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<body>  <div class="head"><p><a href="http://www.w3.org/"><img src="http://www.w3.org/Icons/w3c_home"
alt="W3C" height="48" width="72"/></a></p><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> </dd>
<dd><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">&lt;tbray@textuality.com></a></dd>
<dd>Jean Paoli, Microsoft  <a href="mailto:jeanpa@microsoft.com">&lt;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">&lt;cmsmcq@uic.edu></a> </dd>
<dd>Eve Maler, Sun Microsystems, Inc. <a href="mailto:elm@east.sun.com">&lt;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>&nbsp;&copy;&nbsp;2000&nbsp;<a
href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>&reg;</sup>
(<a href="http://www.lcs.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a
href="http://www.inria.fr/"><abbr title="Institut National de Recherche en Informatique et Automatique"
lang="fr">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 class="html_compat"/><div><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>
<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 class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;1.1 <a
href="#sec-origin-goals">Origin and Goals</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;1.2 <a
href="#sec-terminology">Terminology</a><br class="html_compat"/>2 <a href="#sec-documents">Documents</a><br
class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.1 <a href="#sec-well-formed">Well-Formed
XML Documents</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.2 <a href="#charsets">Characters</a><br
class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.3 <a href="#sec-common-syn">Common
Syntactic Constructs</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.4 <a
href="#syntax">Character Data and Markup</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.5 <a
href="#sec-comments">Comments</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.6 <a
href="#sec-pi">Processing Instructions</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.7 <a
href="#sec-cdata-sect">CDATA Sections</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.8 <a
href="#sec-prolog-dtd">Prolog and Document Type Declaration</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.9 <a
href="#sec-rmd">Standalone Document Declaration</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.10 <a
href="#sec-white-space">White Space Handling</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.11 <a
href="#sec-line-ends">End-of-Line Handling</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;2.12 <a
href="#sec-lang-tag">Language Identification</a><br class="html_compat"/>3 <a
href="#sec-logical-struct">Logical Structures</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;3.1 <a
href="#sec-starttags">Start-Tags, End-Tags, and Empty-Element Tags</a><br
class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;3.2 <a href="#elemdecls">Element
Type Declarations</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.2.1 <a
href="#sec-element-content">Element Content</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.2.2 <a
href="#sec-mixed-content">Mixed Content</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;3.3 <a
href="#attdecls">Attribute-List Declarations</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.3.1 <a
href="#sec-attribute-types">Attribute Types</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.3.2 <a
href="#sec-attr-defaults">Attribute Defaults</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.3.3 <a
href="#AVNormalize">Attribute-Value Normalization</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;3.4 <a
href="#sec-condition-sect">Conditional Sections</a><br class="html_compat"/>4 <a
href="#sec-physical-struct">Physical Structures</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;4.1 <a
href="#sec-references">Character and Entity References</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;4.2 <a
href="#sec-entity-decl">Entity Declarations</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.2.1 <a
href="#sec-internal-ent">Internal Entities</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.2.2 <a
href="#sec-external-ent">External Entities</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;4.3 <a
href="#TextEntities">Parsed Entities</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.3.1 <a
href="#sec-TextDecl">The Text Declaration</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.3.2 <a
href="#wf-entities">Well-Formed Parsed Entities</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.3.3 <a
href="#charencoding">Character Encoding in Entities</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;4.4 <a
href="#entproc">XML Processor Treatment of Entities and References</a><br
class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.1 <a
href="#not-recognized">Not Recognized</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.2 <a
href="#included">Included</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.3 <a
href="#include-if-valid">Included If Validating</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.4 <a
href="#forbidden">Forbidden</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.5 <a
href="#inliteral">Included in Literal</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.6 <a
href="#notify">Notify</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.7 <a
href="#bypass">Bypassed</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.8 <a
href="#as-PE">Included as PE</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;4.5 <a
href="#intern-replacement">Construction of Internal Entity Replacement Text</a><br
class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;4.6 <a href="#sec-predefined-ent">Predefined
Entities</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;4.7 <a href="#Notations">Notation
Declarations</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;4.8 <a href="#sec-doc-entity">Document
Entity</a><br class="html_compat"/>5 <a href="#sec-conformance">Conformance</a><br
class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;5.1 <a href="#proc-types">Validating
and Non-Validating Processors</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;5.2 <a
href="#safe-behavior">Using XML Processors</a><br class="html_compat"/>6 <a
href="#sec-notation">Notation</a><br class="html_compat"/></p><h3>Appendices</h3><p
class="toc">A <a href="#sec-bibliography">References</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;A.1 <a
href="#sec-existing-stds">Normative References</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;A.2 <a
href="#null">Other References</a><br class="html_compat"/>B <a href="#CharClasses">Character
Classes</a><br class="html_compat"/>C <a href="#sec-xml-and-sgml">XML and
SGML</a> (Non-Normative)<br class="html_compat"/>D <a href="#sec-entexpand">Expansion
of Entity and Character References</a> (Non-Normative)<br class="html_compat"/>E <a
href="#determinism">Deterministic Content Models</a> (Non-Normative)<br class="html_compat"/>F <a
href="#sec-guessing">Autodetection of Character Encodings</a> (Non-Normative)<br
class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;F.1 <a href="#sec-guessing-no-ext-info">Detection
Without External Encoding Information</a><br class="html_compat"/>&nbsp;&nbsp;&nbsp;&nbsp;F.2 <a
href="#sec-guessing-with-ext-info">Priorities in the Presence of External
Encoding Information</a><br class="html_compat"/>G <a href="#sec-xml-wg">W3C
XML Working Group</a> (Non-Normative)<br class="html_compat"/>H <a href="#sec-core-wg">W3C
XML Core Group</a> (Non-Normative)<br class="html_compat"/>I <a href="#b4d250b6c21">Production
Notes</a> (Non-Normative)<br class="html_compat"/></p></div><hr class="html_compat"/><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 title="XML Processor" name="dt-xml-proc">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 title="Application"
name="dt-app">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 title="May" name="dt-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 title="Must" name="dt-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 title="Error" name="dt-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 title="Fatal Error" name="dt-fatal">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 title="At user option" name="dt-atuseroption">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 title="Validity constraint" name="dt-vc">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 title="Well-formedness constraint" name="dt-wfc">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 title="match" name="dt-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 title="For Compatibility" name="dt-compat">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 title="For interoperability" name="dt-interop">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 title="XML Document" name="dt-xml-doc">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 title="Well-Formed" name="dt-wellformed">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"><tbody>
