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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<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)</title><style type="text/css">
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<h1>Extensible Markup Language (XML) 1.0 (Second Edition)</h1>
<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>
(<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
review 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>
<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>
<dd>Tim Bray, Textuality and Netscape <a href="mailto:tbray@textuality.com"><tbray@textuality.com></a></dd>
<dd>Jean Paoli, Microsoft <a href="mailto:jeanpa@microsoft.com"><jeanpa@microsoft.com></a></dd>
<dd>C. M. Sperberg-McQueen, University
of Illinois at Chicago and Text Encoding Initiative <a href="mailto:cmsmcq@uic.edu"><cmsmcq@uic.edu></a></dd>
<dd>Eve Maler, Sun Microsystems,
Inc. <a href="mailto:elm@east.sun.com"><eve.maler@east.sun.com></a> - Second Edition</dd>
</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">
<h2><a name="abstract">Abstract</a></h2>
<p>The Extensible Markup Language (XML) is a subset of SGML that is completely
described in this document. Its goal is to enable generic SGML to be served,
received, and processed on the Web in the way that is now possible with HTML.
XML has been designed for ease of implementation and for interoperability
with both SGML and HTML.</p>
</div><div id="status">
<h2><a name="status">Status of this Document</a></h2>
<p>This document has been reviewed by W3C Members and other interested parties
and has been endorsed by the Director as a W3C Recommendation. It is a stable
document and may be used as reference material or cited as a normative reference
from another document. W3C's role in making the Recommendation is to draw
attention to the specification and to promote its widespread deployment. This
enhances the functionality and interoperability of the Web.</p>
<p>This document specifies a syntax created by subsetting an existing, widely
used international text processing standard (Standard Generalized Markup Language,
ISO 8879:1986(E) as amended and corrected) for use on the World Wide Web.
It 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>.
The English version of this specification is the only normative version. However,
for translations of this document, see <a href="http://www.w3.org/XML/#trans">http://www.w3.org/XML/#trans</a>. A
list of current W3C Recommendations and other technical documents can be found
at <a href="http://www.w3.org/TR/">http://www.w3.org/TR</a>.</p>
<p>This second edition is <em>not</em> a new version of XML (first published 10 February 1998);
it merely incorporates the changes dictated by the first-edition errata (available
at <a href="http://www.w3.org/XML/xml-19980210-errata">http://www.w3.org/XML/xml-19980210-errata</a>)
as a convenience to readers. The errata list for this second edition is available
at <a href="http://www.w3.org/XML/xml-V10-2e-errata">http://www.w3.org/XML/xml-V10-2e-errata</a>.</p>
<p>Please report errors in this document to <a href="mailto:xml-editor@w3.org">xml-editor@w3.org</a>; <a href="http://lists.w3.org/Archives/Public/xml-editor">archives</a> are available.</p>
<div class="note"><p class="prefix"><b>Note:</b></p>
<p>C. M. Sperberg-McQueen's affiliation has changed since the publication
of the first edition. He is now at the World Wide Web Consortium, and can
be contacted at <a href="mailto:cmsmcq@w3.org">cmsmcq@w3.org</a>.</p>
</div>
</div>
<div class="toc">
<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
Normalization</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>
<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
of 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">
<div class="div1">
<h2><a name="sec-intro"></a>1 Introduction</h2>
<p>Extensible Markup Language, abbreviated XML, describes a class of data
objects called <a title="XML Document" href="#dt-xml-doc">XML documents</a> and partially
describes the behavior of computer programs which process them. XML is an
application profile or restricted form of SGML, the Standard Generalized Markup
Language <a href="#ISO8879">[ISO 8879]</a>. By construction, XML documents are conforming
SGML documents.</p>
<p>XML documents are made up of storage units called <a title="Entity" href="#dt-entity">entities</a>,
which 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
data</a>, and some of which form <a title="Markup" href="#dt-markup">markup</a>.
Markup encodes a description of the document's storage layout and logical
structure. XML provides a mechanism to impose constraints on the storage layout
and logical structure.</p>
<p>[<a name="dt-xml-proc" title="XML Processor">Definition</a>: A software module called
an <b>XML processor</b> is used to read XML documents and provide access
to their content and structure.] [<a name="dt-app" title="Application">Definition</a>: It
is assumed that an XML processor is doing its work on behalf of another module,
called the <b>application</b>.] This specification describes
the required behavior of an XML processor in terms of how it must read XML
data and the information it must provide to the application.</p>
<div class="div2">
<h3><a name="sec-origin-goals"></a>1.1 Origin and Goals</h3>
<p>XML was developed by an XML Working Group (originally known as the SGML
Editorial Review Board) formed under the auspices of the World Wide Web Consortium
(W3C) in 1996. It was chaired by Jon Bosak of Sun Microsystems with the active
participation of an XML Special Interest Group (previously known as the SGML
Working Group) also organized by the W3C. The membership of the XML Working
Group is given in an appendix. Dan Connolly served as the WG's contact with
the W3C.</p>
<p>The design goals for XML are:</p>
<ol>
<li><p>XML shall be straightforwardly usable over the Internet.</p></li>
<li><p>XML shall support a wide variety of applications.</p></li>
<li><p>XML shall be compatible with SGML.</p></li>
<li><p>It shall be easy to write programs which process XML documents.</p>
</li>
<li><p>The number of optional features in XML is to be kept to the absolute
minimum, ideally zero.</p></li>
<li><p>XML documents should be human-legible and reasonably clear.</p></li>
<li><p>The XML design should be prepared quickly.</p></li>
<li><p>The design of XML shall be formal and concise.</p></li>
<li><p>XML documents shall be easy to create.</p></li>
<li><p>Terseness in XML markup is of minimal importance.</p></li>
</ol>
<p>This specification, together with associated standards (Unicode and ISO/IEC
10646 for characters, Internet RFC 1766 for language identification tags,
ISO 639 for language name codes, and ISO 3166 for country name codes), provides
all the information necessary to understand XML Version 1.0 and
construct computer programs to process it.</p>
<p>This version of the XML specification may be distributed freely, as long as
all text and legal notices remain intact.</p>
</div>
<div class="div2">
<h3><a name="sec-terminology"></a>1.2 Terminology</h3>
<p>The terminology used to describe XML documents is defined in the body of
this specification. The terms defined in the following list are used in building
those definitions and in describing the actions of an XML processor: </p><dl>
<dt class="label">may</dt>
<dd>
<p>[<a name="dt-may" title="May">Definition</a>: Conforming documents and XML processors
are permitted to but need not behave as described.]</p>
</dd>
<dt class="label">must</dt>
<dd>
<p>[<a name="dt-must" title="Must">Definition</a>: Conforming documents and XML processors
are required to behave as described; otherwise they are in error. ]</p>
</dd>
<dt class="label">error</dt>
<dd>
<p>[<a name="dt-error" title="Error">Definition</a>: A violation of the rules of this specification;
results are undefined. Conforming software may detect and report an error
and may recover from it.]</p>
</dd>
<dt class="label">fatal error</dt>
<dd>
<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.
After encountering a fatal error, the processor may continue processing the
data to search for further errors and may report such errors to the application.
In order to support correction of errors, the processor may make unprocessed
data from the document (with intermingled character data and markup) available
to the application. Once a fatal error is detected, however, the processor
must not continue normal processing (i.e., it must not continue to pass character
data and information about the document's logical structure to the application
in the normal way).]</p>
</dd>
<dt class="label">at user option</dt>
<dd>
<p>[<a name="dt-atuseroption" title="At user option">Definition</a>: Conforming software
may or must (depending on the modal verb in the sentence) behave as described;
if it does, it must provide users a means to enable or disable the behavior
described.]</p>
</dd>
<dt class="label">validity constraint</dt>
<dd>
<p>[<a name="dt-vc" title="Validity constraint">Definition</a>: A rule which applies to
all <a title="Validity" href="#dt-valid">valid</a> XML documents. Violations of validity
constraints are errors; they must, at user option, be reported by <a title="Validating Processor" href="#dt-validating">validating XML processors</a>.]</p>
</dd>
<dt class="label">well-formedness constraint</dt>
<dd>
<p>[<a name="dt-wfc" title="Well-formedness constraint">Definition</a>: A rule which applies
to all <a title="Well-Formed" href="#dt-wellformed">well-formed</a> XML documents. Violations
of well-formedness constraints are <a title="Fatal Error" href="#dt-fatal">fatal errors</a>.]</p>
</dd>
<dt class="label">match</dt>
<dd>
<p>[<a name="dt-match" title="match">Definition</a>: (Of strings or names:) Two strings
or names being compared must be identical. Characters with multiple possible
representations in ISO/IEC 10646 (e.g. characters with both precomposed and
base+diacritic forms) match only if they have the same representation in both
strings. No
case folding is performed. (Of strings and rules in the grammar:) A string
matches a grammatical production if it belongs to the language generated by
that production. (Of content and content models:) An element matches its declaration
when it conforms in the fashion described in the constraint <a href="#elementvalid"><b>[VC: Element Valid]</b></a>.]</p>
</dd>
<dt class="label">for compatibility</dt>
<dd>
<p>[<a name="dt-compat" title="For Compatibility">Definition</a>: Marks
a sentence describing a feature of XML included solely to ensure
that XML remains compatible with SGML.]</p>
</dd>
<dt class="label">for interoperability</dt>
<dd>
<p>[<a name="dt-interop" title="For interoperability">Definition</a>: Marks
a sentence describing a non-binding recommendation included to increase
the chances that XML documents can be processed by the existing installed
base of SGML processors which predate the WebSGML Adaptations Annex to ISO 8879.]</p>
</dd>
</dl><p></p>
</div>
</div>
<div class="div1">
<h2><a name="sec-documents"></a>2 Documents</h2>
<p>[<a name="dt-xml-doc" title="XML Document">Definition</a>: A data object is an <b>XML
document</b> if it is <a title="Well-Formed" href="#dt-wellformed">well-formed</a>,
as defined in this specification. A well-formed XML document may in addition
be <a title="Validity" href="#dt-valid">valid</a> if it meets certain further constraints.]</p>
<p>Each XML document has both a logical and a physical structure. Physically,
the document is composed of units called <a title="Entity" href="#dt-entity">entities</a>.
An entity may <a title="Entity Reference" href="#dt-entref">refer</a> to other entities to
cause their inclusion in the document. A document begins in a "root"
or <a title="Document Entity" href="#dt-docent">document entity</a>. Logically, the document
is composed of declarations, elements, comments, character references, and
processing instructions, all of which are indicated in the document by explicit
markup. The logical and physical structures must nest properly, as described
in <a href="#wf-entities"><b>4.3.2 Well-Formed Parsed Entities</b></a>.</p>
<div class="div2">
<h3><a name="sec-well-formed"></a>2.1 Well-Formed XML Documents</h3>
<p>[<a name="dt-wellformed" title="Well-Formed">Definition</a>: A textual object is a <b>well-formed</b>
XML document if:]</p>
<ol>
<li><p>Taken as a whole, it matches the production labeled <a href="#NT-document">document</a>.</p>
</li>
<li><p>It meets all the well-formedness constraints given in this specification.</p>
</li>
<li><p>Each of the <a title="Text Entity" href="#dt-parsedent">parsed entities</a>
which is referenced directly or indirectly within the document is <a title="Well-Formed" href="#dt-wellformed">well-formed</a>.</p></li>
</ol>
<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>
<p>Matching the <a href="#NT-document">document</a> production implies that:</p>
<ol>
<li><p>It contains one or more <a title="Element" href="#dt-element">elements</a>.</p>
</li>
<li><p>[<a name="dt-root" title="Root Element">Definition</a>: There is exactly one element,
called the <b>root</b>, or document element, no part of which appears
in the <a title="Content" href="#dt-content">content</a> of any other element.] For
all other elements, if the <a title="Start-Tag" href="#dt-stag">start-tag</a> is in
the content of another element, the <a title="End Tag" href="#dt-etag">end-tag</a>
is in the content of the same element. More simply stated, the elements,
delimited by start- and end-tags, nest properly within each other.</p></li>
</ol>
<p>[<a name="dt-parentchild" title="Parent/Child">Definition</a>: As a consequence of this,
for each non-root element <code>C</code> in the document, there is one other element <code>P</code>
in the document such that <code>C</code> is in the content of <code>P</code>, but
is not in the content of any other element that is in the content of <code>P</code>. <code>P</code>
is referred to as the <b>parent</b> of <code>C</code>, and <code>C</code> as
a <b>child</b> of <code>P</code>.]</p>
</div>
<div class="div2">
<h3><a name="charsets"></a>2.2 Characters</h3>
<p>[<a name="dt-text" title="Text">Definition</a>: A parsed entity contains <b>text</b>,
a sequence of <a title="Character" href="#dt-character">characters</a>, which may
represent markup or character data.] [<a name="dt-character" title="Character">Definition</a>: A <b>character</b>
is an atomic unit of text as specified by ISO/IEC 10646 <a href="#ISO10646">[ISO/IEC 10646]</a> (see
also <a href="#ISO10646-2000">[ISO/IEC 10646-2000]</a>). Legal characters are tab, carriage
return, line feed, and the legal characters
of Unicode and ISO/IEC 10646. The
versions of these standards cited in <a href="#sec-existing-stds"><b>A.1 Normative References</b></a> were
current at the time this document was prepared. New characters may be added
to these standards by amendments or new editions. Consequently, XML processors
must accept any character in the range specified for <a href="#NT-Char">Char</a>.
The use of "compatibility characters", as defined in section
6.8 of <a href="#Unicode">[Unicode]</a> (see
also D21 in section 3.6 of <a href="#Unicode3">[Unicode3]</a>), is discouraged.]</p>
<h5>Character Range</h5><table class="scrap" summary="Scrap"><tbody>
<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>
</tbody></table>
<p>The mechanism for encoding character code points into bit patterns may
vary from entity to entity. All XML processors must accept the UTF-8 and UTF-16
encodings of 10646; the mechanisms for signaling which of the two is in use,
or for bringing other encodings into play, are discussed later, in <a href="#charencoding"><b>4.3.3 Character Encoding in Entities</b></a>.</p>
</div>
<div class="div2">
<h3><a name="sec-common-syn"></a>2.3 Common Syntactic Constructs</h3>
<p>This section defines some symbols used widely in the grammar.</p>
<p><a href="#NT-S">S</a> (white space) consists of one or more space (#x20)
characters, carriage returns, line feeds, or tabs.</p>
<h5>White Space</h5><table class="scrap" summary="Scrap"><tbody>
<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>
</tbody></table>
<p>Characters are classified for convenience as letters, digits, or other
characters. A
letter consists of an alphabetic or syllabic base character or an ideographic
character. Full definitions of the specific characters in each class
are given in <a href="#CharClasses"><b>B Character Classes</b></a>.</p>
<p>[<a name="dt-name" title="Name">Definition</a>: A <b>Name</b> is a token beginning
with a letter or one of a few punctuation characters, and continuing with
letters, digits, hyphens, underscores, colons, or full stops, together known
as name characters.] Names beginning with the string "<code>xml</code>",
or any string which would match <code>(('X'|'x') ('M'|'m') ('L'|'l'))</code>,
are reserved for standardization in this or future versions of this specification.</p>
<div class="note"><p class="prefix"><b>Note:</b></p>
<p>The
Namespaces in XML Recommendation <a href="#xml-names">[XML Names]</a> assigns a meaning
to names containing colon characters. Therefore, authors should not use the
colon in XML names except for namespace purposes, but XML processors must
accept the colon as a name character.</p>
</div>
<p>An <a href="#NT-Nmtoken">Nmtoken</a> (name token) is any mixture of name
characters.</p>
<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>
| '.' | '-' | '_' | ':' | <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>
<p>Literal data is any quoted string not containing the quotation mark used
as a delimiter for that string. Literals are used for specifying the content
of internal entities (<a href="#NT-EntityValue">EntityValue</a>), the values
of attributes (<a href="#NT-AttValue">AttValue</a>), and external identifiers
(<a href="#NT-SystemLiteral">SystemLiteral</a>). Note that a <a href="#NT-SystemLiteral">SystemLiteral</a>
can be parsed without scanning for markup.</p>
<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>
| <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>)*
'"' </code></td><xsltdebug></xsltdebug></tr><tr valign="baseline"><td></td><td></td><td></td><td><code>| "'" ([^<&'] | <a href="#NT-Reference">Reference</a>)*
"'"</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>* '"'
| "'" (<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>
<div class="note"><p class="prefix"><b>Note:</b></p>
<p>Although
the <a href="#NT-EntityValue">EntityValue</a> production allows the definition
of an entity consisting of a single explicit <code><</code> in the literal
(e.g., <code><!ENTITY mylt "<"></code>), it is strongly advised to avoid
this practice since any reference to that entity will cause a well-formedness
error.</p>
</div>
</div>
<div class="div2">
<h3><a name="syntax"></a>2.4 Character Data and Markup</h3>
<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
references</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
type declarations</a>, <a title="Processing instruction" href="#dt-pi">processing instructions</a>, <a href="#NT-XMLDecl">XML declarations</a>, <a href="#NT-TextDecl">text declarations</a>,
and any white space that is at the top level of the document entity (that
is, outside the document element and not inside any other markup).]</p>
<p>[<a name="dt-chardata" title="Character Data">Definition</a>: All text that is not markup
constitutes the <b>character data</b> of the document.]</p>
<p>The ampersand character (&) and the left angle bracket (<) may appear
in their literal form <em>only</em> when used as markup delimiters, or
within a <a title="Comment" href="#dt-comment">comment</a>, a <a title="Processing instruction" href="#dt-pi">processing
instruction</a>, or a <a title="CDATA Section" href="#dt-cdsection">CDATA section</a>.
