The Text Declaration</a><br>��������4.3.2 <a href="#wf-entities">Well-Formed Parsed Entities</a><br>��������4.3.3 <a href="#charencoding">Character Encoding in Entities</a><br>����4.4 <a href="#entproc">XML Processor Treatment of Entities and References</a><br>��������4.4.1 <a href="#not-recognized">Not Recognized</a><br>��������4.4.2 <a href="#included">Included</a><br>��������4.4.3 <a href="#include-if-valid">Included If Validating</a><br>��������4.4.4 <a href="#forbidden">Forbidden</a><br>��������4.4.5 <a href="#inliteral">Included in Literal</a><br>��������4.4.6 <a href="#notify">Notify</a><br>��������4.4.7 <a href="#bypass">Bypassed</a><br>��������4.4.8 <a href="#as-PE">Included as PE</a><br>����4.5 <a href="#intern-replacement">Construction of Internal Entity Replacement Text</a><br>����4.6 <a href="#sec-predefined-ent">Predefined Entities</a><br>����4.7 <a href="#Notations">Notation Declarations</a><br>����4.8 <a href="#sec-doc-entity">Document Entity</a><br>5 <a href="#sec-conformance">Conformance</a><br>����5.1 <a href="#proc-types">Validating and Non-Validating Processors</a><br>����5.2 <a href="#safe-behavior">Using XML Processors</a><br>6 <a href="#sec-notation">Notation</a><br></p> 84<h3>Appendices</h3><p class="toc">A <a href="#sec-bibliography">References</a><br>����A.1 <a href="#sec-existing-stds">Normative References</a><br>����A.2 <a href="#null">Other References</a><br>B <a href="#CharClasses">Character Classes</a><br>C <a href="#sec-xml-and-sgml">XML and SGML</a> (Non-Normative)<br>D <a href="#sec-entexpand">Expansion of Entity and Character References</a> (Non-Normative)<br>E <a href="#determinism">Deterministic Content Models</a> (Non-Normative)<br>F <a href="#sec-guessing">Autodetection 85of Character Encodings</a> (Non-Normative)<br>����F.1 <a href="#sec-guessing-no-ext-info">Detection Without External Encoding Information</a><br>����F.2 <a href="#sec-guessing-with-ext-info">Priorities in the Presence of External Encoding Information</a><br>G <a href="#sec-xml-wg">W3C XML Working Group</a> (Non-Normative)<br>H <a href="#sec-core-wg">W3C XML Core Group</a> (Non-Normative)<br>I <a href="#id2683713">Production Notes</a> (Non-Normative)<br></p></div><hr><div class="body"> 86<div class="div1"> 87 88<h2><a name="sec-intro"></a>1 Introduction</h2> 89<p>Extensible Markup Language, abbreviated XML, describes a class of data 90objects called <a title="XML Document" href="#dt-xml-doc">XML documents</a> and partially 91describes the behavior of computer programs which process them. XML is an 92application profile or restricted form of SGML, the Standard Generalized Markup 93Language <a href="#ISO8879">[ISO 8879]</a>. By construction, XML documents are conforming 94SGML documents.</p> 95<p>XML documents are made up of storage units called <a title="Entity" href="#dt-entity">entities</a>, 96which contain either parsed or unparsed data. Parsed data is made up of <a title="Character" href="#dt-character">characters</a>, some of which form <a title="Character Data" href="#dt-chardata">character 97data</a>, and some of which form <a title="Markup" href="#dt-markup">markup</a>. 98Markup encodes a description of the document's storage layout and logical 99structure. XML provides a mechanism to impose constraints on the storage layout 100and logical structure.</p> 101<p>[<a name="dt-xml-proc" title="XML Processor">Definition</a>: A software module called 102an <b>XML processor</b> is used to read XML documents and provide access 103to their content and structure.] [<a name="dt-app" title="Application">Definition</a>: It 104is assumed that an XML processor is doing its work on behalf of another module, 105called the <b>application</b>.] This specification describes 106the required behavior of an XML processor in terms of how it must read XML 107data and the information it must provide to the application.</p> 108<div class="div2"> 109 110<h3><a name="sec-origin-goals"></a>1.1 Origin and Goals</h3> 111<p>XML was developed by an XML Working Group (originally known as the SGML 112Editorial Review Board) formed under the auspices of the World Wide Web Consortium 113(W3C) in 1996. It was chaired by Jon Bosak of Sun Microsystems with the active 114participation of an XML Special Interest Group (previously known as the SGML 115Working Group) also organized by the W3C. The membership of the XML Working 116Group is given in an appendix. Dan Connolly served as the WG's contact with 117the W3C.</p> 118<p>The design goals for XML are:</p> 119<ol> 120<li><p>XML shall be straightforwardly usable over the Internet.</p></li> 121<li><p>XML shall support a wide variety of applications.</p></li> 122<li><p>XML shall be compatible with SGML.</p></li> 123<li><p>It shall be easy to write programs which process XML documents.</p> 124</li> 125<li><p>The number of optional features in XML is to be kept to the absolute 126minimum, ideally zero.</p></li> 127<li><p>XML documents should be human-legible and reasonably clear.</p></li> 128<li><p>The XML design should be prepared quickly.</p></li> 129<li><p>The design of XML shall be formal and concise.</p></li> 130<li><p>XML documents shall be easy to create.</p></li> 131<li><p>Terseness in XML markup is of minimal importance.</p></li> 132</ol> 133<p>This specification, together with associated standards (Unicode and ISO/IEC 13410646 for characters, Internet RFC 1766 for language identification tags, 135ISO 639 for language name codes, and ISO 3166 for country name codes), provides 136all the information necessary to understand XML Version 1.0 and 137construct computer programs to process it.</p> 138<p>This version of the XML specification may be distributed freely, as long as 139all text and legal notices remain intact.</p> 140</div> 141<div class="div2"> 142 143<h3><a name="sec-terminology"></a>1.2 Terminology</h3> 144<p>The terminology used to describe XML documents is defined in the body of 145this specification. The terms defined in the following list are used in building 146those definitions and in describing the actions of an XML processor: </p><dl> 147<dt class="label">may</dt> 148<dd> 149<p>[<a name="dt-may" title="May">Definition</a>: Conforming documents and XML processors 150are permitted to but need not behave as described.]</p> 151</dd> 152<dt class="label">must</dt> 153<dd> 154<p>[<a name="dt-must" title="Must">Definition</a>: Conforming documents and XML processors 155are required to behave as described; otherwise they are in error. ]</p> 156</dd> 157<dt class="label">error</dt> 158<dd> 159<p>[<a name="dt-error" title="Error">Definition</a>: A violation of the rules of this specification; 160results are undefined. Conforming software may detect and report an error 161and may recover from it.]</p> 162</dd> 163<dt class="label">fatal error</dt> 164<dd> 165<p>[<a name="dt-fatal" title="Fatal Error">Definition</a>: An error which a conforming <a title="XML Processor" href="#dt-xml-proc">XML processor</a> must detect and report to the application. 166After encountering a fatal error, the processor may continue processing the 167data to search for further errors and may report such errors to the application. 168In order to support correction of errors, the processor may make unprocessed 169data from the document (with intermingled character data and markup) available 170to the application. Once a fatal error is detected, however, the processor 171must not continue normal processing (i.e., it must not continue to pass character 172data and information about the document's logical structure to the application 173in the normal way).]</p> 174</dd> 175<dt class="label">at user option</dt> 176<dd> 177<p>[<a name="dt-atuseroption" title="At user option">Definition</a>: Conforming software 178may or must (depending on the modal verb in the sentence) behave as described; 179if it does, it must provide users a means to enable or disable the behavior 180described.]</p> 181</dd> 182<dt class="label">validity constraint</dt> 183<dd> 184<p>[<a name="dt-vc" title="Validity constraint">Definition</a>: A rule which applies to 185all <a title="Validity" href="#dt-valid">valid</a> XML documents. Violations of validity 186constraints are errors; they must, at user option, be reported by <a title="Validating Processor" href="#dt-validating">validating XML processors</a>.]</p> 187</dd> 188<dt class="label">well-formedness constraint</dt> 189<dd> 190<p>[<a name="dt-wfc" title="Well-formedness constraint">Definition</a>: A rule which applies 191to all <a title="Well-Formed" href="#dt-wellformed">well-formed</a> XML documents. Violations 192of well-formedness constraints are <a title="Fatal Error" href="#dt-fatal">fatal errors</a>.]</p> 193</dd> 194<dt class="label">match</dt> 195<dd> 196<p>[<a name="dt-match" title="match">Definition</a>: (Of strings or names:) Two strings 197or names being compared must be identical. Characters with multiple possible 198representations in ISO/IEC 10646 (e.g. characters with both precomposed and 199base+diacritic forms) match only if they have the same representation in both 200strings. <span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E85">[E85]</a>At 201user option, processors may normalize such characters to some canonical form. </span>No 202case folding is performed. (Of strings and rules in the grammar:) A string 203matches a grammatical production if it belongs to the language generated by 204that production. (Of content and content models:) An element matches its declaration 205when it conforms in the fashion described in the constraint <a href="#elementvalid"><b>[VC: Element Valid]</b></a>.]</p> 206</dd> 207<dt class="label">for compatibility</dt> 208<dd> 209<p>[<a name="dt-compat" title="For Compatibility">Definition</a>: <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E87">[E87]</a>Marks 210a sentence describing</span> a feature of XML included solely to ensure 211that XML remains compatible with SGML.]</p> 212</dd> 213<dt class="label">for interoperability</dt> 214<dd> 215<p>[<a name="dt-interop" title="For interoperability">Definition</a>: <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E87">[E87]</a>Marks 216a sentence describing</span> a non-binding recommendation included to increase 217the chances that XML documents can be processed by the existing installed 218base of SGML processors which predate the WebSGML Adaptations Annex to ISO 8879.]</p> 219</dd> 220</dl><p></p> 221</div> 222</div> 223 224<div class="div1"> 225 226<h2><a name="sec-documents"></a>2 Documents</h2> 227<p>[<a name="dt-xml-doc" title="XML Document">Definition</a>: A data object is an <b>XML 228document</b> if it is <a title="Well-Formed" href="#dt-wellformed">well-formed</a>, 229as defined in this specification. A well-formed XML document may in addition 230be <a title="Validity" href="#dt-valid">valid</a> if it meets certain further constraints.]</p> 231<p>Each XML document has both a logical and a physical structure. Physically, 232the document is composed of units called <a title="Entity" href="#dt-entity">entities</a>. 233An entity may <a title="Entity Reference" href="#dt-entref">refer</a> to other entities to 234cause their inclusion in the document. A document begins in a "root" 235or <a title="Document Entity" href="#dt-docent">document entity</a>. Logically, the document 236is composed of declarations, elements, comments, character references, and 237processing instructions, all of which are indicated in the document by explicit 238markup. The logical and physical structures must nest properly, as described 239in <a href="#wf-entities"><b>4.3.2 Well-Formed Parsed Entities</b></a>.</p> 240<div class="div2"> 241 242<h3><a name="sec-well-formed"></a>2.1 Well-Formed XML Documents</h3> 243<p>[<a name="dt-wellformed" title="Well-Formed">Definition</a>: A textual object is a <b>well-formed</b> 244XML document if:]</p> 245<ol> 246<li><p>Taken as a whole, it matches the production labeled <a href="#NT-document">document</a>.</p> 247</li> 248<li><p>It meets all the well-formedness constraints given in this specification.</p> 249</li> 250<li><p>Each of the <a title="Text Entity" href="#dt-parsedent">parsed entities</a> 251which is referenced directly or indirectly within the document is <a title="Well-Formed" href="#dt-wellformed">well-formed</a>.</p></li> 252</ol> 253 254<h5>Document</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-document"></a>[1]���</td><td><code>document</code></td><td>���::=���</td><td><code><a href="#NT-prolog">prolog</a> <a href="#NT-element">element</a> <a href="#NT-Misc">Misc</a>*</code></td><xsltdebug></xsltdebug></tr></tbody></table> 255<p>Matching the <a href="#NT-document">document</a> production implies that:</p> 256<ol> 257<li><p>It contains one or more <a title="Element" href="#dt-element">elements</a>.</p> 258</li> 259 260<li><p>[<a name="dt-root" title="Root Element">Definition</a>: There is exactly one element, 261called the <b>root</b>, or document element, no part of which appears 262in the <a title="Content" href="#dt-content">content</a> of any other element.] <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E17">[E17]</a>For 263all other elements, if the <a title="Start-Tag" href="#dt-stag">start-tag</a> is in 264the content of another element, the <a title="End Tag" href="#dt-etag">end-tag</a> 265is in the content of the same element.</span> More simply stated, the elements, 266delimited by start- and end-tags, nest properly within each other.</p></li> 267</ol> 268<p>[<a name="dt-parentchild" title="Parent/Child">Definition</a>: As a consequence of this, 269for each non-root element <code>C</code> in the document, there is one other element <code>P</code> 270in the document such that <code>C</code> is in the content of <code>P</code>, but 271is not in the content of any other element that is in the content of <code>P</code>. <code>P</code> 272is referred to as the <b>parent</b> of <code>C</code>, and <code>C</code> as 273a <b>child</b> of <code>P</code>.]</p> 274</div> 275<div class="div2"> 276 277<h3><a name="charsets"></a>2.2 Characters</h3> 278<p>[<a name="dt-text" title="Text">Definition</a>: A parsed entity contains <b>text</b>, 279a sequence of <a title="Character" href="#dt-character">characters</a>, which may 280represent markup or character data.] [<a name="dt-character" title="Character">Definition</a>: A <b>character</b> 281is an atomic unit of text as specified by ISO/IEC 10646 <a href="#ISO10646">[ISO/IEC 10646]</a> <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</a>(see 282also <a href="#ISO10646-2000">[ISO/IEC 10646-2000]</a>)</span>. Legal characters are tab, carriage 283return, line feed, and the legal <span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E35">[E35]</a>graphic </span>characters 284of Unicode and ISO/IEC 10646. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E69">[E69]</a>The 285versions of these standards cited in <a href="#sec-existing-stds"><b>A.1 Normative References</b></a> were 286current at the time this document was prepared. New characters may be added 287to these standards by amendments or new editions. Consequently, XML processors 288must accept any character in the range specified for <a href="#NT-Char">Char</a>.</span> 289The use of "compatibility characters", as defined in section 2906.8 of <a href="#Unicode">[Unicode]</a> <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</a>(see 291also D21 in section 3.6 of <a href="#Unicode3">[Unicode3]</a>)</span>, is discouraged.]</p> 292 293<h5>Character Range</h5><table class="scrap" summary="Scrap"><tbody> 294<tr valign="baseline"><td><a name="NT-Char"></a>[2]���</td><td><code>Char</code></td><td>���::=���</td><td><code>#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]</code></td><xsltdebug></xsltdebug><td><i>/* any Unicode character, excluding the surrogate blocks, FFFE, and FFFF. */</i></td></tr> 295</tbody></table> 296<p>The mechanism for encoding character code points into bit patterns may 297vary from entity to entity. All XML processors must accept the UTF-8 and UTF-16 298encodings of 10646; the mechanisms for signaling which of the two is in use, 299or for bringing other encodings into play, are discussed later, in <a href="#charencoding"><b>4.3.3 Character Encoding in Entities</b></a>.</p> 300 301</div> 302<div class="div2"> 303 304<h3><a name="sec-common-syn"></a>2.3 Common Syntactic Constructs</h3> 305<p>This section defines some symbols used widely in the grammar.</p> 306<p><a href="#NT-S">S</a> (white space) consists of one or more space (#x20) 307characters, carriage returns, line feeds, or tabs.</p> 308 309<h5>White Space</h5><table class="scrap" summary="Scrap"><tbody> 310<tr valign="baseline"><td><a name="NT-S"></a>[3]���</td><td><code>S</code></td><td>���::=���</td><td><code>(#x20 | #x9 | #xD | #xA)+</code></td><xsltdebug></xsltdebug></tr> 311</tbody></table> 312<p>Characters are classified for convenience as letters, digits, or other 313characters. <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E30">[E30]</a>A 314letter consists of an alphabetic or syllabic base character or an ideographic 315character.</span> Full definitions of the specific characters in each class 316are given in <a href="#CharClasses"><b>B Character Classes</b></a>.</p> 317<p>[<a name="dt-name" title="Name">Definition</a>: A <b>Name</b> is a token beginning 318with a letter or one of a few punctuation characters, and continuing with 319letters, digits, hyphens, underscores, colons, or full stops, together known 320as name characters.] Names beginning with the string "<code>xml</code>", 321or any string which would match <code>(('X'|'x') ('M'|'m') ('L'|'l'))</code>, 322are reserved for standardization in this or future versions of this specification.</p> 323<div class="note"><p class="prefix"><b>Note:</b></p> 324<div class="diff-chg"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E98">[E98]</a>The 325Namespaces in XML Recommendation <a href="#xml-names">[XML Names]</a> assigns a meaning 326to names containing colon characters. Therefore, authors should not use the 327colon in XML names except for namespace purposes, but XML processors must 328accept the colon as a name character.</p></div> 329</div> 330<p>An <a href="#NT-Nmtoken">Nmtoken</a> (name token) is any mixture of name 331characters.</p> 332 333<h5>Names and Tokens</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-NameChar"></a>[4]���</td><td><code>NameChar</code></td><td>���::=���</td><td><code><a href="#NT-Letter">Letter</a> | <a href="#NT-Digit">Digit</a> 334| '.' | '-' | '_' | ':' | <a href="#NT-CombiningChar">CombiningChar</a> | <a href="#NT-Extender">Extender</a></code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Name"></a>[5]���</td><td><code>Name</code></td><td>���::=���</td><td><code>(<a href="#NT-Letter">Letter</a> | '_' | ':') (<a href="#NT-NameChar">NameChar</a>)*</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Names"></a>[6]���</td><td><code>Names</code></td><td>���::=���</td><td><code><a href="#NT-Name">Name</a> (<a href="#NT-S">S</a> <a href="#NT-Name">Name</a>)*</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Nmtoken"></a>[7]���</td><td><code>Nmtoken</code></td><td>���::=���</td><td><code>(<a href="#NT-NameChar">NameChar</a>)+</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Nmtokens"></a>[8]���</td><td><code>Nmtokens</code></td><td>���::=���</td><td><code><a href="#NT-Nmtoken">Nmtoken</a> (<a href="#NT-S">S</a> <a href="#NT-Nmtoken">Nmtoken</a>)*</code></td><xsltdebug></xsltdebug></tr></tbody></table> 335<p>Literal data is any quoted string not containing the quotation mark used 336as a delimiter for that string. Literals are used for specifying the content 337of internal entities (<a href="#NT-EntityValue">EntityValue</a>), the values 338of attributes (<a href="#NT-AttValue">AttValue</a>), and external identifiers 339(<a href="#NT-SystemLiteral">SystemLiteral</a>). Note that a <a href="#NT-SystemLiteral">SystemLiteral</a> 340can be parsed without scanning for markup.</p> 341 342<h5>Literals</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-EntityValue"></a>[9]���</td><td><code>EntityValue</code></td><td>���::=���</td><td><code>'"' ([^%&"] | <a href="#NT-PEReference">PEReference</a> 343| <a href="#NT-Reference">Reference</a>)* '"' </code></td><xsltdebug></xsltdebug></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>|� "'" ([^%&'] | <a href="#NT-PEReference">PEReference</a> | <a href="#NT-Reference">Reference</a>)* "'"</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-AttValue"></a>[10]���</td><td><code>AttValue</code></td><td>���::=���</td><td><code>'"' ([^<&"] | <a href="#NT-Reference">Reference</a>)* 344'"' </code></td><xsltdebug></xsltdebug></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>|� "'" ([^<&'] | <a href="#NT-Reference">Reference</a>)* 345"'"</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-SystemLiteral"></a>[11]���</td><td><code>SystemLiteral</code></td><td>���::=���</td><td><code>('"' [^"]* '"') |�("'" [^']* "'") </code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PubidLiteral"></a>[12]���</td><td><code>PubidLiteral</code></td><td>���::=���</td><td><code>'"' <a href="#NT-PubidChar">PubidChar</a>* '"' 346| "'" (<a href="#NT-PubidChar">PubidChar</a> - "'")* "'"</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PubidChar"></a>[13]���</td><td><code>PubidChar</code></td><td>���::=���</td><td><code>#x20 | #xD | #xA |�[a-zA-Z0-9] |�[-'()+,./:=?;!*#@$_%]</code></td><xsltdebug></xsltdebug></tr></tbody></table> 347<div class="diff-add"><div class="note"><p class="prefix"><b>Note:</b></p> 348<p><a href="http://www.w3.org/XML/xml-19980210-errata#E72">[E72]</a>Although 349the <a href="#NT-EntityValue">EntityValue</a> production allows the definition 350of an entity consisting of a single explicit <code><</code> in the literal 351(e.g., <code><!ENTITY mylt "<"></code>), it is strongly advised to avoid 352this practice since any reference to that entity will cause a well-formedness 353error.</p> 354</div></div> 355</div> 356<div class="div2"> 357 358<h3><a name="syntax"></a>2.4 Character Data and Markup</h3> 359<p><a title="Text" href="#dt-text">Text</a> consists of intermingled <a title="Character Data" href="#dt-chardata">character data</a> and markup. [<a name="dt-markup" title="Markup">Definition</a>: <b>Markup</b> takes the form of <a title="Start-Tag" href="#dt-stag">start-tags</a>, <a title="End Tag" href="#dt-etag">end-tags</a>, <a title="Empty" href="#dt-empty">empty-element tags</a>, <a title="Entity Reference" href="#dt-entref">entity references</a>, <a title="Character Reference" href="#dt-charref">character 360references</a>, <a title="Comment" href="#dt-comment">comments</a>, <a title="CDATA Section" href="#dt-cdsection">CDATA section</a> delimiters, <a title="Document Type Declaration" href="#dt-doctype">document 361type declarations</a>, <a title="Processing instruction" href="#dt-pi">processing instructions</a>, <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E89">[E89]</a><a href="#NT-XMLDecl">XML declarations</a>, <a href="#NT-TextDecl">text declarations</a>, 362and any white space that is at the top level of the document entity (that 363is, outside the document element and not inside any other markup).</span>]</p> 364<p>[<a name="dt-chardata" title="Character Data">Definition</a>: All text that is not markup 365constitutes the <b>character data</b> of the document.]</p> 366<p>The ampersand character (&) and the left angle bracket (<) may appear 367in their literal form <em>only</em> when used as markup delimiters, or 368within a <a title="Comment" href="#dt-comment">comment</a>, a <a title="Processing instruction" href="#dt-pi">processing 369instruction</a>, or a <a title="CDATA Section" href="#dt-cdsection">CDATA section</a>.<span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E18">[E18]</a>They 370are also legal within the <a title="Literal Entity Value" href="#dt-litentval">literal entity value</a> 371of an internal entity declaration; see <a href="#wf-entities"><b>4.3.2 Well-Formed Parsed Entities</b></a>.</span> 372If they are needed elsewhere, they must be <a title="escape" href="#dt-escape">escaped</a> 373using either <a title="Character Reference" href="#dt-charref">numeric character references</a> 374or the strings "<code>&amp;</code>" and "<code>&lt;</code>" 375respectively. The right angle bracket (>) may be represented using the string "<code>&gt;</code>", 376and must, <a title="For Compatibility" href="#dt-compat">for compatibility</a>, be escaped 377using "<code>&gt;</code>" or a character reference when it 378appears in the string "<code>]]></code>" in content, when 379that string is not marking the end of a <a title="CDATA Section" href="#dt-cdsection">CDATA 380section</a>.</p> 381<p>In the content of elements, character data is any string of characters 382which does not contain the start-delimiter of any markup. In a CDATA section, 383character data is any string of characters not including the CDATA-section-close 384delimiter, "<code>]]></code>".</p> 385<p>To allow attribute values to contain both single and double quotes, the 386apostrophe or single-quote character (') may be represented as "<code>&apos;</code>", 387and the double-quote character (") as "<code>&quot;</code>".