<tr valign="baseline">
<td><a name="NT-document"></a>[1]&nbsp;&nbsp;&nbsp;</td>
<td><code>document</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-prolog">prolog</a> <a href="#NT-element">element</a> <a
href="#NT-Misc">Misc</a>*</code></td>
</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 title="Root Element" name="dt-root">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 title="Parent/Child" name="dt-parentchild">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 title="Text" name="dt-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 title="Character" name="dt-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"><tbody>
<tr valign="baseline">
<td><a name="NT-Char"></a>[2]&nbsp;&nbsp;&nbsp;</td>
<td><code>Char</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]</code></td>
<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">
<tbody>
<tr valign="baseline">
<td><a name="NT-S"></a>[3]&nbsp;&nbsp;&nbsp;</td>
<td><code>S</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>(#x20 | #x9 | #xD | #xA)+</code></td>
</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 title="Name" name="dt-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"><tbody>
<tr valign="baseline">
<td><a name="NT-NameChar"></a>[4]&nbsp;&nbsp;&nbsp;</td>
<td><code>NameChar</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-Name"></a>[5]&nbsp;&nbsp;&nbsp;</td>
<td><code>Name</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>(<a href="#NT-Letter">Letter</a> | '_' | ':') (<a href="#NT-NameChar">NameChar</a>)*</code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-Names"></a>[6]&nbsp;&nbsp;&nbsp;</td>
<td><code>Names</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-Name">Name</a> (<a href="#NT-S">S</a> <a href="#NT-Name">Name</a>)*</code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-Nmtoken"></a>[7]&nbsp;&nbsp;&nbsp;</td>
<td><code>Nmtoken</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>(<a href="#NT-NameChar">NameChar</a>)+</code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-Nmtokens"></a>[8]&nbsp;&nbsp;&nbsp;</td>
<td><code>Nmtokens</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-Nmtoken">Nmtoken</a> (<a href="#NT-S">S</a> <a href="#NT-Nmtoken">Nmtoken</a>)*</code></td>
</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"><tbody>
<tr valign="baseline">
<td><a name="NT-EntityValue"></a>[9]&nbsp;&nbsp;&nbsp;</td>
<td><code>EntityValue</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'"' ([^%&amp;"] | <a href="#NT-PEReference">PEReference</a> | <a
href="#NT-Reference">Reference</a>)* '"' </code></td>
</tr>
<tr valign="baseline">
<td></td>
<td></td>
<td></td>
<td><code>|&nbsp; "'" ([^%&amp;'] | <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]&nbsp;&nbsp;&nbsp;</td>
<td><code>AttValue</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'"' ([^&lt;&amp;"] | <a href="#NT-Reference">Reference</a>)* '"' </code></td>
</tr>
<tr valign="baseline">
<td></td>
<td></td>
<td></td>
<td><code>|&nbsp; "'" ([^&lt;&amp;'] | <a href="#NT-Reference">Reference</a>)*
"'"</code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-SystemLiteral"></a>[11]&nbsp;&nbsp;&nbsp;</td>
<td><code>SystemLiteral</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>('"' [^"]* '"') |&nbsp;("'" [^']* "'") </code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-PubidLiteral"></a>[12]&nbsp;&nbsp;&nbsp;</td>
<td><code>PubidLiteral</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'"' <a href="#NT-PubidChar">PubidChar</a>* '"' | "'" (<a href="#NT-PubidChar">PubidChar</a>
- "'")* "'"</code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-PubidChar"></a>[13]&nbsp;&nbsp;&nbsp;</td>
<td><code>PubidChar</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>#x20 | #xD | #xA |&nbsp;[a-zA-Z0-9] |&nbsp;[-'()+,./:=?;!*#@$_%]</code></td>
</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>&lt;</code> in the literal
(e.g., <code>&lt;!ENTITY mylt "&lt;"></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 title="Markup" name="dt-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 title="Character Data" name="dt-chardata">Definition</a>:
All text that is not markup constitutes the <b>character data</b> of the document.]</p> <p>The
ampersand character (&amp;) and the left angle bracket (&lt;) 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;amp;</code>"
and "<code>&amp;lt;</code>" respectively. The right angle bracket (>) may
be represented using the string "<code>&amp;gt;</code>", and must, <a title="For Compatibility"
href="#dt-compat">for compatibility</a>, be escaped using "<code>&amp;gt;</code>"
or a character reference when it appears in the string "<code>]]&gt;</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>]]&gt;</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>&amp;apos;</code>",
and the double-quote character (") as "<code>&amp;quot;</code>".</p> <h5>Character
Data</h5><table class="scrap"><tbody>
<tr valign="baseline">
<td><a name="NT-CharData"></a>[14]&nbsp;&nbsp;&nbsp;</td>
<td><code>CharData</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>[^&lt;&amp;]* - ([^&lt;&amp;]* ']]&gt;' [^&lt;&amp;]*)</code></td>
</tr>
</tbody></table> </div> <div class="div2"> <h3><a name="sec-comments"></a>2.5
Comments</h3> <p>[<a title="Comment" name="dt-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"><tbody>
<tr valign="baseline">
<td><a name="NT-Comment"></a>[15]&nbsp;&nbsp;&nbsp;</td>
<td><code>Comment</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;!--' ((<a href="#NT-Char">Char</a> - '-') | ('-' (<a href="#NT-Char">Char</a>
- '-')))* '-->'</code></td>
</tr>
</tbody></table> <p>An example of a comment:</p> <table class="eg" width="100%"
border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!-- declarations for &lt;head> &amp; &lt;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" width="100%"
border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!-- 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 title="Processing instruction" name="dt-pi">Definition</a>: <b>Processing
instructions</b> (PIs) allow documents to contain instructions for applications.]</p> <h5>Processing
Instructions</h5><table class="scrap"><tbody>
<tr valign="baseline">
<td><a name="NT-PI"></a>[16]&nbsp;&nbsp;&nbsp;</td>
<td><code>PI</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;?' <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>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-PITarget"></a>[17]&nbsp;&nbsp;&nbsp;</td>
<td><code>PITarget</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-Name">Name</a> - (('X' | 'x') ('M' | 'm') ('L' | 'l'))</code></td>
</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 title="CDATA Section"
name="dt-cdsection">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>&lt;![CDATA[</code>" and end with the string "<code>]]&gt;</code>":]</p> <h5>CDATA
Sections</h5><table class="scrap"><tbody>
<tr valign="baseline">
<td><a name="NT-CDSect"></a>[18]&nbsp;&nbsp;&nbsp;</td>
<td><code>CDSect</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-CDStart">CDStart</a> <a href="#NT-CData">CData</a> <a
href="#NT-CDEnd">CDEnd</a></code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-CDStart"></a>[19]&nbsp;&nbsp;&nbsp;</td>
<td><code>CDStart</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;![CDATA['</code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-CData"></a>[20]&nbsp;&nbsp;&nbsp;</td>
<td><code>CData</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>(<a href="#NT-Char">Char</a>* - (<a href="#NT-Char">Char</a>* ']]&gt;' <a
href="#NT-Char">Char</a>*)) </code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-CDEnd"></a>[21]&nbsp;&nbsp;&nbsp;</td>
<td><code>CDEnd</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>']]&gt;'</code></td>
</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>&amp;lt;</code>" and "<code>&amp;amp;</code>". CDATA sections cannot
nest.</p> <p>An example of a CDATA section, in which "<code>&lt;greeting></code>"
and "<code>&lt;/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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;![CDATA[&lt;greeting>Hello, world!&lt;/greeting>]]&gt; </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 title="XML Declaration" name="dt-xmldecl">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"
width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;?xml version="1.0"?> &lt;greeting>Hello, world!&lt;/greeting> </pre></td>
</tr>
</table> <p>and so is this:</p> <table class="eg" width="100%" border="1"
cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;greeting>Hello, world!&lt;/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 title="Validity" name="dt-valid">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"><tbody>
<tr valign="baseline">
<td><a name="NT-prolog"></a>[22]&nbsp;&nbsp;&nbsp;</td>
<td><code>prolog</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
</tr>