If they are needed elsewhere, they must be <a title="escape" href="#dt-escape">escaped</a>
using either <a title="Character Reference" href="#dt-charref">numeric character references</a>
or the strings "<code>&amp;</code>" and "<code>&lt;</code>"
respectively. The right angle bracket (>) may be represented using the string "<code>&gt;</code>",
and must, <a title="For Compatibility" href="#dt-compat">for compatibility</a>, be escaped
using "<code>&gt;</code>" or a character reference when it
appears in the string "<code>]]></code>" in content, when
that string is not marking the end of a <a title="CDATA Section" href="#dt-cdsection">CDATA
section</a>.</p>
<p>In the content of elements, character data is any string of characters
which does not contain the start-delimiter of any markup. In a CDATA section,
character data is any string of characters not including the CDATA-section-close
delimiter, "<code>]]></code>".</p>
<p>To allow attribute values to contain both single and double quotes, the
apostrophe or single-quote character (') may be represented as "<code>&apos;</code>",
and the double-quote character (") as "<code>&quot;</code>".</p>
<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>
</div>
<div class="div2">
<h3><a name="sec-comments"></a>2.5 Comments</h3>
<p>[<a name="dt-comment" title="Comment">Definition</a>: <b>Comments</b> may appear
anywhere in a document outside other <a title="Markup" href="#dt-markup">markup</a>;
in addition, they may appear within the document type declaration at places
allowed by the grammar. They are not part of the document's <a title="Character Data" href="#dt-chardata">character
data</a>; an XML processor may, but need not, make it possible for an
application to retrieve the text of comments. <a title="For Compatibility" href="#dt-compat">For
compatibility</a>, the string "<code>--</code>" (double-hyphen)
must not occur within comments.] Parameter
entity references are not recognized within comments.</p>
<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> - '-') | ('-'
(<a href="#NT-Char">Char</a> - '-')))* '-->'</code></td><xsltdebug></xsltdebug></tr></tbody></table>
<p>An example of a comment:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!-- declarations for <head> & <body> --></pre></td></tr></table>
<p>Note
that the grammar does not allow a comment ending in <code>---></code>. The
following example is <em>not</em> well-formed.</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!-- B+, B, or B---></pre></td></tr></table>
</div>
<div class="div2">
<h3><a name="sec-pi"></a>2.6 Processing Instructions</h3>
<p>[<a name="dt-pi" title="Processing instruction">Definition</a>: <b>Processing instructions</b>
(PIs) allow documents to contain instructions for applications.]</p>
<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>
(<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' |
'm') ('L' | 'l'))</code></td><xsltdebug></xsltdebug></tr></tbody></table>
<p>PIs are not part of the document's <a title="Character Data" href="#dt-chardata">character
data</a>, but must be passed through to the application. The PI begins
with a target (<a href="#NT-PITarget">PITarget</a>) used to identify the application
to which the instruction is directed. The target names "<code>XML</code>", "<code>xml</code>",
and so on are reserved for standardization in this or future versions of this
specification. The XML <a title="Notation" href="#dt-notation">Notation</a> mechanism
may be used for formal declaration of PI targets. Parameter
entity references are not recognized within processing instructions.</p>
</div>
<div class="div2">
<h3><a name="sec-cdata-sect"></a>2.7 CDATA Sections</h3>
<p>[<a name="dt-cdsection" title="CDATA Section">Definition</a>: <b>CDATA sections</b>
may occur anywhere character data may occur; they are used to escape blocks
of text containing characters which would otherwise be recognized as markup.
CDATA sections begin with the string "<code><![CDATA[</code>"
and end with the string "<code>]]></code>":]</p>
<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>*
']]>' <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>
<p>Within a CDATA section, only the <a href="#NT-CDEnd">CDEnd</a> string is
recognized as markup, so that left angle brackets and ampersands may occur
in their literal form; they need not (and cannot) be escaped using "<code>&lt;</code>"
and "<code>&amp;</code>". CDATA sections cannot nest.</p>
<p>An example of a CDATA section, in which "<code><greeting></code>"
and "<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>
<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>
</div>
<div class="div2">
<h3><a name="sec-prolog-dtd"></a>2.8 Prolog and Document Type Declaration</h3>
<p>[<a name="dt-xmldecl" title="XML Declaration">Definition</a>: XML documents should
begin with an <b>XML declaration</b> which specifies the version of
XML 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>
<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>
<p>and so is this:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><greeting>Hello, world!</greeting></pre></td></tr></table>
<p>The version number "<code>1.0</code>" should be used to indicate
conformance to this version of this specification; it is an error for a document
to use the value "<code>1.0</code>" if it does not conform to
this version of this specification. It is the intent of the XML working group
to give later versions of this specification numbers other than "<code>1.0</code>",
but this intent does not indicate a commitment to produce any future versions
of XML, nor if any are produced, to use any particular numbering scheme. Since
future versions are not ruled out, this construct is provided as a means to
allow the possibility of automatic version recognition, should it become necessary.
Processors may signal an error if they receive documents labeled with versions
they do not support.</p>
<p>The function of the markup in an XML document is to describe its storage
and logical structure and to associate attribute-value pairs with its logical
structures. XML provides a mechanism, the <a title="Document Type Declaration" href="#dt-doctype">document
type declaration</a>, to define constraints on the logical structure
and 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
document type declaration and if the document complies with the constraints
expressed in it.]</p>
<p>The document type declaration must appear before the first <a title="Element" href="#dt-element">element</a>
in the document.</p>
<h5>Prolog</h5><table class="scrap" summary="Scrap"><tbody>
<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>*
(<a href="#NT-doctypedecl">doctypedecl</a> <a href="#NT-Misc">Misc</a>*)?</code></td><xsltdebug></xsltdebug></tr>
<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>
<tr valign="baseline"><td><a name="NT-VersionInfo"></a>[24] </td><td><code>VersionInfo</code></td><td> ::= </td><td><code><a href="#NT-S">S</a> 'version' <a href="#NT-Eq">Eq</a>
("'" <a href="#NT-VersionNum">VersionNum</a> "'" | '"' <a href="#NT-VersionNum">VersionNum</a>
'"')<i>/* */</i></code></td><xsltdebug></xsltdebug></tr>
<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>
<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>
<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>
| <a href="#NT-S">S</a></code></td><xsltdebug></xsltdebug></tr>
</tbody></table>
<p>[<a name="dt-doctype" title="Document Type Declaration">Definition</a>: The XML <b>document
type declaration</b> contains or points to <a title="markup declaration" href="#dt-markupdecl">markup
declarations</a> that provide a grammar for a class of documents. This
grammar is known as a document type definition, or <b>DTD</b>. The document
type declaration can point to an external subset (a special kind of <a title="External Entity" href="#dt-extent">external entity</a>) containing markup declarations,
or can contain the markup declarations directly in an internal subset, or
can do both. The DTD for a document consists of both subsets taken together.]</p>
<p>[<a name="dt-markupdecl" title="markup declaration">Definition</a>: A <b>markup declaration</b>
is 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
declaration</a>, or a <a title="Notation Declaration" href="#dt-notdecl">notation declaration</a>.]
These declarations may be contained in whole or in part within <a title="Parameter entity" href="#dt-PE">parameter
entities</a>, as described in the well-formedness and validity constraints
below. For further
information, see <a href="#sec-physical-struct"><b>4 Physical Structures</b></a>.</p>
<h5>Document Type Definition</h5><table class="scrap" summary="Scrap"><tbody>
<tr valign="baseline"><td><a name="NT-doctypedecl"></a>[28] </td><td><code>doctypedecl</code></td><td> ::= </td><td><code>'<!DOCTYPE' <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-S">S</a>?
('[' (<a href="#NT-markupdecl">markupdecl</a> | <a href="#NT-DeclSep">DeclSep</a>)*
']' <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><a href="#ExtSubset">[WFC: External
Subset]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><i>/* */</i></td></tr>
<tr valign="baseline"><td><a name="NT-DeclSep"></a>[28a] </td><td><code>DeclSep</code></td><td> ::= </td><td><code><a href="#NT-PEReference">PEReference</a> | <a href="#NT-S">S</a></code></td><xsltdebug></xsltdebug><td><a href="#PE-between-Decls">[WFC: PE
Between Declarations]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><i>/* */</i></td></tr>
<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>
| <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>
</tbody></table>
<p>Note
that it is possible to construct a well-formed document containing a <a href="#NT-doctypedecl">doctypedecl</a>
that neither points to an external subset nor contains an internal subset.</p>
<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
entities</a>. The productions later in this specification for individual
nonterminals (<a href="#NT-elementdecl">elementdecl</a>, <a href="#NT-AttlistDecl">AttlistDecl</a>,
and so on) describe the declarations <em>after</em> all the parameter
entities have been <a title="Include" href="#dt-include">included</a>.</p>
<p>Parameter
entity references are recognized anywhere in the DTD (internal and external
subsets and external parameter entities), except in literals, processing instructions,
comments, and the contents of ignored conditional sections (see <a href="#sec-condition-sect"><b>3.4 Conditional Sections</b></a>).
They are also recognized in entity value literals. The use of parameter entities
in the internal subset is restricted as described below.</p>
<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>
in the document type declaration must match the element type of the <a title="Root Element" href="#dt-root">root element</a>.</p>
</div>
<div class="constraint"><p class="prefix"><a name="vc-PEinMarkupDecl"></a><b>Validity constraint: Proper Declaration/PE Nesting</b></p>
<p>Parameter-entity <a title="Replacement Text" href="#dt-repltext">replacement text</a>
must be properly nested with markup declarations. That is to say, if either
the first character or the last character of a markup declaration (<a href="#NT-markupdecl">markupdecl</a>
above) is contained in the replacement text for a <a title="Parameter-entity reference" href="#dt-PERef">parameter-entity
reference</a>, both must be contained in the same replacement text.</p>
</div>
<div class="constraint"><p class="prefix"><a name="wfc-PEinInternalSubset"></a><b>Well-formedness constraint: PEs in Internal Subset</b></p><p>In
the internal DTD subset, <a title="Parameter-entity reference" href="#dt-PERef">parameter-entity references</a>
can occur only where markup declarations can occur, not within markup declarations.
(This does not apply to references that occur in external parameter entities
or to the external subset.)</p>
</div>
<div class="constraint"><p class="prefix"><a name="ExtSubset"></a><b>Well-formedness constraint: External
Subset</b></p><p>The external subset, if any, must match the production for <a href="#NT-extSubset">extSubset</a>.</p>
</div>
<div class="constraint"><p class="prefix"><a name="PE-between-Decls"></a><b>Well-formedness constraint: PE
Between Declarations</b></p><p>The replacement text of a parameter entity reference
in a <a href="#NT-DeclSep">DeclSep</a> must match the production <a href="#NT-extSubsetDecl">extSubsetDecl</a>.</p>
</div>
<p>Like the internal subset, the external subset and any external parameter
entities referenced
in a <a href="#NT-DeclSep">DeclSep</a> must consist of a series of
complete 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
the contents of the external subset or of these
external parameter entities may conditionally be ignored by using the <a title="conditional section" href="#dt-cond-section">conditional section</a> construct; this is not
allowed in the internal subset.</p>
<h5>External Subset</h5><table class="scrap" summary="Scrap"><tbody>
<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>
<tr valign="baseline"><td><a name="NT-extSubsetDecl"></a>[31] </td><td><code>extSubsetDecl</code></td><td> ::= </td><td><code>( <a href="#NT-markupdecl">markupdecl</a> | <a href="#NT-conditionalSect">conditionalSect</a> | <a href="#NT-DeclSep">DeclSep</a>)*</code></td><xsltdebug></xsltdebug><td><i>/* */</i></td></tr>
</tbody></table>
<p>The external subset and external parameter entities also differ from the
internal subset in that in them, <a title="Parameter-entity reference" href="#dt-PERef">parameter-entity
references</a> are permitted <em>within</em> markup declarations,
not only <em>between</em> markup declarations.</p>
<p>An example of an XML document with a document type declaration:</p>
<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>
<p>The <a title="System Identifier" href="#dt-sysid">system identifier</a> "<code>hello.dtd</code>"
gives the address
(a URI reference) of a DTD for the document.</p>
<p>The declarations can also be given locally, as in this example:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE greeting [
<!ELEMENT greeting (#PCDATA)>
]>
<greeting>Hello, world!</greeting></pre></td></tr></table>
<p>If both the external and internal subsets are used, the internal subset
is considered to occur before the external subset.
This has the effect that entity and attribute-list declarations in the internal
subset take precedence over those in the external subset.</p>
</div>
<div class="div2">
<h3><a name="sec-rmd"></a>2.9 Standalone Document Declaration</h3>
<p>Markup declarations can affect the content of the document, as passed from
an <a title="XML Processor" href="#dt-xml-proc">XML processor</a> to an application; examples
are attribute defaults and entity declarations. The standalone document declaration,
which may appear as a component of the XML declaration, signals whether or
not there are such declarations which appear external to the <a title="Document Entity" href="#dt-docent">document
entity</a>
or in parameter entities. [<a name="dt-extmkpdecl" title="External Markup Declaration">Definition</a>: An <b>external
markup declaration</b> is defined as a markup declaration occurring in
the external subset or in a parameter entity (external or internal, the latter
being included because non-validating processors are not required to read
them).]</p>
<h5>Standalone Document Declaration</h5><table class="scrap" summary="Scrap"><tbody>
<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>
(("'" ('yes' | 'no') "'") | ('"' ('yes' | 'no') '"')) </code></td><xsltdebug></xsltdebug><td><a href="#vc-check-rmd">[VC: Standalone Document Declaration]</a></td></tr>
</tbody></table>
<p>In a standalone document declaration, the value "yes" indicates
that there are no <a title="External Markup Declaration" href="#dt-extmkpdecl">external markup declarations</a> which
affect the information passed from the XML processor to the application. The
value "no" indicates that there are or may be such external
markup declarations. Note that the standalone document declaration only denotes
the presence of external <em>declarations</em>; the presence, in a document,
of references to external <em>entities</em>, when those entities are internally
declared, does not change its standalone status.</p>
<p>If there are no external markup declarations, the standalone document declaration
has no meaning. If there are external markup declarations but there is no
standalone document declaration, the value "no" is assumed.</p>
<p>Any XML document for which <code>standalone="no"</code> holds can be converted
algorithmically to a standalone document, which may be desirable for some
network delivery applications.</p>
<div class="constraint"><p class="prefix"><a name="vc-check-rmd"></a><b>Validity constraint: Standalone Document Declaration</b></p><p>The
standalone document declaration must have the value "no" if
any external markup declarations contain declarations of:</p>
<ul>
<li><p>attributes with <a title="Attribute Default" href="#dt-default">default</a> values,
if elements to which these attributes apply appear in the document without
specifications of values for these attributes, or</p></li>
<li><p>entities (other than <code>amp</code>,
<code>lt</code>,
<code>gt</code>,
<code>apos</code>,
<code>quot</code>), if <a title="Entity Reference" href="#dt-entref">references</a>
to those entities appear in the document, or</p></li>
<li><p>attributes with values subject to <a href="#AVNormalize"><cite>normalization</cite></a>,
where the attribute appears in the document with a value which will change
as a result of normalization, or</p></li>
<li><p>element types with <a title="Element content" href="#dt-elemcontent">element content</a>,
if white space occurs directly within any instance of those types.</p></li>
</ul>
</div>
<p>An example XML declaration with a standalone document declaration:</p>
<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>
</div>
<div class="div2">
<h3><a name="sec-white-space"></a>2.10 White Space Handling</h3>
<p>In editing XML documents, it is often convenient to use "white space"
(spaces, tabs, and blank lines)
to set apart the markup for greater readability. Such white space is typically
not intended for inclusion in the delivered version of the document. On the
other hand, "significant" white space that should be preserved
in the delivered version is common, for example in poetry and source code.</p>
<p>An <a title="XML Processor" href="#dt-xml-proc">XML processor</a> must always pass
all characters in a document that are not markup through to the application.
A <a title="Validating Processor" href="#dt-validating"> validating XML processor</a> must also
inform the application which of these characters constitute white space appearing
in <a title="Element content" href="#dt-elemcontent">element content</a>.</p>
<p>A special <a title="Attribute" href="#dt-attr">attribute</a> named <code>xml:space</code>
may be attached to an element to signal an intention that in that element,
white space should be preserved by applications. In valid documents, this
attribute, like any other, must be <a title="Attribute-List Declaration" href="#dt-attdecl">declared</a>
if it is used. When declared, it must be given as an <a title="Enumerated Attribute Values" href="#dt-enumerated">enumerated
type</a> whose values
are one or both of "default" and "preserve".