</p> 388 389<h5>Character Data</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-CharData"></a>[14]���</td><td><code>CharData</code></td><td>���::=���</td><td><code>[^<&]* - ([^<&]* ']]>' [^<&]*)</code></td><xsltdebug></xsltdebug></tr></tbody></table> 390</div> 391<div class="div2"> 392 393<h3><a name="sec-comments"></a>2.5 Comments</h3> 394<p>[<a name="dt-comment" title="Comment">Definition</a>: <b>Comments</b> may appear 395anywhere in a document outside other <a title="Markup" href="#dt-markup">markup</a>; 396in addition, they may appear within the document type declaration at places 397allowed by the grammar. They are not part of the document's <a title="Character Data" href="#dt-chardata">character 398data</a>; an XML processor may, but need not, make it possible for an 399application to retrieve the text of comments. <a title="For Compatibility" href="#dt-compat">For 400compatibility</a>, the string "<code>--</code>" (double-hyphen) 401must not occur within comments.] <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E63">[E63]</a>Parameter 402entity references are not recognized within comments.</span></p> 403 404<h5>Comments</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-Comment"></a>[15]���</td><td><code>Comment</code></td><td>���::=���</td><td><code>'<!--' ((<a href="#NT-Char">Char</a> - '-') | ('-' 405(<a href="#NT-Char">Char</a> - '-')))* '-->'</code></td><xsltdebug></xsltdebug></tr></tbody></table> 406<p>An example of a comment:</p> 407<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!-- declarations for <head> & <body> --></pre></td></tr></table> 408<div class="diff-add"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E27">[E27]</a>Note 409that the grammar does not allow a comment ending in <code>---></code>. The 410following example is <em>not</em> well-formed.</p></div> 411<div class="diff-add"><table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td class="diff-add"><pre><!-- B+, B, or B---></pre></td></tr></table></div> 412</div> 413<div class="div2"> 414 415<h3><a name="sec-pi"></a>2.6 Processing Instructions</h3> 416<p>[<a name="dt-pi" title="Processing instruction">Definition</a>: <b>Processing instructions</b> 417(PIs) allow documents to contain instructions for applications.]</p> 418 419<h5>Processing Instructions</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-PI"></a>[16]���</td><td><code>PI</code></td><td>���::=���</td><td><code>'<?' <a href="#NT-PITarget">PITarget</a> (<a href="#NT-S">S</a> 420(<a href="#NT-Char">Char</a>* - (<a href="#NT-Char">Char</a>* '?>' <a href="#NT-Char">Char</a>*)))? '?>'</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PITarget"></a>[17]���</td><td><code>PITarget</code></td><td>���::=���</td><td><code><a href="#NT-Name">Name</a> - (('X' | 'x') ('M' | 421'm') ('L' | 'l'))</code></td><xsltdebug></xsltdebug></tr></tbody></table> 422<p>PIs are not part of the document's <a title="Character Data" href="#dt-chardata">character 423data</a>, but must be passed through to the application. The PI begins 424with a target (<a href="#NT-PITarget">PITarget</a>) used to identify the application 425to which the instruction is directed. The target names "<code>XML</code>", "<code>xml</code>", 426and so on are reserved for standardization in this or future versions of this 427specification. The XML <a title="Notation" href="#dt-notation">Notation</a> mechanism 428may be used for formal declaration of PI targets. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E63">[E63]</a>Parameter 429entity references are not recognized within processing instructions.</span></p> 430</div> 431<div class="div2"> 432 433<h3><a name="sec-cdata-sect"></a>2.7 CDATA Sections</h3> 434<p>[<a name="dt-cdsection" title="CDATA Section">Definition</a>: <b>CDATA sections</b> 435may occur anywhere character data may occur; they are used to escape blocks 436of text containing characters which would otherwise be recognized as markup. 437CDATA sections begin with the string "<code><![CDATA[</code>" 438and end with the string "<code>]]></code>":]</p> 439 440<h5>CDATA Sections</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-CDSect"></a>[18]���</td><td><code>CDSect</code></td><td>���::=���</td><td><code><a href="#NT-CDStart">CDStart</a> <a href="#NT-CData">CData</a> <a href="#NT-CDEnd">CDEnd</a></code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-CDStart"></a>[19]���</td><td><code>CDStart</code></td><td>���::=���</td><td><code>'<![CDATA['</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-CData"></a>[20]���</td><td><code>CData</code></td><td>���::=���</td><td><code>(<a href="#NT-Char">Char</a>* - (<a href="#NT-Char">Char</a>* 441']]>' <a href="#NT-Char">Char</a>*)) </code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-CDEnd"></a>[21]���</td><td><code>CDEnd</code></td><td>���::=���</td><td><code>']]>'</code></td><xsltdebug></xsltdebug></tr></tbody></table> 442<p>Within a CDATA section, only the <a href="#NT-CDEnd">CDEnd</a> string is 443recognized as markup, so that left angle brackets and ampersands may occur 444in their literal form; they need not (and cannot) be escaped using "<code>&lt;</code>" 445and "<code>&amp;</code>". CDATA sections cannot nest.</p> 446<p>An example of a CDATA section, in which "<code><greeting></code>" 447and "<code></greeting></code>" are recognized as <a title="Character Data" href="#dt-chardata">character data</a>, not <a title="Markup" href="#dt-markup">markup</a>:</p> 448<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><![CDATA[<greeting>Hello, world!</greeting>]]> </pre></td></tr></table> 449</div> 450<div class="div2"> 451 452<h3><a name="sec-prolog-dtd"></a>2.8 Prolog and Document Type Declaration</h3> 453<p>[<a name="dt-xmldecl" title="XML Declaration">Definition</a>: XML documents <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E107">[E107]</a>should</span> 454begin with an <b>XML declaration</b> which specifies the version of 455XML being used.] For example, the following is a complete XML document, <a title="Well-Formed" href="#dt-wellformed">well-formed</a> but not <a title="Validity" href="#dt-valid">valid</a>:</p> 456<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><?xml version="1.0"?> <greeting>Hello, world!</greeting> </pre></td></tr></table> 457<p>and so is this:</p> 458<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><greeting>Hello, world!</greeting></pre></td></tr></table> 459<p>The version number "<code>1.0</code>" should be used to indicate 460conformance to this version of this specification; it is an error for a document 461to use the value "<code>1.0</code>" if it does not conform to 462this version of this specification. It is the intent of the XML working group 463to give later versions of this specification numbers other than "<code>1.0</code>", 464but this intent does not indicate a commitment to produce any future versions 465of XML, nor if any are produced, to use any particular numbering scheme. Since 466future versions are not ruled out, this construct is provided as a means to 467allow the possibility of automatic version recognition, should it become necessary. 468Processors may signal an error if they receive documents labeled with versions 469they do not support.</p> 470<p>The function of the markup in an XML document is to describe its storage 471and logical structure and to associate attribute-value pairs with its logical 472structures. XML provides a mechanism, the <a title="Document Type Declaration" href="#dt-doctype">document 473type declaration</a>, to define constraints on the logical structure 474and to support the use of predefined storage units. [<a name="dt-valid" title="Validity">Definition</a>: An XML document is <b>valid</b> if it has an associated 475document type declaration and if the document complies with the constraints 476expressed in it.]</p> 477<p>The document type declaration must appear before the first <a title="Element" href="#dt-element">element</a> 478in the document.</p> 479 480<h5>Prolog</h5><table class="scrap" summary="Scrap"><tbody> 481<tr valign="baseline"><td><a name="NT-prolog"></a>[22]���</td><td><code>prolog</code></td><td>���::=���</td><td><code><a href="#NT-XMLDecl">XMLDecl</a>? <a href="#NT-Misc">Misc</a>* 482(<a href="#NT-doctypedecl">doctypedecl</a> <a href="#NT-Misc">Misc</a>*)?</code></td><xsltdebug></xsltdebug></tr> 483<tr valign="baseline"><td><a name="NT-XMLDecl"></a>[23]���</td><td><code>XMLDecl</code></td><td>���::=���</td><td><code>'<?xml' <a href="#NT-VersionInfo">VersionInfo</a> <a href="#NT-EncodingDecl">EncodingDecl</a>? <a href="#NT-SDDecl">SDDecl</a>? <a href="#NT-S">S</a>? '?>'</code></td><xsltdebug></xsltdebug></tr> 484<tr valign="baseline"><td class="diff-chg"><a name="NT-VersionInfo"></a>[24]���</td><td class="diff-chg"><code>VersionInfo</code></td><td class="diff-chg">���::=���</td><td class="diff-chg"><code><a href="#NT-S">S</a> 'version' <a href="#NT-Eq">Eq</a> 485("'" <a href="#NT-VersionNum">VersionNum</a> "'" | '"' <a href="#NT-VersionNum">VersionNum</a> 486'"')<i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E15">[E15]</a> */</i></code></td><xsltdebug></xsltdebug></tr> 487<tr valign="baseline"><td><a name="NT-Eq"></a>[25]���</td><td><code>Eq</code></td><td>���::=���</td><td><code><a href="#NT-S">S</a>? '=' <a href="#NT-S">S</a>?</code></td><xsltdebug></xsltdebug></tr> 488<tr valign="baseline"><td><a name="NT-VersionNum"></a>[26]���</td><td><code>VersionNum</code></td><td>���::=���</td><td><code>([a-zA-Z0-9_.:] | '-')+</code></td><xsltdebug></xsltdebug></tr> 489<tr valign="baseline"><td><a name="NT-Misc"></a>[27]���</td><td><code>Misc</code></td><td>���::=���</td><td><code><a href="#NT-Comment">Comment</a> | <a href="#NT-PI">PI</a> 490| <a href="#NT-S">S</a></code></td><xsltdebug></xsltdebug></tr> 491</tbody></table> 492<p>[<a name="dt-doctype" title="Document Type Declaration">Definition</a>: The XML <b>document 493type declaration</b> contains or points to <a title="markup declaration" href="#dt-markupdecl">markup 494declarations</a> that provide a grammar for a class of documents. This 495grammar is known as a document type definition, or <b>DTD</b>. The document 496type declaration can point to an external subset (a special kind of <a title="External Entity" href="#dt-extent">external entity</a>) containing markup declarations, 497or can contain the markup declarations directly in an internal subset, or 498can do both. The DTD for a document consists of both subsets taken together.]</p> 499<p>[<a name="dt-markupdecl" title="markup declaration">Definition</a>: A <b>markup declaration</b> 500is an <a title="Element Type declaration" href="#dt-eldecl">element type declaration</a>, an <a title="Attribute-List Declaration" href="#dt-attdecl">attribute-list declaration</a>, an <a title="entity declaration" href="#dt-entdecl">entity 501declaration</a>, or a <a title="Notation Declaration" href="#dt-notdecl">notation declaration</a>.] 502These declarations may be contained in whole or in part within <a title="Parameter entity" href="#dt-PE">parameter 503entities</a>, as described in the well-formedness and validity constraints 504below. For <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E14">[E14]</a>further</span> 505information, see <a href="#sec-physical-struct"><b>4 Physical Structures</b></a>.</p> 506 507<h5>Document Type Definition</h5><table class="scrap" summary="Scrap"><tbody> 508<tr valign="baseline"><td class="diff-chg"><a name="NT-doctypedecl"></a>[28]���</td><td class="diff-chg"><code>doctypedecl</code></td><td class="diff-chg">���::=���</td><td class="diff-chg"><code>'<!DOCTYPE' <a href="#NT-S">S</a> <a href="#NT-Name">Name</a> 509(<a href="#NT-S">S</a> <a href="#NT-ExternalID">ExternalID</a>)? <a href="#NT-S">S</a>? 510('[' (<a href="#NT-markupdecl">markupdecl</a> | <a href="#NT-DeclSep">DeclSep</a>)* 511']' <a href="#NT-S">S</a>?)? '>'</code></td><xsltdebug></xsltdebug><td><a href="#vc-roottype">[VC: Root Element Type]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td class="diff-add"><a href="#ExtSubset">[WFC: External 512Subset]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td class="diff-chg"><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</a> */</i></td></tr> 513<tr valign="baseline"><td class="diff-add"><a name="NT-DeclSep"></a>[28a]���</td><td class="diff-add"><code>DeclSep</code></td><td class="diff-add">���::=���</td><td class="diff-add"><code><a href="#NT-PEReference">PEReference</a> | <a href="#NT-S">S</a></code></td><xsltdebug></xsltdebug><td class="diff-add"><a href="#PE-between-Decls">[WFC: PE 514Between Declarations]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td class="diff-add"><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</a> */</i></td></tr> 515<tr valign="baseline"><td><a name="NT-markupdecl"></a>[29]���</td><td><code>markupdecl</code></td><td>���::=���</td><td><code><a href="#NT-elementdecl">elementdecl</a> | <a href="#NT-AttlistDecl">AttlistDecl</a> | <a href="#NT-EntityDecl">EntityDecl</a> 516| <a href="#NT-NotationDecl">NotationDecl</a> | <a href="#NT-PI">PI</a> | <a href="#NT-Comment">Comment</a> </code></td><xsltdebug></xsltdebug><td><a href="#vc-PEinMarkupDecl">[VC: Proper Declaration/PE Nesting]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#wfc-PEinInternalSubset">[WFC: PEs in Internal Subset]</a></td></tr> 517</tbody></table> 518<div class="diff-add"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E82">[E82]</a>Note 519that it is possible to construct a well-formed document containing a <a href="#NT-doctypedecl">doctypedecl</a> 520that neither points to an external subset nor contains an internal subset.</p></div> 521<p>The markup declarations may be made up in whole or in part of the <a title="Replacement Text" href="#dt-repltext">replacement text</a> of <a title="Parameter entity" href="#dt-PE">parameter 522entities</a>. The productions later in this specification for individual 523nonterminals (<a href="#NT-elementdecl">elementdecl</a>, <a href="#NT-AttlistDecl">AttlistDecl</a>, 524and so on) describe the declarations <em>after</em> all the parameter 525entities have been <a title="Include" href="#dt-include">included</a>.</p> 526<div class="diff-add"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E75">[E75]</a>Parameter 527entity references are recognized anywhere in the DTD (internal and external 528subsets and external parameter entities), except in literals, processing instructions, 529comments, and the contents of ignored conditional sections (see <a href="#sec-condition-sect"><b>3.4 Conditional Sections</b></a>). 530They are also recognized in entity value literals. The use of parameter entities 531in the internal subset is restricted as described below.</p></div> 532<div class="constraint"><p class="prefix"><a name="vc-roottype"></a><b>Validity constraint: Root Element Type</b></p><p>The <a href="#NT-Name">Name</a> 533in the document type declaration must match the element type of the <a title="Root Element" href="#dt-root">root element</a>.</p> 534</div> 535<div class="constraint"><p class="prefix"><a name="vc-PEinMarkupDecl"></a><b>Validity constraint: Proper Declaration/PE Nesting</b></p> 536<p>Parameter-entity <a title="Replacement Text" href="#dt-repltext">replacement text</a> 537must be properly nested with markup declarations. That is to say, if either 538the first character or the last character of a markup declaration (<a href="#NT-markupdecl">markupdecl</a> 539above) is contained in the replacement text for a <a title="Parameter-entity reference" href="#dt-PERef">parameter-entity 540reference</a>, both must be contained in the same replacement text.</p> 541</div> 542<div class="constraint"><p class="prefix"><a name="wfc-PEinInternalSubset"></a><b>Well-formedness constraint: PEs in Internal Subset</b></p><p>In 543the internal DTD subset, <a title="Parameter-entity reference" href="#dt-PERef">parameter-entity references</a> 544can occur only where markup declarations can occur, not within markup declarations. 545(This does not apply to references that occur in external parameter entities 546or to the external subset.)</p> 547</div> 548<div class="diff-add"><div class="constraint"><p class="prefix"><a name="ExtSubset"></a><b>Well-formedness constraint: <a href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</a>External 549Subset</b></p><p>The external subset, if any, must match the production for <a href="#NT-extSubset">extSubset</a>.</p> 550</div></div> 551<div class="diff-add"><div class="constraint"><p class="prefix"><a name="PE-between-Decls"></a><b>Well-formedness constraint: <a href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</a>PE 552Between Declarations</b></p><p>The replacement text of a parameter entity reference 553in a <a href="#NT-DeclSep">DeclSep</a> must match the production <a href="#NT-extSubsetDecl">extSubsetDecl</a>.</p> 554</div></div> 555<p>Like the internal subset, the external subset and any external parameter 556entities <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</a>referenced 557in a <a href="#NT-DeclSep">DeclSep</a></span> must consist of a series of 558complete markup declarations of the types allowed by the non-terminal symbol <a href="#NT-markupdecl">markupdecl</a>, interspersed with white space or <a title="Parameter-entity reference" href="#dt-PERef">parameter-entity references</a>. However, portions of 559the contents of the external subset or of <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</a>these </span> 560external parameter entities may conditionally be ignored by using the <a title="conditional section" href="#dt-cond-section">conditional section</a> construct; this is not 561allowed in the internal subset.</p> 562 563<h5>External Subset</h5><table class="scrap" summary="Scrap"><tbody> 564<tr valign="baseline"><td><a name="NT-extSubset"></a>[30]���</td><td><code>extSubset</code></td><td>���::=���</td><td><code><a href="#NT-TextDecl">TextDecl</a>? <a href="#NT-extSubsetDecl">extSubsetDecl</a></code></td><xsltdebug></xsltdebug></tr> 565<tr valign="baseline"><td class="diff-chg"><a name="NT-extSubsetDecl"></a>[31]���</td><td class="diff-chg"><code>extSubsetDecl</code></td><td class="diff-chg">���::=���</td><td class="diff-chg"><code>( <a href="#NT-markupdecl">markupdecl</a> | <a href="#NT-conditionalSect">conditionalSect</a> | <a href="#NT-DeclSep">DeclSep</a>)*</code></td><xsltdebug></xsltdebug><td class="diff-chg"><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</a> */</i></td></tr> 566</tbody></table> 567<p>The external subset and external parameter entities also differ from the 568internal subset in that in them, <a title="Parameter-entity reference" href="#dt-PERef">parameter-entity 569references</a> are permitted <em>within</em> markup declarations, 570not only <em>between</em> markup declarations.</p> 571<p>An example of an XML document with a document type declaration:</p> 572<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><?xml version="1.0"?> <!DOCTYPE greeting SYSTEM "hello.dtd"> <greeting>Hello, world!</greeting> </pre></td></tr></table> 573<p>The <a title="System Identifier" href="#dt-sysid">system identifier</a> "<code>hello.dtd</code>" 574gives the <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E78">[E78]</a>address 575(a URI reference)</span> of a DTD for the document.</p> 576<p>The declarations can also be given locally, as in this example:</p> 577<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><?xml version="1.0" encoding="UTF-8" ?> 578<!DOCTYPE greeting [ 579 <!ELEMENT greeting (#PCDATA)> 580]> 581<greeting>Hello, world!</greeting></pre></td></tr></table> 582<p>If both the external and internal subsets are used, the internal subset 583is considered to occur before the external subset. 584This has the effect that entity and attribute-list declarations in the internal 585subset take precedence over those in the external subset.</p> 586</div> 587<div class="div2"> 588 589<h3><a name="sec-rmd"></a>2.9 Standalone Document Declaration</h3> 590<p>Markup declarations can affect the content of the document, as passed from 591an <a title="XML Processor" href="#dt-xml-proc">XML processor</a> to an application; examples 592are attribute defaults and entity declarations. The standalone document declaration, 593which may appear as a component of the XML declaration, signals whether or 594not there are such declarations which appear external to the <a title="Document Entity" href="#dt-docent">document 595entity</a><span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E64">[E64]</a> 596or in parameter entities. [<a name="dt-extmkpdecl" title="External Markup Declaration">Definition</a>: An <b>external 597markup declaration</b> is defined as a markup declaration occurring in 598the external subset or in a parameter entity (external or internal, the latter 599being included because non-validating processors are not required to read 600them).]</span></p> 601 602<h5>Standalone Document Declaration</h5><table class="scrap" summary="Scrap"><tbody> 603<tr valign="baseline"><td><a name="NT-SDDecl"></a>[32]���</td><td><code>SDDecl</code></td><td>���::=���</td><td><code> <a href="#NT-S">S</a> 'standalone' <a href="#NT-Eq">Eq</a> 604(("'" ('yes' | 'no') "'") | ('"' ('yes' | 'no') '"')) </code></td><xsltdebug></xsltdebug><td><a href="#vc-check-rmd">[VC: Standalone Document Declaration]</a></td></tr> 605</tbody></table> 606<p>In a standalone document declaration, the value "yes" indicates 607that there are no <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E64">[E64]</a><a title="External Markup Declaration" href="#dt-extmkpdecl">external markup declarations</a></span> which 608affect the information passed from the XML processor to the application. The 609value "no" indicates that there are or may be such external 610markup declarations. Note that the standalone document declaration only denotes 611the presence of external <em>declarations</em>; the presence, in a document, 612of references to external <em>entities</em>, when those entities are internally 613declared, does not change its standalone status.</p> 614<p>If there are no external markup declarations, the standalone document declaration 615has no meaning. If there are external markup declarations but there is no 616standalone document declaration, the value "no" is assumed.</p> 617<p>Any XML document for which <code>standalone="no"</code> holds can be converted 618algorithmically to a standalone document, which may be desirable for some 619network delivery applications.</p> 620<div class="constraint"><p class="prefix"><a name="vc-check-rmd"></a><b>Validity constraint: Standalone Document Declaration</b></p><p>The 621standalone document declaration must have the value "no" if 622any external markup declarations contain declarations of:</p> 623<ul> 624<li><p>attributes with <a title="Attribute Default" href="#dt-default">default</a> values, 625if elements to which these attributes apply appear in the document without 626specifications of values for these attributes, or</p></li> 627<li><p>entities (other than <code>amp</code>, 628<code>lt</code>, 629<code>gt</code>, 630<code>apos</code>, 631<code>quot</code>), if <a title="Entity Reference" href="#dt-entref">references</a> 632to those entities appear in the document, or</p></li> 633<li><p>attributes with values subject to <a href="#AVNormalize"><cite>normalization</cite></a>, 634where the attribute appears in the document with a value which will change 635as a result of normalization, or</p></li> 636<li><p>element types with <a title="Element content" href="#dt-elemcontent">element content</a>, 637if white space occurs directly within any instance of those types.</p></li> 638</ul> 639</div> 640<p>An example XML declaration with a standalone document declaration:</p> 641<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><?xml version="1.0" standalone='yes'?></pre></td></tr></table> 642</div> 643<div class="div2"> 644 645<h3><a name="sec-white-space"></a>2.10 White Space Handling</h3> 646<p>In editing XML documents, it is often convenient to use "white space" 647(spaces, tabs, and blank lines<span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E39">[E39]</a>, 648denoted by the nonterminal <a href="#NT-S">S</a> in this specification</span>) 649to set apart the markup for greater readability. Such white space is typically 650not intended for inclusion in the delivered version of the document. On the 651other hand, "significant" white space that should be preserved 652in the delivered version is common, for example in poetry and source code.</p> 653<p>An <a title="XML Processor" href="#dt-xml-proc">XML processor</a> must always pass 654all characters in a document that are not markup through to the application. 655A <a title="Validating Processor" href="#dt-validating"> validating XML processor</a> must also 656inform the application which of these characters constitute white space appearing 657in <a title="Element content" href="#dt-elemcontent">element content</a>.</p> 658<p>A special <a title="Attribute" href="#dt-attr">attribute</a> named <code>xml:space</code> 659may be attached to an element to signal an intention that in that element, 660white space should be preserved by applications. In valid documents, this 661attribute, like any other, must be <a title="Attribute-List Declaration" href="#dt-attdecl">declared</a> 662if it is used. When declared, it must be given as an <a title="Enumerated Attribute Values" href="#dt-enumerated">enumerated 663type</a> whose <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E81">[E81]</a>values 664are one or both of</span> "default" and "preserve". 