<tr valign="baseline">
<td><a name="NT-XMLDecl"></a>[23]&nbsp;&nbsp;&nbsp;</td>
<td><code>XMLDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;?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>
</tr>
<tr valign="baseline">
<td><a name="NT-VersionInfo"></a>[24]&nbsp;&nbsp;&nbsp;</td>
<td><code>VersionInfo</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
</tr>
<tr valign="baseline">
<td><a name="NT-Eq"></a>[25]&nbsp;&nbsp;&nbsp;</td>
<td><code>Eq</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-S">S</a>? '=' <a href="#NT-S">S</a>?</code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-VersionNum"></a>[26]&nbsp;&nbsp;&nbsp;</td>
<td><code>VersionNum</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>([a-zA-Z0-9_.:] | '-')+</code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-Misc"></a>[27]&nbsp;&nbsp;&nbsp;</td>
<td><code>Misc</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-Comment">Comment</a> | <a href="#NT-PI">PI</a> | <a
href="#NT-S">S</a></code></td>
</tr>
</tbody></table> <p>[<a title="Document Type Declaration" name="dt-doctype">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 title="markup declaration" name="dt-markupdecl">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"><tbody>
<tr valign="baseline">
<td><a name="NT-doctypedecl"></a>[28]&nbsp;&nbsp;&nbsp;</td>
<td><code>doctypedecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;!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>
<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]&nbsp;&nbsp;&nbsp;</td>
<td><code>DeclSep</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-PEReference">PEReference</a> | <a href="#NT-S">S</a></code></td>
<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]&nbsp;&nbsp;&nbsp;</td>
<td><code>markupdecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
<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"><tbody>
<tr valign="baseline">
<td><a name="NT-extSubset"></a>[30]&nbsp;&nbsp;&nbsp;</td>
<td><code>extSubset</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-TextDecl">TextDecl</a>? <a href="#NT-extSubsetDecl">extSubsetDecl</a></code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-extSubsetDecl"></a>[31]&nbsp;&nbsp;&nbsp;</td>
<td><code>extSubsetDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>( <a href="#NT-markupdecl">markupdecl</a> | <a href="#NT-conditionalSect">conditionalSect</a>
| <a href="#NT-DeclSep">DeclSep</a>)*</code></td>
<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"
width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;?xml version="1.0"?> &lt;!DOCTYPE greeting SYSTEM "hello.dtd"> &lt;greeting>Hello, world!&lt;/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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;?xml version="1.0" encoding="UTF-8" ?>
&lt;!DOCTYPE greeting [
  &lt;!ELEMENT greeting (#PCDATA)>
]>
&lt;greeting>Hello, world!&lt;/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 title="External Markup Declaration"
name="dt-extmkpdecl">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"><tbody>
<tr valign="baseline">
<td><a name="NT-SDDecl"></a>[32]&nbsp;&nbsp;&nbsp;</td>
<td><code>SDDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code> <a href="#NT-S">S</a> 'standalone' <a href="#NT-Eq">Eq</a> (("'"
('yes' | 'no') "'") | ('"' ('yes' | 'no') '"')) </code></td>
<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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;?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" width="100%"
border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ATTLIST poem  xml:space (default|preserve) 'preserve'>

&lt;!-- -->
&lt;!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" width="100%"
border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;p xml:lang="en">The quick brown fox jumps over the lazy dog.&lt;/p>
&lt;p xml:lang="en-GB">What colour is it?&lt;/p>
&lt;p xml:lang="en-US">What color is it?&lt;/p>
&lt;sp who="Faust" desc='leise' xml:lang="de">
  &lt;l>Habe nun, ach! Philosophie,&lt;/l>
  &lt;l>Juristerei, und Medizin&lt;/l>
  &lt;l>und leider auch Theologie&lt;/l>
  &lt;l>durchaus studiert mit hei&szlig;em Bem&uuml;h'n.&lt;/l>
&lt;/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" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ATTLIST poem   xml:lang NMTOKEN 'fr'>
&lt;!ATTLIST gloss  xml:lang NMTOKEN 'en'>
&lt;!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 title="Element" name="dt-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"><tbody>
<tr valign="baseline">
<td><a name="NT-element"></a>[39]&nbsp;&nbsp;&nbsp;</td>
<td><code>element</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-EmptyElemTag">EmptyElemTag</a></code></td>
</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 title="Start-Tag" name="dt-stag">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"><tbody>
<tr valign="baseline">
<td><a name="NT-STag"></a>[40]&nbsp;&nbsp;&nbsp;</td>
<td><code>STag</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;' <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>
<td><a href="#uniqattspec">[WFC: Unique Att Spec]</a></td>
</tr>
<tr valign="baseline">
<td><a name="NT-Attribute"></a>[41]&nbsp;&nbsp;&nbsp;</td>
<td><code>Attribute</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-Name">Name</a> <a href="#NT-Eq">Eq</a> <a href="#NT-AttValue">AttValue</a></code></td>
<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 &lt; 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 title="Attribute" name="dt-attr">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
title="Attribute Name" name="dt-attrname">Definition</a>: with the <a href="#NT-Name">Name</a>
in each pair referred to as the <b>attribute name</b>] and [<a title="Attribute Value"
name="dt-attrval">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>&lt;</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>&lt;</code>.</p> </div> <p>An
example of a start-tag:</p> <table class="eg" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<tr>
<td><pre>&lt;termdef id="dt-dog" term="dog"></pre></td>
</tr>
</table> <p>[<a title="End Tag" name="dt-etag">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"><tbody>
<tr valign="baseline">
<td><a name="NT-ETag"></a>[42]&nbsp;&nbsp;&nbsp;</td>
<td><code>ETag</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;/' <a href="#NT-Name">Name</a> <a href="#NT-S">S</a>? '>'</code></td>
</tr>
</tbody></table> <p>An example of an end-tag:</p> <table class="eg" width="100%"
border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;/termdef></pre></td>
</tr>
</table> <p>[<a title="Content" name="dt-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"><tbody>
<tr valign="baseline">
<td><a name="NT-content"></a>[43]&nbsp;&nbsp;&nbsp;</td>
<td><code>content</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
<td><i>/*  */</i></td>
</tr>
</tbody></table> <p>[<a title="Empty" name="dt-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 title="empty-element tag" name="dt-eetag">Definition</a>: An <b>empty-element
tag</b> takes a special form:]</p> <h5>Tags for Empty Elements</h5><table
class="scrap"><tbody>
<tr valign="baseline">
<td><a name="NT-EmptyElemTag"></a>[44]&nbsp;&nbsp;&nbsp;</td>
<td><code>EmptyElemTag</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;' <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>
<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"
width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;IMG align="left"
 src="http://www.w3.org/Icons/WWW/w3c_home" />
&lt;br>&lt;/br>
&lt;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
title="Element Type declaration" name="dt-eldecl">Definition</a>: An <b>element
type declaration</b> takes the form:]</p> <h5>Element Type Declaration</h5><table
class="scrap"><tbody>
<tr valign="baseline">
<td><a name="NT-elementdecl"></a>[45]&nbsp;&nbsp;&nbsp;</td>
<td><code>elementdecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;!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>
<td><a href="#EDUnique">[VC: Unique Element Type Declaration]</a></td>
</tr>
<tr valign="baseline">
<td><a name="NT-contentspec"></a>[46]&nbsp;&nbsp;&nbsp;</td>
<td><code>contentspec</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'EMPTY' | 'ANY' | <a href="#NT-Mixed">Mixed</a> | <a href="#NT-children">children</a> </code></td>
</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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ELEMENT br EMPTY>
&lt;!ELEMENT p (#PCDATA|emph)* >
&lt;!ELEMENT %name.para; %content.para; >
&lt;!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 title="Element content" name="dt-elemcontent">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 title="Content model"
name="dt-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"><tbody>
<tr valign="baseline">
<td><a name="NT-children"></a>[47]&nbsp;&nbsp;&nbsp;</td>
<td><code>children</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>(<a href="#NT-choice">choice</a> | <a href="#NT-seq">seq</a>) ('?'