For example:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ATTLIST poem xml:space (default|preserve) 'preserve'>
<!-- -->
<!ATTLIST pre xml:space (preserve) #FIXED 'preserve'></pre></td></tr></table>
<p>The value "default" signals that applications' default white-space
processing modes are acceptable for this element; the value "preserve"
indicates the intent that applications preserve all the white space. This
declared intent is considered to apply to all elements within the content
of the element where it is specified, unless overriden with another instance
of the <code>xml:space</code> attribute.</p>
<p>The <a title="Root Element" href="#dt-root">root element</a> of any document is considered
to have signaled no intentions as regards application space handling, unless
it provides a value for this attribute or the attribute is declared with a
default value.</p>
</div>
<div class="div2">
<h3><a name="sec-line-ends"></a>2.11 End-of-Line Handling</h3>
<p>XML <a title="Text Entity" href="#dt-parsedent">parsed entities</a> are often stored
in computer files which, for editing convenience, are organized into lines.
These lines are typically separated by some combination of the characters
carriage-return (#xD) and line-feed (#xA).</p>
<p>To
simplify the tasks of <a title="Application" href="#dt-app">applications</a>, the characters
passed to an application by the <a title="XML Processor" href="#dt-xml-proc">XML processor</a>
must be as if the XML processor normalized all line breaks in external parsed
entities (including the document entity) on input, before parsing, by translating
both the two-character sequence #xD #xA and any #xD that is not followed by
#xA to a single #xA character.</p>
</div>
<div class="div2">
<h3><a name="sec-lang-tag"></a>2.12 Language Identification</h3>
<p>In document processing, it is often useful to identify the natural or formal
language in which the content is written. A special <a title="Attribute" href="#dt-attr">attribute</a>
named <code>xml:lang</code> may be inserted in documents to specify the language
used in the contents and attribute values of any element in an XML document.
In valid documents, this attribute, like any other, must be <a title="Attribute-List Declaration" href="#dt-attdecl">declared</a>
if it is used. The
values of the attribute are language identifiers as defined by <a href="#RFC1766">[IETF RFC 1766]</a>, <cite>Tags
for the Identification of Languages</cite>, or its successor on the IETF
Standards Track.</p>
<div class="note"><p class="prefix"><b>Note:</b></p>
<p><a href="#RFC1766">[IETF RFC 1766]</a> tags are constructed from two-letter language codes as defined
by <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
Assigned Numbers Authority <a href="#IANA-LANGCODES">[IANA-LANGCODES]</a>. It is expected that the successor
to <a href="#RFC1766">[IETF RFC 1766]</a> will introduce three-letter language codes for
languages not presently covered by <a href="#ISO639">[ISO 639]</a>.</p>
</div>
<p>(Productions
33 through 38 have been removed.)</p>
<p>For example:</p>
<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>
<p xml:lang="en-GB">What colour is it?</p>
<p xml:lang="en-US">What color is it?</p>
<sp who="Faust" desc='leise' xml:lang="de">
<l>Habe nun, ach! Philosophie,</l>
<l>Juristerei, und Medizin</l>
<l>und leider auch Theologie</l>
<l>durchaus studiert mit heißem Bemüh'n.</l>
</sp></pre></td></tr></table>
<p>The intent declared with <code>xml:lang</code> is considered to apply to
all attributes and content of the element where it is specified, unless overridden
with an instance of <code>xml:lang</code> on another element within that content.</p>
<p>A simple declaration for <code>xml:lang</code> might take the form</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>xml:lang NMTOKEN #IMPLIED</pre></td></tr></table>
<p>but specific default values may also be given, if appropriate. In a collection
of French poems for English students, with glosses and notes in English, the <code>xml:lang</code>
attribute might be declared this way:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ATTLIST poem xml:lang NMTOKEN 'fr'>
<!ATTLIST gloss xml:lang NMTOKEN 'en'>
<!ATTLIST note xml:lang NMTOKEN 'en'></pre></td></tr></table>
</div>
</div>
<div class="div1">
<h2><a name="sec-logical-struct"></a>3 Logical Structures</h2>
<p>[<a name="dt-element" title="Element">Definition</a>: Each <a title="XML Document" href="#dt-xml-doc">XML
document</a> contains one or more <b>elements</b>, the boundaries
of which are either delimited by <a title="Start-Tag" href="#dt-stag">start-tags</a>
and <a title="End Tag" href="#dt-etag">end-tags</a>, or, for <a title="Empty" href="#dt-empty">empty</a>
elements, by an <a title="empty-element tag" href="#dt-eetag">empty-element tag</a>. Each
element has a type, identified by name, sometimes called its "generic
identifier" (GI), and may have a set of attribute specifications.]
Each attribute specification has a <a title="Attribute Name" href="#dt-attrname">name</a>
and a <a title="Attribute Value" href="#dt-attrval">value</a>.</p>
<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>
<p>This specification does not constrain the semantics, use, or (beyond syntax)
names of the element types and attributes, except that names beginning with
a match to <code>(('X'|'x')('M'|'m')('L'|'l'))</code> are reserved for standardization
in this or future versions of this specification.</p>
<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>
in an element's end-tag must match the element type in the start-tag.</p>
</div>
<div class="constraint"><p class="prefix"><a name="elementvalid"></a><b>Validity constraint: Element Valid</b></p><p>An element is valid
if there is a declaration matching <a href="#NT-elementdecl">elementdecl</a>
where the <a href="#NT-Name">Name</a> matches the element type, and one of
the following holds:</p>
<ol>
<li><p>The declaration matches <b>EMPTY</b> and the element has no <a title="Content" href="#dt-content">content</a>.</p></li>
<li><p>The declaration matches <a href="#NT-children">children</a> and the
sequence of <a title="Parent/Child" href="#dt-parentchild">child elements</a> belongs
to the language generated by the regular expression in the content model,
with optional white space (characters matching the nonterminal <a href="#NT-S">S</a>)
between the
start-tag and the first child element, between child elements, or between
the last child element and the end-tag. Note that a CDATA section containing
only white space does not match the nonterminal <a href="#NT-S">S</a>, and
hence cannot appear in these positions.</p></li>
<li><p>The declaration matches <a href="#NT-Mixed">Mixed</a> and the content
consists 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
content model.</p></li>
<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>
</ol>
</div>
<div class="div2">
<h3><a name="sec-starttags"></a>3.1 Start-Tags, End-Tags, and Empty-Element Tags</h3>
<p>[<a name="dt-stag" title="Start-Tag">Definition</a>: The beginning of every non-empty
XML element is marked by a <b>start-tag</b>.]</p>
<h5>Start-tag</h5><table class="scrap" summary="Scrap"><tbody>
<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>
<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>
</tbody></table>
<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>
pairs are referred to as the <b>attribute specifications</b> of the
element], [<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>]
and [<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>
delimiters) as the <b>attribute value</b>.]Note
that the order of attribute specifications in a start-tag or empty-element
tag is not significant.</p>
<div class="constraint"><p class="prefix"><a name="uniqattspec"></a><b>Well-formedness constraint: Unique Att Spec</b></p><p>No attribute name
may appear more than once in the same start-tag or empty-element tag.</p>
</div>
<div class="constraint"><p class="prefix"><a name="ValueType"></a><b>Validity constraint: Attribute Value Type</b></p><p>The attribute must
have been declared; the value must be of the type declared for it. (For attribute
types, see <a href="#attdecls"><b>3.3 Attribute-List Declarations</b></a>.)</p>
</div>
<div class="constraint"><p class="prefix"><a name="NoExternalRefs"></a><b>Well-formedness constraint: No External Entity References</b></p><p>Attribute
values cannot contain direct or indirect entity references to external entities.</p>
</div>
<div class="constraint"><p class="prefix"><a name="CleanAttrVals"></a><b>Well-formedness constraint: No <code><</code> in Attribute Values</b></p>
<p>The <a title="Replacement Text" href="#dt-repltext">replacement text</a> of any entity
referred to directly or indirectly in an attribute value must not contain a <code><</code>.</p>
</div>
<p>An example of a start-tag:</p>
<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>
<p>[<a name="dt-etag" title="End Tag">Definition</a>: The end of every element that begins
with a start-tag must be marked by an <b>end-tag</b> containing a name
that echoes the element's type as given in the start-tag:]</p>
<h5>End-tag</h5><table class="scrap" summary="Scrap"><tbody>
<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>?
'>'</code></td><xsltdebug></xsltdebug></tr>
</tbody></table>
<p>An example of an end-tag:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre></termdef></pre></td></tr></table>
<p>[<a name="dt-content" title="Content">Definition</a>: The <a title="Text" href="#dt-text">text</a>
between the start-tag and end-tag is called the element's <b>content</b>:]</p>
<h5>Content of Elements</h5><table class="scrap" summary="Scrap"><tbody>
<tr valign="baseline"><td><a name="NT-content"></a>[43] </td><td><code>content</code></td><td> ::= </td><td><code><a href="#NT-CharData">CharData</a>? ((<a href="#NT-element">element</a>
| <a href="#NT-Reference">Reference</a> | <a href="#NT-CDSect">CDSect</a>
| <a href="#NT-PI">PI</a> | <a href="#NT-Comment">Comment</a>) <a href="#NT-CharData">CharData</a>?)*</code></td><xsltdebug></xsltdebug><td><i>/* */</i></td></tr>
</tbody></table>
<p>[<a name="dt-empty" title="Empty">Definition</a>: An element
with no content is said to be <b>empty</b>.] The representation
of an empty element is either a start-tag immediately followed by an end-tag,
or an empty-element tag. [<a name="dt-eetag" title="empty-element tag">Definition</a>: An <b>empty-element
tag</b> takes a special form:]</p>
<h5>Tags for Empty Elements</h5><table class="scrap" summary="Scrap"><tbody>
<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>
</tbody></table>
<p>Empty-element tags may be used for any element which has no content, whether
or not it is declared using the keyword <b>EMPTY</b>. <a title="For interoperability" href="#dt-interop">For
interoperability</a>, the empty-element tag should
be used, and should only be used, for elements which are declared
EMPTY.</p>
<p>Examples of empty elements:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><IMG align="left"
src="http://www.w3.org/Icons/WWW/w3c_home" />
<br></br>
<br/></pre></td></tr></table>
</div>
<div class="div2">
<h3><a name="elemdecls"></a>3.2 Element Type Declarations</h3>
<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>
purposes, be constrained using element type and attribute-list declarations.
An element type declaration constrains the element's <a title="Content" href="#dt-content">content</a>.</p>
<p>Element type declarations often constrain which element types can appear
as <a title="Parent/Child" href="#dt-parentchild">children</a> of the element. At user
option, an XML processor may issue a warning when a declaration mentions an
element type for which no declaration is provided, but this is not an error.</p>
<p>[<a name="dt-eldecl" title="Element Type declaration">Definition</a>: An <b>element
type declaration</b> takes the form:]</p>
<h5>Element Type Declaration</h5><table class="scrap" summary="Scrap"><tbody>
<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>?
'>'</code></td><xsltdebug></xsltdebug><td><a href="#EDUnique">[VC: Unique Element Type Declaration]</a></td></tr>
<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>
| <a href="#NT-children">children</a> </code></td><xsltdebug></xsltdebug></tr>
</tbody></table>
<p>where the <a href="#NT-Name">Name</a> gives the element type being declared.</p>
<div class="constraint"><p class="prefix"><a name="EDUnique"></a><b>Validity constraint: Unique Element Type Declaration</b></p><p>No element
type may be declared more than once.</p>
</div>
<p>Examples of element type declarations:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ELEMENT br EMPTY>
<!ELEMENT p (#PCDATA|emph)* >
<!ELEMENT %name.para; %content.para; >
<!ELEMENT container ANY></pre></td></tr></table>
<div class="div3">
<h4><a name="sec-element-content"></a>3.2.1 Element Content</h4>
<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
of that type must contain only <a title="Parent/Child" href="#dt-parentchild">child</a>
elements (no character data), optionally separated by white space (characters
matching 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 <b>content
model</b>, a simple grammar governing the allowed types of the
child elements and the order in which they are allowed to appear.]
The grammar is built on content particles (<a href="#NT-cp">cp</a>s), which
consist of names, choice lists of content particles, or sequence lists of
content particles:</p>
<h5>Element-content Models</h5><table class="scrap" summary="Scrap"><tbody>
<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>)
('?' | '*' | '+')?</code></td><xsltdebug></xsltdebug></tr>
<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>
| <a href="#NT-seq">seq</a>) ('?' | '*' | '+')?</code></td><xsltdebug></xsltdebug></tr>
<tr valign="baseline"><td><a name="NT-choice"></a>[49] </td><td><code>choice</code></td><td> ::= </td><td><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><i>/* */</i></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><i>/* */</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>
<tr valign="baseline"><td><a name="NT-seq"></a>[50] </td><td><code>seq</code></td><td> ::= </td><td><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><i>/* */</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>
</tbody></table>
<p>where each <a href="#NT-Name">Name</a> is the type of an element which
may appear as a <a title="Parent/Child" href="#dt-parentchild">child</a>. Any content
particle in a choice list may appear in the <a title="Element content" href="#dt-elemcontent">element
content</a> at the location where the choice list appears in the grammar;
content 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.
The optional character following a name or list governs whether the element
or the content particles in the list may occur one or more (<code>+</code>),
zero or more (<code>*</code>), or zero or one times (<code>?</code>). The
absence of such an operator means that the element or content particle must
appear exactly once. This syntax and meaning are identical to those used in
the productions in this specification.</p>
<p>The content of an element matches a content model if and only if it is
possible to trace out a path through the content model, obeying the sequence,
choice, and repetition operators and matching each element in the content
against an element type in the content model. <a title="For Compatibility" href="#dt-compat">For
compatibility</a>, it is an error if an element in the document can
match more than one occurrence of an element type in the content model. For
more information, see <a href="#determinism"><b>E Deterministic Content Models</b></a>.</p>
<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 parenthesized
groups. That is to say, if either of the opening or closing parentheses in
a <a href="#NT-choice">choice</a>, <a href="#NT-seq">seq</a>, or <a href="#NT-Mixed">Mixed</a>
construct is contained in the replacement text for a <a title="Parameter-entity reference" href="#dt-PERef">parameter
entity</a>, both must be contained in the same replacement text.</p>
<p><a title="For interoperability" href="#dt-interop">For interoperability</a>, if a parameter-entity reference
appears 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
least one non-blank character, and neither the first nor last non-blank character
of the replacement text should be a connector (<code>|</code> or <code>,</code>).</p>
</div>
<p>Examples of element-content models:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ELEMENT spec (front, body, back?)>
<!ELEMENT div1 (head, (p | list | note)*, div2*)>
<!ELEMENT dictionary-body (%div.mix; | %dict.mix;)*></pre></td></tr></table>
</div>
<div class="div3">
<h4><a name="sec-mixed-content"></a>3.2.2 Mixed Content</h4>
<p>[<a name="dt-mixed" title="Mixed Content">Definition</a>: An element <a title="Start-Tag" href="#dt-stag">type</a>
has <b>mixed content</b> when elements of that type may contain character
data, optionally interspersed with <a title="Parent/Child" href="#dt-parentchild">child</a>
elements.] In this case, the types of the child elements may be constrained,
but not their order or their number of occurrences:</p>
<h5>Mixed-content Declaration</h5><table class="scrap" summary="Scrap"><tbody>
<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>?
'|' <a href="#NT-S">S</a>? <a href="#NT-Name">Name</a>)* <a href="#NT-S">S</a>?
')*' </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>
</tbody></table>
<p>where the <a href="#NT-Name">Name</a>s give the types of elements that
may appear as children. The
keyword <b>#PCDATA</b> derives historically from the term "parsed
character data."</p>
<div class="constraint"><p class="prefix"><a name="vc-MixedChildrenUnique"></a><b>Validity constraint: No Duplicate Types</b></p><p>The
same name must not appear more than once in a single mixed-content declaration.</p>
</div>
<p>Examples of mixed content declarations:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ELEMENT p (#PCDATA|a|ul|b|i|em)*>
<!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* >
<!ELEMENT b (#PCDATA)></pre></td></tr></table>
</div>
</div>
<div class="div2">
<h3><a name="attdecls"></a>3.3 Attribute-List Declarations</h3>
<p><a title="Attribute" href="#dt-attr">Attributes</a> are used to associate name-value
pairs with <a title="Element" href="#dt-element">elements</a>. Attribute specifications
may 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
recognize them appear in <a href="#sec-starttags"><b>3.1 Start-Tags, End-Tags, and Empty-Element Tags</b></a>. Attribute-list declarations
may be used:</p>
<ul>
<li><p>To define the set of attributes pertaining to a given element type.</p>
</li>
<li><p>To establish type constraints for these attributes.</p></li>
<li><p>To provide <a title="Attribute Default" href="#dt-default">default values</a> for
attributes.</p></li>
</ul>
<p>[<a name="dt-attdecl" title="Attribute-List Declaration">Definition</a>: <b>Attribute-list
declarations</b> specify the name, data type, and default value (if any)
of each attribute associated with a given element type:]</p>
<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>
<p>The <a href="#NT-Name">Name</a> in the <a href="#NT-AttlistDecl">AttlistDecl</a>
rule is the type of an element. At user option, an XML processor may issue
a warning if attributes are declared for an element type not itself declared,
but this is not an error. The <a href="#NT-Name">Name</a> in the <a href="#NT-AttDef">AttDef</a>
rule is the name of the attribute.</p>
<p>When more than one <a href="#NT-AttlistDecl">AttlistDecl</a> is provided
for a given element type, the contents of all those provided are merged. When
more than one definition is provided for the same attribute of a given element
type, the first declaration is binding and later declarations are ignored. <a title="For interoperability" href="#dt-interop">For interoperability,</a> writers of DTDs may choose
to provide at most one attribute-list declaration for a given element type,
at most one attribute definition for a given attribute name in an attribute-list
declaration, and at least one attribute definition in each attribute-list
declaration. For interoperability, an XML processor may at user option
issue a warning when more than one attribute-list declaration is provided
for a given element type, or more than one attribute definition is provided
for a given attribute, but this is not an error.</p>
<div class="div3">
<h4><a name="sec-attribute-types"></a>3.3.1 Attribute Types</h4>
<p>XML attribute types are of three kinds: a string type, a set of tokenized
types, and enumerated types. The string type may take any literal string as
a value; the tokenized types have varying lexical and semantic constraints.