665For example:</p> 666<div class="diff-chg"><table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td class="diff-chg"><pre><!ATTLIST poem xml:space (default|preserve) 'preserve'> 667 668<!-- <a href="http://www.w3.org/XML/xml-19980210-errata#E81">[E81]</a>--> 669<!ATTLIST pre xml:space (preserve) #FIXED 'preserve'></pre></td></tr></table></div> 670<p>The value "default" signals that applications' default white-space 671processing modes are acceptable for this element; the value "preserve" 672indicates the intent that applications preserve all the white space. This 673declared intent is considered to apply to all elements within the content 674of the element where it is specified, unless overriden with another instance 675of the <code>xml:space</code> attribute.</p> 676<p>The <a title="Root Element" href="#dt-root">root element</a> of any document is considered 677to have signaled no intentions as regards application space handling, unless 678it provides a value for this attribute or the attribute is declared with a 679default value.</p> 680</div> 681<div class="div2"> 682 683<h3><a name="sec-line-ends"></a>2.11 End-of-Line Handling</h3> 684<p>XML <a title="Text Entity" href="#dt-parsedent">parsed entities</a> are often stored 685in computer files which, for editing convenience, are organized into lines. 686These lines are typically separated by some combination of the characters 687carriage-return (#xD) and line-feed (#xA).</p> 688<div class="diff-del"><p>To simplify the tasks of <a title="Application" href="#dt-app">applications</a>, 689wherever an external parsed entity or the literal entity value of an internal 690parsed entity contains either the literal two-character sequence "#xD#xA" 691or a standalone literal #xD, an <a title="XML Processor" href="#dt-xml-proc">XML processor</a> 692must pass to the application the single character #xA. (This behavior can 693conveniently be produced by normalizing all line breaks to #xA on input, before 694parsing.)</p></div> 695<div class="diff-add"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E104">[E104]</a>To 696simplify the tasks of <a title="Application" href="#dt-app">applications</a>, the characters 697passed to an application by the <a title="XML Processor" href="#dt-xml-proc">XML processor</a> 698must be as if the XML processor normalized all line breaks in external parsed 699entities (including the document entity) on input, before parsing, by translating 700both the two-character sequence #xD #xA and any #xD that is not followed by 701#xA to a single #xA character.</p></div> 702</div> 703<div class="div2"> 704 705<h3><a name="sec-lang-tag"></a>2.12 Language Identification</h3> 706<p>In document processing, it is often useful to identify the natural or formal 707language in which the content is written. A special <a title="Attribute" href="#dt-attr">attribute</a> 708named <code>xml:lang</code> may be inserted in documents to specify the language 709used in the contents and attribute values of any element in an XML document. 710In valid documents, this attribute, like any other, must be <a title="Attribute-List Declaration" href="#dt-attdecl">declared</a> 711if it is used. <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E73">[E73]</a>The 712values of the attribute are language identifiers as defined by <a href="#RFC1766">[IETF RFC 1766]</a>, <cite>Tags 713for the Identification of Languages</cite>, or its successor on the IETF 714Standards Track.</span></p> 715<div class="diff-add"><div class="note"><p class="prefix"><b>Note:</b></p> 716<p><a href="http://www.w3.org/XML/xml-19980210-errata#E73">[E73]</a><a href="#RFC1766">[IETF RFC 1766]</a> tags are constructed from two-letter language codes as defined 717by <a href="#ISO639">[ISO 639]</a>, from two-letter country codes as defined by <a href="#ISO3166">[ISO 3166]</a>, or from language identifiers registered with the Internet 718Assigned Numbers Authority <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E58">[E58]</a><span class="diff-chg"><a href="#IANA-LANGCODES">[IANA-LANGCODES]</a></span></span>. It is expected that the successor 719to <a href="#RFC1766">[IETF RFC 1766]</a> will introduce three-letter language codes for 720languages not presently covered by <a href="#ISO639">[ISO 639]</a>.</p> 721</div></div> 722<div class="diff-add"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E73">[E73]</a>(Productions 72333 through 38 have been removed.)</p></div> 724<div class="diff-del"> 725<h5>Language Identification</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td class="diff-del"><a name="NT-LanguageID"></a>[33]���</td><td class="diff-del"><code>LanguageID</code></td><td class="diff-del">���::=���</td><td class="diff-del"><code><a href="#NT-Langcode">Langcode</a> ('-' <a href="#NT-Subcode">Subcode</a>)*</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td class="diff-del"><a name="NT-Langcode"></a>[34]���</td><td class="diff-del"><code>Langcode</code></td><td class="diff-del">���::=���</td><td class="diff-del"><code><a href="#NT-ISO639Code">ISO639Code</a> | <a href="#NT-IanaCode">IanaCode</a> 726| <a href="#NT-UserCode">UserCode</a></code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td class="diff-del"><a name="NT-ISO639Code"></a>[35]���</td><td class="diff-del"><code>ISO639Code</code></td><td class="diff-del">���::=���</td><td class="diff-del"><code>([a-z] | [A-Z]) ([a-z] | [A-Z])</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td class="diff-del"><a name="NT-IanaCode"></a>[36]���</td><td class="diff-del"><code>IanaCode</code></td><td class="diff-del">���::=���</td><td class="diff-del"><code>('i' | 'I') '-' ([a-z] | [A-Z])+</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td class="diff-del"><a name="NT-UserCode"></a>[37]���</td><td class="diff-del"><code>UserCode</code></td><td class="diff-del">���::=���</td><td class="diff-del"><code>('x' | 'X') '-' ([a-z] | [A-Z])+</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td class="diff-del"><a name="NT-Subcode"></a>[38]���</td><td class="diff-del"><code>Subcode</code></td><td class="diff-del">���::=���</td><td class="diff-del"><code>([a-z] | [A-Z])+</code></td><xsltdebug></xsltdebug></tr></tbody></table></div> 727<div class="diff-del"><p>The <a href="#NT-Langcode">Langcode</a> may be any of the following:</p></div> 728<div class="diff-del"><ul> 729<li><p>a two-letter language code as defined by <a href="#ISO639">[ISO 639]</a>, <cite>Codes 730for the representation of names of languages</cite></p></li> 731<li><p>a language identifier registered with the Internet Assigned Numbers 732Authority <span class="diff-chg"><a href="#IANA-LANGCODES">[IANA-LANGCODES]</a></span>; these begin with the 733prefix "<code>i-</code>" (or "<code>I-</code>")</p> 734</li> 735<li><p>a language identifier assigned by the user, or agreed on between 736parties in private use; these must begin with the prefix "<code>x-</code>" 737or "<code>X-</code>" in order to ensure that they do not conflict 738with names later standardized or registered with IANA</p></li> 739</ul></div> 740<div class="diff-del"><p>There may be any number of <a href="#NT-Subcode">Subcode</a> 741segments; if the first subcode segment exists and the Subcode consists of 742two letters, then it must be a country code from <a href="#ISO3166">[ISO 3166]</a>, 743"Codes for the representation of names of countries." If the first subcode 744consists of more than two letters, it must be a subcode for the language in 745question registered with IANA, unless the <a href="#NT-Langcode">Langcode</a> 746begins with the prefix "<code>x-</code>" or "<code>X-</code>". </p></div> 747<div class="diff-del"><p>It is customary to give the language code in lower case, and 748the country code (if any) in upper case. Note that these values, unlike other 749names in XML documents, are case insensitive.</p></div> 750<p>For example:</p> 751<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><p xml:lang="en">The quick brown fox jumps over the lazy dog.</p> 752<p xml:lang="en-GB">What colour is it?</p> 753<p xml:lang="en-US">What color is it?</p> 754<sp who="Faust" desc='leise' xml:lang="de"> 755 <l>Habe nun, ach! Philosophie,</l> 756 <l>Juristerei, und Medizin</l> 757 <l>und leider auch Theologie</l> 758 <l>durchaus studiert mit hei�em Bem�h'n.</l> 759</sp></pre></td></tr></table> 760 761<p>The intent declared with <code>xml:lang</code> is considered to apply to 762all attributes and content of the element where it is specified, unless overridden 763with an instance of <code>xml:lang</code> on another element within that content.</p> 764 765<p>A simple declaration for <code>xml:lang</code> might take the form</p> 766<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>xml:lang NMTOKEN #IMPLIED</pre></td></tr></table> 767<p>but specific default values may also be given, if appropriate. In a collection 768of French poems for English students, with glosses and notes in English, the <code>xml:lang</code> 769attribute might be declared this way:</p> 770<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ATTLIST poem xml:lang NMTOKEN 'fr'> 771<!ATTLIST gloss xml:lang NMTOKEN 'en'> 772<!ATTLIST note xml:lang NMTOKEN 'en'></pre></td></tr></table> 773</div> 774</div> 775 776<div class="div1"> 777 778<h2><a name="sec-logical-struct"></a>3 Logical Structures</h2> 779<p>[<a name="dt-element" title="Element">Definition</a>: Each <a title="XML Document" href="#dt-xml-doc">XML 780document</a> contains one or more <b>elements</b>, the boundaries 781of which are either delimited by <a title="Start-Tag" href="#dt-stag">start-tags</a> 782and <a title="End Tag" href="#dt-etag">end-tags</a>, or, for <a title="Empty" href="#dt-empty">empty</a> 783elements, by an <a title="empty-element tag" href="#dt-eetag">empty-element tag</a>. Each 784element has a type, identified by name, sometimes called its "generic 785identifier" (GI), and may have a set of attribute specifications.] 786Each attribute specification has a <a title="Attribute Name" href="#dt-attrname">name</a> 787and a <a title="Attribute Value" href="#dt-attrval">value</a>.</p> 788 789<h5>Element</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-element"></a>[39]���</td><td><code>element</code></td><td>���::=���</td><td><code><a href="#NT-EmptyElemTag">EmptyElemTag</a></code></td><xsltdebug></xsltdebug></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| <a href="#NT-STag">STag</a> <a href="#NT-content">content</a> <a href="#NT-ETag">ETag</a></code></td><td><a href="#GIMatch">[WFC: Element Type Match]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#elementvalid">[VC: Element Valid]</a></td></tr></tbody></table> 790<p>This specification does not constrain the semantics, use, or (beyond syntax) 791names of the element types and attributes, except that names beginning with 792a match to <code>(('X'|'x')('M'|'m')('L'|'l'))</code> are reserved for standardization 793in this or future versions of this specification.</p> 794<div class="constraint"><p class="prefix"><a name="GIMatch"></a><b>Well-formedness constraint: Element Type Match</b></p><p>The <a href="#NT-Name">Name</a> 795in an element's end-tag must match the element type in the start-tag.</p> 796</div> 797<div class="constraint"><p class="prefix"><a name="elementvalid"></a><b>Validity constraint: Element Valid</b></p><p>An element is valid 798if there is a declaration matching <a href="#NT-elementdecl">elementdecl</a> 799where the <a href="#NT-Name">Name</a> matches the element type, and one of 800the following holds:</p> 801<ol> 802<li><p>The declaration matches <b>EMPTY</b> and the element has no <a title="Content" href="#dt-content">content</a>.</p></li> 803<li><p>The declaration matches <a href="#NT-children">children</a> and the 804sequence of <a title="Parent/Child" href="#dt-parentchild">child elements</a> belongs 805to the language generated by the regular expression in the content model, 806with optional white space (characters matching the nonterminal <a href="#NT-S">S</a>) 807between <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E59">[E59]</a>the 808start-tag and the first child element, between child elements, or between 809the last child element and the end-tag. Note that a CDATA section containing 810only white space does not match the nonterminal <a href="#NT-S">S</a>, and 811hence cannot appear in these positions.</span></p></li> 812<li><p>The declaration matches <a href="#NT-Mixed">Mixed</a> and the content 813consists of <a title="Character Data" href="#dt-chardata">character data</a> and <a title="Parent/Child" href="#dt-parentchild">child elements</a> whose types match names in the 814content model.</p></li> 815<li><p>The declaration matches <b>ANY</b>, and the types of any <a title="Parent/Child" href="#dt-parentchild">child elements</a> have been declared.</p></li> 816</ol> 817</div> 818<div class="div2"> 819 820<h3><a name="sec-starttags"></a>3.1 Start-Tags, End-Tags, and Empty-Element Tags</h3> 821<p>[<a name="dt-stag" title="Start-Tag">Definition</a>: The beginning of every non-empty 822XML element is marked by a <b>start-tag</b>.]</p> 823 824<h5>Start-tag</h5><table class="scrap" summary="Scrap"><tbody> 825<tr valign="baseline"><td><a name="NT-STag"></a>[40]���</td><td><code>STag</code></td><td>���::=���</td><td><code>'<' <a href="#NT-Name">Name</a> (<a href="#NT-S">S</a> <a href="#NT-Attribute">Attribute</a>)* <a href="#NT-S">S</a>? '>'</code></td><xsltdebug></xsltdebug><td><a href="#uniqattspec">[WFC: Unique Att Spec]</a></td></tr> 826<tr valign="baseline"><td><a name="NT-Attribute"></a>[41]���</td><td><code>Attribute</code></td><td>���::=���</td><td><code><a href="#NT-Name">Name</a> <a href="#NT-Eq">Eq</a> <a href="#NT-AttValue">AttValue</a></code></td><xsltdebug></xsltdebug><td><a href="#ValueType">[VC: Attribute Value Type]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#NoExternalRefs">[WFC: No External Entity References]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#CleanAttrVals">[WFC: No < in Attribute Values]</a></td></tr> 827</tbody></table> 828<p>The <a href="#NT-Name">Name</a> in the start- and end-tags gives the element's <b>type</b>. [<a name="dt-attr" title="Attribute">Definition</a>: The <a href="#NT-Name">Name</a>-<a href="#NT-AttValue">AttValue</a> 829pairs are referred to as the <b>attribute specifications</b> of the 830element], [<a name="dt-attrname" title="Attribute Name">Definition</a>: with the <a href="#NT-Name">Name</a> in each pair referred to as the <b>attribute name</b>] 831and [<a name="dt-attrval" title="Attribute Value">Definition</a>: the content of the <a href="#NT-AttValue">AttValue</a> (the text between the <code>'</code> or <code>"</code> 832delimiters) as the <b>attribute value</b>.]<span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E46">[E46]</a>Note 833that the order of attribute specifications in a start-tag or empty-element 834tag is not significant.</span></p> 835<div class="constraint"><p class="prefix"><a name="uniqattspec"></a><b>Well-formedness constraint: Unique Att Spec</b></p><p>No attribute name 836may appear more than once in the same start-tag or empty-element tag.</p> 837</div> 838<div class="constraint"><p class="prefix"><a name="ValueType"></a><b>Validity constraint: Attribute Value Type</b></p><p>The attribute must 839have been declared; the value must be of the type declared for it. (For attribute 840types, see <a href="#attdecls"><b>3.3 Attribute-List Declarations</b></a>.)</p> 841</div> 842<div class="constraint"><p class="prefix"><a name="NoExternalRefs"></a><b>Well-formedness constraint: No External Entity References</b></p><p>Attribute 843values cannot contain direct or indirect entity references to external entities.</p> 844</div> 845<div class="constraint"><p class="prefix"><a name="CleanAttrVals"></a><b>Well-formedness constraint: No <code><</code> in Attribute Values</b></p> 846<p>The <a title="Replacement Text" href="#dt-repltext">replacement text</a> of any entity 847referred to directly or indirectly in an attribute value <span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E83">[E83]</a>(other 848than "<code>&lt;</code>") </span>must not contain a <code><</code>.</p> 849</div> 850<p>An example of a start-tag:</p> 851<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><termdef id="dt-dog" term="dog"></pre></td></tr></table> 852<p>[<a name="dt-etag" title="End Tag">Definition</a>: The end of every element that begins 853with a start-tag must be marked by an <b>end-tag</b> containing a name 854that echoes the element's type as given in the start-tag:]</p> 855 856<h5>End-tag</h5><table class="scrap" summary="Scrap"><tbody> 857<tr valign="baseline"><td><a name="NT-ETag"></a>[42]���</td><td><code>ETag</code></td><td>���::=���</td><td><code>'</' <a href="#NT-Name">Name</a> <a href="#NT-S">S</a>? 858'>'</code></td><xsltdebug></xsltdebug></tr> 859</tbody></table> 860<p>An example of an end-tag:</p> 861<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre></termdef></pre></td></tr></table> 862<p>[<a name="dt-content" title="Content">Definition</a>: The <a title="Text" href="#dt-text">text</a> 863between the start-tag and end-tag is called the element's <b>content</b>:]</p> 864 865<h5>Content of Elements</h5><table class="scrap" summary="Scrap"><tbody> 866<tr valign="baseline"><td class="diff-chg"><a name="NT-content"></a>[43]���</td><td class="diff-chg"><code>content</code></td><td class="diff-chg">���::=���</td><td class="diff-chg"><code><a href="#NT-CharData">CharData</a>? ((<a href="#NT-element">element</a> 867| <a href="#NT-Reference">Reference</a> | <a href="#NT-CDSect">CDSect</a> 868| <a href="#NT-PI">PI</a> | <a href="#NT-Comment">Comment</a>) <a href="#NT-CharData">CharData</a>?)*</code></td><xsltdebug></xsltdebug><td class="diff-chg"><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E71">[E71]</a> */</i></td></tr> 869</tbody></table> 870<p><span class="diff-chg">[<a name="dt-empty" title="Empty">Definition</a>: <a href="http://www.w3.org/XML/xml-19980210-errata#E97">[E97]</a>An element 871with no content is said to be <b>empty</b>.] The representation 872of an empty element is either a start-tag immediately followed by an end-tag, 873or an empty-element tag.</span> [<a name="dt-eetag" title="empty-element tag">Definition</a>: An <b>empty-element 874tag</b> takes a special form:]</p> 875 876<h5>Tags for Empty Elements</h5><table class="scrap" summary="Scrap"><tbody> 877<tr valign="baseline"><td><a name="NT-EmptyElemTag"></a>[44]���</td><td><code>EmptyElemTag</code></td><td>���::=���</td><td><code>'<' <a href="#NT-Name">Name</a> (<a href="#NT-S">S</a> <a href="#NT-Attribute">Attribute</a>)* <a href="#NT-S">S</a>? '/>'</code></td><xsltdebug></xsltdebug><td><a href="#uniqattspec">[WFC: Unique Att Spec]</a></td></tr> 878</tbody></table> 879<p>Empty-element tags may be used for any element which has no content, whether 880or not it is declared using the keyword <b>EMPTY</b>. <a title="For interoperability" href="#dt-interop">For 881interoperability</a>, the empty-element tag <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E45">[E45]</a>should 882be used, and should only be used,</span> for elements which are declared 883EMPTY.</p> 884<p>Examples of empty elements:</p> 885<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><IMG align="left" 886 src="http://www.w3.org/Icons/WWW/w3c_home" /> 887<br></br> 888<br/></pre></td></tr></table> 889</div> 890<div class="div2"> 891 892<h3><a name="elemdecls"></a>3.2 Element Type Declarations</h3> 893<p>The <a title="Element" href="#dt-element">element</a> structure of an <a title="XML Document" href="#dt-xml-doc">XML document</a> may, for <a title="Validity" href="#dt-valid">validation</a> 894purposes, be constrained using element type and attribute-list declarations. 895An element type declaration constrains the element's <a title="Content" href="#dt-content">content</a>.</p> 896<p>Element type declarations often constrain which element types can appear 897as <a title="Parent/Child" href="#dt-parentchild">children</a> of the element. At user 898option, an XML processor may issue a warning when a declaration mentions an 899element type for which no declaration is provided, but this is not an error.</p> 900<p>[<a name="dt-eldecl" title="Element Type declaration">Definition</a>: An <b>element 901type declaration</b> takes the form:]</p> 902 903<h5>Element Type Declaration</h5><table class="scrap" summary="Scrap"><tbody> 904<tr valign="baseline"><td><a name="NT-elementdecl"></a>[45]���</td><td><code>elementdecl</code></td><td>���::=���</td><td><code>'<!ELEMENT' <a href="#NT-S">S</a> <a href="#NT-Name">Name</a> <a href="#NT-S">S</a> <a href="#NT-contentspec">contentspec</a> <a href="#NT-S">S</a>? 905'>'</code></td><xsltdebug></xsltdebug><td><a href="#EDUnique">[VC: Unique Element Type Declaration]</a></td></tr> 906<tr valign="baseline"><td><a name="NT-contentspec"></a>[46]���</td><td><code>contentspec</code></td><td>���::=���</td><td><code>'EMPTY' | 'ANY' | <a href="#NT-Mixed">Mixed</a> 907| <a href="#NT-children">children</a> </code></td><xsltdebug></xsltdebug></tr> 908</tbody></table> 909<p>where the <a href="#NT-Name">Name</a> gives the element type being declared.</p> 910<div class="constraint"><p class="prefix"><a name="EDUnique"></a><b>Validity constraint: Unique Element Type Declaration</b></p><p>No element 911type may be declared more than once.</p> 912</div> 913<p>Examples of element type declarations:</p> 914<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ELEMENT br EMPTY> 915<!ELEMENT p (#PCDATA|emph)* > 916<!ELEMENT %name.para; %content.para; > 917<!ELEMENT container ANY></pre></td></tr></table> 918<div class="div3"> 919 920<h4><a name="sec-element-content"></a>3.2.1 Element Content</h4> 921<p>[<a name="dt-elemcontent" title="Element content">Definition</a>: An element <a title="Start-Tag" href="#dt-stag">type</a> has <b>element content</b> when elements 922of that type must contain only <a title="Parent/Child" href="#dt-parentchild">child</a> 923elements (no character data), optionally separated by white space (characters 924matching the nonterminal <a href="#NT-S">S</a>).][<a name="dt-content-model" title="Content model">Definition</a>: In this case, the constraint includes a <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E55">[E55]</a><b>content 925model</b></span>, a simple grammar governing the allowed types of the 926child elements and the order in which they are allowed to appear.] 927The grammar is built on content particles (<a href="#NT-cp">cp</a>s), which 928consist of names, choice lists of content particles, or sequence lists of 929content particles:</p> 930 931<h5>Element-content Models</h5><table class="scrap" summary="Scrap"><tbody> 932<tr valign="baseline"><td><a name="NT-children"></a>[47]���</td><td><code>children</code></td><td>���::=���</td><td><code>(<a href="#NT-choice">choice</a> | <a href="#NT-seq">seq</a>) 933('?' | '*' | '+')?</code></td><xsltdebug></xsltdebug></tr> 934<tr valign="baseline"><td><a name="NT-cp"></a>[48]���</td><td><code>cp</code></td><td>���::=���</td><td><code>(<a href="#NT-Name">Name</a> | <a href="#NT-choice">choice</a> 935| <a href="#NT-seq">seq</a>) ('?' | '*' | '+')?</code></td><xsltdebug></xsltdebug></tr> 936<tr valign="baseline"><td class="diff-chg"><a name="NT-choice"></a>[49]���</td><td class="diff-chg"><code>choice</code></td><td class="diff-chg">���::=���</td><td class="diff-chg"><code>'(' <a href="#NT-S">S</a>? <a href="#NT-cp">cp</a> ( <a href="#NT-S">S</a>? '|' <a href="#NT-S">S</a>? <a href="#NT-cp">cp</a> )+ <a href="#NT-S">S</a>? ')'</code></td><xsltdebug></xsltdebug><td class="diff-chg"><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E50">[E50]</a> */</i></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td class="diff-chg"><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E52">[E52]</a> */</i></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#vc-PEinGroup">[VC: Proper Group/PE Nesting]</a></td></tr> 937<tr valign="baseline"><td class="diff-chg"><a name="NT-seq"></a>[50]���</td><td class="diff-chg"><code>seq</code></td><td class="diff-chg">���::=���</td><td class="diff-chg"><code>'(' <a href="#NT-S">S</a>? <a href="#NT-cp">cp</a> ( <a href="#NT-S">S</a>? ',' <a href="#NT-S">S</a>? <a href="#NT-cp">cp</a> )* <a href="#NT-S">S</a>? ')'</code></td><xsltdebug></xsltdebug><td class="diff-chg"><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E52">[E52]</a> */</i></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#vc-PEinGroup">[VC: Proper Group/PE Nesting]</a></td></tr> 938</tbody></table> 939<p>where each <a href="#NT-Name">Name</a> is the type of an element which 940may appear as a <a title="Parent/Child" href="#dt-parentchild">child</a>. Any content 941particle in a choice list may appear in the <a title="Element content" href="#dt-elemcontent">element 942content</a> at the location where the choice list appears in the grammar; 943content particles occurring in a sequence list must each appear in the <a title="Element content" href="#dt-elemcontent">element content</a> in the order given in the list. 944The optional character following a name or list governs whether the element 945or the content particles in the list may occur one or more (<code>+</code>), 946zero or more (<code>*</code>), or zero or one times (<code>?