| '*' | '+')?</code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-cp"></a>[48]&nbsp;&nbsp;&nbsp;</td>
<td><code>cp</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>(<a href="#NT-Name">Name</a> | <a href="#NT-choice">choice</a> | <a
href="#NT-seq">seq</a>) ('?' | '*' | '+')?</code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-choice"></a>[49]&nbsp;&nbsp;&nbsp;</td>
<td><code>choice</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
<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]&nbsp;&nbsp;&nbsp;</td>
<td><code>seq</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
<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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ELEMENT spec (front, body, back?)>
&lt;!ELEMENT div1 (head, (p | list | note)*, div2*)>
&lt;!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 title="Mixed Content" name="dt-mixed">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"><tbody>
<tr valign="baseline">
<td><a name="NT-Mixed"></a>[51]&nbsp;&nbsp;&nbsp;</td>
<td><code>Mixed</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
</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" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ELEMENT p (#PCDATA|a|ul|b|i|em)*>
&lt;!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* >
&lt;!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 title="Attribute-List Declaration" name="dt-attdecl">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"><tbody>
<tr valign="baseline">
<td><a name="NT-AttlistDecl"></a>[52]&nbsp;&nbsp;&nbsp;</td>
<td><code>AttlistDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;!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>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-AttDef"></a>[53]&nbsp;&nbsp;&nbsp;</td>
<td><code>AttDef</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
</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"><tbody>
<tr valign="baseline">
<td><a name="NT-AttType"></a>[54]&nbsp;&nbsp;&nbsp;</td>
<td><code>AttType</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-StringType">StringType</a> | <a href="#NT-TokenizedType">TokenizedType</a>
| <a href="#NT-EnumeratedType">EnumeratedType</a> </code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-StringType"></a>[55]&nbsp;&nbsp;&nbsp;</td>
<td><code>StringType</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'CDATA'</code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-TokenizedType"></a>[56]&nbsp;&nbsp;&nbsp;</td>
<td><code>TokenizedType</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'ID'</code></td>
<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
title="Enumerated Attribute Values" name="dt-enumerated">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"><tbody>
<tr valign="baseline">
<td><a name="NT-EnumeratedType"></a>[57]&nbsp;&nbsp;&nbsp;</td>
<td><code>EnumeratedType</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-NotationType">NotationType</a> | <a href="#NT-Enumeration">Enumeration</a> </code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-NotationType"></a>[58]&nbsp;&nbsp;&nbsp;</td>
<td><code>NotationType</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
<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]&nbsp;&nbsp;&nbsp;</td>
<td><code>Enumeration</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
<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">
<tbody>
<tr valign="baseline">
<td><a name="NT-DefaultDecl"></a>[60]&nbsp;&nbsp;&nbsp;</td>
<td><code>DefaultDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'#REQUIRED' |&nbsp;'#IMPLIED' </code></td>
</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 &lt; 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 title="Attribute Default" name="dt-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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ATTLIST termdef
          id      ID      #REQUIRED
          name    CDATA   #IMPLIED>
&lt;!ATTLIST list
          type    (bullets|ordered|glossary)  "ordered">
&lt;!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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ENTITY d "&amp;#xD;">
&lt;!ENTITY a "&amp;#xA;">
&lt;!ENTITY da "&amp;#xD;&amp;#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" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<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" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<tr>
<td><pre>a="&amp;d;&amp;d;A&amp;a;&amp;a;B&amp;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" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<tr>
<td><pre>a=
"&amp;#xd;&amp;#xd;A&amp;#xa;&amp;#xa;B&amp;#xd;&amp;#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
title="conditional section" name="dt-cond-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"><tbody>
<tr valign="baseline">
<td><a name="NT-conditionalSect"></a>[61]&nbsp;&nbsp;&nbsp;</td>
<td><code>conditionalSect</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-includeSect">includeSect</a> | <a href="#NT-ignoreSect">ignoreSect</a> </code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-includeSect"></a>[62]&nbsp;&nbsp;&nbsp;</td>
<td><code>includeSect</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;![' S? 'INCLUDE' S? '[' <a href="#NT-extSubsetDecl">extSubsetDecl</a>
']]&gt;' </code></td>
<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]&nbsp;&nbsp;&nbsp;</td>
<td><code>ignoreSect</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;![' S? 'IGNORE' S? '[' <a href="#NT-ignoreSectContents">ignoreSectContents</a>*
']]&gt;'</code></td>
<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]&nbsp;&nbsp;&nbsp;</td>
<td><code>ignoreSectContents</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-Ignore">Ignore</a> ('&lt;![' <a href="#NT-ignoreSectContents">ignoreSectContents</a>
']]&gt;' <a href="#NT-Ignore">Ignore</a>)*</code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-Ignore"></a>[65]&nbsp;&nbsp;&nbsp;</td>
<td><code>Ignore</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-Char">Char</a>* - (<a href="#NT-Char">Char</a>* ('&lt;!['
| ']]&gt;') <a href="#NT-Char">Char</a>*) </code></td>
</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>&lt;![</code>", "<code>[</code>", or "<code>]]&gt;</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>&lt;![</code>"
and ends "<code>]]&gt;</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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ENTITY % draft 'INCLUDE' >
&lt;!ENTITY % final 'IGNORE' >

&lt;![%draft;[
&lt;!ELEMENT book (comments*, title, body, supplements?)>
]]&gt;
&lt;![%final;[
&lt;!ELEMENT book (title, body, supplements?)>
]]&gt;</pre></td>
</tr>
</table> </div>  </div>  <div class="div1"> <h2><a name="sec-physical-struct"></a>4
Physical Structures</h2> <p>[<a title="Entity" name="dt-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 title="Text Entity" name="dt-parsedent">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 title="Unparsed Entity"
name="dt-unparsed">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 title="general entity" name="gen-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 title="Parameter entity" name="dt-PE">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
title="Character Reference" name="dt-charref">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"><tbody>
<tr valign="baseline">
<td><a name="NT-CharRef"></a>[66]&nbsp;&nbsp;&nbsp;</td>
<td><code>CharRef</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&amp;#' [0-9]+ ';' </code></td>
</tr>
<tr valign="baseline">
<td></td>
<td></td>
<td></td>
<td><code>| '&amp;#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>&amp;#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>&amp;#</code>",
the digits up to the terminating <code>;</code> provide a decimal representation
of the character's code point.</p> <p>[<a title="Entity Reference" name="dt-entref">Definition</a>:
An <b>entity reference</b> refers to the content of a named entity.] [<a title="General Entity Reference"
name="dt-GERef">Definition</a>: References to parsed general entities use
ampersand (<code>&amp;</code>) and semicolon (<code>;</code>) as delimiters.]