The validity constraints noted in the grammar are applied after the attribute
value has been normalized as described in <a href="#attdecls"><b>3.3 Attribute-List Declarations</b></a>.</p>
<h5>Attribute Types</h5><table class="scrap" summary="Scrap"><tbody>
<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>
| <a href="#NT-EnumeratedType">EnumeratedType</a> </code></td><xsltdebug></xsltdebug></tr>
<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>
<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>
</tbody></table>
<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
in an XML document as a value of this type; i.e., ID values must uniquely
identify the elements which bear them.</p>
</div>
<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
type may have more than one ID attribute specified.</p>
</div>
<div class="constraint"><p class="prefix"><a name="id-default"></a><b>Validity constraint: ID Attribute Default</b></p><p>An ID attribute
must have a declared default of <b>#IMPLIED</b> or <b>#REQUIRED</b>.</p>
</div>
<div class="constraint"><p class="prefix"><a name="idref"></a><b>Validity constraint: IDREF</b></p><p>Values of type <b>IDREF</b> must
match the <a href="#NT-Name">Name</a> production, and values of type <b>IDREFS</b>
must match <a href="#NT-Names">Names</a>; each <a href="#NT-Name">Name</a>
must match the value of an ID attribute on some element in the XML document;
i.e. <b>IDREF</b> values must match the value of some ID attribute.</p>
</div>
<div class="constraint"><p class="prefix"><a name="entname"></a><b>Validity constraint: Entity Name</b></p><p>Values of type <b>ENTITY</b>
must match the <a href="#NT-Name">Name</a> production, values of type <b>ENTITIES</b>
must match <a href="#NT-Names">Names</a>; each <a href="#NT-Name">Name</a>
must match the name of an <a title="Unparsed Entity" href="#dt-unparsed">unparsed entity</a>
declared in the <a title="Document Type Declaration" href="#dt-doctype">DTD</a>.</p>
</div>
<div class="constraint"><p class="prefix"><a name="nmtok"></a><b>Validity constraint: Name Token</b></p><p>Values of type <b>NMTOKEN</b>
must match the <a href="#NT-Nmtoken">Nmtoken</a> production; values of type <b>NMTOKENS</b>
must match <a title="" href="#NT-Nmtokens">Nmtokens</a>.</p>
</div>
<p>[<a name="dt-enumerated" title="Enumerated Attribute Values">Definition</a>: <b>Enumerated attributes</b> can take one of a list of values
provided in the declaration]. There are two kinds of enumerated types:</p>
<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>
| <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><a href="#OneNotationPer">[VC: One
Notation Per Element Type]</a></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#NoNotationEmpty">[VC: No
Notation 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>
(<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>
<p>A <b>NOTATION</b> attribute identifies a <a title="Notation" href="#dt-notation">notation</a>,
declared in the DTD with associated system and/or public identifiers, to be
used in interpreting the element to which the attribute is attached.</p>
<div class="constraint"><p class="prefix"><a name="notatn"></a><b>Validity constraint: Notation Attributes</b></p><p>Values of this type
must match one of the <a href="#Notations"><cite>notation</cite></a> names
included in the declaration; all notation names in the declaration must be
declared.</p>
</div>
<div class="constraint"><p class="prefix"><a name="OneNotationPer"></a><b>Validity constraint: One
Notation Per Element Type</b></p><p>No element type may have more than one <b>NOTATION</b>
attribute specified.</p>
</div>
<div class="constraint"><p class="prefix"><a name="NoNotationEmpty"></a><b>Validity constraint: No
Notation on Empty Element</b></p><p><a title="For Compatibility" href="#dt-compat">For compatibility</a>,
an attribute of type <b>NOTATION</b> must not be declared on an element
declared <b>EMPTY</b>.</p>
</div>
<div class="constraint"><p class="prefix"><a name="enum"></a><b>Validity constraint: Enumeration</b></p><p>Values of this type must match
one of the <a href="#NT-Nmtoken">Nmtoken</a> tokens in the declaration.</p>
</div>
<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
attribute types of a single element type.</p>
</div>
<div class="div3">
<h4><a name="sec-attr-defaults"></a>3.3.2 Attribute Defaults</h4>
<p>An <a title="Attribute-List Declaration" href="#dt-attdecl">attribute declaration</a> provides information
on whether the attribute's presence is required, and if not, how an XML processor
should react if a declared attribute is absent in a document.</p>
<h5>Attribute Defaults</h5><table class="scrap" summary="Scrap"><tbody>
<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>
</tbody></table>
<p>In an attribute declaration, <b>#REQUIRED</b> means that the attribute
must always be provided, <b>#IMPLIED</b> that no default value is provided. [<a name="dt-default" title="Attribute Default">Definition</a>: If
the declaration is neither <b>#REQUIRED</b> nor <b>#IMPLIED</b>, then
the <a href="#NT-AttValue">AttValue</a> value contains the declared <b>default</b>
value; the <b>#FIXED</b> keyword states that the attribute must always have
the default value. If a default value is declared, when an XML processor encounters
an omitted attribute, it is to behave as though the attribute were present
with the declared default value.]</p>
<div class="constraint"><p class="prefix"><a name="RequiredAttr"></a><b>Validity constraint: Required Attribute</b></p><p>If the default
declaration is the keyword <b>#REQUIRED</b>, then the attribute must be
specified for all elements of the type in the attribute-list declaration.</p>
</div>
<div class="constraint"><p class="prefix"><a name="defattrvalid"></a><b>Validity constraint: Attribute Default Legal</b></p><p>The declared
default value must meet the lexical constraints of the declared attribute
type.</p>
</div>
<div class="constraint"><p class="prefix"><a name="FixedAttr"></a><b>Validity constraint: Fixed Attribute Default</b></p><p>If an attribute
has a default value declared with the <b>#FIXED</b> keyword, instances of
that attribute must match the default value.</p>
</div>
<p>Examples of attribute-list declarations:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ATTLIST termdef
id ID #REQUIRED
name CDATA #IMPLIED>
<!ATTLIST list
type (bullets|ordered|glossary) "ordered">
<!ATTLIST form
method CDATA #FIXED "POST"></pre></td></tr></table>
</div>
<div class="div3">
<h4><a name="AVNormalize"></a>3.3.3 Attribute-Value
Normalization</h4>
<p>Before the value of an attribute is passed to the application or checked
for validity, the XML processor must normalize the attribute value by applying
the algorithm below, or by using some other method such that the value passed
to the application is the same as that produced by the algorithm.</p>
<ol>
<li><p>All line breaks must have been normalized on input to #xA as described
in <a href="#sec-line-ends"><b>2.11 End-of-Line Handling</b></a>, so the rest of this algorithm operates
on text normalized in this way.</p></li>
<li><p>Begin with a normalized value consisting of the empty string.</p>
</li>
<li><p>For each character, entity reference, or character reference in the
unnormalized attribute value, beginning with the first and continuing to the
last, do the following:</p>
<ul>
<li><p>For a character reference, append the referenced character to the
normalized value.</p></li>
<li><p>For an entity reference, recursively apply step 3 of this algorithm
to the replacement text of the entity.</p></li>
<li><p>For a white space character (#x20, #xD, #xA, #x9), append a space
character (#x20) to the normalized value.</p></li>
<li><p>For another character, append the character to the normalized value.</p>
</li>
</ul>
</li>
</ol>
<p>If the attribute type is not CDATA, then the XML processor must further
process the normalized attribute value by discarding any leading and trailing
space (#x20) characters, and by replacing sequences of space (#x20) characters
by a single space (#x20) character.</p>
<p>Note that if the unnormalized attribute value contains a character reference
to a white space character other than space (#x20), the normalized value contains
the referenced character itself (#xD, #xA or #x9). This contrasts with the
case where the unnormalized value contains a white space character (not a
reference), which is replaced with a space character (#x20) in the normalized
value and also contrasts with the case where the unnormalized value contains
an entity reference whose replacement text contains a white space character;
being recursively processed, the white space character is replaced with a
space character (#x20) in the normalized value.</p>
<p>All attributes for which no declaration has been read should be treated
by a non-validating processor
as if declared <b>CDATA</b>.</p>
<p>Following are examples of attribute normalization. Given the following
declarations:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY d "&#xD;">
<!ENTITY a "&#xA;">
<!ENTITY da "&#xD;&#xA;"></pre></td></tr></table>
<p>the attribute specifications in the left column below would be normalized
to the character sequences of the middle column if the attribute <code>a</code>
is declared <b>NMTOKENS</b> and to those of the right columns if <code>a</code>
is declared <b>CDATA</b>.</p>
<table border="1" frame="border"><thead><tr><th rowspan="1" colspan="1">Attribute specification</th>
<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="
xyz"</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>
</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
#x20 B</code></td><td rowspan="1" colspan="1"><code>#x20 #x20 A #x20 #x20 B #x20 #x20</code></td>
</tr><tr><td rowspan="1" colspan="1"><table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>a=
"&#xd;&#xd;A&#xa;&#xa;B&#xd;&#xa;"</pre></td></tr></table></td><td rowspan="1" colspan="1"><code>#xD
#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>
</tr></tbody></table>
<p>Note that the last example is invalid (but well-formed) if <code>a</code>
is declared to be of type <b>NMTOKENS</b>.</p>
</div>
</div>
<div class="div2">
<h3><a name="sec-condition-sect"></a>3.4 Conditional Sections</h3>
<p>[<a name="dt-cond-section" title="conditional section">Definition</a>: <b>Conditional
sections</b> are portions of the <a title="Document Type Declaration" href="#dt-doctype">document type
declaration external subset</a> which are included in, or excluded from,
the logical structure of the DTD based on the keyword which governs them.]</p>
<h5>Conditional Section</h5><table class="scrap" summary="Scrap"><tbody>
<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>
<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>
']]>' </code></td><xsltdebug></xsltdebug><td><i>/* */</i></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#condsec-nesting">[VC: Proper
Conditional Section/PE Nesting]</a></td></tr>
<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>*
']]>'</code></td><xsltdebug></xsltdebug><td><i>/* */</i></td></tr><tr valign="baseline"><td></td><td></td><td></td><td></td><td><a href="#condsec-nesting">[VC: Proper
Conditional Section/PE Nesting]</a></td></tr>
<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>
<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>*
('<![' | ']]>') <a href="#NT-Char">Char</a>*) </code></td><xsltdebug></xsltdebug></tr>
</tbody></table>
<div class="constraint"><p class="prefix"><a name="condsec-nesting"></a><b>Validity constraint: Proper
Conditional Section/PE Nesting</b></p><p>If any of the "<code><![</code>",
"<code>[</code>", or "<code>]]></code>" of a conditional section is contained
in the replacement text for a parameter-entity reference, all of them must
be contained in the same replacement text.</p>
</div>
<p>Like the internal and external DTD subsets, a conditional section may contain
one or more complete declarations, comments, processing instructions, or nested
conditional sections, intermingled with white space.</p>
<p>If the keyword of the conditional section is <b>INCLUDE</b>, then the
contents of the conditional section are part of the DTD. If the keyword of
the conditional section is <b>IGNORE</b>, then the contents of the conditional
section are not logically part of the DTD.
If a conditional section with a keyword of <b>INCLUDE</b> occurs within
a larger conditional section with a keyword of <b>IGNORE</b>, both the outer
and the inner conditional sections are ignored. The contents
of an ignored conditional section are parsed by ignoring all characters after
the "<code>[</code>" following the keyword, except conditional section starts
"<code><![</code>" and ends "<code>]]></code>", until the matching conditional
section end is found. Parameter entity references are not recognized in this
process.</p>
<p>If the keyword of the conditional section is a parameter-entity reference,
the parameter entity must be replaced by its content before the processor
decides whether to include or ignore the conditional section.</p>
<p>An example:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY % draft 'INCLUDE' >
<!ENTITY % final 'IGNORE' >
<![%draft;[
<!ELEMENT book (comments*, title, body, supplements?)>
]]>
<![%final;[
<!ELEMENT book (title, body, supplements?)>
]]></pre></td></tr></table>
</div>
</div>
<div class="div1">
<h2><a name="sec-physical-struct"></a>4 Physical Structures</h2>
<p>[<a name="dt-entity" title="Entity">Definition</a>: An XML document may consist of one
or many storage units. These
are called <b>entities</b>; they all have <b>content</b> and are
all (except for the <a title="Document Entity" href="#dt-docent">document entity</a> and
the <a title="Document Type Declaration" href="#dt-doctype">external DTD subset</a>) identified by
entity <b>name</b>.] Each XML document has one entity
called the <a title="Document Entity" href="#dt-docent">document entity</a>, which serves
as the starting point for the <a title="XML Processor" href="#dt-xml-proc">XML processor</a>
and may contain the whole document.</p>
<p>Entities may be either parsed or unparsed. [<a name="dt-parsedent" title="Text Entity">Definition</a>: A <b>parsed
entity's</b> contents are referred to as its <a title="Replacement Text" href="#dt-repltext">replacement
text</a>; this <a title="Text" href="#dt-text">text</a> is considered an
integral part of the document.]</p>
<p>[<a name="dt-unparsed" title="Unparsed Entity">Definition</a>: An <b>unparsed entity</b>
is a resource whose contents may or may not be <a title="Text" href="#dt-text">text</a>,
and if text, may
be other than XML. Each unparsed entity has an associated <a title="Notation" href="#dt-notation">notation</a>, identified by name. Beyond a requirement
that an XML processor make the identifiers for the entity and notation available
to the application, XML places no constraints on the contents of unparsed
entities.]</p>
<p>Parsed entities are invoked by name using entity references; unparsed entities
by name, given in the value of <b>ENTITY</b> or <b>ENTITIES</b> attributes.</p>
<p>[<a name="gen-entity" title="general entity">Definition</a>: <b>General entities</b>
are entities for use within the document content. In this specification, general
entities are sometimes referred to with the unqualified term <em>entity</em>
when this leads to no ambiguity.] [<a name="dt-PE" title="Parameter entity">Definition</a>: <b>Parameter
entities</b> are parsed entities for use within the DTD.]
These two types of entities use different forms of reference and are recognized
in different contexts. Furthermore, they occupy different namespaces; a parameter
entity and a general entity with the same name are two distinct entities.</p>
<div class="div2">
<h3><a name="sec-references"></a>4.1 Character and Entity References</h3>
<p>[<a name="dt-charref" title="Character Reference">Definition</a>: A <b>character
reference</b> refers to a specific character in the ISO/IEC 10646 character
set, for example one not directly accessible from available input devices.]</p>
<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>
<div class="constraint"><p class="prefix"><a name="wf-Legalchar"></a><b>Well-formedness constraint: Legal Character</b></p><p>Characters referred
to using character references must match the production for <a title="" href="#NT-Char">Char</a>.</p>
</div>
<p>If the character reference begins with "<code>&#x</code>",
the digits and letters up to the terminating <code>;</code> provide a hexadecimal
representation of the character's code point in ISO/IEC 10646. If it begins
just with "<code>&#</code>", the digits up to the terminating <code>;</code>
provide a decimal representation of the character's code point.</p>
<p>[<a name="dt-entref" title="Entity Reference">Definition</a>: An <b>entity reference</b>
refers to the content of a named entity.] [<a name="dt-GERef" title="General Entity Reference">Definition</a>: References to parsed general entities use
ampersand (<code>&</code>) and semicolon (<code>;</code>) as delimiters.] [<a name="dt-PERef" title="Parameter-entity reference">Definition</a>: <b>Parameter-entity references</b>
use percent-sign (<code>%</code>) and semicolon (<code>;</code>) as delimiters.]</p>
<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>
<div class="constraint"><p class="prefix"><a name="wf-entdeclared"></a><b>Well-formedness constraint: Entity Declared</b></p><p>In a document
without any DTD, a document with only an internal DTD subset which contains
no parameter entity references, or a document with "<code>standalone='yes'</code>", for
an entity reference that does not occur within the external subset or a parameter
entity, 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
declaration</cite></a> that does not occur within the external subset or a
parameter entity, except that well-formed documents need not declare
any of the following entities: <code>amp</code>,
<code>lt</code>,
<code>gt</code>,
<code>apos</code>,
<code>quot</code>. The
declaration of a general entity must precede any reference to it which appears
in a default value in an attribute-list declaration.</p>
<p>Note that if entities are declared in the external subset or in external
parameter entities, a non-validating processor is <a href="#include-if-valid"><cite>not
obligated to</cite></a> read and process their declarations; for such documents,
the rule that an entity must be declared is a well-formedness constraint only
if <a href="#sec-rmd"><cite>standalone='yes'</cite></a>.</p>
</div>
<div class="constraint"><p class="prefix"><a name="vc-entdeclared"></a><b>Validity constraint: Entity Declared</b></p><p>In a document with
an external subset or external parameter entities with "<code>standalone='no'</code>",
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
declaration</cite></a>. For interoperability, valid documents should declare
the entities <code>amp</code>,
<code>lt</code>,
<code>gt</code>,
<code>apos</code>,
<code>quot</code>, in the form specified in <a href="#sec-predefined-ent"><b>4.6 Predefined Entities</b></a>.