</code>). The 947absence of such an operator means that the element or content particle must 948appear exactly once. This syntax and meaning are identical to those used in 949the productions in this specification.</p> 950<p>The content of an element matches a content model if and only if it is 951possible to trace out a path through the content model, obeying the sequence, 952choice, and repetition operators and matching each element in the content 953against an element type in the content model. <a title="For Compatibility" href="#dt-compat">For 954compatibility</a>, it is an error if an element in the document can 955match more than one occurrence of an element type in the content model. For 956more information, see <a href="#determinism"><b>E Deterministic Content Models</b></a>.</p> 957 958 959<div class="constraint"><p class="prefix"><a name="vc-PEinGroup"></a><b>Validity constraint: Proper Group/PE Nesting</b></p><p>Parameter-entity <a title="Replacement Text" href="#dt-repltext">replacement text</a> must be properly nested with <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E11">[E11]</a>parenthesized</span> 960groups. That is to say, if either of the opening or closing parentheses in 961a <a href="#NT-choice">choice</a>, <a href="#NT-seq">seq</a>, or <a href="#NT-Mixed">Mixed</a> 962construct is contained in the replacement text for a <a title="Parameter-entity reference" href="#dt-PERef">parameter 963entity</a>, both must be contained in the same replacement text.</p> 964<div class="diff-chg"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E19">[E19]</a><a title="For interoperability" href="#dt-interop">For interoperability</a>, if a parameter-entity reference 965appears in a <a href="#NT-choice">choice</a>, <a href="#NT-seq">seq</a>, or <a href="#NT-Mixed">Mixed</a> construct, its replacement text should contain at 966least one non-blank character, and neither the first nor last non-blank character 967of the replacement text should be a connector (<code>|</code> or <code>,</code>).</p></div> 968</div> 969<p>Examples of element-content models:</p> 970<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ELEMENT spec (front, body, back?)> 971<!ELEMENT div1 (head, (p | list | note)*, div2*)> 972<!ELEMENT dictionary-body (%div.mix; | %dict.mix;)*></pre></td></tr></table> 973</div> 974<div class="div3"> 975 976<h4><a name="sec-mixed-content"></a>3.2.2 Mixed Content</h4> 977<p>[<a name="dt-mixed" title="Mixed Content">Definition</a>: An element <a title="Start-Tag" href="#dt-stag">type</a> 978has <b>mixed content</b> when elements of that type may contain character 979data, optionally interspersed with <a title="Parent/Child" href="#dt-parentchild">child</a> 980elements.] In this case, the types of the child elements may be constrained, 981but not their order or their number of occurrences:</p> 982 983<h5>Mixed-content Declaration</h5><table class="scrap" summary="Scrap"><tbody> 984<tr valign="baseline"><td><a name="NT-Mixed"></a>[51]���</td><td><code>Mixed</code></td><td>���::=���</td><td><code>'(' <a href="#NT-S">S</a>? '#PCDATA' (<a href="#NT-S">S</a>? 985'|' <a href="#NT-S">S</a>? <a href="#NT-Name">Name</a>)* <a href="#NT-S">S</a>? 986')*' </code></td><xsltdebug></xsltdebug></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| '(' <a href="#NT-S">S</a>? '#PCDATA' <a href="#NT-S">S</a>? ')' </code></td><td><a href="#vc-PEinGroup">[VC: Proper Group/PE Nesting]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#vc-MixedChildrenUnique">[VC: No Duplicate Types]</a></td></tr> 987</tbody></table> 988<p>where the <a href="#NT-Name">Name</a>s give the types of elements that 989may appear as children. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E10">[E10]</a>The 990keyword <b>#PCDATA</b> derives historically from the term "parsed 991character data."</span></p> 992<div class="constraint"><p class="prefix"><a name="vc-MixedChildrenUnique"></a><b>Validity constraint: No Duplicate Types</b></p><p>The 993same name must not appear more than once in a single mixed-content declaration.</p> 994</div> 995<p>Examples of mixed content declarations:</p> 996<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ELEMENT p (#PCDATA|a|ul|b|i|em)*> 997<!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* > 998<!ELEMENT b (#PCDATA)></pre></td></tr></table> 999</div> 1000</div> 1001<div class="div2"> 1002 1003<h3><a name="attdecls"></a>3.3 Attribute-List Declarations</h3> 1004<p><a title="Attribute" href="#dt-attr">Attributes</a> are used to associate name-value 1005pairs with <a title="Element" href="#dt-element">elements</a>. Attribute specifications 1006may appear only within <a title="Start-Tag" href="#dt-stag">start-tags</a> and <a title="empty-element tag" href="#dt-eetag">empty-element tags</a>; thus, the productions used to 1007recognize them appear in <a href="#sec-starttags"><b>3.1 Start-Tags, End-Tags, and Empty-Element Tags</b></a>. Attribute-list declarations 1008may be used:</p> 1009<ul> 1010<li><p>To define the set of attributes pertaining to a given element type.</p> 1011</li> 1012<li><p>To establish type constraints for these attributes.</p></li> 1013<li><p>To provide <a title="Attribute Default" href="#dt-default">default values</a> for 1014attributes.</p></li> 1015</ul> 1016<p>[<a name="dt-attdecl" title="Attribute-List Declaration">Definition</a>: <b>Attribute-list 1017declarations</b> specify the name, data type, and default value (if any) 1018of each attribute associated with a given element type:]</p> 1019 1020<h5>Attribute-list Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-AttlistDecl"></a>[52]���</td><td><code>AttlistDecl</code></td><td>���::=���</td><td><code>'<!ATTLIST' <a href="#NT-S">S</a> <a href="#NT-Name">Name</a> <a href="#NT-AttDef">AttDef</a>* <a href="#NT-S">S</a>? '>'</code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-AttDef"></a>[53]���</td><td><code>AttDef</code></td><td>���::=���</td><td><code><a href="#NT-S">S</a> <a href="#NT-Name">Name</a> <a href="#NT-S">S</a> <a href="#NT-AttType">AttType</a> <a href="#NT-S">S</a> <a href="#NT-DefaultDecl">DefaultDecl</a></code></td><xsltdebug></xsltdebug></tr></tbody></table> 1021<p>The <a href="#NT-Name">Name</a> in the <a href="#NT-AttlistDecl">AttlistDecl</a> 1022rule is the type of an element. At user option, an XML processor may issue 1023a warning if attributes are declared for an element type not itself declared, 1024but this is not an error. The <a href="#NT-Name">Name</a> in the <a href="#NT-AttDef">AttDef</a> 1025rule is the name of the attribute.</p> 1026<p>When more than one <a href="#NT-AttlistDecl">AttlistDecl</a> is provided 1027for a given element type, the contents of all those provided are merged. When 1028more than one definition is provided for the same attribute of a given element 1029type, the first declaration is binding and later declarations are ignored. <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E9">[E9]</a><a title="For interoperability" href="#dt-interop">For interoperability,</a> writers of DTDs may choose 1030to provide at most one attribute-list declaration for a given element type, 1031at most one attribute definition for a given attribute name in an attribute-list 1032declaration, and at least one attribute definition in each attribute-list 1033declaration.</span> For interoperability, an XML processor may at user option 1034issue a warning when more than one attribute-list declaration is provided 1035for a given element type, or more than one attribute definition is provided 1036for a given attribute, but this is not an error.</p> 1037<div class="div3"> 1038 1039<h4><a name="sec-attribute-types"></a>3.3.1 Attribute Types</h4> 1040<p>XML attribute types are of three kinds: a string type, a set of tokenized 1041types, and enumerated types. The string type may take any literal string as 1042a value; the tokenized types have varying lexical and semantic constraints<span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E8">[E8]</a>. 1043The validity constraints noted in the grammar are applied after the attribute 1044value has been normalized as described in <a href="#attdecls"><b>3.3 Attribute-List Declarations</b></a>.</span></p> 1045 1046<h5>Attribute Types</h5><table class="scrap" summary="Scrap"><tbody> 1047<tr valign="baseline"><td><a name="NT-AttType"></a>[54]���</td><td><code>AttType</code></td><td>���::=���</td><td><code><a href="#NT-StringType">StringType</a> | <a href="#NT-TokenizedType">TokenizedType</a> 1048| <a href="#NT-EnumeratedType">EnumeratedType</a> </code></td><xsltdebug></xsltdebug></tr> 1049<tr valign="baseline"><td><a name="NT-StringType"></a>[55]���</td><td><code>StringType</code></td><td>���::=���</td><td><code>'CDATA'</code></td><xsltdebug></xsltdebug></tr> 1050<tr valign="baseline"><td><a name="NT-TokenizedType"></a>[56]���</td><td><code>TokenizedType</code></td><td>���::=���</td><td><code>'ID'</code></td><xsltdebug></xsltdebug><td><a href="#id">[VC: ID]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#one-id-per-el">[VC: One ID per Element Type]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#id-default">[VC: ID Attribute Default]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| 'IDREF'</code></td><td><a href="#idref">[VC: IDREF]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| 'IDREFS'</code></td><td><a href="#idref">[VC: IDREF]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| 'ENTITY'</code></td><td><a href="#entname">[VC: Entity Name]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| 'ENTITIES'</code></td><td><a href="#entname">[VC: Entity Name]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| 'NMTOKEN'</code></td><td><a href="#nmtok">[VC: Name Token]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| 'NMTOKENS'</code></td><td><a href="#nmtok">[VC: Name Token]</a></td></tr> 1051</tbody></table> 1052<div class="constraint"><p class="prefix"><a name="id"></a><b>Validity constraint: ID</b></p><p>Values of type <b>ID</b> must match the <a href="#NT-Name">Name</a> production. A name must not appear more than once 1053in an XML document as a value of this type; i.e., ID values must uniquely 1054identify the elements which bear them.</p> 1055</div> 1056<div class="constraint"><p class="prefix"><a name="one-id-per-el"></a><b>Validity constraint: One ID per Element Type</b></p><p>No element 1057type may have more than one ID attribute specified.</p> 1058</div> 1059<div class="constraint"><p class="prefix"><a name="id-default"></a><b>Validity constraint: ID Attribute Default</b></p><p>An ID attribute 1060must have a declared default of <b>#IMPLIED</b> or <b>#REQUIRED</b>.</p> 1061</div> 1062<div class="constraint"><p class="prefix"><a name="idref"></a><b>Validity constraint: IDREF</b></p><p>Values of type <b>IDREF</b> must 1063match the <a href="#NT-Name">Name</a> production, and values of type <b>IDREFS</b> 1064must match <a href="#NT-Names">Names</a>; each <a href="#NT-Name">Name</a> 1065must match the value of an ID attribute on some element in the XML document; 1066i.e. <b>IDREF</b> values must match the value of some ID attribute.</p> 1067</div> 1068<div class="constraint"><p class="prefix"><a name="entname"></a><b>Validity constraint: Entity Name</b></p><p>Values of type <b>ENTITY</b> 1069must match the <a href="#NT-Name">Name</a> production, values of type <b>ENTITIES</b> 1070must match <a href="#NT-Names">Names</a>; each <a href="#NT-Name">Name</a> 1071must match the name of an <a title="Unparsed Entity" href="#dt-unparsed">unparsed entity</a> 1072declared in the <a title="Document Type Declaration" href="#dt-doctype">DTD</a>.</p> 1073</div> 1074<div class="constraint"><p class="prefix"><a name="nmtok"></a><b>Validity constraint: Name Token</b></p><p>Values of type <b>NMTOKEN</b> 1075must match the <a href="#NT-Nmtoken">Nmtoken</a> production; values of type <b>NMTOKENS</b> 1076must match <a title="" href="#NT-Nmtokens">Nmtokens</a>.</p> 1077</div> 1078 1079<p>[<a name="dt-enumerated" title="Enumerated Attribute Values">Definition</a>: <b>Enumerated attributes</b> can take one of a list of values 1080provided in the declaration]. There are two kinds of enumerated types:</p> 1081 1082<h5>Enumerated Attribute Types</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-EnumeratedType"></a>[57]���</td><td><code>EnumeratedType</code></td><td>���::=���</td><td><code><a href="#NT-NotationType">NotationType</a> 1083| <a href="#NT-Enumeration">Enumeration</a> </code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-NotationType"></a>[58]���</td><td><code>NotationType</code></td><td>���::=���</td><td><code>'NOTATION' <a href="#NT-S">S</a> '(' <a href="#NT-S">S</a>? <a href="#NT-Name">Name</a> (<a href="#NT-S">S</a>? '|' <a href="#NT-S">S</a>? <a href="#NT-Name">Name</a>)* <a href="#NT-S">S</a>? ')' </code></td><xsltdebug></xsltdebug><td><a href="#notatn">[VC: Notation Attributes]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td class="diff-add"><a href="#OneNotationPer">[VC: One 1084Notation Per Element Type]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td class="diff-add"><a href="#NoNotationEmpty">[VC: No 1085Notation on Empty Element]</a></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Enumeration"></a>[59]���</td><td><code>Enumeration</code></td><td>���::=���</td><td><code>'(' <a href="#NT-S">S</a>? <a href="#NT-Nmtoken">Nmtoken</a> 1086(<a href="#NT-S">S</a>? '|' <a href="#NT-S">S</a>? <a href="#NT-Nmtoken">Nmtoken</a>)* <a href="#NT-S">S</a>? ')'</code></td><xsltdebug></xsltdebug><td><a href="#enum">[VC: Enumeration]</a></td></tr></tbody></table> 1087<p>A <b>NOTATION</b> attribute identifies a <a title="Notation" href="#dt-notation">notation</a>, 1088declared in the DTD with associated system and/or public identifiers, to be 1089used in interpreting the element to which the attribute is attached.</p> 1090<div class="constraint"><p class="prefix"><a name="notatn"></a><b>Validity constraint: Notation Attributes</b></p><p>Values of this type 1091must match one of the <a href="#Notations"><cite>notation</cite></a> names 1092included in the declaration; all notation names in the declaration must be 1093declared.</p> 1094</div> 1095<div class="diff-add"><div class="constraint"><p class="prefix"><a name="OneNotationPer"></a><b>Validity constraint: <a href="http://www.w3.org/XML/xml-19980210-errata#E7">[E7]</a>One 1096Notation Per Element Type</b></p><p>No element type may have more than one <b>NOTATION</b> 1097attribute specified.</p> 1098</div></div> 1099<div class="diff-add"><div class="constraint"><p class="prefix"><a name="NoNotationEmpty"></a><b>Validity constraint: <a href="http://www.w3.org/XML/xml-19980210-errata#E68">[E68]</a>No 1100Notation on Empty Element</b></p><p><a title="For Compatibility" href="#dt-compat">For compatibility</a>, 1101an attribute of type <b>NOTATION</b> must not be declared on an element 1102declared <b>EMPTY</b>.</p> 1103</div></div> 1104<div class="constraint"><p class="prefix"><a name="enum"></a><b>Validity constraint: Enumeration</b></p><p>Values of this type must match 1105one of the <a href="#NT-Nmtoken">Nmtoken</a> tokens in the declaration.</p> 1106</div> 1107<p><a title="For interoperability" href="#dt-interop">For interoperability,</a> the same <a href="#NT-Nmtoken">Nmtoken</a> should not occur more than once in the enumerated 1108attribute types of a single element type.</p> 1109</div> 1110<div class="div3"> 1111 1112<h4><a name="sec-attr-defaults"></a>3.3.2 Attribute Defaults</h4> 1113<p>An <a title="Attribute-List Declaration" href="#dt-attdecl">attribute declaration</a> provides information 1114on whether the attribute's presence is required, and if not, how an XML processor 1115should react if a declared attribute is absent in a document.</p> 1116 1117<h5>Attribute Defaults</h5><table class="scrap" summary="Scrap"><tbody> 1118<tr valign="baseline"><td><a name="NT-DefaultDecl"></a>[60]���</td><td><code>DefaultDecl</code></td><td>���::=���</td><td><code>'#REQUIRED' |�'#IMPLIED' </code></td><xsltdebug></xsltdebug></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| (('#FIXED' S)? <a href="#NT-AttValue">AttValue</a>)</code></td><td><a href="#RequiredAttr">[VC: Required Attribute]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#defattrvalid">[VC: Attribute Default Legal]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#CleanAttrVals">[WFC: No < in Attribute Values]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#FixedAttr">[VC: Fixed Attribute Default]</a></td></tr> 1119</tbody></table> 1120<p>In an attribute declaration, <b>#REQUIRED</b> means that the attribute 1121must always be provided, <b>#IMPLIED</b> that no default value is provided. [<a name="dt-default" title="Attribute Default">Definition</a>: If 1122the declaration is neither <b>#REQUIRED</b> nor <b>#IMPLIED</b>, then 1123the <a href="#NT-AttValue">AttValue</a> value contains the declared <b>default</b> 1124value; the <b>#FIXED</b> keyword states that the attribute must always have 1125the default value. If a default value is declared, when an XML processor encounters 1126an omitted attribute, it is to behave as though the attribute were present 1127with the declared default value.]</p> 1128<div class="constraint"><p class="prefix"><a name="RequiredAttr"></a><b>Validity constraint: Required Attribute</b></p><p>If the default 1129declaration is the keyword <b>#REQUIRED</b>, then the attribute must be 1130specified for all elements of the type in the attribute-list declaration.</p> 1131</div> 1132<div class="constraint"><p class="prefix"><a name="defattrvalid"></a><b>Validity constraint: Attribute Default Legal</b></p><p>The declared 1133default value must meet the lexical constraints of the declared attribute 1134type.</p> 1135</div> 1136<div class="constraint"><p class="prefix"><a name="FixedAttr"></a><b>Validity constraint: Fixed Attribute Default</b></p><p>If an attribute 1137has a default value declared with the <b>#FIXED</b> keyword, instances of 1138that attribute must match the default value.</p> 1139</div> 1140<p>Examples of attribute-list declarations:</p> 1141<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ATTLIST termdef 1142 id ID #REQUIRED 1143 name CDATA #IMPLIED> 1144<!ATTLIST list 1145 type (bullets|ordered|glossary) "ordered"> 1146<!ATTLIST form 1147 method CDATA #FIXED "POST"></pre></td></tr></table> 1148</div> 1149<div class="diff-chg"><div class="div3"> 1150 1151<h4><a name="AVNormalize"></a>3.3.3 <a href="http://www.w3.org/XML/xml-19980210-errata#E70">[E70]</a>Attribute-Value 1152Normalization</h4> 1153<p>Before the value of an attribute is passed to the application or checked 1154for validity, the XML processor must normalize the attribute value by applying 1155the algorithm below, or by using some other method such that the value passed 1156to the application is the same as that produced by the algorithm.</p> 1157<ol> 1158<li><p>All line breaks must have been normalized on input to #xA as described 1159in <a href="#sec-line-ends"><b>2.11 End-of-Line Handling</b></a>, so the rest of this algorithm operates 1160on text normalized in this way.</p></li> 1161<li><p>Begin with a normalized value consisting of the empty string.</p> 1162</li> 1163<li><p>For each character, entity reference, or character reference in the 1164unnormalized attribute value, beginning with the first and continuing to the 1165last, do the following:</p> 1166<ul> 1167<li><p>For a character reference, append the referenced character to the 1168normalized value.</p></li> 1169<li><p>For an entity reference, recursively apply step 3 of this algorithm 1170to the replacement text of the entity.</p></li> 1171<li><p>For a white space character (#x20, #xD, #xA, #x9), append a space 1172character (#x20) to the normalized value.</p></li> 1173<li><p>For another character, append the character to the normalized value.</p> 1174</li> 1175</ul> 1176</li> 1177</ol> 1178<p>If the attribute type is not CDATA, then the XML processor must further 1179process the normalized attribute value by discarding any leading and trailing 1180space (#x20) characters, and by replacing sequences of space (#x20) characters 1181by a single space (#x20) character.</p> 1182<p>Note that if the unnormalized attribute value contains a character reference 1183to a white space character other than space (#x20), the normalized value contains 1184the referenced character itself (#xD, #xA or #x9). This contrasts with the 1185case where the unnormalized value contains a white space character (not a 1186reference), which is replaced with a space character (#x20) in the normalized 1187value and also contrasts with the case where the unnormalized value contains 1188an entity reference whose replacement text contains a white space character; 1189being recursively processed, the white space character is replaced with a 1190space character (#x20) in the normalized value.</p> 1191<p>All attributes for which no declaration has been read should be treated 1192by a non-validating <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E95">[E95]</a>processor</span> 1193as if declared <b>CDATA</b>.</p> 1194<p>Following are examples of attribute normalization. Given the following 1195declarations:</p> 1196<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY d "&#xD;"> 1197<!ENTITY a "&#xA;"> 1198<!ENTITY da "&#xD;&#xA;"></pre></td></tr></table> 1199<p>the attribute specifications in the left column below would be normalized 1200to the character sequences of the middle column if the attribute <code>a</code> 1201is declared <b>NMTOKENS</b> and to those of the right columns if <code>a</code> 1202is declared <b>CDATA</b>.</p> 1203<table border="1" frame="border"><thead><tr><th rowspan="1" colspan="1">Attribute specification</th> 1204<th rowspan="1" colspan="1">a is NMTOKENS</th><th rowspan="1" colspan="1">a is CDATA</th></tr></thead><tbody><tr><td rowspan="1" colspan="1"><table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>a=" 1205 1206xyz"</pre></td></tr></table></td><td rowspan="1" colspan="1"><code>x y z</code></td><td rowspan="1" colspan="1"><code>#x20 #x20 x y z</code></td> 1207</tr><tr><td rowspan="1" colspan="1"><table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>a="&d;&d;A&a;&a;B&da;"</pre></td></tr></table></td><td rowspan="1" colspan="1"><code>A 1208#x20 B</code></td><td rowspan="1" colspan="1"><code>#x20 #x20 A #x20 #x20 B #x20 #x20</code></td> 1209</tr><tr><td rowspan="1" colspan="1"><table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>a= 1210"&#xd;&#xd;A&#xa;&#xa;B&#xd;&#xa;"</pre></td></tr></table></td><td rowspan="1" colspan="1"><code>#xD 1211#xD A #xA #xA B #xD #xA</code></td><td rowspan="1" colspan="1"><code>#xD #xD A #xA #xA B #xD #xD</code></td> 1212</tr></tbody></table> 1213<p>Note that the last example is invalid (but well-formed) if <code>a</code> 1214is declared to be of type <b>NMTOKENS</b>.</p> 1215</div></div> 1216</div> 1217<div class="div2"> 1218 1219<h3><a name="sec-condition-sect"></a>3.4 Conditional Sections</h3> 1220<p>[<a name="dt-cond-section" title="conditional section">Definition</a>: <b>Conditional 1221sections</b> are portions of the <a title="Document Type Declaration" href="#dt-doctype">document type 1222declaration external subset</a> which are included in, or excluded from, 1223the logical structure of the DTD based on the keyword which governs them.]</p> 1224 1225<h5>Conditional Section</h5><table class="scrap" summary="Scrap"><tbody> 1226<tr valign="baseline"><td><a name="NT-conditionalSect"></a>[61]���</td><td><code>conditionalSect</code></td><td>���::=���</td><td><code><a href="#NT-includeSect">includeSect</a> | <a href="#NT-ignoreSect">ignoreSect</a> </code></td><xsltdebug></xsltdebug></tr> 1227<tr valign="baseline"><td><a name="NT-includeSect"></a>[62]���</td><td><code>includeSect</code></td><td>���::=���</td><td><code>'<![' S? 'INCLUDE' S? '[' <a href="#NT-extSubsetDecl">extSubsetDecl</a> 1228']]>' </code></td><xsltdebug></xsltdebug><td><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</a> */</i></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td class="diff-add"><a href="#condsec-nesting">[VC: Proper 1229Conditional Section/PE Nesting]</a></td></tr> 1230<tr valign="baseline"><td><a name="NT-ignoreSect"></a>[63]���</td><td><code>ignoreSect</code></td><td>���::=���</td><td><code>'<![' S? 'IGNORE' S? '[' <a href="#NT-ignoreSectContents">ignoreSectContents</a>* 1231']]>'</code></td><xsltdebug></xsltdebug><td><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</a> */</i></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td class="diff-add"><a href="#condsec-nesting">[VC: Proper 1232Conditional Section/PE Nesting]</a></td></tr> 1233<tr valign="baseline"><td><a name="NT-ignoreSectContents"></a>[64]���</td><td><code>ignoreSectContents</code></td><td>���::=���</td><td><code><a href="#NT-Ignore">Ignore</a> ('<![' <a href="#NT-ignoreSectContents">ignoreSectContents</a> ']]>' <a href="#NT-Ignore">Ignore</a>)*</code></td><xsltdebug></xsltdebug></tr> 1234<tr valign="baseline"><td><a name="NT-Ignore"></a>[65]���</td><td><code>Ignore</code></td><td>���::=���</td><td><code><a href="#NT-Char">Char</a>* - (<a href="#NT-Char">Char</a>* 1235('<![' | ']]>') <a href="#NT-Char">Char</a>*) </code></td><xsltdebug></xsltdebug></tr> 1236</tbody></table> 1237<div class="diff-add"><div class="constraint"><p class="prefix"><a name="condsec-nesting"></a><b>Validity constraint: <a href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</a>Proper 1238Conditional Section/PE Nesting</b></p><p>If any of the "<code><![</code>", 1239"<code>[</code>", or "<code>]]></code>" of a conditional section is contained 1240in the replacement text for a parameter-entity reference, all of them must 1241be contained in the same replacement text.