[<a title="Parameter-entity reference" name="dt-PERef">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"><tbody>
<tr valign="baseline">
<td><a name="NT-Reference"></a>[67]&nbsp;&nbsp;&nbsp;</td>
<td><code>Reference</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-EntityRef">EntityRef</a> | <a href="#NT-CharRef">CharRef</a></code></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-EntityRef"></a>[68]&nbsp;&nbsp;&nbsp;</td>
<td><code>EntityRef</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&amp;' <a href="#NT-Name">Name</a> ';'</code></td>
<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]&nbsp;&nbsp;&nbsp;</td>
<td><code>PEReference</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'%' <a href="#NT-Name">Name</a> ';'</code></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="#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" width="100%" border="1"
cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>Type &lt;key>less-than&lt;/key> (&amp;#x3C;) to save options.
This document was prepared on &amp;docdate; and
is classified &amp;security-level;.</pre></td>
</tr>
</table> <p>Example of a parameter-entity reference:</p> <table class="eg"
width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!-- declare the parameter entity "ISOLat2"... -->
&lt;!ENTITY % ISOLat2
         SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" >
&lt;!-- ... 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 title="entity declaration" name="dt-entdecl">Definition</a>:
 Entities are declared thus:]</p> <h5>Entity Declaration</h5><table class="scrap">
<tbody>
<tr valign="baseline">
<td><a name="NT-EntityDecl"></a>[70]&nbsp;&nbsp;&nbsp;</td>
<td><code>EntityDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-GEDecl">GEDecl</a> | <a href="#NT-PEDecl">PEDecl</a></code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-GEDecl"></a>[71]&nbsp;&nbsp;&nbsp;</td>
<td><code>GEDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;!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>
</tr>
<tr valign="baseline">
<td><a name="NT-PEDecl"></a>[72]&nbsp;&nbsp;&nbsp;</td>
<td><code>PEDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;!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>
</tr>
<tr valign="baseline">
<td><a name="NT-EntityDef"></a>[73]&nbsp;&nbsp;&nbsp;</td>
<td><code>EntityDef</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-EntityValue">EntityValue</a> | (<a href="#NT-ExternalID">ExternalID</a> <a
href="#NT-NDataDecl">NDataDecl</a>?)</code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-PEDef"></a>[74]&nbsp;&nbsp;&nbsp;</td>
<td><code>PEDef</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-EntityValue">EntityValue</a> | <a href="#NT-ExternalID">ExternalID</a></code></td>
</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 title="Internal Entity Replacement Text" name="dt-internent">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"
width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!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 title="External Entity" name="dt-extent">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"><tbody>
<tr valign="baseline">
<td><a name="NT-ExternalID"></a>[75]&nbsp;&nbsp;&nbsp;</td>
<td><code>ExternalID</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'SYSTEM' <a href="#NT-S">S</a> <a href="#NT-SystemLiteral">SystemLiteral</a></code></td>
</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]&nbsp;&nbsp;&nbsp;</td>
<td><code>NDataDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-S">S</a> 'NDATA' <a href="#NT-S">S</a> <a href="#NT-Name">Name</a></code></td>
<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
title="System Identifier" name="dt-sysid">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 title="Public identifier" name="dt-pubid">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" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ENTITY open-hatch
         SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml">
&lt;!ENTITY open-hatch
         PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN"
         "http://www.textuality.com/boilerplate/OpenHatch.xml">
&lt;!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">
<tbody>
<tr valign="baseline">
<td><a name="NT-TextDecl"></a>[77]&nbsp;&nbsp;&nbsp;</td>
<td><code>TextDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;?xml' <a href="#NT-VersionInfo">VersionInfo</a>? <a href="#NT-EncodingDecl">EncodingDecl</a> <a
href="#NT-S">S</a>? '?>'</code></td>
</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"><tbody>
<tr valign="baseline">
<td><a name="NT-extParsedEnt"></a>[78]&nbsp;&nbsp;&nbsp;</td>
<td><code>extParsedEnt</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-TextDecl">TextDecl</a>? <a href="#NT-content">content</a></code></td>
</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"><tbody>
<tr valign="baseline">