The declaration of a parameter entity must precede any reference to it. Similarly,
the declaration of a general entity must precede any attribute-list
declaration containing a default value with a direct or indirect reference
to that general entity.</p>
</div>
<div class="constraint"><p class="prefix"><a name="textent"></a><b>Well-formedness constraint: Parsed Entity</b></p><p>An entity reference must
not contain the name of an <a title="Unparsed Entity" href="#dt-unparsed">unparsed entity</a>.
Unparsed entities may be referred to only in <a title="Attribute Value" href="#dt-attrval">attribute
values</a> declared to be of type <b>ENTITY</b> or <b>ENTITIES</b>.</p>
</div>
<div class="constraint"><p class="prefix"><a name="norecursion"></a><b>Well-formedness constraint: No Recursion</b></p><p>A parsed entity must
not contain a recursive reference to itself, either directly or indirectly.</p>
</div>
<div class="constraint"><p class="prefix"><a name="indtd"></a><b>Well-formedness constraint: In DTD</b></p><p>Parameter-entity references may
only appear in the <a title="Document Type Declaration" href="#dt-doctype">DTD</a>.</p>
</div>
<p>Examples of character and entity references:</p>
<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.
This document was prepared on &docdate; and
is classified &security-level;.</pre></td></tr></table>
<p>Example of a parameter-entity reference:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!-- declare the parameter entity "ISOLat2"... -->
<!ENTITY % ISOLat2
SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" >
<!-- ... now reference it. -->
%ISOLat2;</pre></td></tr></table>
</div>
<div class="div2">
<h3><a name="sec-entity-decl"></a>4.2 Entity Declarations</h3>
<p>[<a name="dt-entdecl" title="entity declaration">Definition</a>: Entities are declared
thus:]</p>
<h5>Entity Declaration</h5><table class="scrap" summary="Scrap"><tbody>
<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>
<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>?
'>'</code></td><xsltdebug></xsltdebug></tr>
<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>
<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>
<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>
</tbody></table>
<p>The <a href="#NT-Name">Name</a> identifies the entity in an <a title="Entity Reference" href="#dt-entref">entity
reference</a> or, in the case of an unparsed entity, in the value of
an <b>ENTITY</b> or <b>ENTITIES</b> attribute. If the same entity is declared
more than once, the first declaration encountered is binding; at user option,
an XML processor may issue a warning if entities are declared multiple times.</p>
<div class="div3">
<h4><a name="sec-internal-ent"></a>4.2.1 Internal Entities</h4>
<p>[<a name="dt-internent" title="Internal Entity Replacement Text">Definition</a>: If the
entity definition is an <a href="#NT-EntityValue">EntityValue</a>, the defined
entity is called an <b>internal entity</b>. There is no separate physical
storage object, and the content of the entity is given in the declaration.]
Note 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
the 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>
<p>An internal entity is a <a title="Text Entity" href="#dt-parsedent">parsed entity</a>.</p>
<p>Example of an internal entity declaration:</p>
<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
specification."></pre></td></tr></table>
</div>
<div class="div3">
<h4><a name="sec-external-ent"></a>4.2.2 External Entities</h4>
<p>[<a name="dt-extent" title="External Entity">Definition</a>: If the entity is not internal,
it is an <b>external entity</b>, declared as follows:]</p>
<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>
<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>
<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>
must match the declared name of a <a title="Notation" href="#dt-notation">notation</a>.</p>
</div>
<p>[<a name="dt-sysid" title="System Identifier">Definition</a>: The <a href="#NT-SystemLiteral">SystemLiteral</a> is called the entity's <b>system
identifier</b>. It is a URI
reference
(as defined in <a href="#rfc2396">[IETF RFC 2396]</a>, updated by <a href="#rfc2732">[IETF RFC 2732]</a>), meant
to be dereferenced to obtain input for the XML processor to construct the
entity's replacement text.] It is an error for a fragment identifier
(beginning with a <code>#</code> character) to be part of a system identifier.
Unless otherwise provided by information outside the scope of this specification
(e.g. a special XML element type defined by a particular DTD, or a processing
instruction defined by a particular application specification), relative URIs
are relative to the location of the resource within which the entity declaration
occurs. A URI might thus be relative to the <a title="Document Entity" href="#dt-docent">document
entity</a>, to the entity containing the <a title="Document Type Declaration" href="#dt-doctype">external
DTD subset</a>, or to some other <a title="External Entity" href="#dt-extent">external parameter
entity</a>.</p>
<p>URI
references require encoding and escaping of certain characters. The disallowed
characters include all non-ASCII characters, plus the excluded characters
listed in Section 2.4 of <a href="#rfc2396">[IETF RFC 2396]</a>, except for the number sign
(<code>#</code>) and percent sign (<code>%</code>) characters and the square
bracket characters re-allowed in <a href="#rfc2732">[IETF RFC 2732]</a>. Disallowed characters
must be escaped as follows:</p>
<ol>
<li><p>Each disallowed character is converted to UTF-8 <a href="#rfc2279">[IETF RFC 2279]</a>
as one or more bytes.</p></li>
<li><p>Any octets corresponding to a disallowed character are escaped with
the URI escaping mechanism (that is, converted to <code>%</code><var>HH</var>,
where HH is the hexadecimal notation of the byte value).</p></li>
<li><p>The original character is replaced by the resulting character sequence.</p>
</li>
</ol>
<p>[<a name="dt-pubid" title="Public identifier">Definition</a>: In addition to a system
identifier, an external identifier may include a <b>public identifier</b>.]
An XML processor attempting to retrieve the entity's content may use the public
identifier to try to generate an alternative URI reference.
If the processor is unable to do so, it must use the URI
reference specified in the system literal. Before a match is attempted,
all strings of white space in the public identifier must be normalized to
single space characters (#x20), and leading and trailing white space must
be removed.</p>
<p>Examples of external entity declarations:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY open-hatch
SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml">
<!ENTITY open-hatch
PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN"
"http://www.textuality.com/boilerplate/OpenHatch.xml">
<!ENTITY hatch-pic
SYSTEM "../grafix/OpenHatch.gif"
NDATA gif ></pre></td></tr></table>
</div>
</div>
<div class="div2">
<h3><a name="TextEntities"></a>4.3 Parsed Entities</h3>
<div class="div3">
<h4><a name="sec-TextDecl"></a>4.3.1 The Text Declaration</h4>
<p>External parsed entities should each begin with a <b>text declaration</b>.</p>
<h5>Text Declaration</h5><table class="scrap" summary="Scrap"><tbody>
<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>
</tbody></table>
<p>The text declaration must be provided literally, not by reference to a
parsed entity. No text declaration may appear at any position other than the
beginning of an external parsed entity. The text declaration
in an external parsed entity is not considered part of its <a title="Replacement Text" href="#dt-repltext">replacement
text</a>.</p>
</div>
<div class="div3">
<h4><a name="wf-entities"></a>4.3.2 Well-Formed Parsed Entities</h4>
<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
if it matches the production labeled <a href="#NT-extParsedEnt">extParsedEnt</a>. All
external parameter entities are well-formed by definition.</p>
<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></table>
<p>An internal general parsed entity is well-formed if its replacement text
matches the production labeled <a href="#NT-content">content</a>. All internal
parameter entities are well-formed by definition.</p>
<p>A consequence of well-formedness in entities is that the logical and physical
structures 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
reference</a>, or <a title="Entity Reference" href="#dt-entref">entity reference</a>
can begin in one entity and end in another.</p>
</div>
<div class="div3">
<h4><a name="charencoding"></a>4.3.3 Character Encoding in Entities</h4>
<p>Each external parsed entity in an XML document may use a different encoding
for its characters. All XML processors must be able to read entities in both
the UTF-8 and UTF-16 encodings. The terms "UTF-8"
and "UTF-16" in this specification do not apply to character
encodings with any other labels, even if the encodings or labels are very
similar to UTF-8 or UTF-16.</p>
<p>Entities encoded in UTF-16 must begin with the Byte Order Mark described
by Annex
F of <a href="#ISO10646">[ISO/IEC 10646]</a>, Annex H of <a href="#ISO10646-2000">[ISO/IEC 10646-2000]</a>, section
2.4 of <a href="#Unicode">[Unicode]</a>, and section 2.7 of <a href="#Unicode3">[Unicode3]</a>
(the ZERO WIDTH NO-BREAK SPACE character, #xFEFF). This is an encoding signature,
not part of either the markup or the character data of the XML document. XML
processors must be able to use this character to differentiate between UTF-8
and UTF-16 encoded documents.</p>
<p>Although an XML processor is required to read only entities in the UTF-8
and UTF-16 encodings, it is recognized that other encodings are used around
the world, and it may be desired for XML processors to read entities that
use them. In
the absence of external character encoding information (such as MIME headers),
parsed entities which are stored in an encoding other than UTF-8 or UTF-16
must begin with a text declaration (see <a href="#sec-TextDecl"><b>4.3.1 The Text Declaration</b></a>) containing
an encoding declaration:</p>
<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>
('"' <a href="#NT-EncName">EncName</a> '"' | "'" <a href="#NT-EncName">EncName</a>
"'" ) </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
name contains only Latin characters */</i></td></tr></tbody></table>
<p>In the <a title="Document Entity" href="#dt-docent">document entity</a>, the encoding
declaration is part of the <a title="XML Declaration" href="#dt-xmldecl">XML declaration</a>.
The <a href="#NT-EncName">EncName</a> is the name of the encoding used.</p>
<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
for the various encodings and transformations of Unicode / ISO/IEC 10646,
the values "<code>ISO-8859-1</code>", "<code>ISO-8859-2</code>",
... "<code>ISO-8859-</code><var>n</var>" (where <var>n</var>
is the part number) should be used for the parts of ISO 8859, and
the values "<code>ISO-2022-JP</code>", "<code>Shift_JIS</code>",
and "<code>EUC-JP</code>" should be used for the various encoded
forms of JIS X-0208-1997. It
is recommended that character encodings registered (as <em>charset</em>s)
with the Internet Assigned Numbers Authority <a href="#IANA">[IANA-CHARSETS]</a>,
other than those just listed, be referred to using their registered names;
other encodings should use names starting with an "x-" prefix.
XML processors should match character encoding names in a case-insensitive
way and should either interpret an IANA-registered name as the encoding registered
at IANA for that name or treat it as unknown (processors are, of course, not
required to support all IANA-registered encodings).</p>
<p>In the absence of information provided by an external transport protocol
(e.g. HTTP or MIME), it is an <a title="Error" href="#dt-error">error</a> for
an entity including an encoding declaration to be presented to the XML processor
in an encoding other than that named in the declaration, or for an entity which begins with neither a Byte Order Mark
nor an encoding declaration to use an encoding other than UTF-8. Note that
since ASCII is a subset of UTF-8, ordinary ASCII entities do not strictly
need an encoding declaration.</p>
<p>It
is a
fatal error for a <a href="#NT-TextDecl">TextDecl</a> to occur other
than at the beginning of an external entity.</p>
<p>It is a <a title="Fatal Error" href="#dt-fatal">fatal error</a> when an XML processor
encounters an entity with an encoding that it is unable to process. It
is a fatal error if an XML entity is determined (via default, encoding declaration,
or higher-level protocol) to be in a certain encoding but contains octet sequences
that are not legal in that encoding. It is also a fatal error if an XML entity
contains no encoding declaration and its content is not legal UTF-8 or UTF-16.</p>
<p>Examples of text
declarations containing encoding declarations:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><?xml encoding='UTF-8'?>
<?xml encoding='EUC-JP'?></pre></td></tr></table>
</div>
</div>
<div class="div2">
<h3><a name="entproc"></a>4.4 XML Processor Treatment of Entities and References</h3>
<p>The table below summarizes the contexts in which character references,
entity references, and invocations of unparsed entities might appear and the
required behavior of an <a title="XML Processor" href="#dt-xml-proc">XML processor</a>
in each case. The labels in the leftmost column describe the recognition context: </p><dl>
<dt class="label">Reference in Content</dt>
<dd>
<p>as a reference anywhere after the <a title="Start-Tag" href="#dt-stag">start-tag</a>
and before the <a title="End Tag" href="#dt-etag">end-tag</a> of an element; corresponds
to the nonterminal <a href="#NT-content">content</a>.</p>
</dd>
<dt class="label">Reference in Attribute Value</dt>
<dd>
<p>as a reference within either the value of an attribute in a <a title="Start-Tag" href="#dt-stag">start-tag</a>,
or a default value in an <a title="Attribute-List Declaration" href="#dt-attdecl">attribute declaration</a>;
corresponds to the nonterminal <a href="#NT-AttValue">AttValue</a>.</p>
</dd>
<dt class="label">Occurs as Attribute Value</dt>
<dd>
<p>as a <a href="#NT-Name">Name</a>, not a reference, appearing either as
the value of an attribute which has been declared as type <b>ENTITY</b>,
or as one of the space-separated tokens in the value of an attribute which
has been declared as type <b>ENTITIES</b>.</p>
</dd>
<dt class="label">Reference in Entity Value</dt>
<dd>
<p>as a reference within a parameter or internal entity's <a title="Literal Entity Value" href="#dt-litentval">literal
entity value</a> in the entity's declaration; corresponds to the nonterminal <a href="#NT-EntityValue">EntityValue</a>.</p>
</dd>
<dt class="label">Reference in DTD</dt>
<dd>
<p>as
a 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>,
or the contents of an ignored conditional section (see <a href="#sec-condition-sect"><b>3.4 Conditional Sections</b></a>).</p>
<p>.</p>
</dd>
</dl><p></p>
<table border="1" frame="border" cellpadding="7"><tbody align="center"><tr>
<td rowspan="2" colspan="1"></td><td colspan="4" align="center" valign="bottom" rowspan="1">Entity
Type</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
General</td><td rowspan="1" colspan="1">Unparsed</td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Reference
in Content</td><td rowspan="1" colspan="1"><a href="#not-recognized"><cite>Not recognized</cite></a></td>
<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
if validating</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td>
<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
in literal</cite></a></td><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><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">Occurs as 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="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#notify"><cite>Notify</cite></a></td>
<td rowspan="1" colspan="1"><a href="#not-recognized"><cite>Not recognized</cite></a></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>
<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>
<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
as PE</cite></a></td><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><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></tr></tbody></table>
<div class="div3">
<h4><a name="not-recognized"></a>4.4.1 Not Recognized</h4>
<p>Outside the DTD, the <code>%</code> character has no special significance;
thus, what would be parameter entity references in the DTD are not recognized
as markup in <a href="#NT-content">content</a>. Similarly, the names of unparsed
entities are not recognized except when they appear in the value of an appropriately
declared attribute.</p>
</div>
<div class="div3">
<h4><a name="included"></a>4.4.2 Included</h4>
<p>[<a name="dt-include" title="Include">Definition</a>: An entity is <b>included</b>
when its <a title="Replacement Text" href="#dt-repltext">replacement text</a> is retrieved
and processed, in place of the reference itself, as though it were part of
the document at the location the reference was recognized.] The replacement
text may contain both <a title="Character Data" href="#dt-chardata">character data</a>
and (except for parameter entities) <a title="Markup" href="#dt-markup">markup</a>,
which must be recognized in the usual way. (The string "<code>AT&amp;T;</code>"
expands to "<code>AT&T;</code>" and the remaining ampersand
is not recognized as an entity-reference delimiter.) A character reference
is <b>included</b> when the indicated character is processed in place
of the reference itself. </p>
</div>
<div class="div3">
<h4><a name="include-if-valid"></a>4.4.3 Included If Validating</h4>
<p>When an XML processor recognizes a reference to a parsed entity, in order
to <a title="Validity" href="#dt-valid">validate</a> the document, the processor
must <a title="Include" href="#dt-include">include</a> its replacement text. If
the entity is external, and the processor is not attempting to validate the
XML document, the processor <a title="May" href="#dt-may">may</a>, but need
not, include the entity's replacement text. If a non-validating processor
does not include the replacement text, it must inform the application that
it recognized, but did not read, the entity.</p>
<p>This rule is based on the recognition that the automatic inclusion provided
by the SGML and XML entity mechanism, primarily designed to support modularity
in authoring, is not necessarily appropriate for other applications, in particular
document browsing. Browsers, for example, when encountering an external parsed
entity reference, might choose to provide a visual indication of the entity's
presence and retrieve it for display only on demand.</p>
</div>
<div class="div3">
<h4><a name="forbidden"></a>4.4.4 Forbidden</h4>