</p> 1242</div></div> 1243<p>Like the internal and external DTD subsets, a conditional section may contain 1244one or more complete declarations, comments, processing instructions, or nested 1245conditional sections, intermingled with white space.</p> 1246<p>If the keyword of the conditional section is <b>INCLUDE</b>, then the 1247contents of the conditional section are part of the DTD. If the keyword of 1248the conditional section is <b>IGNORE</b>, then the contents of the conditional 1249section are not logically part of the DTD. <span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</a>Note that 1250for reliable parsing, the contents of even ignored conditional sections must 1251be read in order to detect nested conditional sections and ensure that the 1252end of the outermost (ignored) conditional section is properly detected.</span> 1253If a conditional section with a keyword of <b>INCLUDE</b> occurs within 1254a larger conditional section with a keyword of <b>IGNORE</b>, both the outer 1255and the inner conditional sections are ignored.<span class="diff-add"> <a href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</a>The contents 1256of an ignored conditional section are parsed by ignoring all characters after 1257the "<code>[</code>" following the keyword, except conditional section starts 1258"<code><![</code>" and ends "<code>]]></code>", until the matching conditional 1259section end is found. Parameter entity references are not recognized in this 1260process.</span></p> 1261<p>If the keyword of the conditional section is a parameter-entity reference, 1262the parameter entity must be replaced by its content before the processor 1263decides whether to include or ignore the conditional section.</p> 1264<p>An example:</p> 1265<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY % draft 'INCLUDE' > 1266<!ENTITY % final 'IGNORE' > 1267 1268<![%draft;[ 1269<!ELEMENT book (comments*, title, body, supplements?)> 1270]]> 1271<![%final;[ 1272<!ELEMENT book (title, body, supplements?)> 1273]]></pre></td></tr></table> 1274</div> 1275 1276</div> 1277 1278<div class="div1"> 1279 1280<h2><a name="sec-physical-struct"></a>4 Physical Structures</h2> 1281<p>[<a name="dt-entity" title="Entity">Definition</a>: An XML document may consist of one 1282or many storage units. <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E6">[E6]</a>These 1283are called <b>entities</b>; they all have <b>content</b> and are 1284all (except for the <a title="Document Entity" href="#dt-docent">document entity</a> and 1285the <a title="Document Type Declaration" href="#dt-doctype">external DTD subset</a>) identified by 1286entity <b>name</b></span>.] Each XML document has one entity 1287called the <a title="Document Entity" href="#dt-docent">document entity</a>, which serves 1288as the starting point for the <a title="XML Processor" href="#dt-xml-proc">XML processor</a> 1289and may contain the whole document.</p> 1290<p>Entities may be either parsed or unparsed. [<a name="dt-parsedent" title="Text Entity">Definition</a>: A <b>parsed 1291entity's</b> contents are referred to as its <a title="Replacement Text" href="#dt-repltext">replacement 1292text</a>; this <a title="Text" href="#dt-text">text</a> is considered an 1293integral part of the document.]</p> 1294<p>[<a name="dt-unparsed" title="Unparsed Entity">Definition</a>: An <b>unparsed entity</b> 1295is a resource whose contents may or may not be <a title="Text" href="#dt-text">text</a>, 1296and if text, <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E25">[E25]</a>may 1297be other than</span> XML. Each unparsed entity has an associated <a title="Notation" href="#dt-notation">notation</a>, identified by name. Beyond a requirement 1298that an XML processor make the identifiers for the entity and notation available 1299to the application, XML places no constraints on the contents of unparsed 1300entities.]</p> 1301<p>Parsed entities are invoked by name using entity references; unparsed entities 1302by name, given in the value of <b>ENTITY</b> or <b>ENTITIES</b> attributes.</p> 1303<p>[<a name="gen-entity" title="general entity">Definition</a>: <b>General entities</b> 1304are entities for use within the document content. In this specification, general 1305entities are sometimes referred to with the unqualified term <em>entity</em> 1306when this leads to no ambiguity.] [<a name="dt-PE" title="Parameter entity">Definition</a>: <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E53">[E53]</a><b>Parameter 1307entities</b></span> are parsed entities for use within the DTD.] 1308These two types of entities use different forms of reference and are recognized 1309in different contexts. Furthermore, they occupy different namespaces; a parameter 1310entity and a general entity with the same name are two distinct entities.</p> 1311<div class="div2"> 1312 1313<h3><a name="sec-references"></a>4.1 Character and Entity References</h3> 1314<p>[<a name="dt-charref" title="Character Reference">Definition</a>: A <b>character 1315reference</b> refers to a specific character in the ISO/IEC 10646 character 1316set, for example one not directly accessible from available input devices.]</p> 1317 1318<h5>Character Reference</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-CharRef"></a>[66]���</td><td><code>CharRef</code></td><td>���::=���</td><td><code>'&#' [0-9]+ ';' </code></td><xsltdebug></xsltdebug></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| '&#x' [0-9a-fA-F]+ ';'</code></td><td><a href="#wf-Legalchar">[WFC: Legal Character]</a></td></tr></tbody></table> 1319<div class="constraint"><p class="prefix"><a name="wf-Legalchar"></a><b>Well-formedness constraint: Legal Character</b></p><p>Characters referred 1320to using character references must match the production for <a title="" href="#NT-Char">Char</a>.</p> 1321</div> 1322<p>If the character reference begins with "<code>&#x</code>", 1323the digits and letters up to the terminating <code>;</code> provide a hexadecimal 1324representation of the character's code point in ISO/IEC 10646. If it begins 1325just with "<code>&#</code>", the digits up to the terminating <code>;</code> 1326provide a decimal representation of the character's code point.</p> 1327<p>[<a name="dt-entref" title="Entity Reference">Definition</a>: An <b>entity reference</b> 1328refers to the content of a named entity.] [<a name="dt-GERef" title="General Entity Reference">Definition</a>: References to parsed general entities use 1329ampersand (<code>&</code>) and semicolon (<code>;</code>) as delimiters.] [<a name="dt-PERef" title="Parameter-entity reference">Definition</a>: <b>Parameter-entity references</b> 1330use percent-sign (<code>%</code>) and semicolon (<code>;</code>) as delimiters.]</p> 1331 1332<h5>Entity Reference</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-Reference"></a>[67]���</td><td><code>Reference</code></td><td>���::=���</td><td><code><a href="#NT-EntityRef">EntityRef</a> | <a href="#NT-CharRef">CharRef</a></code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-EntityRef"></a>[68]���</td><td><code>EntityRef</code></td><td>���::=���</td><td><code>'&' <a href="#NT-Name">Name</a> ';'</code></td><xsltdebug></xsltdebug><td><a href="#wf-entdeclared">[WFC: Entity Declared]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#vc-entdeclared">[VC: Entity Declared]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#textent">[WFC: Parsed Entity]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#norecursion">[WFC: No Recursion]</a></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PEReference"></a>[69]���</td><td><code>PEReference</code></td><td>���::=���</td><td><code>'%' <a href="#NT-Name">Name</a> ';'</code></td><xsltdebug></xsltdebug><td><a href="#vc-entdeclared">[VC: Entity Declared]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#norecursion">[WFC: No Recursion]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#indtd">[WFC: In DTD]</a></td></tr></tbody></table> 1333<div class="constraint"><p class="prefix"><a name="wf-entdeclared"></a><b>Well-formedness constraint: Entity Declared</b></p><p>In a document 1334without any DTD, a document with only an internal DTD subset which contains 1335no parameter entity references, or a document with "<code>standalone='yes'</code>", <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E34">[E34]</a>for 1336an entity reference that does not occur within the external subset or a parameter 1337entity, the <a href="#NT-Name">Name</a> given in the entity reference must <a title="match" href="#dt-match">match</a> that in an <a href="#sec-entity-decl"><cite>entity 1338declaration</cite></a> that does not occur within the external subset or a 1339parameter entity</span>, except that well-formed documents need not declare 1340any of the following entities: <code>amp</code>, 1341<code>lt</code>, 1342<code>gt</code>, 1343<code>apos</code>, 1344<code>quot</code>. <span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E29">[E29]</a>The declaration 1345of a parameter entity must precede any reference to it. Similarly, </span>The 1346declaration of a general entity must precede any reference to it which appears 1347in a default value in an attribute-list declaration.</p> 1348<p>Note that if entities are declared in the external subset or in external 1349parameter entities, a non-validating processor is <a href="#include-if-valid"><cite>not 1350obligated to</cite></a> read and process their declarations; for such documents, 1351the rule that an entity must be declared is a well-formedness constraint only 1352if <a href="#sec-rmd"><cite>standalone='yes'</cite></a>.</p> 1353</div> 1354<div class="constraint"><p class="prefix"><a name="vc-entdeclared"></a><b>Validity constraint: Entity Declared</b></p><p>In a document with 1355an external subset or external parameter entities with "<code>standalone='no'</code>", 1356the <a href="#NT-Name">Name</a> given in the entity reference must <a title="match" href="#dt-match">match</a> that in an <a href="#sec-entity-decl"><cite>entity 1357declaration</cite></a>. For interoperability, valid documents should declare 1358the entities <code>amp</code>, 1359<code>lt</code>, 1360<code>gt</code>, 1361<code>apos</code>, 1362<code>quot</code>, in the form specified in <a href="#sec-predefined-ent"><b>4.6 Predefined Entities</b></a>. 1363The declaration of a parameter entity must precede any reference to it. Similarly, 1364the declaration of a general entity must precede any <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E92">[E92]</a>attribute-list 1365declaration containing a default value with a direct or indirect reference 1366to that general entity.</span></p> 1367</div> 1368 1369<div class="constraint"><p class="prefix"><a name="textent"></a><b>Well-formedness constraint: Parsed Entity</b></p><p>An entity reference must 1370not contain the name of an <a title="Unparsed Entity" href="#dt-unparsed">unparsed entity</a>. 1371Unparsed entities may be referred to only in <a title="Attribute Value" href="#dt-attrval">attribute 1372values</a> declared to be of type <b>ENTITY</b> or <b>ENTITIES</b>.</p> 1373</div> 1374<div class="constraint"><p class="prefix"><a name="norecursion"></a><b>Well-formedness constraint: No Recursion</b></p><p>A parsed entity must 1375not contain a recursive reference to itself, either directly or indirectly.</p> 1376</div> 1377<div class="constraint"><p class="prefix"><a name="indtd"></a><b>Well-formedness constraint: In DTD</b></p><p>Parameter-entity references may 1378only appear in the <a title="Document Type Declaration" href="#dt-doctype">DTD</a>.</p> 1379</div> 1380<p>Examples of character and entity references:</p> 1381<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>Type <key>less-than</key> (&#x3C;) to save options. 1382This document was prepared on &docdate; and 1383is classified &security-level;.</pre></td></tr></table> 1384<p>Example of a parameter-entity reference:</p> 1385<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!-- declare the parameter entity "ISOLat2"... --> 1386<!ENTITY % ISOLat2 1387 SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" > 1388<!-- ... now reference it. --> 1389%ISOLat2;</pre></td></tr></table> 1390</div> 1391<div class="div2"> 1392 1393<h3><a name="sec-entity-decl"></a>4.2 Entity Declarations</h3> 1394<p>[<a name="dt-entdecl" title="entity declaration">Definition</a>: Entities are declared 1395thus:]</p> 1396 1397<h5>Entity Declaration</h5><table class="scrap" summary="Scrap"><tbody> 1398<tr valign="baseline"><td><a name="NT-EntityDecl"></a>[70]���</td><td><code>EntityDecl</code></td><td>���::=���</td><td><code><a href="#NT-GEDecl">GEDecl</a> | <a href="#NT-PEDecl">PEDecl</a></code></td><xsltdebug></xsltdebug></tr> 1399<tr valign="baseline"><td><a name="NT-GEDecl"></a>[71]���</td><td><code>GEDecl</code></td><td>���::=���</td><td><code>'<!ENTITY' <a href="#NT-S">S</a> <a href="#NT-Name">Name</a> <a href="#NT-S">S</a> <a href="#NT-EntityDef">EntityDef</a> <a href="#NT-S">S</a>? 1400'>'</code></td><xsltdebug></xsltdebug></tr> 1401<tr valign="baseline"><td><a name="NT-PEDecl"></a>[72]���</td><td><code>PEDecl</code></td><td>���::=���</td><td><code>'<!ENTITY' <a href="#NT-S">S</a> '%' <a href="#NT-S">S</a> <a href="#NT-Name">Name</a> <a href="#NT-S">S</a> <a href="#NT-PEDef">PEDef</a> <a href="#NT-S">S</a>? '>'</code></td><xsltdebug></xsltdebug></tr> 1402<tr valign="baseline"><td><a name="NT-EntityDef"></a>[73]���</td><td><code>EntityDef</code></td><td>���::=���</td><td><code><a href="#NT-EntityValue">EntityValue</a> | (<a href="#NT-ExternalID">ExternalID</a> <a href="#NT-NDataDecl">NDataDecl</a>?)</code></td><xsltdebug></xsltdebug></tr> 1403 1404<tr valign="baseline"><td><a name="NT-PEDef"></a>[74]���</td><td><code>PEDef</code></td><td>���::=���</td><td><code><a href="#NT-EntityValue">EntityValue</a> | <a href="#NT-ExternalID">ExternalID</a></code></td><xsltdebug></xsltdebug></tr> 1405</tbody></table> 1406<p>The <a href="#NT-Name">Name</a> identifies the entity in an <a title="Entity Reference" href="#dt-entref">entity 1407reference</a> or, in the case of an unparsed entity, in the value of 1408an <b>ENTITY</b> or <b>ENTITIES</b> attribute. If the same entity is declared 1409more than once, the first declaration encountered is binding; at user option, 1410an XML processor may issue a warning if entities are declared multiple times.</p> 1411<div class="div3"> 1412 1413<h4><a name="sec-internal-ent"></a>4.2.1 Internal Entities</h4> 1414<p>[<a name="dt-internent" title="Internal Entity Replacement Text">Definition</a>: If the 1415entity definition is an <a href="#NT-EntityValue">EntityValue</a>, the defined 1416entity is called an <b>internal entity</b>. There is no separate physical 1417storage object, and the content of the entity is given in the declaration.] 1418Note that some processing of entity and character references in the <a title="Literal Entity Value" href="#dt-litentval">literal entity value</a> may be required to produce 1419the correct <a title="Replacement Text" href="#dt-repltext">replacement text</a>: see <a href="#intern-replacement"><b>4.5 Construction of Internal Entity Replacement Text</b></a>.</p> 1420<p>An internal entity is a <a title="Text Entity" href="#dt-parsedent">parsed entity</a>.</p> 1421<p>Example of an internal entity declaration:</p> 1422<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY Pub-Status "This is a pre-release of the 1423 specification."></pre></td></tr></table> 1424</div> 1425<div class="div3"> 1426 1427<h4><a name="sec-external-ent"></a>4.2.2 External Entities</h4> 1428<p>[<a name="dt-extent" title="External Entity">Definition</a>: If the entity is not internal, 1429it is an <b>external entity</b>, declared as follows:]</p> 1430 1431<h5>External Entity Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-ExternalID"></a>[75]���</td><td><code>ExternalID</code></td><td>���::=���</td><td><code>'SYSTEM' <a href="#NT-S">S</a> <a href="#NT-SystemLiteral">SystemLiteral</a></code></td><xsltdebug></xsltdebug></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| 'PUBLIC' <a href="#NT-S">S</a> <a href="#NT-PubidLiteral">PubidLiteral</a> <a href="#NT-S">S</a> <a href="#NT-SystemLiteral">SystemLiteral</a> </code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-NDataDecl"></a>[76]���</td><td><code>NDataDecl</code></td><td>���::=���</td><td><code><a href="#NT-S">S</a> 'NDATA' <a href="#NT-S">S</a> <a href="#NT-Name">Name</a></code></td><xsltdebug></xsltdebug><td><a href="#not-declared">[VC: Notation Declared]</a></td></tr></tbody></table> 1432<p>If the <a href="#NT-NDataDecl">NDataDecl</a> is present, this is a general <a title="Unparsed Entity" href="#dt-unparsed">unparsed entity</a>; otherwise it is a parsed entity.</p> 1433<div class="constraint"><p class="prefix"><a name="not-declared"></a><b>Validity constraint: Notation Declared</b></p><p>The <a href="#NT-Name">Name</a> 1434must match the declared name of a <a title="Notation" href="#dt-notation">notation</a>.</p> 1435</div> 1436<p><span class="diff-chg">[<a name="dt-sysid" title="System Identifier">Definition</a>: The <a href="#NT-SystemLiteral">SystemLiteral</a> is called the entity's <b>system 1437identifier</b>. It is a <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E88">[E88]</a>URI 1438reference</span><span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E66">[E66]</a> 1439(as defined in <a href="#rfc2396">[IETF RFC 2396]</a>, updated by <a href="#rfc2732">[IETF RFC 2732]</a>)</span>, <a href="http://www.w3.org/XML/xml-19980210-errata#E76">[E76]</a>meant 1440to be dereferenced to obtain input for the XML processor to construct the 1441entity's replacement text.] It is an error for a fragment identifier 1442(beginning with a <code>#</code> character) to be part of a system identifier.</span> 1443Unless otherwise provided by information outside the scope of this specification 1444(e.g. a special XML element type defined by a particular DTD, or a processing 1445instruction defined by a particular application specification), relative URIs 1446are relative to the location of the resource within which the entity declaration 1447occurs. A URI might thus be relative to the <a title="Document Entity" href="#dt-docent">document 1448entity</a>, to the entity containing the <a title="Document Type Declaration" href="#dt-doctype">external 1449DTD subset</a>, or to some other <a title="External Entity" href="#dt-extent">external parameter 1450entity</a>.</p> 1451<div class="diff-chg"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E78">[E78]</a>URI 1452references require encoding and escaping of certain characters. The disallowed 1453characters include all non-ASCII characters, plus the excluded characters 1454listed in Section 2.4 of <a href="#rfc2396">[IETF RFC 2396]</a>, except for the number sign 1455(<code>#</code>) and percent sign (<code>%</code>) characters and the square 1456bracket characters re-allowed in <a href="#rfc2732">[IETF RFC 2732]</a>. Disallowed characters 1457must be escaped as follows:</p></div> 1458<div class="diff-add"><ol> 1459<li><p>Each disallowed character is converted to UTF-8 <a href="#rfc2279">[IETF RFC 2279]</a> 1460as one or more bytes.</p></li> 1461<li><p>Any octets corresponding to a disallowed character are escaped with 1462the URI escaping mechanism (that is, converted to <code>%</code><var>HH</var>, 1463where HH is the hexadecimal notation of the byte value).</p></li> 1464<li><p>The original character is replaced by the resulting character sequence.</p> 1465</li> 1466</ol></div> 1467<p>[<a name="dt-pubid" title="Public identifier">Definition</a>: In addition to a system 1468identifier, an external identifier may include a <b>public identifier</b>.] 1469An XML processor attempting to retrieve the entity's content may use the public 1470identifier to try to generate an alternative <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E88">[E88]</a>URI reference</span>. 1471If the processor is unable to do so, it must use the <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E88">[E88]</a>URI 1472reference</span> specified in the system literal. Before a match is attempted, 1473all strings of white space in the public identifier must be normalized to 1474single space characters (#x20), and leading and trailing white space must 1475be removed.</p> 1476<p>Examples of external entity declarations:</p> 1477<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY open-hatch 1478 SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml"> 1479<!ENTITY open-hatch 1480 PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN" 1481 "http://www.textuality.com/boilerplate/OpenHatch.xml"> 1482<!ENTITY hatch-pic 1483 SYSTEM "/grafix/OpenHatch.gif" 1484 NDATA gif ></pre></td></tr></table> 1485</div> 1486</div> 1487<div class="div2"> 1488 1489<h3><a name="TextEntities"></a>4.3 Parsed Entities</h3> 1490<div class="div3"> 1491 1492<h4><a name="sec-TextDecl"></a>4.3.1 The Text Declaration</h4> 1493<p>External parsed entities <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E107">[E107]</a>should</span> each begin with a <b>text declaration</b>.</p> 1494 1495<h5>Text Declaration</h5><table class="scrap" summary="Scrap"><tbody> 1496<tr valign="baseline"><td><a name="NT-TextDecl"></a>[77]���</td><td><code>TextDecl</code></td><td>���::=���</td><td><code>'<?xml' <a href="#NT-VersionInfo">VersionInfo</a>? <a href="#NT-EncodingDecl">EncodingDecl</a> <a href="#NT-S">S</a>? '?>'</code></td><xsltdebug></xsltdebug></tr> 1497</tbody></table> 1498<p>The text declaration must be provided literally, not by reference to a 1499parsed entity. No text declaration may appear at any position other than the 1500beginning of an external parsed entity. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E94">[E94]</a>The text declaration 1501in an external parsed entity is not considered part of its <a title="Replacement Text" href="#dt-repltext">replacement 1502text</a>.</span></p> 1503</div> 1504<div class="div3"> 1505 1506<h4><a name="wf-entities"></a>4.3.2 Well-Formed Parsed Entities</h4> 1507<p>The document entity is well-formed if it matches the production labeled <a href="#NT-document">document</a>. An external general parsed entity is well-formed 1508if it matches the production labeled <a href="#NT-extParsedEnt">extParsedEnt</a>. <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</a>All 1509external parameter entities are well-formed by definition.</span></p> 1510 1511<h5>Well-Formed External Parsed Entity</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-extParsedEnt"></a>[78]���</td><td><code>extParsedEnt</code></td><td>���::=���</td><td><code><a href="#NT-TextDecl">TextDecl</a>? <a href="#NT-content">content</a></code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td class="diff-del"><a name="NT-extPE"></a>[79]���</td><td class="diff-del"><code>extPE</code></td><td class="diff-del">���::=���</td><td class="diff-del"><code><a href="#NT-TextDecl">TextDecl</a>? <a href="#NT-extSubsetDecl">extSubsetDecl</a></code></td><xsltdebug></xsltdebug><td class="diff-del"><i>/* <a href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</a> */</i></td></tr></tbody></table> 1512<p>An internal general parsed entity is well-formed if its replacement text 1513matches the production labeled <a href="#NT-content">content</a>. All internal 1514parameter entities are well-formed by definition.</p> 1515<p>A consequence of well-formedness in entities is that the logical and physical 1516structures in an XML document are properly nested; no <a title="Start-Tag" href="#dt-stag">start-tag</a>, <a title="End Tag" href="#dt-etag">end-tag</a>, <a title="Empty" href="#dt-empty">empty-element tag</a>, <a title="Element" href="#dt-element">element</a>, <a title="Comment" href="#dt-comment">comment</a>, <a title="Processing instruction" href="#dt-pi">processing instruction</a>, <a title="Character Reference" href="#dt-charref">character 1517reference</a>, or <a title="Entity Reference" href="#dt-entref">entity reference</a> 1518can begin in one entity and end in another.</p> 1519</div> 1520<div class="div3"> 1521 1522<h4><a name="charencoding"></a>4.3.3 Character Encoding in Entities</h4> 1523<p>Each external parsed entity in an XML document may use a different encoding 1524for its characters. All XML processors must be able to read entities in <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E56">[E56]</a>both 1525the UTF-8 and UTF-16 encodings.</span> <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E77">[E77]</a>The terms "UTF-8" 1526and "UTF-16" in this specification do not apply to character 1527encodings with any other labels, even if the encodings or labels are very 1528similar to UTF-8 or UTF-16.