<td><a name="NT-EncodingDecl"></a>[80]&nbsp;&nbsp;&nbsp;</td>
<td><code>EncodingDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</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>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-EncName"></a>[81]&nbsp;&nbsp;&nbsp;</td>
<td><code>EncName</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>[A-Za-z] ([A-Za-z0-9._] | '-')*</code></td>
<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"
width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;?xml encoding='UTF-8'?>
&lt;?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 rowspan="1" colspan="4" align="center" valign="bottom">Entity Type</td>
<td rowspan="2" colspan="1" align="center">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 rowspan="1" colspan="1" align="right">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 rowspan="1" colspan="1" align="right">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 rowspan="1" colspan="1" align="right">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 rowspan="1" colspan="1" align="right">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 rowspan="1" colspan="1" align="right">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 title="Include" name="dt-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;amp;T;</code>"
expands to "<code>AT&amp;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" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<tr>
<td><pre>&lt;!--  -->
&lt;!ENTITY % YN '"Yes"' >
&lt;!ENTITY WhatHeSaid "He said %YN;" ></pre></td>
</tr>
</table> <p>while this is not:</p> <table class="eg" width="100%" border="1"
cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ENTITY EndAttr "27'" >
&lt;element attribute='a-&amp;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 title="Literal Entity Value"
name="dt-litentval">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 title="Replacement Text"
name="dt-repltext">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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ENTITY % pub    "&amp;#xc9;ditions Gallimard" >
&lt;!ENTITY   rights "All rights reserved" >
&lt;!ENTITY   book   "La Peste: Albert Camus,
&amp;#xA9; 1947 %pub;. &amp;rights;" ></pre></td>
</tr>
</table> <p>then the replacement text for the entity "<code>book</code>" is:</p> <table
class="eg" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>La Peste: Albert Camus,
&copy; 1947 &Eacute;ditions Gallimard. &amp;rights;</pre></td>
</tr>
</table> <p>The general-entity reference "<code>&amp;rights;</code>" would
be expanded should the reference "<code>&amp;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 title="escape"
name="dt-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>&amp;#60;</code>" and "<code>&amp;#38;</code>"
may be used to escape <code>&lt;</code> and <code>&amp;</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" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ENTITY lt     "&amp;#38;#60;">
&lt;!ENTITY gt     "&amp;#62;">
&lt;!ENTITY amp    "&amp;#38;#38;">
&lt;!ENTITY apos   "&amp;#39;">
&lt;!ENTITY quot   "&amp;#34;"></pre></td>
</tr>
</table>  </div> <div class="div2"> <h3><a name="Notations"></a>4.7 Notation
Declarations</h3> <p>[<a title="Notation" name="dt-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 title="Notation Declaration" name="dt-notdecl">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">
<tbody>
<tr valign="baseline">
<td><a name="NT-NotationDecl"></a>[82]&nbsp;&nbsp;&nbsp;</td>
<td><code>NotationDecl</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'&lt;!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>
<td><a href="#UniqueNotationName">[VC: Unique Notation Name]</a></td>
</tr>
</tbody><tbody>
<tr valign="baseline">
<td><a name="NT-PublicID"></a>[83]&nbsp;&nbsp;&nbsp;</td>
<td><code>PublicID</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>'PUBLIC' <a href="#NT-S">S</a> <a href="#NT-PubidLiteral">PubidLiteral</a> </code></td>
</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 title="Document Entity" name="dt-docent">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 title="Validating Processor" name="dt-validating">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 title="Process Declarations"
name="dt-use-mdecl">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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<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>Br&uuml;ggemann-Klein</dt>
<dd>Br&uuml;ggemann-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>Br&uuml;ggemann-Klein and Wood</dt>
<dd>Br&uuml;ggemann-Klein, Anne, and Derick Wood. <cite>Deterministic Regular
Languages</cite>. Universit&auml;t Freiburg, Institut f&uuml;r 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">
<tbody>
<tr valign="baseline">
<td><a name="NT-Letter"></a>[84]&nbsp;&nbsp;&nbsp;</td>