<p>The following are forbidden, and constitute <a title="Fatal Error" href="#dt-fatal">fatal</a>
errors:</p>
<ul>
<li><p>the appearance of a reference to an <a title="Unparsed Entity" href="#dt-unparsed">unparsed
entity</a>.</p></li>
<li><p>the appearance of any character or general-entity reference in the
DTD except within an <a href="#NT-EntityValue">EntityValue</a> or <a href="#NT-AttValue">AttValue</a>.</p>
</li>
<li><p>a reference to an external entity in an attribute value.</p></li>
</ul>
</div>
<div class="div3">
<h4><a name="inliteral"></a>4.4.5 Included in Literal</h4>
<p>When an <a title="Entity Reference" href="#dt-entref">entity reference</a> appears in
an attribute value, or a parameter entity reference appears in a literal entity
value, its <a title="Replacement Text" href="#dt-repltext">replacement text</a> is processed
in place of the reference itself as though it were part of the document at
the location the reference was recognized, except that a single or double
quote character in the replacement text is always treated as a normal data
character and will not terminate the literal. For example, this is well-formed:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!-- -->
<!ENTITY % YN '"Yes"' >
<!ENTITY WhatHeSaid "He said %YN;" ></pre></td></tr></table>
<p>while this is not:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY EndAttr "27'" >
<element attribute='a-&EndAttr;></pre></td></tr></table>
</div>
<div class="div3">
<h4><a name="notify"></a>4.4.6 Notify</h4>
<p>When the name of an <a title="Unparsed Entity" href="#dt-unparsed">unparsed entity</a>
appears as a token in the value of an attribute of declared type <b>ENTITY</b>
or <b>ENTITIES</b>, a validating processor must inform the application of
the <a title="System Identifier" href="#dt-sysid">system</a> and <a title="Public identifier" href="#dt-pubid">public</a>
(if any) identifiers for both the entity and its associated <a title="Notation" href="#dt-notation">notation</a>.</p>
</div>
<div class="div3">
<h4><a name="bypass"></a>4.4.7 Bypassed</h4>
<p>When a general entity reference appears in the <a href="#NT-EntityValue">EntityValue</a>
in an entity declaration, it is bypassed and left as is.</p>
</div>
<div class="div3">
<h4><a name="as-PE"></a>4.4.8 Included as PE</h4>
<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
reference is recognized in the DTD and included, its <a title="Replacement Text" href="#dt-repltext">replacement
text</a> is enlarged by the attachment of one leading and one following
space (#x20) character; the intent is to constrain the replacement text of
parameter entities to contain an integral number of grammatical tokens in
the DTD. This
behavior does not apply to parameter entity references within entity values;
these are described in <a href="#inliteral"><b>4.4.5 Included in Literal</b></a>.</p>
</div>
</div>
<div class="div2">
<h3><a name="intern-replacement"></a>4.5 Construction of Internal Entity Replacement Text</h3>
<p>In discussing the treatment of internal entities, it is useful to distinguish
two forms of the entity's value. [<a name="dt-litentval" title="Literal Entity Value">Definition</a>: The <b>literal
entity value</b> is the quoted string actually present in the entity declaration,
corresponding to the non-terminal <a href="#NT-EntityValue">EntityValue</a>.] [<a name="dt-repltext" title="Replacement Text">Definition</a>: The <b>replacement text</b>
is the content of the entity, after replacement of character references and
parameter-entity references.]</p>
<p>The literal entity value as given in an internal entity declaration (<a href="#NT-EntityValue">EntityValue</a>) may contain character, parameter-entity,
and general-entity references. Such references must be contained entirely
within 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
text</em> of any parameter entities referred to, and must contain the character
referred to, in place of any character references in the literal entity value;
however, general-entity references must be left as-is, unexpanded. For example,
given the following declarations:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY % pub "&#xc9;ditions Gallimard" >
<!ENTITY rights "All rights reserved" >
<!ENTITY book "La Peste: Albert Camus,
&#xA9; 1947 %pub;. &rights;" ></pre></td></tr></table>
<p>then the replacement text for the entity "<code>book</code>"
is:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>La Peste: Albert Camus,
© 1947 Éditions Gallimard. &rights;</pre></td></tr></table>
<p>The general-entity reference "<code>&rights;</code>" would
be expanded should the reference "<code>&book;</code>" appear
in the document's content or an attribute value.</p>
<p>These simple rules may have complex interactions; for a detailed discussion
of a difficult example, see <a href="#sec-entexpand"><b>D Expansion of Entity and Character References</b></a>.</p>
</div>
<div class="div2">
<h3><a name="sec-predefined-ent"></a>4.6 Predefined Entities</h3>
<p>[<a name="dt-escape" title="escape">Definition</a>: Entity and character references can
both be used to <b>escape</b> the left angle bracket, ampersand, and
other delimiters. A set of general entities (<code>amp</code>,
<code>lt</code>,
<code>gt</code>,
<code>apos</code>,
<code>quot</code>) is specified for
this purpose. Numeric character references may also be used; they are expanded
immediately when recognized and must be treated as character data, so the
numeric character references "<code>&#60;</code>" and "<code>&#38;</code>"
may be used to escape <code><</code> and <code>&</code> when they occur
in character data.]</p>
<p>All XML processors must recognize these entities whether they are declared
or not. <a title="For interoperability" href="#dt-interop">For interoperability</a>, valid XML
documents should declare these entities, like any others, before using them. If
the entities <code>lt</code> or <code>amp</code> are declared, they must be
declared as internal entities whose replacement text is a character reference
to the respective
character (less-than sign or ampersand) being escaped; the double
escaping is required for these entities so that references to them produce
a well-formed result. If the entities <code>gt</code>, <code>apos</code>,
or <code>quot</code> are declared, they must be declared as internal entities
whose replacement text is the single character being escaped (or a character
reference to that character; the double escaping here is unnecessary but harmless).
For example:</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><!ENTITY lt "&#38;#60;">
<!ENTITY gt "&#62;">
<!ENTITY amp "&#38;#38;">
<!ENTITY apos "&#39;">
<!ENTITY quot "&#34;"></pre></td></tr></table>
</div>
<div class="div2">
<h3><a name="Notations"></a>4.7 Notation Declarations</h3>
<p>[<a name="dt-notation" title="Notation">Definition</a>: <b>Notations</b> identify
by name the format of <a title="External Entity" href="#dt-extent">unparsed entities</a>,
the format of elements which bear a notation attribute, or the application
to which a <a title="Processing instruction" href="#dt-pi">processing instruction</a> is addressed.]</p>
<p>[<a name="dt-notdecl" title="Notation Declaration">Definition</a>: <b>Notation declarations</b>
provide a name for the notation, for use in entity and attribute-list declarations
and in attribute specifications, and an external identifier for the notation
which may allow an XML processor or its client application to locate a helper
application capable of processing data in the given notation.]</p>
<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><a href="#UniqueNotationName">[VC: Unique
Notation 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>
<div class="constraint"><p class="prefix"><a name="UniqueNotationName"></a><b>Validity constraint: Unique
Notation Name</b></p><p>Only one notation declaration can declare a given <a href="#NT-Name">Name</a>.</p>
</div>
<p>XML processors must provide applications with the name and external identifier(s)
of any notation declared and referred to in an attribute value, attribute
definition, or entity declaration. They may additionally resolve the external
identifier into the <a title="System Identifier" href="#dt-sysid">system identifier</a>, file
name, or other information needed to allow the application to call a processor
for data in the notation described. (It is not an error, however, for XML
documents to declare and refer to notations for which notation-specific applications
are not available on the system where the XML processor or application is
running.)</p>
</div>
<div class="div2">
<h3><a name="sec-doc-entity"></a>4.8 Document Entity</h3>
<p>[<a name="dt-docent" title="Document Entity">Definition</a>: The <b>document entity</b>
serves 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
not specify how the document entity is to be located by an XML processor;
unlike other entities, the document entity has no name and might well appear
on a processor input stream without any identification at all.</p>
</div>
</div>
<div class="div1">
<h2><a name="sec-conformance"></a>5 Conformance</h2>
<div class="div2">
<h3><a name="proc-types"></a>5.1 Validating and Non-Validating Processors</h3>
<p>Conforming <a title="XML Processor" href="#dt-xml-proc">XML processors</a> fall into
two classes: validating and non-validating.</p>
<p>Validating and non-validating processors alike must report violations of
this 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
entities</a> that they read.</p>
<p>[<a name="dt-validating" title="Validating Processor">Definition</a>: <b>Validating
processors</b> must,
at user option, report violations of the constraints expressed by
the declarations in the <a title="Document Type Declaration" href="#dt-doctype">DTD</a>, and failures
to fulfill the validity constraints given in this specification.]
To accomplish this, validating XML processors must read and process the entire
DTD and all external parsed entities referenced in the document.</p>
<p>Non-validating processors are required to check only the <a title="Document Entity" href="#dt-docent">document
entity</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
to check the document for validity, they are required to <b>process</b>
all the declarations they read in the internal DTD subset and in any parameter
entity that they read, up to the first reference to a parameter entity that
they do <em>not</em> read; that is to say, they must use the information
in those declarations to <a href="#AVNormalize"><cite>normalize</cite></a>
attribute values, <a href="#included"><cite>include</cite></a> the replacement
text of internal entities, and supply <a href="#sec-attr-defaults"><cite>default
attribute values</cite></a>.] Except when <code>standalone="yes"</code>, they
must not <a title="Process Declarations" href="#dt-use-mdecl">process</a> <a title="entity declaration" href="#dt-entdecl">entity
declarations</a> or <a title="Attribute-List Declaration" href="#dt-attdecl">attribute-list declarations</a>
encountered after a reference to a parameter entity that is not read, since
the entity may have contained overriding declarations.</p>
</div>
<div class="div2">
<h3><a name="safe-behavior"></a>5.2 Using XML Processors</h3>
<p>The behavior of a validating XML processor is highly predictable; it must
read every piece of a document and report all well-formedness and validity
violations. Less is required of a non-validating processor; it need not read
any part of the document other than the document entity. This has two effects
that may be important to users of XML processors:</p>
<ul>
<li><p>Certain well-formedness errors, specifically those that require reading
external entities, may not be detected by a non-validating processor. Examples
include 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
Recursion</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>
<li><p>The information passed from the processor to the application may
vary, depending on whether the processor reads parameter and external entities.
For example, a non-validating processor may not <a href="#AVNormalize"><cite>normalize</cite></a>
attribute values, <a href="#included"><cite>include</cite></a> the replacement
text of internal entities, or supply <a href="#sec-attr-defaults"><cite>default
attribute values</cite></a>, where doing so depends on having read declarations
in external or parameter entities.</p></li>
</ul>
<p>For maximum reliability in interoperating between different XML processors,
applications which use non-validating processors should not rely on any behaviors
not required of such processors. Applications which require facilities such
as the use of default attributes or internal entities which are declared in
external entities should use validating XML processors.</p>
</div>
</div>
<div class="div1">
<h2><a name="sec-notation"></a>6 Notation</h2>
<p>The formal grammar of XML is given in this specification using a simple
Extended Backus-Naur Form (EBNF) notation. Each rule in the grammar defines
one symbol, in the form</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>symbol ::= expression</pre></td></tr></table>
<p>Symbols are written with an initial capital letter if they are the
start symbol of a regular language, otherwise with an initial lower
case letter. Literal strings are quoted.</p>
<p>Within the expression on the right-hand side of a rule, the following expressions
are used to match strings of one or more characters: </p><dl>
<dt class="label"><code>#xN</code></dt>
<dd>
<p>where <code>N</code> is a hexadecimal integer, the expression matches the
character in ISO/IEC 10646 whose canonical (UCS-4) code value, when interpreted
as an unsigned binary number, has the value indicated. The number of leading
zeros in the <code>#xN</code> form is insignificant; the number of leading
zeros in the corresponding code value is governed by the character encoding
in use and is not significant for XML.</p>
</dd>
<dt class="label"><code>[a-zA-Z]</code>, <code>[#xN-#xN]</code></dt>
<dd>
<p>matches any <a href="#NT-Char">Char</a> with a value in the range(s) indicated (inclusive).</p>
</dd>
<dt class="label"><code>[abc]</code>, <code>[#xN#xN#xN]</code></dt>
<dd>
<p>matches any <a href="#NT-Char">Char</a> with a value among the characters
enumerated. Enumerations and ranges can be mixed in one set of brackets.</p>
</dd>
<dt class="label"><code>[^a-z]</code>, <code>[^#xN-#xN]</code></dt>
<dd>
<p>matches any <a href="#NT-Char">Char</a> with a value <em>outside</em> the range
indicated.</p>
</dd>
<dt class="label"><code>[^abc]</code>, <code>[^#xN#xN#xN]</code></dt>
<dd>
<p>matches any <a href="#NT-Char">Char</a> with a value not among the characters given. Enumerations
and ranges of forbidden values can be mixed in one set of brackets.</p>
</dd>
<dt class="label"><code>"string"</code></dt>
<dd>
<p>matches a literal string <a title="match" href="#dt-match">matching</a> that
given inside the double quotes.</p>
</dd>
<dt class="label"><code>'string'</code></dt>
<dd>
<p>matches a literal string <a title="match" href="#dt-match">matching</a> that
given inside the single quotes.</p>
</dd>
</dl><p> These symbols may be combined to match more complex patterns as follows,
where <code>A</code> and <code>B</code> represent simple expressions: </p><dl>
<dt class="label">(<code>expression</code>)</dt>
<dd>
<p><code>expression</code> is treated as a unit and may be combined as described
in this list.</p>
</dd>
<dt class="label"><code>A?</code></dt>
<dd>
<p>matches <code>A</code> or nothing; optional <code>A</code>.</p>
</dd>
<dt class="label"><code>A B</code></dt>
<dd>
<p>matches <code>A</code> followed by <code>B</code>. This
operator has higher precedence than alternation; thus <code>A B | C D</code>
is identical to <code>(A B) | (C D)</code>.</p>
</dd>
<dt class="label"><code>A | B</code></dt>
<dd>
<p>matches <code>A</code> or <code>B</code> but not both.</p>
</dd>
<dt class="label"><code>A - B</code></dt>
<dd>
<p>matches any string that matches <code>A</code> but does not match <code>B</code>.</p>
</dd>
<dt class="label"><code>A+</code></dt>
<dd>
<p>matches one or more occurrences of <code>A</code>.Concatenation
has higher precedence than alternation; thus <code>A+ | B+</code> is identical
to <code>(A+) | (B+)</code>.</p>
</dd>
<dt class="label"><code>A*</code></dt>
<dd>
<p>matches zero or more occurrences of <code>A</code>. Concatenation
has higher precedence than alternation; thus <code>A* | B*</code> is identical
to <code>(A*) | (B*)</code>.</p>
</dd>
</dl><p> Other notations used in the productions are: </p><dl>
<dt class="label"><code>/* ... */</code></dt>
<dd>
<p>comment.</p>
</dd>
<dt class="label"><code>[ wfc: ... ]</code></dt>
<dd>
<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>
</dd>
<dt class="label"><code>[ vc: ... ]</code></dt>
<dd>
<p>validity constraint; this identifies by name a constraint on <a title="Validity" href="#dt-valid">valid</a>
documents associated with a production.</p>
</dd>
</dl><p></p>
</div>
</div><div class="back">
<div class="div1">
<h2><a name="sec-bibliography"></a>A References</h2>
<div class="div2">
<h3><a name="sec-existing-stds"></a>A.1 Normative References</h3>
<dl>
<dt class="label"><a name="IANA"></a>IANA-CHARSETS</dt><dd>(Internet
Assigned Numbers Authority) <cite>Official Names for Character Sets</cite>,
ed. 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>. </dd>
<dt class="label"><a name="RFC1766"></a>IETF RFC 1766</dt><dd>IETF
(Internet Engineering Task Force). <cite>RFC 1766: Tags for the Identification
of 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>
<dt class="label"><a name="ISO10646"></a>ISO/IEC 10646</dt><dd>ISO (International Organization for
Standardization). <cite>ISO/IEC 10646-1993 (E). Information technology --
Universal Multiple-Octet Coded Character Set (UCS) -- Part 1: Architecture
and Basic Multilingual Plane.</cite> [Geneva]: International Organization
for Standardization, 1993 (plus amendments AM 1 through AM 7).</dd>
<dt class="label"><a name="ISO10646-2000"></a>ISO/IEC 10646-2000</dt><dd> ISO (International
Organization for Standardization). <cite>ISO/IEC 10646-1:2000. Information
technology -- Universal Multiple-Octet Coded Character Set (UCS) --
Part 1: Architecture and Basic Multilingual Plane.</cite> [Geneva]: International
Organization for Standardization, 2000.</dd>
<dt class="label"><a name="Unicode"></a>Unicode</dt><dd>The Unicode Consortium. <em>The Unicode
Standard, Version 2.0.</em> Reading, Mass.: Addison-Wesley Developers Press,
1996.</dd>
<dt class="label"><a name="Unicode3"></a>Unicode3</dt><dd>
The Unicode Consortium. <em>The Unicode Standard, Version 3.0.</em> Reading,
Mass.: Addison-Wesley Developers Press, 2000. ISBN 0-201-61633-5.</dd>
</dl></div>
<div class="div2">
<h3><a name="null"></a>A.2 Other References</h3>
<dl>
<dt class="label"><a name="Aho"></a>Aho/Ullman</dt><dd>Aho, Alfred V., Ravi Sethi, and Jeffrey D.