</span></p> 1529<p>Entities encoded in UTF-16 must begin with the Byte Order Mark described 1530by <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</a>Annex 1531F of <a href="#ISO10646">[ISO/IEC 10646]</a>, Annex H of <a href="#ISO10646-2000">[ISO/IEC 10646-2000]</a>, section 15322.4 of <a href="#Unicode">[Unicode]</a>, and section 2.7 of <a href="#Unicode3">[Unicode3]</a></span> 1533(the ZERO WIDTH NO-BREAK SPACE character, #xFEFF). This is an encoding signature, 1534not part of either the markup or the character data of the XML document. XML 1535processors must be able to use this character to differentiate between UTF-8 1536and UTF-16 encoded documents.</p> 1537<p>Although an XML processor is required to read only entities in the UTF-8 1538and UTF-16 encodings, it is recognized that other encodings are used around 1539the world, and it may be desired for XML processors to read entities that 1540use them. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E47">[E47]</a>In 1541the absence of external character encoding information (such as MIME headers),</span> 1542parsed entities which are stored in an encoding other than UTF-8 or UTF-16 1543must begin with a text declaration <span class="diff-add">(see <a href="#sec-TextDecl"><b>4.3.1 The Text Declaration</b></a>) </span>containing 1544an encoding declaration:</p> 1545 1546<h5>Encoding Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-EncodingDecl"></a>[80]���</td><td><code>EncodingDecl</code></td><td>���::=���</td><td><code><a href="#NT-S">S</a> 'encoding' <a href="#NT-Eq">Eq</a> 1547('"' <a href="#NT-EncName">EncName</a> '"' | "'" <a href="#NT-EncName">EncName</a> 1548"'" ) </code></td><xsltdebug></xsltdebug></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-EncName"></a>[81]���</td><td><code>EncName</code></td><td>���::=���</td><td><code>[A-Za-z] ([A-Za-z0-9._] | '-')*</code></td><xsltdebug></xsltdebug><td><i>/* Encoding 1549name contains only Latin characters */</i></td></tr></tbody></table> 1550<p>In the <a title="Document Entity" href="#dt-docent">document entity</a>, the encoding 1551declaration is part of the <a title="XML Declaration" href="#dt-xmldecl">XML declaration</a>. 1552The <a href="#NT-EncName">EncName</a> is the name of the encoding used.</p> 1553 1554<p>In an encoding declaration, the values "<code>UTF-8</code>", "<code>UTF-16</code>", "<code>ISO-10646-UCS-2</code>", and "<code>ISO-10646-UCS-4</code>" should be used 1555for the various encodings and transformations of Unicode / ISO/IEC 10646, 1556the values "<code>ISO-8859-1</code>", "<code>ISO-8859-2</code>", 1557... <a href="http://www.w3.org/XML/xml-19980210-errata#E106">[E106]</a><span class="diff-chg">"<code>ISO-8859-</code><var>n</var>" (where <var>n</var> 1558is the part number)</span> should be used for the parts of ISO 8859, and 1559the values "<code>ISO-2022-JP</code>", "<code>Shift_JIS</code>", 1560and "<code>EUC-JP</code>" should be used for the various encoded 1561forms of JIS X-0208-1997. <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E57">[E57]</a>It 1562is recommended that character encodings registered (as <em>charset</em>s) 1563with the Internet Assigned Numbers Authority <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E58">[E58]</a><a href="#IANA">[IANA-CHARSETS]</a></span>, 1564other than those just listed, be referred to using their registered names; 1565other encodings should use names starting with an "x-" prefix. 1566XML processors should match character encoding names in a case-insensitive 1567way and should either interpret an IANA-registered name as the encoding registered 1568at IANA for that name or treat it as unknown (processors are, of course, not 1569required to support all IANA-registered encodings).</span></p> 1570<p>In the absence of information provided by an external transport protocol 1571(e.g. HTTP or MIME), it is an <a title="Error" href="#dt-error">error</a> for 1572an entity including an encoding declaration to be presented to the XML processor 1573in an encoding other than that named in the declaration, <span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E5">[E5]</a>for 1574an encoding declaration to occur other than at the beginning of an external 1575entity, </span>or for an entity which begins with neither a Byte Order Mark 1576nor an encoding declaration to use an encoding other than UTF-8. Note that 1577since ASCII is a subset of UTF-8, ordinary ASCII entities do not strictly 1578need an encoding declaration.</p> 1579<div class="diff-add"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E5">[E5]</a>It 1580is <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E36">[E36]</a>a 1581fatal</span> error for a <a href="#NT-TextDecl">TextDecl</a> to occur other 1582than at the beginning of an external entity.</p></div> 1583<p>It is a <a title="Fatal Error" href="#dt-fatal">fatal error</a> when an XML processor 1584encounters an entity with an encoding that it is unable to process. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E79">[E79]</a>It 1585is a fatal error if an XML entity is determined (via default, encoding declaration, 1586or higher-level protocol) to be in a certain encoding but contains octet sequences 1587that are not legal in that encoding. It is also a fatal error if an XML entity 1588contains no encoding declaration and its content is not legal UTF-8 or UTF-16.</span></p> 1589<p>Examples of <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E23">[E23]</a>text 1590declarations containing </span>encoding declarations:</p> 1591<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><?xml encoding='UTF-8'?> 1592<?xml encoding='EUC-JP'?></pre></td></tr></table> 1593</div> 1594</div> 1595<div class="div2"> 1596 1597<h3><a name="entproc"></a>4.4 XML Processor Treatment of Entities and References</h3> 1598<p>The table below summarizes the contexts in which character references, 1599entity references, and invocations of unparsed entities might appear and the 1600required behavior of an <a title="XML Processor" href="#dt-xml-proc">XML processor</a> 1601in each case. The labels in the leftmost column describe the recognition context: </p><dl> 1602<dt class="label">Reference in Content</dt> 1603<dd> 1604<p>as a reference anywhere after the <a title="Start-Tag" href="#dt-stag">start-tag</a> 1605and before the <a title="End Tag" href="#dt-etag">end-tag</a> of an element; corresponds 1606to the nonterminal <a href="#NT-content">content</a>.</p> 1607</dd> 1608<dt class="label">Reference in Attribute Value</dt> 1609<dd> 1610<p>as a reference within either the value of an attribute in a <a title="Start-Tag" href="#dt-stag">start-tag</a>, 1611or a default value in an <a title="Attribute-List Declaration" href="#dt-attdecl">attribute declaration</a>; 1612corresponds to the nonterminal <a href="#NT-AttValue">AttValue</a>.</p> 1613</dd> 1614<dt class="label">Occurs as Attribute Value</dt> 1615<dd> 1616<p>as a <a href="#NT-Name">Name</a>, not a reference, appearing either as 1617the value of an attribute which has been declared as type <b>ENTITY</b>, 1618or as one of the space-separated tokens in the value of an attribute which 1619has been declared as type <b>ENTITIES</b>.</p> 1620</dd> 1621<dt class="label">Reference in Entity Value</dt> 1622<dd> 1623<p>as a reference within a parameter or internal entity's <a title="Literal Entity Value" href="#dt-litentval">literal 1624entity value</a> in the entity's declaration; corresponds to the nonterminal <a href="#NT-EntityValue">EntityValue</a>.</p> 1625</dd> 1626<dt class="label">Reference in DTD</dt> 1627<dd> 1628<div class="diff-chg"><p><a href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</a>as 1629a reference within either the internal or external subsets of the <a title="Document Type Declaration" href="#dt-doctype">DTD</a>, but outside of an <a href="#NT-EntityValue">EntityValue</a>, <a href="#NT-AttValue">AttValue</a>, <a href="#NT-PI">PI</a>, <a href="#NT-Comment">Comment</a>, <a href="#NT-SystemLiteral">SystemLiteral</a>, <a href="#NT-PubidLiteral">PubidLiteral</a>, 1630or the contents of an ignored conditional section (see <a href="#sec-condition-sect"><b>3.4 Conditional Sections</b></a>).</p></div> 1631<p>.</p> 1632</dd> 1633</dl><p></p> 1634<table border="1" frame="border" cellpadding="7"><tbody align="center"><tr> 1635<td rowspan="2" colspan="1"></td><td colspan="4" align="center" valign="bottom" rowspan="1">Entity 1636Type</td><td rowspan="2" align="center" colspan="1">Character</td></tr><tr align="center" valign="bottom"><td rowspan="1" colspan="1">Parameter</td><td rowspan="1" colspan="1">Internal General</td><td rowspan="1" colspan="1">External Parsed 1637General</td><td rowspan="1" colspan="1">Unparsed</td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Reference 1638in Content</td><td rowspan="1" colspan="1"><a href="#not-recognized"><cite>Not recognized</cite></a></td> 1639<td rowspan="1" colspan="1"><a href="#included"><cite>Included</cite></a></td><td rowspan="1" colspan="1"><a href="#include-if-valid"><cite>Included 1640if validating</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td> 1641<td rowspan="1" colspan="1"><a href="#included"><cite>Included</cite></a></td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Reference in Attribute Value</td><td rowspan="1" colspan="1"><a href="#not-recognized"><cite>Not recognized</cite></a></td><td rowspan="1" colspan="1"><a href="#inliteral"><cite>Included 1642in literal</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td> 1643<td rowspan="1" colspan="1"><a href="http://www.w3.org/XML/xml-19980210-errata#E51">[E51]</a><div class="diff-chg"><a href="#forbidden"><cite>Forbidden</cite></a></div></td><td rowspan="1" colspan="1"><a href="#included"><cite>Included</cite></a></td> 1644</tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Occurs as Attribute 1645Value</td><td rowspan="1" colspan="1"><a href="#not-recognized"><cite>Not recognized</cite></a></td> 1646<td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="http://www.w3.org/XML/xml-19980210-errata#E51">[E51]</a><div class="diff-chg"><a href="#forbidden"><cite>Forbidden</cite></a></div></td><td rowspan="1" colspan="1"><a href="#notify"><cite>Notify</cite></a></td> 1647<td rowspan="1" colspan="1"><a href="http://www.w3.org/XML/xml-19980210-errata#E51">[E51]</a><div class="diff-chg"><a href="#not-recognized"><cite>Not recognized</cite></a></div></td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Reference in EntityValue</td><td rowspan="1" colspan="1"><a href="#inliteral"><cite>Included in literal</cite></a></td><td rowspan="1" colspan="1"><a href="#bypass"><cite>Bypassed</cite></a></td> 1648<td rowspan="1" colspan="1"><a href="#bypass"><cite>Bypassed</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td> 1649<td rowspan="1" colspan="1"><a href="#included"><cite>Included</cite></a></td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Reference in DTD</td><td rowspan="1" colspan="1"><a href="#as-PE"><cite>Included 1650as PE</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td> 1651<td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td> 1652<td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td></tr></tbody></table> 1653<div class="div3"> 1654 1655<h4><a name="not-recognized"></a>4.4.1 Not Recognized</h4> 1656<p>Outside the DTD, the <code>%</code> character has no special significance; 1657thus, what would be parameter entity references in the DTD are not recognized 1658as markup in <a href="#NT-content">content</a>. Similarly, the names of unparsed 1659entities are not recognized except when they appear in the value of an appropriately 1660declared attribute.</p> 1661</div> 1662<div class="div3"> 1663 1664<h4><a name="included"></a>4.4.2 Included</h4> 1665<p>[<a name="dt-include" title="Include">Definition</a>: An entity is <b>included</b> 1666when its <a title="Replacement Text" href="#dt-repltext">replacement text</a> is retrieved 1667and processed, in place of the reference itself, as though it were part of 1668the document at the location the reference was recognized.] The replacement 1669text may contain both <a title="Character Data" href="#dt-chardata">character data</a> 1670and (except for parameter entities) <a title="Markup" href="#dt-markup">markup</a>, 1671which must be recognized in the usual way<span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E65">[E65]</a>, except that 1672the replacement text of entities used to escape markup delimiters (the entities <code>amp</code>, 1673<code>lt</code>, 1674<code>gt</code>, 1675<code>apos</code>, 1676<code>quot</code>) 1677is always treated as data</span>. (The string "<code>AT&amp;T;</code>" 1678expands to "<code>AT&T;</code>" and the remaining ampersand 1679is not recognized as an entity-reference delimiter.) A character reference 1680is <b>included</b> when the indicated character is processed in place 1681of the reference itself. </p> 1682</div> 1683<div class="div3"> 1684 1685<h4><a name="include-if-valid"></a>4.4.3 Included If Validating</h4> 1686<p>When an XML processor recognizes a reference to a parsed entity, in order 1687to <a title="Validity" href="#dt-valid">validate</a> the document, the processor 1688must <a title="Include" href="#dt-include">include</a> its replacement text. If 1689the entity is external, and the processor is not attempting to validate the 1690XML document, the processor <a title="May" href="#dt-may">may</a>, but need 1691not, include the entity's replacement text. If a non-validating <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E95">[E95]</a>processor</span> 1692does not include the replacement text, it must inform the application that 1693it recognized, but did not read, the entity.</p> 1694<p>This rule is based on the recognition that the automatic inclusion provided 1695by the SGML and XML entity mechanism, primarily designed to support modularity 1696in authoring, is not necessarily appropriate for other applications, in particular 1697document browsing. Browsers, for example, when encountering an external parsed 1698entity reference, might choose to provide a visual indication of the entity's 1699presence and retrieve it for display only on demand.</p> 1700</div> 1701<div class="div3"> 1702 1703<h4><a name="forbidden"></a>4.4.4 Forbidden</h4> 1704<p>The following are forbidden, and constitute <a title="Fatal Error" href="#dt-fatal">fatal</a> 1705errors:</p> 1706<ul> 1707<li><p>the appearance of a reference to an <a title="Unparsed Entity" href="#dt-unparsed">unparsed 1708entity</a>.</p></li> 1709<li><p>the appearance of any character or general-entity reference in the 1710DTD except within an <a href="#NT-EntityValue">EntityValue</a> or <a href="#NT-AttValue">AttValue</a>.</p> 1711</li> 1712<li><p>a reference to an external entity in an attribute value.</p></li> 1713</ul> 1714</div> 1715<div class="div3"> 1716 1717<h4><a name="inliteral"></a>4.4.5 Included in Literal</h4> 1718<p>When an <a title="Entity Reference" href="#dt-entref">entity reference</a> appears in 1719an attribute value, or a parameter entity reference appears in a literal entity 1720value, its <a title="Replacement Text" href="#dt-repltext">replacement text</a> is processed 1721in place of the reference itself as though it were part of the document at 1722the location the reference was recognized, except that a single or double 1723quote character in the replacement text is always treated as a normal data 1724character and will not terminate the literal. For example, this is well-formed:</p> 1725<div class="diff-chg"><table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td class="diff-chg"><pre><!-- <a href="http://www.w3.org/XML/xml-19980210-errata#E4">[E4]</a> --> 1726<!ENTITY % YN '"Yes"' > 1727<!ENTITY WhatHeSaid "He said %YN;" ></pre></td></tr></table></div> 1728<p>while this is not:</p> 1729<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY EndAttr "27'" > 1730<element attribute='a-&EndAttr;></pre></td></tr></table> 1731</div> 1732<div class="div3"> 1733 1734<h4><a name="notify"></a>4.4.6 Notify</h4> 1735<p>When the name of an <a title="Unparsed Entity" href="#dt-unparsed">unparsed entity</a> 1736appears as a token in the value of an attribute of declared type <b>ENTITY</b> 1737or <b>ENTITIES</b>, a validating processor must inform the application of 1738the <a title="System Identifier" href="#dt-sysid">system</a> and <a title="Public identifier" href="#dt-pubid">public</a> 1739(if any) identifiers for both the entity and its associated <a title="Notation" href="#dt-notation">notation</a>.</p> 1740</div> 1741<div class="div3"> 1742 1743<h4><a name="bypass"></a>4.4.7 Bypassed</h4> 1744<p>When a general entity reference appears in the <a href="#NT-EntityValue">EntityValue</a> 1745in an entity declaration, it is bypassed and left as is.</p> 1746</div> 1747<div class="div3"> 1748 1749<h4><a name="as-PE"></a>4.4.8 Included as PE</h4> 1750<p>Just as with external parsed entities, parameter entities need only be <a href="#include-if-valid"><cite>included if validating</cite></a>. When a parameter-entity 1751reference is recognized in the DTD and included, its <a title="Replacement Text" href="#dt-repltext">replacement 1752text</a> is enlarged by the attachment of one leading and one following 1753space (#x20) character; the intent is to constrain the replacement text of 1754parameter entities to contain an integral number of grammatical tokens in 1755the DTD. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E96">[E96]</a>This 1756behavior does not apply to parameter entity references within entity values; 1757these are described in <a href="#inliteral"><b>4.4.5 Included in Literal</b></a>.</span></p> 1758</div> 1759</div> 1760<div class="div2"> 1761 1762<h3><a name="intern-replacement"></a>4.5 Construction of Internal Entity Replacement Text</h3> 1763<p>In discussing the treatment of internal entities, it is useful to distinguish 1764two forms of the entity's value. [<a name="dt-litentval" title="Literal Entity Value">Definition</a>: The <b>literal 1765entity value</b> is the quoted string actually present in the entity declaration, 1766corresponding to the non-terminal <a href="#NT-EntityValue">EntityValue</a>.] [<a name="dt-repltext" title="Replacement Text">Definition</a>: The <b>replacement text</b> 1767is the content of the entity, after replacement of character references and 1768parameter-entity references.]</p> 1769<p>The literal entity value as given in an internal entity declaration (<a href="#NT-EntityValue">EntityValue</a>) may contain character, parameter-entity, 1770and general-entity references. Such references must be contained entirely 1771within the literal entity value. The actual replacement text that is <a title="Include" href="#dt-include">included</a> as described above must contain the <em>replacement 1772text</em> of any parameter entities referred to, and must contain the character 1773referred to, in place of any character references in the literal entity value; 1774however, general-entity references must be left as-is, unexpanded. For example, 1775given the following declarations:</p> 1776<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY % pub "&#xc9;ditions Gallimard" > 1777<!ENTITY rights "All rights reserved" > 1778<!ENTITY book "La Peste: Albert Camus, 1779&#xA9; 1947 %pub;. &rights;" ></pre></td></tr></table> 1780<p>then the replacement text for the entity "<code>book</code>" 1781is:</p> 1782<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>La Peste: Albert Camus, 1783� 1947 �ditions Gallimard. &rights;</pre></td></tr></table> 1784<p>The general-entity reference "<code>&rights;</code>" would 1785be expanded should the reference "<code>&book;</code>" appear 1786in the document's content or an attribute value.</p> 1787<p>These simple rules may have complex interactions; for a detailed discussion 1788of a difficult example, see <a href="#sec-entexpand"><b>D Expansion of Entity and Character References</b></a>.</p> 1789</div> 1790<div class="div2"> 1791 1792<h3><a name="sec-predefined-ent"></a>4.6 Predefined Entities</h3> 1793<p>[<a name="dt-escape" title="escape">Definition</a>: Entity and character references can 1794both be used to <b>escape</b> the left angle bracket, ampersand, and 1795other delimiters. A set of general entities (<code>amp</code>, 1796<code>lt</code>, 1797<code>gt</code>, 1798<code>apos</code>, 1799<code>quot</code>) is specified for 1800this purpose. Numeric character references may also be used; they are expanded 1801immediately when recognized and must be treated as character data, so the 1802numeric character references "<code>&#60;</code>" and "<code>&#38;</code>" 1803may be used to escape <code><</code> and <code>&</code> when they occur 1804in character data.]</p> 1805<p>All XML processors must recognize these entities whether they are declared 1806or not. <a title="For interoperability" href="#dt-interop">For interoperability</a>, valid XML 1807documents should declare these entities, like any others, before using them. <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E80">[E80]</a>If 1808the entities <code>lt</code> or <code>amp</code> are declared, they must be 1809declared as internal entities whose replacement text is a character reference 1810to the <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E103">[E103]</a>respective 1811character (less-than sign or ampersand)</span> being escaped; the double 1812escaping is required for these entities so that references to them produce 1813a well-formed result. If the entities <code>gt</code>, <code>apos</code>, 1814or <code>quot</code> are declared, they must be declared as internal entities 1815whose replacement text is the single character being escaped (or a character 1816reference to that character; the double escaping here is unnecessary but harmless). 1817For example:</span></p> 1818<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY lt "&#38;#60;"> 1819<!ENTITY gt "&#62;"> 1820<!ENTITY amp "&#38;#38;"> 1821<!ENTITY apos "&#39;"> 1822<!ENTITY quot "&#34;"></pre></td></tr></table> 1823<div class="diff-del"><p>Note that the <code><</code> and <code>&</code> characters 1824in the declarations of "<code>lt</code>" and "<code>amp</code>" 1825are doubly escaped to meet the requirement that entity replacement be well-formed.</p></div> 1826</div> 1827<div class="div2"> 1828 1829<h3><a name="Notations"></a>4.7 Notation Declarations</h3> 1830<p>[<a name="dt-notation" title="Notation">Definition</a>: <b>Notations</b> identify 1831by name the format of <a title="External Entity" href="#dt-extent">unparsed entities</a>, 1832the format of elements which bear a notation attribute, or the application 1833to which a <a title="Processing instruction" href="#dt-pi">processing instruction</a> is addressed.]</p> 1834<p>[<a name="dt-notdecl" title="Notation Declaration">Definition</a>: <b>Notation declarations</b> 1835provide a name for the notation, for use in entity and attribute-list declarations 1836and in attribute specifications, and an external identifier for the notation 1837which may allow an XML processor or its client application to locate a helper 1838application capable of processing data in the given notation.]</p> 1839 1840<h5>Notation Declarations</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-NotationDecl"></a>[82]���</td><td><code>NotationDecl</code></td><td>���::=���</td><td><code>'<!NOTATION' <a href="#NT-S">S</a> <a href="#NT-Name">Name</a> <a href="#NT-S">S</a> (<a href="#NT-ExternalID">ExternalID</a> | <a href="#NT-PublicID">PublicID</a>) <a href="#NT-S">S</a>? '>'</code></td><xsltdebug></xsltdebug><td class="diff-add"><a href="#UniqueNotationName">[VC: Unique 1841Notation Name]</a></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PublicID"></a>[83]���</td><td><code>PublicID</code></td><td>���::=���</td><td><code>'PUBLIC' <a href="#NT-S">S</a> <a href="#NT-PubidLiteral">PubidLiteral</a> </code></td><xsltdebug></xsltdebug></tr></tbody></table> 1842<div class="diff-add"><div class="constraint"><p class="prefix"><a name="UniqueNotationName"></a><b>Validity constraint: <a href="http://www.w3.org/XML/xml-19980210-errata#E22">[E22]</a>Unique 1843Notation Name</b></p><p>Only one notation declaration can declare a given <a href="#NT-Name">Name</a>.</p> 1844</div></div> 1845<p>XML processors must provide applications with the name and external identifier(s) 1846of any notation declared and referred to in an attribute value, attribute 1847definition, or entity declaration. They may additionally resolve the external 1848identifier into the <a title="System Identifier" href="#dt-sysid">system identifier</a>, file 1849name, or other information needed to allow the application to call a processor 1850for data in the notation described. (It is not an error, however, for XML 1851documents to declare and refer to notations for which notation-specific applications 1852are not available on the system where the XML processor or application is 1853running.)