<td><code>Letter</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code><a href="#NT-BaseChar">BaseChar</a> | <a href="#NT-Ideographic">Ideographic</a></code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-BaseChar"></a>[85]&nbsp;&nbsp;&nbsp;</td>
<td><code>BaseChar</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>[#x0041-#x005A] |&nbsp;[#x0061-#x007A] |&nbsp;[#x00C0-#x00D6] |&nbsp;[#x00D8-#x00F6]
|&nbsp;[#x00F8-#x00FF] |&nbsp;[#x0100-#x0131] |&nbsp;[#x0134-#x013E] |&nbsp;[#x0141-#x0148]
|&nbsp;[#x014A-#x017E] |&nbsp;[#x0180-#x01C3] |&nbsp;[#x01CD-#x01F0] |&nbsp;[#x01F4-#x01F5]
|&nbsp;[#x01FA-#x0217] |&nbsp;[#x0250-#x02A8] |&nbsp;[#x02BB-#x02C1] |&nbsp;#x0386
|&nbsp;[#x0388-#x038A] |&nbsp;#x038C |&nbsp;[#x038E-#x03A1] |&nbsp;[#x03A3-#x03CE]
|&nbsp;[#x03D0-#x03D6] |&nbsp;#x03DA |&nbsp;#x03DC |&nbsp;#x03DE |&nbsp;#x03E0
|&nbsp;[#x03E2-#x03F3] |&nbsp;[#x0401-#x040C] |&nbsp;[#x040E-#x044F] |&nbsp;[#x0451-#x045C]
|&nbsp;[#x045E-#x0481] |&nbsp;[#x0490-#x04C4] |&nbsp;[#x04C7-#x04C8] |&nbsp;[#x04CB-#x04CC]
|&nbsp;[#x04D0-#x04EB] |&nbsp;[#x04EE-#x04F5] |&nbsp;[#x04F8-#x04F9] |&nbsp;[#x0531-#x0556]
|&nbsp;#x0559 |&nbsp;[#x0561-#x0586] |&nbsp;[#x05D0-#x05EA] |&nbsp;[#x05F0-#x05F2]
|&nbsp;[#x0621-#x063A] |&nbsp;[#x0641-#x064A] |&nbsp;[#x0671-#x06B7] |&nbsp;[#x06BA-#x06BE]
|&nbsp;[#x06C0-#x06CE] |&nbsp;[#x06D0-#x06D3] |&nbsp;#x06D5 |&nbsp;[#x06E5-#x06E6]
|&nbsp;[#x0905-#x0939] |&nbsp;#x093D |&nbsp;[#x0958-#x0961] |&nbsp;[#x0985-#x098C]
|&nbsp;[#x098F-#x0990] |&nbsp;[#x0993-#x09A8] |&nbsp;[#x09AA-#x09B0] |&nbsp;#x09B2
|&nbsp;[#x09B6-#x09B9] |&nbsp;[#x09DC-#x09DD] |&nbsp;[#x09DF-#x09E1] |&nbsp;[#x09F0-#x09F1]
|&nbsp;[#x0A05-#x0A0A] |&nbsp;[#x0A0F-#x0A10] |&nbsp;[#x0A13-#x0A28] |&nbsp;[#x0A2A-#x0A30]
|&nbsp;[#x0A32-#x0A33] |&nbsp;[#x0A35-#x0A36] |&nbsp;[#x0A38-#x0A39] |&nbsp;[#x0A59-#x0A5C]
|&nbsp;#x0A5E |&nbsp;[#x0A72-#x0A74] |&nbsp;[#x0A85-#x0A8B] |&nbsp;#x0A8D
|&nbsp;[#x0A8F-#x0A91] |&nbsp;[#x0A93-#x0AA8] |&nbsp;[#x0AAA-#x0AB0] |&nbsp;[#x0AB2-#x0AB3]
|&nbsp;[#x0AB5-#x0AB9] |&nbsp;#x0ABD |&nbsp;#x0AE0 |&nbsp;[#x0B05-#x0B0C]
|&nbsp;[#x0B0F-#x0B10] |&nbsp;[#x0B13-#x0B28] |&nbsp;[#x0B2A-#x0B30] |&nbsp;[#x0B32-#x0B33]
|&nbsp;[#x0B36-#x0B39] |&nbsp;#x0B3D |&nbsp;[#x0B5C-#x0B5D] |&nbsp;[#x0B5F-#x0B61]
|&nbsp;[#x0B85-#x0B8A] |&nbsp;[#x0B8E-#x0B90] |&nbsp;[#x0B92-#x0B95] |&nbsp;[#x0B99-#x0B9A]
|&nbsp;#x0B9C |&nbsp;[#x0B9E-#x0B9F] |&nbsp;[#x0BA3-#x0BA4] |&nbsp;[#x0BA8-#x0BAA]
|&nbsp;[#x0BAE-#x0BB5] |&nbsp;[#x0BB7-#x0BB9] |&nbsp;[#x0C05-#x0C0C] |&nbsp;[#x0C0E-#x0C10]
|&nbsp;[#x0C12-#x0C28] |&nbsp;[#x0C2A-#x0C33] |&nbsp;[#x0C35-#x0C39] |&nbsp;[#x0C60-#x0C61]
|&nbsp;[#x0C85-#x0C8C] |&nbsp;[#x0C8E-#x0C90] |&nbsp;[#x0C92-#x0CA8] |&nbsp;[#x0CAA-#x0CB3]
|&nbsp;[#x0CB5-#x0CB9] |&nbsp;#x0CDE |&nbsp;[#x0CE0-#x0CE1] |&nbsp;[#x0D05-#x0D0C]
|&nbsp;[#x0D0E-#x0D10] |&nbsp;[#x0D12-#x0D28] |&nbsp;[#x0D2A-#x0D39] |&nbsp;[#x0D60-#x0D61]
|&nbsp;[#x0E01-#x0E2E] |&nbsp;#x0E30 |&nbsp;[#x0E32-#x0E33] |&nbsp;[#x0E40-#x0E45]
|&nbsp;[#x0E81-#x0E82] |&nbsp;#x0E84 |&nbsp;[#x0E87-#x0E88] |&nbsp;#x0E8A
|&nbsp;#x0E8D |&nbsp;[#x0E94-#x0E97] |&nbsp;[#x0E99-#x0E9F] |&nbsp;[#x0EA1-#x0EA3]
|&nbsp;#x0EA5 |&nbsp;#x0EA7 |&nbsp;[#x0EAA-#x0EAB] |&nbsp;[#x0EAD-#x0EAE]
|&nbsp;#x0EB0 |&nbsp;[#x0EB2-#x0EB3] |&nbsp;#x0EBD |&nbsp;[#x0EC0-#x0EC4]
|&nbsp;[#x0F40-#x0F47] |&nbsp;[#x0F49-#x0F69] |&nbsp;[#x10A0-#x10C5] |&nbsp;[#x10D0-#x10F6]
|&nbsp;#x1100 |&nbsp;[#x1102-#x1103] |&nbsp;[#x1105-#x1107] |&nbsp;#x1109
|&nbsp;[#x110B-#x110C] |&nbsp;[#x110E-#x1112] |&nbsp;#x113C |&nbsp;#x113E
|&nbsp;#x1140 |&nbsp;#x114C |&nbsp;#x114E |&nbsp;#x1150 |&nbsp;[#x1154-#x1155]
|&nbsp;#x1159 |&nbsp;[#x115F-#x1161] |&nbsp;#x1163 |&nbsp;#x1165 |&nbsp;#x1167
|&nbsp;#x1169 |&nbsp;[#x116D-#x116E] |&nbsp;[#x1172-#x1173] |&nbsp;#x1175
|&nbsp;#x119E |&nbsp;#x11A8 |&nbsp;#x11AB |&nbsp;[#x11AE-#x11AF] |&nbsp;[#x11B7-#x11B8]
|&nbsp;#x11BA |&nbsp;[#x11BC-#x11C2] |&nbsp;#x11EB |&nbsp;#x11F0 |&nbsp;#x11F9
|&nbsp;[#x1E00-#x1E9B] |&nbsp;[#x1EA0-#x1EF9] |&nbsp;[#x1F00-#x1F15] |&nbsp;[#x1F18-#x1F1D]
|&nbsp;[#x1F20-#x1F45] |&nbsp;[#x1F48-#x1F4D] |&nbsp;[#x1F50-#x1F57] |&nbsp;#x1F59
|&nbsp;#x1F5B |&nbsp;#x1F5D |&nbsp;[#x1F5F-#x1F7D] |&nbsp;[#x1F80-#x1FB4]
|&nbsp;[#x1FB6-#x1FBC] |&nbsp;#x1FBE |&nbsp;[#x1FC2-#x1FC4] |&nbsp;[#x1FC6-#x1FCC]
|&nbsp;[#x1FD0-#x1FD3] |&nbsp;[#x1FD6-#x1FDB] |&nbsp;[#x1FE0-#x1FEC] |&nbsp;[#x1FF2-#x1FF4]
|&nbsp;[#x1FF6-#x1FFC] |&nbsp;#x2126 |&nbsp;[#x212A-#x212B] |&nbsp;#x212E
|&nbsp;[#x2180-#x2182] |&nbsp;[#x3041-#x3094] |&nbsp;[#x30A1-#x30FA] |&nbsp;[#x3105-#x312C]
|&nbsp;[#xAC00-#xD7A3] </code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-Ideographic"></a>[86]&nbsp;&nbsp;&nbsp;</td>
<td><code>Ideographic</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>[#x4E00-#x9FA5] |&nbsp;#x3007 |&nbsp;[#x3021-#x3029] </code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-CombiningChar"></a>[87]&nbsp;&nbsp;&nbsp;</td>
<td><code>CombiningChar</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>[#x0300-#x0345] |&nbsp;[#x0360-#x0361] |&nbsp;[#x0483-#x0486] |&nbsp;[#x0591-#x05A1]