Ullman. <cite>Compilers: Principles, Techniques, and Tools</cite>.
Reading: Addison-Wesley, 1986, rpt. corr. 1988.</dd>
<dt class="label"><a name="Berners-Lee"></a>Berners-Lee et al.</dt><dd> Berners-Lee, T., R. Fielding,
and L. Masinter. <cite>Uniform Resource Identifiers (URI): Generic Syntax
and Semantics</cite>. 1997. (Work in progress; see updates to RFC1738.)</dd>
<dt class="label"><a name="ABK"></a>Brüggemann-Klein</dt><dd>Brüggemann-Klein,
Anne. Formal Models in Document Processing. Habilitationsschrift. Faculty
of 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>.)</dd>
<dt class="label"><a name="ABKDW"></a>Brüggemann-Klein and Wood</dt><dd>Brüggemann-Klein,
Anne, and Derick Wood. <cite>Deterministic Regular Languages</cite>.
Universität Freiburg, Institut für Informatik, Bericht 38, Oktober 1991. Extended
abstract in A. Finkel, M. Jantzen, Hrsg., STACS 1992, S. 173-184. Springer-Verlag,
Berlin 1992. Lecture Notes in Computer Science 577. Full version titled <cite>One-Unambiguous
Regular Languages</cite> in Information and Computation 140 (2): 229-253,
February 1998.</dd>
<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>
<dt class="label"><a name="IANA-LANGCODES"></a>IANA-LANGCODES</dt><dd>(Internet
Assigned Numbers Authority) <cite>Registry of Language Tags</cite>,
ed. 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>.)</dd>
<dt class="label"><a name="RFC2141"></a>IETF RFC2141</dt><dd>IETF
(Internet Engineering Task Force). <em>RFC 2141: URN Syntax</em>, ed.
R. Moats. 1997. (See <a href="http://www.ietf.org/rfc/rfc2141.txt">http://www.ietf.org/rfc/rfc2141.txt</a>.)</dd>
<dt class="label"><a name="rfc2279"></a>IETF RFC 2279</dt><dd>IETF
(Internet Engineering Task Force). <cite>RFC 2279: UTF-8, a transformation
format of ISO 10646</cite>, ed. F. Yergeau, 1998. (See <a href="http://www.ietf.org/rfc/rfc2279.txt">http://www.ietf.org/rfc/rfc2279.txt</a>.)</dd>
<dt class="label"><a name="rfc2376"></a>IETF RFC 2376</dt><dd>IETF
(Internet Engineering Task Force). <cite>RFC 2376: XML Media Types</cite>.
ed. E. Whitehead, M. Murata. 1998. (See <a href="http://www.ietf.org/rfc/rfc2376.txt">http://www.ietf.org/rfc/rfc2376.txt</a>.)</dd>
<dt class="label"><a name="rfc2396"></a>IETF RFC 2396</dt><dd>IETF
(Internet Engineering Task Force). <cite>RFC 2396: Uniform Resource Identifiers
(URI): Generic Syntax</cite>. T. Berners-Lee, R. Fielding, L. Masinter.
1998. (See <a href="http://www.ietf.org/rfc/rfc2396.txt">http://www.ietf.org/rfc/rfc2396.txt</a>.)</dd>
<dt class="label"><a name="rfc2732"></a>IETF RFC 2732</dt><dd>IETF
(Internet Engineering Task Force). <cite>RFC 2732: Format for Literal
IPv6 Addresses in URL's</cite>. R. Hinden, B. Carpenter, L. Masinter.
1999. (See <a href="http://www.ietf.org/rfc/rfc2732.txt">http://www.ietf.org/rfc/rfc2732.txt</a>.)</dd>
<dt class="label"><a name="rfc2781"></a>IETF RFC 2781</dt><dd>
IETF (Internet Engineering Task Force). <em>RFC 2781: UTF-16, an encoding
of 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>.)</dd>
<dt class="label"><a name="ISO639"></a>ISO 639</dt><dd>
(International Organization for Standardization). <cite>ISO 639:1988 (E).
Code for the representation of names of languages.</cite> [Geneva]: International
Organization for Standardization, 1988.</dd>
<dt class="label"><a name="ISO3166"></a>ISO 3166</dt><dd>
(International Organization for Standardization). <cite>ISO 3166-1:1997
(E). Codes for the representation of names of countries and their subdivisions --
Part 1: Country codes</cite> [Geneva]: International Organization for
Standardization, 1997.</dd>
<dt class="label"><a name="ISO8879"></a>ISO 8879</dt><dd>ISO (International Organization for Standardization). <cite>ISO
8879:1986(E). Information processing -- Text and Office Systems --
Standard Generalized Markup Language (SGML).</cite> First edition --
1986-10-15. [Geneva]: International Organization for Standardization, 1986. </dd>
<dt class="label"><a name="ISO10744"></a>ISO/IEC 10744</dt><dd>ISO (International Organization for
Standardization). <cite>ISO/IEC 10744-1992 (E). Information technology --
Hypermedia/Time-based Structuring Language (HyTime). </cite> [Geneva]:
International Organization for Standardization, 1992. <em>Extended Facilities
Annexe.</em> [Geneva]: International Organization for Standardization, 1996. </dd>
<dt class="label"><a name="websgml"></a>WEBSGML</dt><dd>ISO
(International Organization for Standardization). <cite>ISO 8879:1986
TC2. Information technology -- Document Description and Processing Languages. </cite>
[Geneva]: International Organization for Standardization, 1998. (See <a href="http://www.sgmlsource.com/8879rev/n0029.htm">http://www.sgmlsource.com/8879rev/n0029.htm</a>.)</dd>
<dt class="label"><a name="xml-names"></a>XML Names</dt><dd>Tim Bray,
Dave Hollander, and Andrew Layman, editors. <cite>Namespaces in XML</cite>.
Textuality, 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>.)</dd>
</dl></div>
</div>
<div class="div1">
<h2><a name="CharClasses"></a>B Character Classes</h2>
<p>Following the characteristics defined in the Unicode standard, characters
are classed as base characters (among others, these contain the alphabetic
characters of the Latin alphabet), ideographic characters, and combining characters (among
others, this class contains most diacritics) Digits and extenders are also
distinguished.</p>
<h5>Characters</h5><table class="scrap" summary="Scrap"><tbody>
<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>
<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]
| [#x00D8-#x00F6] | [#x00F8-#x00FF] | [#x0100-#x0131] | [#x0134-#x013E]
| [#x0141-#x0148] | [#x014A-#x017E] | [#x0180-#x01C3] | [#x01CD-#x01F0]
| [#x01F4-#x01F5] | [#x01FA-#x0217] | [#x0250-#x02A8] | [#x02BB-#x02C1]
| #x0386 | [#x0388-#x038A] | #x038C | [#x038E-#x03A1]
| [#x03A3-#x03CE] | [#x03D0-#x03D6] | #x03DA | #x03DC
| #x03DE | #x03E0 | [#x03E2-#x03F3] | [#x0401-#x040C]
| [#x040E-#x044F] | [#x0451-#x045C] | [#x045E-#x0481] | [#x0490-#x04C4]
| [#x04C7-#x04C8] | [#x04CB-#x04CC] | [#x04D0-#x04EB] | [#x04EE-#x04F5]
| [#x04F8-#x04F9] | [#x0531-#x0556] | #x0559 | [#x0561-#x0586]
| [#x05D0-#x05EA] | [#x05F0-#x05F2] | [#x0621-#x063A] | [#x0641-#x064A]
| [#x0671-#x06B7] | [#x06BA-#x06BE] | [#x06C0-#x06CE] | [#x06D0-#x06D3]
| #x06D5 | [#x06E5-#x06E6] | [#x0905-#x0939] | #x093D
| [#x0958-#x0961] | [#x0985-#x098C] | [#x098F-#x0990] | [#x0993-#x09A8]
| [#x09AA-#x09B0] | #x09B2 | [#x09B6-#x09B9] | [#x09DC-#x09DD]
| [#x09DF-#x09E1] | [#x09F0-#x09F1] | [#x0A05-#x0A0A] | [#x0A0F-#x0A10]
| [#x0A13-#x0A28] | [#x0A2A-#x0A30] | [#x0A32-#x0A33] | [#x0A35-#x0A36]
| [#x0A38-#x0A39] | [#x0A59-#x0A5C] | #x0A5E | [#x0A72-#x0A74]
| [#x0A85-#x0A8B] | #x0A8D | [#x0A8F-#x0A91] | [#x0A93-#x0AA8]
| [#x0AAA-#x0AB0] | [#x0AB2-#x0AB3] | [#x0AB5-#x0AB9] | #x0ABD
| #x0AE0 | [#x0B05-#x0B0C] | [#x0B0F-#x0B10] | [#x0B13-#x0B28]
| [#x0B2A-#x0B30] | [#x0B32-#x0B33] | [#x0B36-#x0B39] | #x0B3D
| [#x0B5C-#x0B5D] | [#x0B5F-#x0B61] | [#x0B85-#x0B8A] | [#x0B8E-#x0B90]
| [#x0B92-#x0B95] | [#x0B99-#x0B9A] | #x0B9C | [#x0B9E-#x0B9F]
| [#x0BA3-#x0BA4] | [#x0BA8-#x0BAA] | [#x0BAE-#x0BB5] | [#x0BB7-#x0BB9]
| [#x0C05-#x0C0C] | [#x0C0E-#x0C10] | [#x0C12-#x0C28] | [#x0C2A-#x0C33]
| [#x0C35-#x0C39] | [#x0C60-#x0C61] | [#x0C85-#x0C8C] | [#x0C8E-#x0C90]
| [#x0C92-#x0CA8] | [#x0CAA-#x0CB3] | [#x0CB5-#x0CB9] | #x0CDE
| [#x0CE0-#x0CE1] | [#x0D05-#x0D0C] | [#x0D0E-#x0D10] | [#x0D12-#x0D28]
| [#x0D2A-#x0D39] | [#x0D60-#x0D61] | [#x0E01-#x0E2E] | #x0E30
| [#x0E32-#x0E33] | [#x0E40-#x0E45] | [#x0E81-#x0E82] | #x0E84
| [#x0E87-#x0E88] | #x0E8A | #x0E8D | [#x0E94-#x0E97]
| [#x0E99-#x0E9F] | [#x0EA1-#x0EA3] | #x0EA5 | #x0EA7
| [#x0EAA-#x0EAB] | [#x0EAD-#x0EAE] | #x0EB0 | [#x0EB2-#x0EB3]
| #x0EBD | [#x0EC0-#x0EC4] | [#x0F40-#x0F47] | [#x0F49-#x0F69]
| [#x10A0-#x10C5] | [#x10D0-#x10F6] | #x1100 | [#x1102-#x1103]
| [#x1105-#x1107] | #x1109 | [#x110B-#x110C] | [#x110E-#x1112]
| #x113C | #x113E | #x1140 | #x114C | #x114E | #x1150
| [#x1154-#x1155] | #x1159 | [#x115F-#x1161] | #x1163
| #x1165 | #x1167 | #x1169 | [#x116D-#x116E] | [#x1172-#x1173]
| #x1175 | #x119E | #x11A8 | #x11AB | [#x11AE-#x11AF]
| [#x11B7-#x11B8] | #x11BA | [#x11BC-#x11C2] | #x11EB
| #x11F0 | #x11F9 | [#x1E00-#x1E9B] | [#x1EA0-#x1EF9]
| [#x1F00-#x1F15] | [#x1F18-#x1F1D] | [#x1F20-#x1F45] | [#x1F48-#x1F4D]
| [#x1F50-#x1F57] | #x1F59 | #x1F5B | #x1F5D | [#x1F5F-#x1F7D]
| [#x1F80-#x1FB4] | [#x1FB6-#x1FBC] | #x1FBE | [#x1FC2-#x1FC4]
| [#x1FC6-#x1FCC] | [#x1FD0-#x1FD3] | [#x1FD6-#x1FDB] | [#x1FE0-#x1FEC]
| [#x1FF2-#x1FF4] | [#x1FF6-#x1FFC] | #x2126 | [#x212A-#x212B]
| #x212E | [#x2180-#x2182] | [#x3041-#x3094] | [#x30A1-#x30FA]
| [#x3105-#x312C] | [#xAC00-#xD7A3] </code></td><xsltdebug></xsltdebug></tr>
<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>
<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]
| [#x0591-#x05A1] | [#x05A3-#x05B9] | [#x05BB-#x05BD] | #x05BF
| [#x05C1-#x05C2] | #x05C4 | [#x064B-#x0652] | #x0670
| [#x06D6-#x06DC] | [#x06DD-#x06DF] | [#x06E0-#x06E4] | [#x06E7-#x06E8]
| [#x06EA-#x06ED] | [#x0901-#x0903] | #x093C | [#x093E-#x094C]
| #x094D | [#x0951-#x0954] | [#x0962-#x0963] | [#x0981-#x0983]
| #x09BC | #x09BE | #x09BF | [#x09C0-#x09C4] | [#x09C7-#x09C8]
| [#x09CB-#x09CD] | #x09D7 | [#x09E2-#x09E3] | #x0A02
| #x0A3C | #x0A3E | #x0A3F | [#x0A40-#x0A42] | [#x0A47-#x0A48]
| [#x0A4B-#x0A4D] | [#x0A70-#x0A71] | [#x0A81-#x0A83] | #x0ABC
| [#x0ABE-#x0AC5] | [#x0AC7-#x0AC9] | [#x0ACB-#x0ACD] | [#x0B01-#x0B03]
| #x0B3C | [#x0B3E-#x0B43] | [#x0B47-#x0B48] | [#x0B4B-#x0B4D]
| [#x0B56-#x0B57] | [#x0B82-#x0B83] | [#x0BBE-#x0BC2] | [#x0BC6-#x0BC8]
| [#x0BCA-#x0BCD] | #x0BD7 | [#x0C01-#x0C03] | [#x0C3E-#x0C44]
| [#x0C46-#x0C48] | [#x0C4A-#x0C4D] | [#x0C55-#x0C56] | [#x0C82-#x0C83]
| [#x0CBE-#x0CC4] | [#x0CC6-#x0CC8] | [#x0CCA-#x0CCD] | [#x0CD5-#x0CD6]
| [#x0D02-#x0D03] | [#x0D3E-#x0D43] | [#x0D46-#x0D48] | [#x0D4A-#x0D4D]
| #x0D57 | #x0E31 | [#x0E34-#x0E3A] | [#x0E47-#x0E4E]
| #x0EB1 | [#x0EB4-#x0EB9] | [#x0EBB-#x0EBC] | [#x0EC8-#x0ECD]
| [#x0F18-#x0F19] | #x0F35 | #x0F37 | #x0F39 | #x0F3E
| #x0F3F | [#x0F71-#x0F84] | [#x0F86-#x0F8B] | [#x0F90-#x0F95]
| #x0F97 | [#x0F99-#x0FAD] | [#x0FB1-#x0FB7] | #x0FB9
| [#x20D0-#x20DC] | #x20E1 | [#x302A-#x302F] | #x3099
| #x309A </code></td><xsltdebug></xsltdebug></tr>
<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]
| [#x0966-#x096F] | [#x09E6-#x09EF] | [#x0A66-#x0A6F] | [#x0AE6-#x0AEF]
| [#x0B66-#x0B6F] | [#x0BE7-#x0BEF] | [#x0C66-#x0C6F] | [#x0CE6-#x0CEF]
| [#x0D66-#x0D6F] | [#x0E50-#x0E59] | [#x0ED0-#x0ED9] | [#x0F20-#x0F29] </code></td><xsltdebug></xsltdebug></tr>
<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
| #x0E46 | #x0EC6 | #x3005 | [#x3031-#x3035] | [#x309D-#x309E]
| [#x30FC-#x30FE] </code></td><xsltdebug></xsltdebug></tr>
</tbody></table>
<p>The character classes defined here can be derived from the Unicode 2.0
character database as follows:</p>
<ul>
<li><p>Name start characters must have one of the categories Ll, Lu, Lo,
Lt, Nl.</p></li>
<li><p>Name characters other than Name-start characters must have one of
the categories Mc, Me, Mn, Lm, or Nd.</p></li>
<li><p>Characters in the compatibility area (i.e. with character code greater
than #xF900 and less than #xFFFE) are not allowed in XML names.</p></li>
<li><p>Characters which have a font or compatibility decomposition (i.e.