</p> 1854</div> 1855<div class="div2"> 1856 1857<h3><a name="sec-doc-entity"></a>4.8 Document Entity</h3> 1858<p>[<a name="dt-docent" title="Document Entity">Definition</a>: The <b>document entity</b> 1859serves as the root of the entity tree and a starting-point for an <a title="XML Processor" href="#dt-xml-proc">XML processor</a>.] This specification does 1860not specify how the document entity is to be located by an XML processor; 1861unlike other entities, the document entity has no name and might well appear 1862on a processor input stream without any identification at all.</p> 1863</div> 1864</div> 1865 1866<div class="div1"> 1867 1868<h2><a name="sec-conformance"></a>5 Conformance</h2> 1869<div class="div2"> 1870 1871<h3><a name="proc-types"></a>5.1 Validating and Non-Validating Processors</h3> 1872<p>Conforming <a title="XML Processor" href="#dt-xml-proc">XML processors</a> fall into 1873two classes: validating and non-validating.</p> 1874<p>Validating and non-validating processors alike must report violations of 1875this specification's well-formedness constraints in the content of the <a title="Document Entity" href="#dt-docent">document entity</a> and any other <a title="Text Entity" href="#dt-parsedent">parsed 1876entities</a> that they read.</p> 1877<p>[<a name="dt-validating" title="Validating Processor">Definition</a>: <b>Validating 1878processors</b> must<span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E21">[E21]</a>, 1879at user option,</span> report violations of the constraints expressed by 1880the declarations in the <a title="Document Type Declaration" href="#dt-doctype">DTD</a>, and failures 1881to fulfill the validity constraints given in this specification.] 1882To accomplish this, validating XML processors must read and process the entire 1883DTD and all external parsed entities referenced in the document.</p> 1884<p>Non-validating processors are required to check only the <a title="Document Entity" href="#dt-docent">document 1885entity</a>, including the entire internal DTD subset, for well-formedness. [<a name="dt-use-mdecl" title="Process Declarations">Definition</a>: While they are not required 1886to check the document for validity, they are required to <b>process</b> 1887all the declarations they read in the internal DTD subset and in any parameter 1888entity that they read, up to the first reference to a parameter entity that 1889they do <em>not</em> read; that is to say, they must use the information 1890in those declarations to <a href="#AVNormalize"><cite>normalize</cite></a> 1891attribute values, <a href="#included"><cite>include</cite></a> the replacement 1892text of internal entities, and supply <a href="#sec-attr-defaults"><cite>default 1893attribute values</cite></a>.] <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E33">[E33]</a>Except when <code>standalone="yes"</code>, </span>they 1894must not <a title="Process Declarations" href="#dt-use-mdecl">process</a> <a title="entity declaration" href="#dt-entdecl">entity 1895declarations</a> or <a title="Attribute-List Declaration" href="#dt-attdecl">attribute-list declarations</a> 1896encountered after a reference to a parameter entity that is not read, since 1897the entity may have contained overriding declarations.</p> 1898</div> 1899<div class="div2"> 1900 1901<h3><a name="safe-behavior"></a>5.2 Using XML Processors</h3> 1902<p>The behavior of a validating XML processor is highly predictable; it must 1903read every piece of a document and report all well-formedness and validity 1904violations. Less is required of a non-validating processor; it need not read 1905any part of the document other than the document entity. This has two effects 1906that may be important to users of XML processors:</p> 1907<ul> 1908<li><p>Certain well-formedness errors, specifically those that require reading 1909external entities, may not be detected by a non-validating processor. Examples 1910include the constraints entitled <a href="#wf-entdeclared"><cite>Entity Declared</cite></a>, <a href="#textent"><cite>Parsed Entity</cite></a>, and <a href="#norecursion"><cite>No 1911Recursion</cite></a>, as well as some of the cases described as <a href="#forbidden"><cite>forbidden</cite></a> in <a href="#entproc"><b>4.4 XML Processor Treatment of Entities and References</b></a>.</p></li> 1912<li><p>The information passed from the processor to the application may 1913vary, depending on whether the processor reads parameter and external entities. 1914For example, a non-validating processor may not <a href="#AVNormalize"><cite>normalize</cite></a> 1915attribute values, <a href="#included"><cite>include</cite></a> the replacement 1916text of internal entities, or supply <a href="#sec-attr-defaults"><cite>default 1917attribute values</cite></a>, where doing so depends on having read declarations 1918in external or parameter entities.</p></li> 1919</ul> 1920<p>For maximum reliability in interoperating between different XML processors, 1921applications which use non-validating processors should not rely on any behaviors 1922not required of such processors. Applications which require facilities such 1923as the use of default attributes or internal entities which are declared in 1924external entities should use validating XML processors.</p> 1925</div> 1926</div> 1927<div class="div1"> 1928 1929<h2><a name="sec-notation"></a>6 Notation</h2> 1930<p>The formal grammar of XML is given in this specification using a simple 1931Extended Backus-Naur Form (EBNF) notation. Each rule in the grammar defines 1932one symbol, in the form</p> 1933<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>symbol ::= expression</pre></td></tr></table> 1934<p>Symbols are written with an initial capital letter if they are <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E42">[E42]</a>the 1935start symbol of a regular language,</span> otherwise with an initial lower 1936case letter. Literal strings are quoted.</p> 1937<p>Within the expression on the right-hand side of a rule, the following expressions 1938are used to match strings of one or more characters: </p><dl> 1939<dt class="label"><code>#xN</code></dt> 1940<dd> 1941<p>where <code>N</code> is a hexadecimal integer, the expression matches the 1942character in ISO/IEC 10646 whose canonical (UCS-4) code value, when interpreted 1943as an unsigned binary number, has the value indicated. The number of leading 1944zeros in the <code>#xN</code> form is insignificant; the number of leading 1945zeros in the corresponding code value is governed by the character encoding 1946in use and is not significant for XML.</p> 1947</dd> 1948<dt class="label"><code>[a-zA-Z]</code>, <code>[#xN-#xN]</code></dt> 1949<dd> 1950<p>matches any <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E93">[E93]</a><a href="#NT-Char">Char</a></span> with a value in the range(s) indicated (inclusive).</p> 1951</dd> 1952<dt class="label"><span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E3">[E3]</a><code>[abc]</code>, <code>[#xN#xN#xN]</code></span></dt> 1953<dd><div class="diff-add"> 1954<p>matches any <a href="#NT-Char">Char</a> with a value among the characters 1955enumerated. Enumerations and ranges can be mixed in one set of brackets.</p> 1956</div></dd> 1957<dt class="label"><code>[^a-z]</code>, <code>[^#xN-#xN]</code></dt> 1958<dd> 1959<p>matches any <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E93">[E93]</a><a href="#NT-Char">Char</a></span> with a value <em>outside</em> the range 1960indicated.</p> 1961</dd> 1962<dt class="label"><code>[^abc]</code>, <code>[^#xN#xN#xN]</code></dt> 1963<dd> 1964<p>matches any <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E93">[E93]</a><a href="#NT-Char">Char</a></span> with a value not among the characters given. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E3">[E3]</a>Enumerations 1965and ranges of forbidden values can be mixed in one set of brackets.</span></p> 1966</dd> 1967<dt class="label"><code>"string"</code></dt> 1968<dd> 1969<p>matches a literal string <a title="match" href="#dt-match">matching</a> that 1970given inside the double quotes.</p> 1971</dd> 1972<dt class="label"><code>'string'</code></dt> 1973<dd> 1974<p>matches a literal string <a title="match" href="#dt-match">matching</a> that 1975given inside the single quotes.</p> 1976</dd> 1977</dl><p> These symbols may be combined to match more complex patterns as follows, 1978where <code>A</code> and <code>B</code> represent simple expressions: </p><dl> 1979<dt class="label">(<code>expression</code>)</dt> 1980<dd> 1981<p><code>expression</code> is treated as a unit and may be combined as described 1982in this list.</p> 1983</dd> 1984<dt class="label"><code>A?</code></dt> 1985<dd> 1986<p>matches <code>A</code> or nothing; optional <code>A</code>.</p> 1987</dd> 1988<dt class="label"><code>A B</code></dt> 1989<dd> 1990<p>matches <code>A</code> followed by <code>B</code>. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E20">[E20]</a>This 1991operator has higher precedence than alternation; thus <code>A B | C D</code> 1992is identical to <code>(A B) | (C D)</code>.</span></p> 1993</dd> 1994<dt class="label"><code>A | B</code></dt> 1995<dd> 1996<p>matches <code>A</code> or <code>B</code> but not both.</p> 1997</dd> 1998<dt class="label"><code>A - B</code></dt> 1999<dd> 2000<p>matches any string that matches <code>A</code> but does not match <code>B</code>.</p> 2001</dd> 2002<dt class="label"><code>A+</code></dt> 2003<dd> 2004<p>matches one or more occurrences of <code>A</code>.<span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E20">[E20]</a>Concatenation 2005has higher precedence than alternation; thus <code>A+ | B+</code> is identical 2006to <code>(A+) | (B+)</code>.</span></p> 2007</dd> 2008<dt class="label"><code>A*</code></dt> 2009<dd> 2010<p>matches zero or more occurrences of <code>A</code>. <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E20">[E20]</a>Concatenation 2011has higher precedence than alternation; thus <code>A* | B*</code> is identical 2012to <code>(A*) | (B*)</code>.</span></p> 2013</dd> 2014</dl><p> Other notations used in the productions are: </p><dl> 2015<dt class="label"><code>/* ... */</code></dt> 2016<dd> 2017<p>comment.</p> 2018</dd> 2019<dt class="label"><code>[ wfc: ... ]</code></dt> 2020<dd> 2021<p>well-formedness constraint; this identifies by name a constraint on <a title="Well-Formed" href="#dt-wellformed">well-formed</a> documents associated with a production.</p> 2022</dd> 2023<dt class="label"><code>[ vc: ... ]</code></dt> 2024<dd> 2025<p>validity constraint; this identifies by name a constraint on <a title="Validity" href="#dt-valid">valid</a> 2026documents associated with a production.</p> 2027</dd> 2028</dl><p></p> 2029</div> 2030</div><div class="back"> 2031 2032 2033<div class="div1"> 2034 2035<h2><a name="sec-bibliography"></a>A References</h2> 2036<div class="div2"> 2037 2038<h3><a name="sec-existing-stds"></a>A.1 Normative References</h3> 2039<dl> 2040<dt class="label"><span class="diff-chg"><a name="IANA"></a>IANA-CHARSETS</span></dt><dd><div class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E58">[E58]</a>(Internet 2041Assigned Numbers Authority) <cite>Official Names for Character Sets</cite>, 2042ed. Keld Simonsen et al. See <a href="ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets">ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets</a>. </div></dd> 2043<dt class="label"><a name="RFC1766"></a>IETF RFC 1766</dt><dd>IETF 2044(Internet Engineering Task Force). <cite>RFC 1766: Tags for the Identification 2045of Languages</cite>, ed. H. Alvestrand. 1995. (See <a href="http://www.ietf.org/rfc/rfc1766.txt">http://www.ietf.org/rfc/rfc1766.txt</a>.)</dd> 2046<dt class="label"><span class="diff-del"><a name="ISO639-old"></a>ISO 639</span></dt><dd><div class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E38">[E38]</a> 2047(International Organization for Standardization). <cite>ISO 639:1988 (E). 2048Code for the representation of names of languages.</cite> [Geneva]: International 2049Organization for Standardization, 1988.</div></dd> 2050<dt class="label"><span class="diff-del"><a name="ISO3166-old"></a>ISO 3166</span></dt><dd><div class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E38">[E38]</a> 2051(International Organization for Standardization). <cite>ISO 3166-1:1997 2052(E). Codes for the representation of names of countries and their subdivisions -- 2053Part 1: Country codes</cite> [Geneva]: International Organization for 2054Standardization, 1997.</div></dd> 2055<dt class="label"><a name="ISO10646"></a>ISO/IEC 10646</dt><dd>ISO (International Organization for 2056Standardization). <cite>ISO/IEC 10646-1993 (E). Information technology -- 2057Universal Multiple-Octet Coded Character Set (UCS) -- Part 1: Architecture 2058and Basic Multilingual Plane.</cite> [Geneva]: International Organization 2059for Standardization, 1993 (plus amendments AM 1 through AM 7).</dd> 2060<dt class="label"><span class="diff-add"><a name="ISO10646-2000"></a>ISO/IEC 10646-2000</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</a> ISO (International 2061Organization for Standardization). <cite>ISO/IEC 10646-1:2000. Information 2062technology -- Universal Multiple-Octet Coded Character Set (UCS) -- 2063Part 1: Architecture and Basic Multilingual Plane.</cite> [Geneva]: International 2064Organization for Standardization, 2000.</div></dd> 2065<dt class="label"><a name="Unicode"></a>Unicode</dt><dd>The Unicode Consortium. <em>The Unicode 2066Standard, Version 2.0.</em> Reading, Mass.: Addison-Wesley Developers Press, 20671996.</dd> 2068<dt class="label"><span class="diff-add"><a name="Unicode3"></a>Unicode3</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</a> 2069The Unicode Consortium. <em>The Unicode Standard, Version 3.0.</em> Reading, 2070Mass.: Addison-Wesley Developers Press, 2000. ISBN 0-201-61633-5.</div></dd> 2071</dl></div> 2072<div class="div2"> 2073 2074 2075<h3><a name="null"></a>A.2 Other References</h3> 2076<dl> 2077<dt class="label"><a name="Aho"></a>Aho/Ullman</dt><dd>Aho, Alfred V., Ravi Sethi, and Jeffrey D. 2078Ullman. <cite>Compilers: Principles, Techniques, and Tools</cite>. 2079Reading: Addison-Wesley, 1986, rpt. corr. 1988.</dd> 2080<dt class="label"><a name="Berners-Lee"></a>Berners-Lee et al.</dt><dd> Berners-Lee, T., R. Fielding, 2081and L. Masinter. <cite>Uniform Resource Identifiers (URI): Generic Syntax 2082and Semantics</cite>. 1997. (Work in progress; see updates to RFC1738.)</dd> 2083<dt class="label"><span class="diff-chg"><a name="ABK"></a>Br�ggemann-Klein</span></dt><dd><div class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E2">[E2]</a>Br�ggemann-Klein, 2084Anne. Formal Models in Document Processing. Habilitationsschrift. Faculty 2085of Mathematics at the University of Freiburg, 1993. (See <a href="ftp://ftp.informatik.uni-freiburg.de/documents/papers/brueggem/habil.ps">ftp://ftp.informatik.uni-freiburg.de/documents/papers/brueggem/habil.ps</a>.)</div></dd> 2086<dt class="label"><span class="diff-chg"><a name="ABKDW"></a>Br�ggemann-Klein and Wood</span></dt><dd><div class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E2">[E2]</a>Br�ggemann-Klein, 2087Anne, and Derick Wood. <cite>Deterministic Regular Languages</cite>. 2088Universit�t Freiburg, Institut f�r Informatik, Bericht 38, Oktober 1991. Extended 2089abstract in A. Finkel, M. Jantzen, Hrsg., STACS 1992, S. 173-184. Springer-Verlag, 2090Berlin 1992. Lecture Notes in Computer Science 577. Full version titled <cite>One-Unambiguous 2091Regular Languages</cite> in Information and Computation 140 (2): 229-253, 2092February 1998.</div></dd> 2093<dt class="label"><a name="Clark"></a>Clark</dt><dd>James Clark. Comparison of SGML and XML. See <a href="http://www.w3.org/TR/NOTE-sgml-xml-971215">http://www.w3.org/TR/NOTE-sgml-xml-971215</a>. </dd> 2094<dt class="label"><span class="diff-add"><a name="IANA-LANGCODES"></a>IANA-LANGCODES</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E58">[E58]</a>(Internet 2095Assigned Numbers Authority) <cite>Registry of Language Tags</cite>, 2096ed. Keld Simonsen et al. (See <a href="http://www.isi.edu/in-notes/iana/assignments/languages/">http://www.isi.edu/in-notes/iana/assignments/languages/</a>.)</div></dd> 2097<dt class="label"><span class="diff-del"><a name="RFC1738"></a>IETF RFC1738</span></dt><dd><div class="diff-del">IETF 2098(Internet Engineering Task Force). <cite>RFC 1738: Uniform Resource Locators 2099(URL)</cite>, ed. T. Berners-Lee, L. Masinter, M. McCahill. 1994. (See <a href="http://www.ietf.org/rfc/rfc1738.txt">http://www.ietf.org/rfc/rfc1738.txt</a>.)</div></dd> 2100<dt class="label"><span class="diff-del"><a name="RFC1808"></a>IETF RFC1808</span></dt><dd><div class="diff-del">IETF 2101(Internet Engineering Task Force). <cite>RFC 1808: Relative Uniform Resource 2102Locators</cite>, ed. R. Fielding. 1995. (See <a href="http://www.ietf.org/rfc/rfc1808.txt">http://www.ietf.org/rfc/rfc1808.txt</a>.)</div></dd> 2103<dt class="label"><a name="RFC2141"></a>IETF RFC2141</dt><dd>IETF 2104(Internet Engineering Task Force). <em>RFC 2141: URN Syntax</em>, ed. 2105R. Moats. 1997. (See <a href="http://www.ietf.org/rfc/rfc2141.txt">http://www.ietf.org/rfc/rfc2141.txt</a>.)</dd> 2106<dt class="label"><span class="diff-add"><a name="rfc2279"></a>IETF RFC 2279</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E78">[E78]</a>IETF 2107(Internet Engineering Task Force). <cite>RFC 2279: UTF-8, a transformation 2108format of ISO 10646</cite>, <span class="diff-add">ed. F. Yergeau, </span>1998. (See <a href="http://www.ietf.org/rfc/rfc2279.txt">http://www.ietf.org/rfc/rfc2279.txt</a>.)</div></dd> 2109<dt class="label"><span class="diff-add"><a name="rfc2376"></a>IETF RFC 2376</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E48">[E48]</a>IETF 2110(Internet Engineering Task Force). <cite>RFC 2376: XML Media Types</cite>. 2111ed. E. Whitehead, M. Murata. 1998. (See <a href="http://www.ietf.org/rfc/rfc2376.txt">http://www.ietf.org/rfc/rfc2376.txt</a>.)</div></dd> 2112<dt class="label"><span class="diff-add"><a name="rfc2396"></a>IETF RFC 2396</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E66">[E66]</a>IETF 2113(Internet Engineering Task Force). <cite>RFC 2396: Uniform Resource Identifiers 2114(URI): Generic Syntax</cite>. T. Berners-Lee, R. Fielding, L. Masinter. 21151998. (See <a href="http://www.ietf.org/rfc/rfc2396.txt">http://www.ietf.org/rfc/rfc2396.txt</a>.)</div></dd> 2116<dt class="label"><span class="diff-add"><a name="rfc2732"></a>IETF RFC 2732</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E66">[E66]</a>IETF 2117(Internet Engineering Task Force). <cite>RFC 2732: Format for Literal 2118IPv6 Addresses in URL's</cite>. R. Hinden, B. Carpenter, L. Masinter. 21191999. (See <a href="http://www.ietf.org/rfc/rfc2732.txt">http://www.ietf.org/rfc/rfc2732.txt</a>.)</div></dd> 2120<dt class="label"><span class="diff-add"><a name="rfc2781"></a>IETF RFC 2781</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E77">[E77]</a> 2121IETF (Internet Engineering Task Force). <em>RFC 2781: UTF-16, an encoding 2122of ISO 10646</em>, ed. P. Hoffman, F. Yergeau. 2000. (See <a href="http://www.ietf.org/rfc/rfc2781.txt">http://www.ietf.org/rfc/rfc2781.txt</a>.)</div></dd> 2123<dt class="label"><span class="diff-add"><a name="ISO639"></a>ISO 639</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E38">[E38]</a> 2124(International Organization for Standardization). <cite>ISO 639:1988 (E). 2125Code for the representation of names of languages.</cite> [Geneva]: International 2126Organization for Standardization, 1988.</div></dd> 2127<dt class="label"><span class="diff-add"><a name="ISO3166"></a>ISO 3166</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E38">[E38]</a> 2128(International Organization for Standardization). <cite>ISO 3166-1:1997 2129(E). Codes for the representation of names of countries and their subdivisions -- 2130Part 1: Country codes</cite> [Geneva]: International Organization for 2131Standardization, 1997.</div></dd> 2132<dt class="label"><a name="ISO8879"></a>ISO 8879</dt><dd>ISO (International Organization for Standardization). <cite>ISO 21338879:1986(E). Information processing -- Text and Office Systems -- 2134Standard Generalized Markup Language (SGML).</cite> First edition -- 21351986-10-15. [Geneva]: International Organization for Standardization, 1986. </dd> 2136<dt class="label"><a name="ISO10744"></a>ISO/IEC 10744</dt><dd>ISO (International Organization for 2137Standardization). <cite>ISO/IEC 10744-1992 (E). Information technology -- 2138Hypermedia/Time-based Structuring Language (HyTime). </cite> [Geneva]: 2139International Organization for Standardization, 1992. <em>Extended Facilities 2140Annexe.</em> [Geneva]: International Organization for Standardization, 1996. </dd> 2141<dt class="label"><span class="diff-add"><a name="websgml"></a>WEBSGML</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E43">[E43]</a>ISO 2142(International Organization for Standardization). <cite>ISO 8879:1986 2143TC2. Information technology -- Document Description and Processing Languages. </cite> 2144[Geneva]: International Organization for Standardization, 1998. (See <a href="http://www.sgmlsource.com/8879rev/n0029.htm">http://www.sgmlsource.com/8879rev/n0029.htm</a>.)</div></dd> 2145<dt class="label"><span class="diff-add"><a name="xml-names"></a>XML Names</span></dt><dd><div class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E98">[E98]</a>Tim Bray, 2146Dave Hollander, and Andrew Layman, editors. <cite>Namespaces in XML</cite>. 2147Textuality, Hewlett-Packard, and Microsoft. World Wide Web Consortium, 1999. (See <a href="http://www.w3.org/TR/REC-xml-names/">http://www.w3.org/TR/REC-xml-names/</a>.)</div></dd> 2148</dl></div> 2149</div> 2150<div class="div1"> 2151 2152<h2><a name="CharClasses"></a>B Character Classes</h2> 2153<p>Following the characteristics defined in the Unicode standard, characters 2154are classed as base characters (among others, these contain the alphabetic 2155characters of the Latin alphabet<span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E84">[E84]</a>, without 2156diacritics</span>), ideographic characters, and combining characters (among 2157others, this class contains most diacritics)<span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E30">[E30]</a>; these classes 2158combine to form the class of letters.</span> Digits and extenders are also 2159distinguished.