|&nbsp;[#x05A3-#x05B9] |&nbsp;[#x05BB-#x05BD] |&nbsp;#x05BF |&nbsp;[#x05C1-#x05C2]
|&nbsp;#x05C4 |&nbsp;[#x064B-#x0652] |&nbsp;#x0670 |&nbsp;[#x06D6-#x06DC]
|&nbsp;[#x06DD-#x06DF] |&nbsp;[#x06E0-#x06E4] |&nbsp;[#x06E7-#x06E8] |&nbsp;[#x06EA-#x06ED]
|&nbsp;[#x0901-#x0903] |&nbsp;#x093C |&nbsp;[#x093E-#x094C] |&nbsp;#x094D
|&nbsp;[#x0951-#x0954] |&nbsp;[#x0962-#x0963] |&nbsp;[#x0981-#x0983] |&nbsp;#x09BC
|&nbsp;#x09BE |&nbsp;#x09BF |&nbsp;[#x09C0-#x09C4] |&nbsp;[#x09C7-#x09C8]
|&nbsp;[#x09CB-#x09CD] |&nbsp;#x09D7 |&nbsp;[#x09E2-#x09E3] |&nbsp;#x0A02
|&nbsp;#x0A3C |&nbsp;#x0A3E |&nbsp;#x0A3F |&nbsp;[#x0A40-#x0A42] |&nbsp;[#x0A47-#x0A48]
|&nbsp;[#x0A4B-#x0A4D] |&nbsp;[#x0A70-#x0A71] |&nbsp;[#x0A81-#x0A83] |&nbsp;#x0ABC
|&nbsp;[#x0ABE-#x0AC5] |&nbsp;[#x0AC7-#x0AC9] |&nbsp;[#x0ACB-#x0ACD] |&nbsp;[#x0B01-#x0B03]
|&nbsp;#x0B3C |&nbsp;[#x0B3E-#x0B43] |&nbsp;[#x0B47-#x0B48] |&nbsp;[#x0B4B-#x0B4D]
|&nbsp;[#x0B56-#x0B57] |&nbsp;[#x0B82-#x0B83] |&nbsp;[#x0BBE-#x0BC2] |&nbsp;[#x0BC6-#x0BC8]
|&nbsp;[#x0BCA-#x0BCD] |&nbsp;#x0BD7 |&nbsp;[#x0C01-#x0C03] |&nbsp;[#x0C3E-#x0C44]
|&nbsp;[#x0C46-#x0C48] |&nbsp;[#x0C4A-#x0C4D] |&nbsp;[#x0C55-#x0C56] |&nbsp;[#x0C82-#x0C83]
|&nbsp;[#x0CBE-#x0CC4] |&nbsp;[#x0CC6-#x0CC8] |&nbsp;[#x0CCA-#x0CCD] |&nbsp;[#x0CD5-#x0CD6]
|&nbsp;[#x0D02-#x0D03] |&nbsp;[#x0D3E-#x0D43] |&nbsp;[#x0D46-#x0D48] |&nbsp;[#x0D4A-#x0D4D]
|&nbsp;#x0D57 |&nbsp;#x0E31 |&nbsp;[#x0E34-#x0E3A] |&nbsp;[#x0E47-#x0E4E]
|&nbsp;#x0EB1 |&nbsp;[#x0EB4-#x0EB9] |&nbsp;[#x0EBB-#x0EBC] |&nbsp;[#x0EC8-#x0ECD]
|&nbsp;[#x0F18-#x0F19] |&nbsp;#x0F35 |&nbsp;#x0F37 |&nbsp;#x0F39 |&nbsp;#x0F3E
|&nbsp;#x0F3F |&nbsp;[#x0F71-#x0F84] |&nbsp;[#x0F86-#x0F8B] |&nbsp;[#x0F90-#x0F95]
|&nbsp;#x0F97 |&nbsp;[#x0F99-#x0FAD] |&nbsp;[#x0FB1-#x0FB7] |&nbsp;#x0FB9
|&nbsp;[#x20D0-#x20DC] |&nbsp;#x20E1 |&nbsp;[#x302A-#x302F] |&nbsp;#x3099
|&nbsp;#x309A </code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-Digit"></a>[88]&nbsp;&nbsp;&nbsp;</td>
<td><code>Digit</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>[#x0030-#x0039] |&nbsp;[#x0660-#x0669] |&nbsp;[#x06F0-#x06F9] |&nbsp;[#x0966-#x096F]
|&nbsp;[#x09E6-#x09EF] |&nbsp;[#x0A66-#x0A6F] |&nbsp;[#x0AE6-#x0AEF] |&nbsp;[#x0B66-#x0B6F]
|&nbsp;[#x0BE7-#x0BEF] |&nbsp;[#x0C66-#x0C6F] |&nbsp;[#x0CE6-#x0CEF] |&nbsp;[#x0D66-#x0D6F]
|&nbsp;[#x0E50-#x0E59] |&nbsp;[#x0ED0-#x0ED9] |&nbsp;[#x0F20-#x0F29] </code></td>
</tr>
<tr valign="baseline">
<td><a name="NT-Extender"></a>[89]&nbsp;&nbsp;&nbsp;</td>
<td><code>Extender</code></td>
<td>&nbsp;&nbsp;&nbsp;::=&nbsp;&nbsp;&nbsp;</td>
<td><code>#x00B7 |&nbsp;#x02D0 |&nbsp;#x02D1 |&nbsp;#x0387 |&nbsp;#x0640 |&nbsp;#x0E46
|&nbsp;#x0EC6 |&nbsp;#x3005 |&nbsp;[#x3031-#x3035] |&nbsp;[#x309D-#x309E]
|&nbsp;[#x30FC-#x30FE] </code></td>
</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 "&lt;") 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" width="100%" border="1" cellpadding="5"
bgcolor="#99ffff">
<tr>
<td><pre>&lt;!ENTITY example "&lt;p>An ampersand (&amp;#38;#38;) may be escaped
numerically (&amp;#38;#38;#38;) or with a general entity
(&amp;amp;amp;).&lt;/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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>&lt;p>An ampersand (&amp;#38;) may be escaped
numerically (&amp;#38;#38;) or with a general entity
(&amp;amp;amp;).&lt;/p></pre></td>
</tr>
</table> <p>A reference in the document to "<code>&amp;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" width="100%" border="1"
cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>An ampersand (&amp;) may be escaped
numerically (&amp;#38;) or with a general entity
(&amp;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" width="100%" border="1" cellpadding="5" bgcolor="#99ffff">
<tr>
<td><pre>1 &lt;?xml version='1.0'?>
2 &lt;!DOCTYPE test [
3 &lt;!ELEMENT test (#PCDATA) >
4 &lt;!ENTITY % xx '&amp;#37;zz;'>
5 &lt;!ENTITY % zz '&amp;#60;!ENTITY tricky "error-prone" >' >
6 %xx;
7 ]>
8 &lt;test>This sample shows a &amp;tricky; method.&lt;/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>&amp;#60;</code>" is expanded
immediately and the parameter entity "<code>zz</code>" is stored with the
replacement text "<code>&lt;!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>&lt;!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 Br&uuml;ggemann-Klein 1991 <a href="#ABK">[Br&uuml;ggemann-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>&lt;?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, '&lt;' 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&nbsp;00&nbsp;00&nbsp;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>Fran&ccedil;ois Yergeau, Alis Technologies  (<i>Errata List Editor</i>) </li>
<li>Kongyi Zhou, Oracle</li>
</ul> </div> <div class="div1"> <h2><a name="b4d250b6c21"></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>
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