those with a "compatibility formatting tag" in field 5 of the
database -- marked by field 5 beginning with a "<") are not
allowed.</p></li>
<li><p>The following characters are treated as name-start characters rather
than name characters, because the property file classifies them as Alphabetic:
[#x02BB-#x02C1], #x0559, #x06E5, #x06E6.</p></li>
<li><p>Characters #x20DD-#x20E0 are excluded (in accordance with Unicode 2.0,
section 5.14).</p></li>
<li><p>Character #x00B7 is classified as an extender, because the property
list so identifies it.</p></li>
<li><p>Character #x0387 is added as a name character, because #x00B7 is
its canonical equivalent.</p></li>
<li><p>Characters ':' and '_' are allowed as name-start characters.</p>
</li>
<li><p>Characters '-' and '.' are allowed as name characters.</p></li>
</ul>
</div>
<div class="div1">
<h2><a name="sec-xml-and-sgml"></a>C XML and SGML (Non-Normative)</h2>
<p>XML
is designed to be a subset of SGML, in that every XML document should also
be a conforming SGML document. For a detailed comparison of the additional
restrictions that XML places on documents beyond those of SGML, see <a href="#Clark">[Clark]</a>.</p>
</div>
<div class="div1">
<h2><a name="sec-entexpand"></a>D Expansion of Entity and Character References (Non-Normative)</h2>
<p>This appendix contains some examples illustrating the sequence of entity-
and character-reference recognition and expansion, as specified in <a href="#entproc"><b>4.4 XML Processor Treatment of Entities and References</b></a>.</p>
<p>If the DTD contains the declaration</p>
<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
numerically (&#38;#38;#38;) or with a general entity
(&amp;amp;).</p>" ></pre></td></tr></table>
<p>then the XML processor will recognize the character references when it
parses the entity declaration, and resolve them before storing the following
string as the value of the entity "<code>example</code>":</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre><p>An ampersand (&#38;) may be escaped
numerically (&#38;#38;) or with a general entity
(&amp;amp;).</p></pre></td></tr></table>
<p>A reference in the document to "<code>&example;</code>"
will cause the text to be reparsed, at which time the start- and end-tags
of the <code>p</code> element will be recognized and the three references will
be recognized and expanded, resulting in a <code>p</code> element with the following
content (all data, no delimiters or markup):</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>An ampersand (&) may be escaped
numerically (&#38;) or with a general entity
(&amp;).</pre></td></tr></table>
<p>A more complex example will illustrate the rules and their effects fully.
In the following example, the line numbers are solely for reference.</p>
<table class="eg" cellpadding="5" border="1" bgcolor="#99ffff" width="100%" summary="Example"><tr><td><pre>1 <?xml version='1.0'?>
2 <!DOCTYPE test [
3 <!ELEMENT test (#PCDATA) >
4 <!ENTITY % xx '&#37;zz;'>
5 <!ENTITY % zz '&#60;!ENTITY tricky "error-prone" >' >
6 %xx;
7 ]>
8 <test>This sample shows a &tricky; method.</test></pre></td></tr></table>
<p>This produces the following:</p>
<ul>
<li><p>in line 4, the reference to character 37 is expanded immediately,
and the parameter entity "<code>xx</code>" is stored in the symbol
table with the value "<code>%zz;</code>". Since the replacement
text is not rescanned, the reference to parameter entity "<code>zz</code>"
is not recognized. (And it would be an error if it were, since "<code>zz</code>"
is not yet declared.)</p></li>
<li><p>in line 5, the character reference "<code>&#60;</code>"
is expanded immediately and the parameter entity "<code>zz</code>"
is stored with the replacement text "<code><!ENTITY tricky "error-prone"
></code>", which is a well-formed entity declaration.</p></li>
<li><p>in line 6, the reference to "<code>xx</code>" is recognized,
and the replacement text of "<code>xx</code>" (namely "<code>%zz;</code>")
is parsed. The reference to "<code>zz</code>" is recognized in
its turn, and its replacement text ("<code><!ENTITY tricky "error-prone"
></code>") is parsed. The general entity "<code>tricky</code>"
has now been declared, with the replacement text "<code>error-prone</code>".</p>
</li>
<li><p>in line 8, the reference to the general entity "<code>tricky</code>"
is recognized, and it is expanded, so the full content of the <code>test</code>
element is the self-describing (and ungrammatical) string <em>This sample
shows a error-prone method.</em></p></li>
</ul>
</div>
<div class="div1">
<h2><a name="determinism"></a>E Deterministic Content Models (Non-Normative)</h2>
<p>As
noted in <a href="#sec-element-content"><b>3.2.1 Element Content</b></a>, it is required that content
models in element type declarations be deterministic. This requirement is <a title="For Compatibility" href="#dt-compat">for compatibility</a> with SGML (which calls deterministic
content models "unambiguous"); XML processors built
using SGML systems may flag non-deterministic content models as errors.</p>
<p>For example, the content model <code>((b, c) | (b, d))</code> is non-deterministic,
because given an initial <code>b</code> the XML processor
cannot know which <code>b</code> in the model is being matched without looking
ahead to see which element follows the <code>b</code>. In this case, the two references
to <code>b</code> can be collapsed into a single reference, making the model read <code>(b,
(c | d))</code>. An initial <code>b</code> now clearly matches only a single name
in the content model. The processor doesn't need to look ahead to see what follows; either <code>c</code> or <code>d</code>
would be accepted.</p>
<p>More formally: a finite state automaton may be constructed from the content
model using the standard algorithms, e.g. algorithm 3.5 in section 3.9 of
Aho, Sethi, and Ullman <a href="#Aho">[Aho/Ullman]</a>. In many such algorithms, a follow
set is constructed for each position in the regular expression (i.e., each
leaf node in the syntax tree for the regular expression); if any position
has a follow set in which more than one following position is labeled with
the same element type name, then the content model is in error and may be
reported as an error.</p>
<p>Algorithms exist which allow many but not all non-deterministic content
models to be reduced automatically to equivalent deterministic models; see
Brüggemann-Klein 1991 <a href="#ABK">[Brüggemann-Klein]</a>.</p>
</div>
<div class="div1">
<h2><a name="sec-guessing"></a>F Autodetection
of Character Encodings (Non-Normative)</h2>
<p>The XML encoding declaration functions as an internal label on each entity,
indicating which character encoding is in use. Before an XML processor can
read the internal label, however, it apparently has to know what character
encoding is in use--which is what the internal label is trying to indicate.
In the general case, this is a hopeless situation. It is not entirely hopeless
in XML, however, because XML limits the general case in two ways: each implementation
is assumed to support only a finite set of character encodings, and the XML
encoding declaration is restricted in position and content in order to make
it feasible to autodetect the character encoding in use in each entity in
normal cases. Also, in many cases other sources of information are available
in addition to the XML data stream itself. Two cases may be distinguished,
depending on whether the XML entity is presented to the processor without,
or with, any accompanying (external) information. We consider the first case
first.</p>
<div class="div2">
<h3><a name="sec-guessing-no-ext-info"></a>F.1 Detection Without External Encoding Information</h3>
<p>Because each XML entity not accompanied by external
encoding information and not in UTF-8 or UTF-16 encoding <em>must</em>
begin with an XML encoding declaration, in which the first characters must
be '<code><?xml</code>', any conforming processor can detect, after two
to four octets of input, which of the following cases apply. In reading this
list, it may help to know that in UCS-4, '<' is "<code>#x0000003C</code>"
and '?' is "<code>#x0000003F</code>", and the Byte Order Mark
required of UTF-16 data streams is "<code>#xFEFF</code>". The notation <var>##</var> is used to denote any byte value except that two consecutive <var>##</var>s cannot be both 00.</p>
<p>With a Byte Order Mark:</p>
<table border="1" frame="border"><tbody><tr><td rowspan="1" colspan="1"><code>00 00 FE
FF</code></td><td rowspan="1" colspan="1">UCS-4, big-endian machine (1234 order)</td></tr><tr><td rowspan="1" colspan="1"><code>FF
FE 00 00</code></td><td rowspan="1" colspan="1">UCS-4, little-endian machine (4321 order)</td></tr>
<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>
</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>
</tr><tr><td rowspan="1" colspan="1"><code>FE FF ## ##</code></td><td rowspan="1" colspan="1">UTF-16, big-endian</td></tr>
<tr><td rowspan="1" colspan="1"><code>FF FE ## ##</code></td><td rowspan="1" colspan="1">UTF-16, little-endian</td></tr><tr>
<td rowspan="1" colspan="1"><code>EF BB BF</code></td><td rowspan="1" colspan="1">UTF-8</td></tr></tbody></table>
<p>Without a Byte Order Mark:</p>
<table border="1" frame="border"><tbody><tr><td rowspan="1" colspan="1"><code>00 00 00 3C</code></td>
<td rowspan="4" colspan="1">UCS-4 or other encoding with a 32-bit code unit and ASCII
characters encoded as ASCII values, in respectively big-endian (1234), little-endian
(4321) and two unusual byte orders (2143 and 3412). The encoding declaration
must be read to determine which of UCS-4 or other supported 32-bit encodings
applies.</td></tr><tr><td rowspan="1" colspan="1"><code>3C 00 00 00</code></td>
</tr><tr><td rowspan="1" colspan="1"><code>00 00 3C 00</code></td>
</tr><tr><td rowspan="1" colspan="1"><code>00 3C 00 00</code></td>
</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
or other encoding with a 16-bit code unit in big-endian order and ASCII characters
encoded as ASCII values (the encoding declaration must be read to determine
which)</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
ISO-10646-UCS-2 or other encoding with a 16-bit code unit in little-endian
order and ASCII characters encoded as ASCII values (the encoding declaration
must be read to determine which)</td></tr><tr><td rowspan="1" colspan="1"><code>3C 3F 78 6D</code></td>
<td rowspan="1" colspan="1">UTF-8, ISO 646, ASCII, some part of ISO 8859, Shift-JIS, EUC, or any other
7-bit, 8-bit, or mixed-width encoding which ensures that the characters of
ASCII have their normal positions, width, and values; the actual encoding
declaration must be read to detect which of these applies, but since all of
these encodings use the same bit patterns for the relevant ASCII characters,
the encoding declaration itself may be read reliably</td></tr><tr><td rowspan="1" colspan="1"><code>4C
6F A7 94</code></td><td rowspan="1" colspan="1">EBCDIC (in some flavor; the full encoding declaration
must be read to tell which code page is in use)</td></tr><tr><td rowspan="1" colspan="1">Other</td>
<td rowspan="1" colspan="1">UTF-8 without an encoding declaration, or else the data stream is mislabeled
(lacking a required encoding declaration), corrupt, fragmentary, or enclosed
in a wrapper of some kind</td></tr></tbody></table>
<div class="note"><p class="prefix"><b>Note:</b></p>
<p>In cases above which do not require reading the encoding declaration to
determine the encoding, section 4.3.3 still requires that the encoding declaration,
if present, be read and that the encoding name be checked to match the actual
encoding of the entity. Also, it is possible that new character encodings
will be invented that will make it necessary to use the encoding declaration
to determine the encoding, in cases where this is not required at present.</p>
</div>
<p>This level of autodetection is enough to read the XML encoding declaration
and parse the character-encoding identifier, which is still necessary to distinguish
the individual members of each family of encodings (e.g. to tell UTF-8 from
8859, and the parts of 8859 from each other, or to distinguish the specific
EBCDIC code page in use, and so on).</p>
<p>Because the contents of the encoding declaration are restricted to characters from the ASCII repertoire (however encoded),
a processor can reliably read the entire encoding declaration as soon as it
has detected which family of encodings is in use. Since in practice, all widely
used character encodings fall into one of the categories above, the XML encoding
declaration allows reasonably reliable in-band labeling of character encodings,
even when external sources of information at the operating-system or transport-protocol
level are unreliable. Character encodings such as UTF-7
that make overloaded usage of ASCII-valued bytes may fail to be reliably detected.</p>
<p>Once the processor has detected the character encoding in use, it can act
appropriately, whether by invoking a separate input routine for each case,
or by calling the proper conversion function on each character of input.</p>
<p>Like any self-labeling system, the XML encoding declaration will not work
if any software changes the entity's character set or encoding without updating
the encoding declaration. Implementors of character-encoding routines should
be careful to ensure the accuracy of the internal and external information
used to label the entity.</p>
</div>
<div class="div2">
<h3><a name="sec-guessing-with-ext-info"></a>F.2 Priorities in the Presence of External Encoding Information</h3>
<p>The second possible case occurs when the XML entity is accompanied by encoding
information, as in some file systems and some network protocols. When multiple
sources of information are available, their relative priority and the preferred
method of handling conflict should be specified as part of the higher-level
protocol used to deliver XML. In particular, please refer
to <a href="#rfc2376">[IETF RFC 2376]</a> or its successor, which defines the <code>text/xml</code>
and <code>application/xml</code> MIME types and provides some useful guidance.
In the interests of interoperability, however, the following rule is recommended.</p>
<ul>
<li><p>If an XML entity is in a file, the Byte-Order Mark and encoding declaration are used (if present) to determine the character encoding.</p>
</li>
</ul>
</div>
</div>
<div class="div1">
<h2><a name="sec-xml-wg"></a>G W3C XML Working Group (Non-Normative)</h2>
<p>This specification was prepared and approved for publication by the W3C
XML Working Group (WG). WG approval of this specification does not necessarily
imply that all WG members voted for its approval. The current and former members
of the XML WG are:</p>
<ul>
<li>Jon Bosak, Sun (<i>Chair</i>)
</li>
<li>James Clark (<i>Technical Lead</i>) </li>
<li>Tim Bray, Textuality and Netscape
(<i>XML Co-editor</i>) </li>
<li>Jean Paoli, Microsoft (<i>XML
Co-editor</i>) </li>
<li>C. M. Sperberg-McQueen, U. of Ill.
(<i>XML Co-editor</i>) </li>
<li>Dan Connolly, W3C (<i>W3C Liaison</i>)
</li>
<li>Paula Angerstein, Texcel</li>
<li>Steve DeRose, INSO</li>
<li>Dave Hollander, HP</li>
<li>Eliot Kimber, ISOGEN</li>
<li>Eve Maler, ArborText</li>
<li>Tom Magliery, NCSA</li>
<li>Murray Maloney, SoftQuad, Grif
SA, Muzmo and Veo Systems</li>
<li>MURATA Makoto (FAMILY Given), Fuji
Xerox Information Systems</li>
<li>Joel Nava, Adobe</li>
<li>Conleth O'Connell, Vignette
</li>
<li>Peter Sharpe, SoftQuad</li>
<li>John Tigue, DataChannel</li>
</ul>
</div>
<div class="div1">
<h2><a name="sec-core-wg"></a>H W3C XML Core Group (Non-Normative)</h2>
<p>The second edition of this specification was prepared by the W3C XML Core
Working Group (WG). The members of the WG at the time of publication of this
edition were:</p>
<ul>
<li>Paula Angerstein, Vignette</li>
<li>Daniel Austin, Ask Jeeves</li>
<li>Tim Boland</li>
<li>Allen Brown, Microsoft</li>
<li>Dan Connolly, W3C (<i>Staff
Contact</i>) </li>
<li>John Cowan, Reuters Limited
</li>
<li>John Evdemon, XMLSolutions Corporation
</li>
<li>Paul Grosso, Arbortext (<i>Co-Chair</i>)
</li>
<li>Arnaud Le Hors, IBM (<i>Co-Chair</i>)
</li>
<li>Eve Maler, Sun Microsystems
(<i>Second Edition Editor</i>) </li>
<li>Jonathan Marsh, Microsoft</li>
<li>MURATA Makoto (FAMILY Given), IBM
</li>
<li>Mark Needleman, Data Research Associates
</li>
<li>David Orchard, Jamcracker</li>
<li>Lew Shannon, NCR</li>
<li>Richard Tobin, University of Edinburgh
</li>
<li>Daniel Veillard, W3C</li>
<li>Dan Vint, Lexica</li>
<li>Norman Walsh, Sun Microsystems
</li>
<li>François Yergeau, Alis Technologies
(<i>Errata List Editor</i>) </li>
<li>Kongyi Zhou, Oracle</li>
</ul>
</div>
<div class="div1">
<h2><a name="id2683713"></a>I Production Notes (Non-Normative)</h2>
<p>This Second Edition was encoded in the <a href="http://www.w3.org/XML/1998/06/xmlspec-v21.dtd">XMLspec
DTD</a> (which has <a href="http://www.w3.org/XML/1998/06/xmlspec-report-v21.htm">documentation</a>
available). 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>,
and <a href="http://www.w3.org/XML/1998/06/REC-xml-2e.xsl">REC-xml-2e.xsl</a>
XSLT stylesheets. The PDF version was produced with the <a href="http://www.tdb.uu.se/~jan/html2ps.html">html2ps</a>
facility and a distiller program.</p>
</div>
</div></body></html>
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