</p> 2160 2161<h5>Characters</h5><table class="scrap" summary="Scrap"><tbody> 2162<tr valign="baseline"><td><a name="NT-Letter"></a>[84]���</td><td><code>Letter</code></td><td>���::=���</td><td><code><a href="#NT-BaseChar">BaseChar</a> | <a href="#NT-Ideographic">Ideographic</a></code></td><xsltdebug></xsltdebug></tr> 2163<tr valign="baseline"><td><a name="NT-BaseChar"></a>[85]���</td><td><code>BaseChar</code></td><td>���::=���</td><td><code>[#x0041-#x005A] |�[#x0061-#x007A] |�[#x00C0-#x00D6] 2164|�[#x00D8-#x00F6] |�[#x00F8-#x00FF] |�[#x0100-#x0131] |�[#x0134-#x013E] 2165|�[#x0141-#x0148] |�[#x014A-#x017E] |�[#x0180-#x01C3] |�[#x01CD-#x01F0] 2166|�[#x01F4-#x01F5] |�[#x01FA-#x0217] |�[#x0250-#x02A8] |�[#x02BB-#x02C1] 2167|�#x0386 |�[#x0388-#x038A] |�#x038C |�[#x038E-#x03A1] 2168|�[#x03A3-#x03CE] |�[#x03D0-#x03D6] |�#x03DA |�#x03DC 2169|�#x03DE |�#x03E0 |�[#x03E2-#x03F3] |�[#x0401-#x040C] 2170|�[#x040E-#x044F] |�[#x0451-#x045C] |�[#x045E-#x0481] |�[#x0490-#x04C4] 2171|�[#x04C7-#x04C8] |�[#x04CB-#x04CC] |�[#x04D0-#x04EB] |�[#x04EE-#x04F5] 2172|�[#x04F8-#x04F9] |�[#x0531-#x0556] |�#x0559 |�[#x0561-#x0586] 2173|�[#x05D0-#x05EA] |�[#x05F0-#x05F2] |�[#x0621-#x063A] |�[#x0641-#x064A] 2174|�[#x0671-#x06B7] |�[#x06BA-#x06BE] |�[#x06C0-#x06CE] |�[#x06D0-#x06D3] 2175|�#x06D5 |�[#x06E5-#x06E6] |�[#x0905-#x0939] |�#x093D 2176|�[#x0958-#x0961] |�[#x0985-#x098C] |�[#x098F-#x0990] |�[#x0993-#x09A8] 2177|�[#x09AA-#x09B0] |�#x09B2 |�[#x09B6-#x09B9] |�[#x09DC-#x09DD] 2178|�[#x09DF-#x09E1] |�[#x09F0-#x09F1] |�[#x0A05-#x0A0A] |�[#x0A0F-#x0A10] 2179|�[#x0A13-#x0A28] |�[#x0A2A-#x0A30] |�[#x0A32-#x0A33] |�[#x0A35-#x0A36] 2180|�[#x0A38-#x0A39] |�[#x0A59-#x0A5C] |�#x0A5E |�[#x0A72-#x0A74] 2181|�[#x0A85-#x0A8B] |�#x0A8D |�[#x0A8F-#x0A91] |�[#x0A93-#x0AA8] 2182|�[#x0AAA-#x0AB0] |�[#x0AB2-#x0AB3] |�[#x0AB5-#x0AB9] |�#x0ABD 2183|�#x0AE0 |�[#x0B05-#x0B0C] |�[#x0B0F-#x0B10] |�[#x0B13-#x0B28] 2184|�[#x0B2A-#x0B30] |�[#x0B32-#x0B33] |�[#x0B36-#x0B39] |�#x0B3D 2185|�[#x0B5C-#x0B5D] |�[#x0B5F-#x0B61] |�[#x0B85-#x0B8A] |�[#x0B8E-#x0B90] 2186|�[#x0B92-#x0B95] |�[#x0B99-#x0B9A] |�#x0B9C |�[#x0B9E-#x0B9F] 2187|�[#x0BA3-#x0BA4] |�[#x0BA8-#x0BAA] |�[#x0BAE-#x0BB5] |�[#x0BB7-#x0BB9] 2188|�[#x0C05-#x0C0C] |�[#x0C0E-#x0C10] |�[#x0C12-#x0C28] |�[#x0C2A-#x0C33] 2189|�[#x0C35-#x0C39] |�[#x0C60-#x0C61] |�[#x0C85-#x0C8C] |�[#x0C8E-#x0C90] 2190|�[#x0C92-#x0CA8] |�[#x0CAA-#x0CB3] |�[#x0CB5-#x0CB9] |�#x0CDE 2191|�[#x0CE0-#x0CE1] |�[#x0D05-#x0D0C] |�[#x0D0E-#x0D10] |�[#x0D12-#x0D28] 2192|�[#x0D2A-#x0D39] |�[#x0D60-#x0D61] |�[#x0E01-#x0E2E] |�#x0E30 2193|�[#x0E32-#x0E33] |�[#x0E40-#x0E45] |�[#x0E81-#x0E82] |�#x0E84 2194|�[#x0E87-#x0E88] |�#x0E8A |�#x0E8D |�[#x0E94-#x0E97] 2195|�[#x0E99-#x0E9F] |�[#x0EA1-#x0EA3] |�#x0EA5 |�#x0EA7 2196|�[#x0EAA-#x0EAB] |�[#x0EAD-#x0EAE] |�#x0EB0 |�[#x0EB2-#x0EB3] 2197|�#x0EBD |�[#x0EC0-#x0EC4] |�[#x0F40-#x0F47] |�[#x0F49-#x0F69] 2198|�[#x10A0-#x10C5] |�[#x10D0-#x10F6] |�#x1100 |�[#x1102-#x1103] 2199|�[#x1105-#x1107] |�#x1109 |�[#x110B-#x110C] |�[#x110E-#x1112] 2200|�#x113C |�#x113E |�#x1140 |�#x114C |�#x114E |�#x1150 2201|�[#x1154-#x1155] |�#x1159 |�[#x115F-#x1161] |�#x1163 2202|�#x1165 |�#x1167 |�#x1169 |�[#x116D-#x116E] |�[#x1172-#x1173] 2203|�#x1175 |�#x119E |�#x11A8 |�#x11AB |�[#x11AE-#x11AF] 2204|�[#x11B7-#x11B8] |�#x11BA |�[#x11BC-#x11C2] |�#x11EB 2205|�#x11F0 |�#x11F9 |�[#x1E00-#x1E9B] |�[#x1EA0-#x1EF9] 2206|�[#x1F00-#x1F15] |�[#x1F18-#x1F1D] |�[#x1F20-#x1F45] |�[#x1F48-#x1F4D] 2207|�[#x1F50-#x1F57] |�#x1F59 |�#x1F5B |�#x1F5D |�[#x1F5F-#x1F7D] 2208|�[#x1F80-#x1FB4] |�[#x1FB6-#x1FBC] |�#x1FBE |�[#x1FC2-#x1FC4] 2209|�[#x1FC6-#x1FCC] |�[#x1FD0-#x1FD3] |�[#x1FD6-#x1FDB] |�[#x1FE0-#x1FEC] 2210|�[#x1FF2-#x1FF4] |�[#x1FF6-#x1FFC] |�#x2126 |�[#x212A-#x212B] 2211|�#x212E |�[#x2180-#x2182] |�[#x3041-#x3094] |�[#x30A1-#x30FA] 2212|�[#x3105-#x312C] |�[#xAC00-#xD7A3] </code></td><xsltdebug></xsltdebug></tr> 2213<tr valign="baseline"><td><a name="NT-Ideographic"></a>[86]���</td><td><code>Ideographic</code></td><td>���::=���</td><td><code>[#x4E00-#x9FA5] |�#x3007 |�[#x3021-#x3029] </code></td><xsltdebug></xsltdebug></tr> 2214<tr valign="baseline"><td><a name="NT-CombiningChar"></a>[87]���</td><td><code>CombiningChar</code></td><td>���::=���</td><td><code>[#x0300-#x0345] |�[#x0360-#x0361] |�[#x0483-#x0486] 2215|�[#x0591-#x05A1] |�[#x05A3-#x05B9] |�[#x05BB-#x05BD] |�#x05BF 2216|�[#x05C1-#x05C2] |�#x05C4 |�[#x064B-#x0652] |�#x0670 2217|�[#x06D6-#x06DC] |�[#x06DD-#x06DF] |�[#x06E0-#x06E4] |�[#x06E7-#x06E8] 2218|�[#x06EA-#x06ED] |�[#x0901-#x0903] |�#x093C |�[#x093E-#x094C] 2219|�#x094D |�[#x0951-#x0954] |�[#x0962-#x0963] |�[#x0981-#x0983] 2220|�#x09BC |�#x09BE |�#x09BF |�[#x09C0-#x09C4] |�[#x09C7-#x09C8] 2221|�[#x09CB-#x09CD] |�#x09D7 |�[#x09E2-#x09E3] |�#x0A02 2222|�#x0A3C |�#x0A3E |�#x0A3F |�[#x0A40-#x0A42] |�[#x0A47-#x0A48] 2223|�[#x0A4B-#x0A4D] |�[#x0A70-#x0A71] |�[#x0A81-#x0A83] |�#x0ABC 2224|�[#x0ABE-#x0AC5] |�[#x0AC7-#x0AC9] |�[#x0ACB-#x0ACD] |�[#x0B01-#x0B03] 2225|�#x0B3C |�[#x0B3E-#x0B43] |�[#x0B47-#x0B48] |�[#x0B4B-#x0B4D] 2226|�[#x0B56-#x0B57] |�[#x0B82-#x0B83] |�[#x0BBE-#x0BC2] |�[#x0BC6-#x0BC8] 2227|�[#x0BCA-#x0BCD] |�#x0BD7 |�[#x0C01-#x0C03] |�[#x0C3E-#x0C44] 2228|�[#x0C46-#x0C48] |�[#x0C4A-#x0C4D] |�[#x0C55-#x0C56] |�[#x0C82-#x0C83] 2229|�[#x0CBE-#x0CC4] |�[#x0CC6-#x0CC8] |�[#x0CCA-#x0CCD] |�[#x0CD5-#x0CD6] 2230|�[#x0D02-#x0D03] |�[#x0D3E-#x0D43] |�[#x0D46-#x0D48] |�[#x0D4A-#x0D4D] 2231|�#x0D57 |�#x0E31 |�[#x0E34-#x0E3A] |�[#x0E47-#x0E4E] 2232|�#x0EB1 |�[#x0EB4-#x0EB9] |�[#x0EBB-#x0EBC] |�[#x0EC8-#x0ECD] 2233|�[#x0F18-#x0F19] |�#x0F35 |�#x0F37 |�#x0F39 |�#x0F3E 2234|�#x0F3F |�[#x0F71-#x0F84] |�[#x0F86-#x0F8B] |�[#x0F90-#x0F95] 2235|�#x0F97 |�[#x0F99-#x0FAD] |�[#x0FB1-#x0FB7] |�#x0FB9 2236|�[#x20D0-#x20DC] |�#x20E1 |�[#x302A-#x302F] |�#x3099 2237|�#x309A </code></td><xsltdebug></xsltdebug></tr> 2238<tr valign="baseline"><td><a name="NT-Digit"></a>[88]���</td><td><code>Digit</code></td><td>���::=���</td><td><code>[#x0030-#x0039] |�[#x0660-#x0669] |�[#x06F0-#x06F9] 2239|�[#x0966-#x096F] |�[#x09E6-#x09EF] |�[#x0A66-#x0A6F] |�[#x0AE6-#x0AEF] 2240|�[#x0B66-#x0B6F] |�[#x0BE7-#x0BEF] |�[#x0C66-#x0C6F] |�[#x0CE6-#x0CEF] 2241|�[#x0D66-#x0D6F] |�[#x0E50-#x0E59] |�[#x0ED0-#x0ED9] |�[#x0F20-#x0F29] </code></td><xsltdebug></xsltdebug></tr> 2242<tr valign="baseline"><td><a name="NT-Extender"></a>[89]���</td><td><code>Extender</code></td><td>���::=���</td><td><code>#x00B7 |�#x02D0 |�#x02D1 |�#x0387 |�#x0640 2243|�#x0E46 |�#x0EC6 |�#x3005 |�[#x3031-#x3035] |�[#x309D-#x309E] 2244|�[#x30FC-#x30FE] </code></td><xsltdebug></xsltdebug></tr> 2245</tbody></table> 2246<p>The character classes defined here can be derived from the Unicode <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</a>2.0</span> 2247character database as follows:</p> 2248<ul> 2249<li><p>Name start characters must have one of the categories Ll, Lu, Lo, 2250Lt, Nl.</p></li> 2251<li><p>Name characters other than Name-start characters must have one of 2252the categories Mc, Me, Mn, Lm, or Nd.</p></li> 2253<li><p>Characters in the compatibility area (i.e. with character code greater 2254than #xF900 and less than #xFFFE) are not allowed in XML names.</p></li> 2255<li><p>Characters which have a font or compatibility decomposition (i.e. 2256those with a "compatibility formatting tag" in field 5 of the 2257database -- marked by field 5 beginning with a "<") are not 2258allowed.</p></li> 2259<li><p>The following characters are treated as name-start characters rather 2260than name characters, because the property file classifies them as Alphabetic: 2261[#x02BB-#x02C1], #x0559, #x06E5, #x06E6.</p></li> 2262<li><p>Characters #x20DD-#x20E0 are excluded (in accordance with Unicode <span class="diff-add"><a href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</a>2.0</span>, 2263section 5.14).</p></li> 2264<li><p>Character #x00B7 is classified as an extender, because the property 2265list so identifies it.</p></li> 2266<li><p>Character #x0387 is added as a name character, because #x00B7 is 2267its canonical equivalent.</p></li> 2268<li><p>Characters ':' and '_' are allowed as name-start characters.</p> 2269</li> 2270<li><p>Characters '-' and '.' are allowed as name characters.</p></li> 2271</ul> 2272</div> 2273<div class="div1"> 2274 2275<h2><a name="sec-xml-and-sgml"></a>C XML and SGML (Non-Normative)</h2> 2276<p><span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E43">[E43]</a>XML 2277is designed to be a subset of SGML, in that every XML document should also 2278be a conforming SGML document.</span> For a detailed comparison of the additional 2279restrictions that XML places on documents beyond those of SGML, see <a href="#Clark">[Clark]</a>.</p> 2280</div> 2281<div class="div1"> 2282 2283<h2><a name="sec-entexpand"></a>D Expansion of Entity and Character References (Non-Normative)</h2> 2284<p>This appendix contains some examples illustrating the sequence of entity- 2285and character-reference recognition and expansion, as specified in <a href="#entproc"><b>4.4 XML Processor Treatment of Entities and References</b></a>.</p> 2286<p>If the DTD contains the declaration</p> 2287<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY example "<p>An ampersand (&#38;#38;) may be escaped 2288numerically (&#38;#38;#38;) or with a general entity 2289(&amp;amp;).</p>" ></pre></td></tr></table> 2290<p>then the XML processor will recognize the character references when it 2291parses the entity declaration, and resolve them before storing the following 2292string as the value of the entity "<code>example</code>":</p> 2293<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><p>An ampersand (&#38;) may be escaped 2294numerically (&#38;#38;) or with a general entity 2295(&amp;amp;).</p></pre></td></tr></table> 2296<p>A reference in the document to "<code>&example;</code>" 2297will cause the text to be reparsed, at which time the start- and end-tags 2298of the <code>p</code> element will be recognized and the three references will 2299be recognized and expanded, resulting in a <code>p</code> element with the following 2300content (all data, no delimiters or markup):</p> 2301<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>An ampersand (&) may be escaped 2302numerically (&#38;) or with a general entity 2303(&amp;).</pre></td></tr></table> 2304<p>A more complex example will illustrate the rules and their effects fully. 2305In the following example, the line numbers are solely for reference.</p> 2306<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>1 <?xml version='1.0'?> 23072 <!DOCTYPE test [ 23083 <!ELEMENT test (#PCDATA) > 23094 <!ENTITY % xx '&#37;zz;'> 23105 <!ENTITY % zz '&#60;!ENTITY tricky "error-prone" >' > 23116 %xx; 23127 ]> 23138 <test>This sample shows a &tricky; method.</test></pre></td></tr></table> 2314<p>This produces the following:</p> 2315<ul> 2316<li><p>in line 4, the reference to character 37 is expanded immediately, 2317and the parameter entity "<code>xx</code>" is stored in the symbol 2318table with the value "<code>%zz;</code>". Since the replacement 2319text is not rescanned, the reference to parameter entity "<code>zz</code>" 2320is not recognized. (And it would be an error if it were, since "<code>zz</code>" 2321is not yet declared.)</p></li> 2322<li><p>in line 5, the character reference "<code>&#60;</code>" 2323is expanded immediately and the parameter entity "<code>zz</code>" 2324is stored with the replacement text "<code><!ENTITY tricky "error-prone" 2325></code>", which is a well-formed entity declaration.</p></li> 2326<li><p>in line 6, the reference to "<code>xx</code>" is recognized, 2327and the replacement text of "<code>xx</code>" (namely "<code>%zz;</code>") 2328is parsed. The reference to "<code>zz</code>" is recognized in 2329its turn, and its replacement text ("<code><!ENTITY tricky "error-prone" 2330></code>") is parsed. The general entity "<code>tricky</code>" 2331has now been declared, with the replacement text "<code>error-prone</code>".</p> 2332</li> 2333<li><p>in line 8, the reference to the general entity "<code>tricky</code>" 2334is recognized, and it is expanded, so the full content of the <code>test</code> 2335element is the self-describing (and ungrammatical) string <em>This sample 2336shows a error-prone method.</em></p></li> 2337</ul> 2338</div> 2339<div class="div1"> 2340 2341<h2><a name="determinism"></a>E Deterministic Content Models (Non-Normative)</h2> 2342<p><span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E102">[E102]</a>As 2343noted in <a href="#sec-element-content"><b>3.2.1 Element Content</b></a>, it is required that content 2344models in element type declarations be deterministic. This requirement is <a title="For Compatibility" href="#dt-compat">for compatibility</a> with SGML (which calls deterministic 2345content models "unambiguous");</span> XML processors built 2346using SGML systems may flag non-deterministic content models as errors.</p> 2347<p>For example, the content model <code>((b, c) | (b, d))</code> is non-deterministic, 2348because given an initial <code>b</code> the <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E95">[E95]</a>XML processor</span> 2349cannot know which <code>b</code> in the model is being matched without looking 2350ahead to see which element follows the <code>b</code>. In this case, the two references 2351to <code>b</code> can be collapsed into a single reference, making the model read <code>(b, 2352(c | d))</code>. An initial <code>b</code> now clearly matches only a single name 2353in the content model. The <span class="diff-chg"><a href="http://www.w3.org/XML/xml-19980210-errata#E95">[E95]</a>processor</span> doesn't need to look ahead to see what follows; either <code>c</code> or <code>d</code> 2354would be accepted.</p> 2355<p>More formally: a finite state automaton may be constructed from the content 2356model using the standard algorithms, e.g. algorithm 3.5 in section 3.9 of 2357Aho, Sethi, and Ullman <a href="#Aho">[Aho/Ullman]</a>. In many such algorithms, a follow 2358set is constructed for each position in the regular expression (i.e., each 2359leaf node in the syntax tree for the regular expression); if any position 2360has a follow set in which more than one following position is labeled with 2361the same element type name, then the content model is in error and may be 2362reported as an error.</p> 2363<p>Algorithms exist which allow many but not all non-deterministic content 2364models to be reduced automatically to equivalent deterministic models; see 2365Br�ggemann-Klein 1991 <a href="#ABK">[Br�ggemann-Klein]</a>.</p> 2366</div> 2367<div class="div1"> 2368 2369<h2><a name="sec-guessing"></a>F <a href="http://www.w3.org/XML/xml-19980210-errata#E105">[E105]</a><a href="http://www.w3.org/XML/xml-19980210-errata#E48">[E48]</a>Autodetection 2370of Character Encodings (Non-Normative)</h2> 2371<p>The XML encoding declaration functions as an internal label on each entity, 2372indicating which character encoding is in use. Before an XML processor can 2373read the internal label, however, it apparently has to know what character 2374encoding is in use--which is what the internal label is trying to indicate. 2375In the general case, this is a hopeless situation. It is not entirely hopeless 2376in XML, however, because XML limits the general case in two ways: each implementation 2377is assumed to support only a finite set of character encodings, and the XML 2378encoding declaration is restricted in position and content in order to make 2379it feasible to autodetect the character encoding in use in each entity in 2380normal cases. Also, in many cases other sources of information are available 2381in addition to the XML data stream itself. Two cases may be distinguished, 2382depending on whether the XML entity is presented to the processor without, 2383or with, any accompanying (external) information. We consider the first case 2384first.</p> 2385<div class="div2"> 2386<div class="diff-add"> 2387<h3><a name="sec-guessing-no-ext-info"></a>F.1 Detection Without External Encoding Information</h3></div> 2388<p>Because each XML entity <span class="diff-add">not accompanied by external 2389encoding information and </span>not in UTF-8 or UTF-16 <span class="diff-chg">encoding</span> <em>must</em> 2390begin with an XML encoding declaration, in which the first characters must 2391be '<code><?xml</code>', any conforming processor can detect, after two 2392to four octets of input, which of the following cases apply. In reading this 2393list, it may help to know that in UCS-4, '<' is "<code>#x0000003C</code>" 2394and '?' is "<code>#x0000003F</code>", and the Byte Order Mark 2395required of UTF-16 data streams is "<code>#xFEFF</code>". <span class="diff-add">The notation <var>##</var> is used to denote any byte value except <span class="diff-chg">that two consecutive <var>##</var>s cannot be both 00</span>.</span></p> 2396<div class="diff-add"><p>With a Byte Order Mark:</p></div> 2397<div class="diff-add"><table border="1" frame="border"><tbody><tr><td rowspan="1" colspan="1"><code>00 00 FE 2398FF</code></td><td rowspan="1" colspan="1">UCS-4, big-endian machine (1234 order)</td></tr><tr><td rowspan="1" colspan="1"><code>FF 2399FE 00 00</code></td><td rowspan="1" colspan="1">UCS-4, little-endian machine (4321 order)</td></tr> 2400<tr><td rowspan="1" colspan="1"><code>00 00 FF FE</code></td><td rowspan="1" colspan="1">UCS-4, unusual octet order (2143)</td> 2401</tr><tr><td rowspan="1" colspan="1"><code>FE FF 00 00</code></td><td rowspan="1" colspan="1">UCS-4, unusual octet order (3412)</td> 2402</tr><tr><td rowspan="1" colspan="1"><code>FE FF ## ##</code></td><td rowspan="1" colspan="1">UTF-16, big-endian</td></tr> 2403<tr><td rowspan="1" colspan="1"><code>FF FE ## ##</code></td><td rowspan="1" colspan="1">UTF-16, little-endian</td></tr><tr> 2404<td rowspan="1" colspan="1"><code>EF BB BF</code></td><td rowspan="1" colspan="1">UTF-8</td></tr></tbody></table></div> 2405<div class="diff-add"><p>Without a Byte Order Mark:</p></div> 2406<div class="diff-add"><table border="1" frame="border"><tbody><tr><td rowspan="1" colspan="1"><code>00�00�00�3C</code></td> 2407<td rowspan="4" colspan="1">UCS-4 or other encoding with a 32-bit code unit and ASCII 2408characters encoded as ASCII values, in respectively big-endian (1234), little-endian 2409(4321) and two unusual byte orders (2143 and 3412). The encoding declaration 2410must be read to determine which of UCS-4 or other supported 32-bit encodings 2411applies.</td></tr><tr><td rowspan="1" colspan="1"><code>3C 00 00 00</code></td> 2412 2413</tr><tr><td rowspan="1" colspan="1"><code>00 00 3C 00</code></td> 2414 2415</tr><tr><td rowspan="1" colspan="1"><code>00 3C 00 00</code></td> 2416 2417</tr><tr><td rowspan="1" colspan="1"><code>00 3C 00 3F</code></td><td rowspan="1" colspan="1">UTF-16BE or big-endian ISO-10646-UCS-2 2418or other encoding with a 16-bit code unit in big-endian order and ASCII characters 2419encoded as ASCII values (the encoding declaration must be read to determine 2420which)</td></tr><tr><td rowspan="1" colspan="1"><code>3C 00 3F 00</code></td><td rowspan="1" colspan="1">UTF-16LE or little-endian 2421ISO-10646-UCS-2 or other encoding with a 16-bit code unit in little-endian 2422order and ASCII characters encoded as ASCII values (the encoding declaration 2423must be read to determine which)</td></tr><tr><td rowspan="1" colspan="1"><code>3C 3F 78 6D</code></td> 2424<td rowspan="1" colspan="1">UTF-8, ISO 646, ASCII, some part of ISO 8859, Shift-JIS, EUC, or any other 24257-bit, 8-bit, or mixed-width encoding which ensures that the characters of 2426ASCII have their normal positions, width, and values; the actual encoding 2427declaration must be read to detect which of these applies, but since all of 2428these encodings use the same bit patterns for the relevant ASCII characters, 2429the encoding declaration itself may be read reliably</td></tr><tr><td rowspan="1" colspan="1"><code>4C 24306F A7 94</code></td><td rowspan="1" colspan="1">EBCDIC (in some flavor; the full encoding declaration 2431must be read to tell which code page is in use)</td></tr><tr><td rowspan="1" colspan="1">Other</td> 2432<td rowspan="1" colspan="1">UTF-8 without an encoding declaration, or else the data stream is mislabeled 2433(lacking a required encoding declaration), corrupt, fragmentary, or enclosed 2434in a wrapper of some kind</td></tr></tbody></table></div> 2435<div class="diff-add"><div class="note"><p class="prefix"><b>Note:</b></p> 2436<p>In cases above which do not require reading the encoding declaration to 2437determine the encoding, section 4.3.3 still requires that the encoding declaration, 2438if present, be read and that the encoding name be checked to match the actual 2439encoding of the entity. Also, it is possible that new character encodings 2440will be invented that will make it necessary to use the encoding declaration 2441to determine the encoding, in cases where this is not required at present.</p> 2442</div></div> 2443<p>This level of autodetection is enough to read the XML encoding declaration 2444and parse the character-encoding identifier, which is still necessary to distinguish 2445the individual members of each family of encodings (e.g. to tell UTF-8 from 24468859, and the parts of 8859 from each other, or to distinguish the specific 2447EBCDIC code page in use, and so on).</p> 2448<p>Because the contents of the encoding declaration are restricted to <span class="diff-chg">characters from the ASCII repertoire (however encoded)</span>, 2449a processor can reliably read the entire encoding declaration as soon as it 2450has detected which family of encodings is in use. Since in practice, all widely 2451used character encodings fall into one of the categories above, the XML encoding 2452declaration allows reasonably reliable in-band labeling of character encodings, 2453even when external sources of information at the operating-system or transport-protocol 2454level are unreliable. <span class="diff-del">Note that since external parsed entities 2455in UTF-16 may begin with any character, this autodetection does not always 2456work. Also, </span><span class="diff-add">Character encodings such as UTF-7 2457that make overloaded usage of ASCII-valued bytes may fail to be reliably detected.</span></p> 2458<p>Once the processor has detected the character encoding in use, it can act 2459appropriately, whether by invoking a separate input routine for each case, 2460or by calling the proper conversion function on each character of input.</p> 2461<p>Like any self-labeling system, the XML encoding declaration will not work 2462if any software changes the entity's character set or encoding without updating 2463the encoding declaration. Implementors of character-encoding routines should 2464be careful to ensure the accuracy of the internal and external information 2465used to label the entity.</p> 2466</div> 2467<div class="div2"> 2468<div class="diff-add"> 2469<h3><a name="sec-guessing-with-ext-info"></a>F.2 Priorities in the Presence of External Encoding Information</h3></div> 2470<p>The second possible case occurs when the XML entity is accompanied by encoding 2471information, as in some file systems and some network protocols. When multiple 2472sources of information are available, their relative priority and the preferred 2473method of handling conflict should be specified as part of the higher-level 2474protocol used to deliver XML. <span class="diff-chg">In particular, please refer 2475to <a href="#rfc2376">[IETF RFC 2376]</a> or its successor, which defines the <code>text/xml</code> 2476and <code>application/xml</code> MIME types and provides some useful guidance. 2477In the interests of interoperability, however, the following rule is recommended.</span></p> 2478<ul> 2479<li><p>If an XML entity is in a file, the Byte-Order Mark and encoding declaration <span class="diff-del">PI </span>are used (if present) to determine the character encoding.<span class="diff-del"><a href="http://www.w3.org/XML/xml-19980210-errata#E74">[E74]</a> 2480All other heuristics and sources of information are solely for error recovery.</span></p> 2481</li> 2482</ul> 2483<div class="diff-del"><ul> 2484<li><p>If an XML entity is delivered with a MIME type of text/xml, then 2485the <code>charset</code> parameter on the MIME type determines the character 2486encoding method; all other heuristics and sources of information are solely 2487for error recovery.</p></li> 2488<li><p>If an XML entity is delivered with a MIME type of application/xml, 2489then the Byte-Order Mark and encoding-declaration PI are used (if present) 2490to determine the character encoding. All other heuristics and sources of information 2491are solely for error recovery.</p></li> 2492</ul></div> 2493<div class="diff-del"><p>These rules apply only in the absence of protocol-level documentation; 2494in particular, when the MIME types text/xml and application/xml are defined, 2495the recommendations of the relevant RFC will supersede these rules.</p></div> 2496</div> 2497</div> 2498<div class="div1"> 2499 2500<h2><a name="sec-xml-wg"></a>G W3C XML Working Group (Non-Normative)</h2> 2501<p>This specification was prepared and approved for publication by the W3C 2502XML Working Group (WG). WG approval of this specification does not necessarily 2503imply that all WG members voted for its approval. The current and former members 2504of the XML WG are:</p> 2505<ul> 2506<li>Jon Bosak, Sun (<i>Chair</i>) 2507</li> 2508<li>James Clark (<i>Technical Lead</i>) </li> 2509<li>Tim Bray, Textuality and Netscape 2510 (<i>XML Co-editor</i>) </li> 2511<li>Jean Paoli, Microsoft (<i>XML 2512Co-editor</i>) </li> 2513<li>C. M. Sperberg-McQueen, U. of Ill. 2514 (<i>XML Co-editor</i>) </li> 2515<li>Dan Connolly, W3C (<i>W3C Liaison</i>) 2516</li> 2517<li>Paula Angerstein, Texcel</li> 2518<li>Steve DeRose, INSO</li> 2519<li>Dave Hollander, HP</li> 2520<li>Eliot Kimber, ISOGEN</li> 2521<li>Eve Maler, ArborText</li> 2522<li>Tom Magliery, NCSA</li> 2523<li>Murray Maloney<span class="diff-chg">, SoftQuad, Grif 2524SA, Muzmo and Veo Systems</span></li> 2525<li><span class="diff-chg">MURATA Makoto (FAMILY Given)</span>, Fuji 2526Xerox Information Systems</li> 2527<li>Joel Nava, Adobe</li> 2528<li>Conleth O'Connell, Vignette 2529</li> 2530<li>Peter Sharpe, SoftQuad</li> 2531<li>John Tigue, DataChannel</li> 2532</ul> 2533</div> 2534<div class="diff-add"><div class="div1"> 2535 2536<h2><a name="sec-core-wg"></a>H W3C XML Core Group (Non-Normative)</h2> 2537<p>The second edition of this specification was prepared by the W3C XML Core 2538Working Group (WG). The members of the WG at the time of publication of this 2539edition were:</p> 2540<ul> 2541<li>Paula Angerstein, Vignette</li> 2542<li>Daniel Austin, Ask Jeeves</li> 2543<li>Tim Boland</li> 2544<li>Allen Brown, Microsoft</li> 2545<li>Dan Connolly, W3C (<i>Staff 2546Contact</i>) </li> 2547<li>John Cowan, Reuters Limited 2548</li> 2549<li>John Evdemon, XMLSolutions Corporation 2550</li> 2551<li>Paul Grosso, Arbortext (<i>Co-Chair</i>) 2552</li> 2553<li>Arnaud Le Hors, IBM (<i>Co-Chair</i>) 2554</li> 2555<li>Eve Maler, Sun Microsystems 2556 (<i>Second Edition Editor</i>) </li> 2557<li>Jonathan Marsh, Microsoft</li> 2558<li>MURATA Makoto (FAMILY Given), IBM 2559</li> 2560<li>Mark Needleman, Data Research Associates 2561</li> 2562<li>David Orchard, Jamcracker</li> 2563<li>Lew Shannon, NCR</li> 2564<li>Richard Tobin, University of Edinburgh 2565</li> 2566<li>Daniel Veillard, W3C</li> 2567<li>Dan Vint, Lexica</li> 2568<li>Norman Walsh, Sun Microsystems 2569</li> 2570<li>Fran�ois Yergeau, Alis Technologies 2571 (<i>Errata List Editor</i>) </li> 2572<li>Kongyi Zhou, Oracle</li> 2573</ul> 2574</div></div> 2575<div class="diff-add"><div class="div1"> 2576 2577<h2><a name="id2683713"></a>I Production Notes (Non-Normative)</h2> 2578<p>This Second Edition was encoded in the <a href="http://www.w3.org/XML/1998/06/xmlspec-v21.dtd">XMLspec 2579DTD</a> (which has <a href="http://www.w3.org/XML/1998/06/xmlspec-report-v21.htm">documentation</a> 2580available). The HTML versions were produced with a combination of the <a href="http://www.w3.org/XML/1998/06/xmlspec.xsl">xmlspec.xsl</a>, <a href="http://www.w3.org/XML/1998/06/diffspec.xsl">diffspec.xsl</a>, 2581and <a href="http://www.w3.org/XML/1998/06/REC-xml-2e.xsl">REC-xml-2e.xsl</a> 2582XSLT stylesheets. The PDF version was produced with the <a href="http://www.tdb.uu.se/~jan/html2ps.html">html2ps</a> 2583facility and a distiller program.</p> 2584</div></div> 2585</div></body></html> 2586
