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<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html lang="EN" xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html;charset=UTF-8" /><title>Extensible Markup Language (XML) 1.1</title><style type="text/css">
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</style><link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-REC.css" /></head><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><a name="title" id="title" />Extensible Markup Language (XML) 1.1</h1>
<h2><a name="w3c-doctype" id="w3c-doctype" />W3C Recommendation 04
             February 2004, edited in place 15 April 2004</h2><dl><dt>This version:</dt><dd><a href="http://www.w3.org/TR/2004/REC-xml11-20040204/">http://www.w3.org/TR/2004/REC-xml11-20040204/</a></dd><dt>Latest version:</dt><dd><a href="http://www.w3.org/TR/xml11">http://www.w3.org/TR/xml11</a></dd><dt>Previous version:</dt><dd><a href="http://www.w3.org/TR/2003/PR-xml11-20031105/">http://www.w3.org/TR/2003/PR-xml11-20031105/</a></dd><dt>Editors:</dt><dd>Tim Bray, Textuality and Netscape <a href="mailto:tbray@textuality.com">&lt;tbray@textuality.com&gt;</a></dd><dd>Jean Paoli, Microsoft <a href="mailto:jeanpa@microsoft.com">&lt;jeanpa@microsoft.com&gt;</a></dd><dd>C. M. Sperberg-McQueen, W3C <a href="mailto:cmsmcq@w3.org">&lt;cmsmcq@w3.org&gt;</a></dd><dd>Eve Maler, Sun Microsystems, Inc. <a href="mailto:elm@east.sun.com">&lt;eve.maler@east.sun.com&gt;</a></dd><dd>François Yergeau <a href="mailto:fyergeau@alis.com">&lt;fyergeau@alis.com&gt;</a></dd><dd>John Cowan <a href="mailto:cowan@ccil.org">&lt;cowan@ccil.org&gt;</a></dd></dl><p>Please refer to the <a href="http://www.w3.org/XML/xml-V11-1e-errata"><strong>errata</strong></a> for this document, which may include some normative corrections.</p><p>This document is also available in these non-normative formats: <a href="REC-xml11-20040204.xml">XML</a> and <a href="REC-xml11-20040204-review.html">XHTML with color-coded revision indicators</a>.</p><p>See also <a href="http://www.w3.org/2003/03/Translations/byTechnology?technology=xml11"><strong>translations</strong></a>.</p><p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2004 <a href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute of Technology">MIT</acronym></a>, <a href="http://www.ercim.org/"><acronym title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></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">document use</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-software">software licensing</a> rules apply.</p></div><hr /><div> <h2><a name="abstract" id="abstract" />Abstract</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" id="status" />Status of this Document</h2><p><em>This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the <a href="http://www.w3.org/TR/">W3C technical reports index</a> at http://www.w3.org/TR/.</em></p><p>This document is a <a href="http://www.w3.org/2003/06/Process-20030618/tr.html#RecsW3C">Recommendation</a> of the W3C.
It 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 <a
             href="http://www.w3.org/XML/Activity.html">W3C XML
             Activity</a>.</p>

<p>On 15 April 2004, this document was edited in place to add two
missing spaces to <a
href="http://www.w3.org/TR/2004/REC-xml11-20040204/Overview.html#NT-document">production
[1]</a> in section 2.1</p>

<p>The English version of this specification is the only normative version. However,
for translations of this document, see <a href="http://www.w3.org/2003/03/Translations/byTechnology?technology=xml11">http://www.w3.org/2003/03/Translations/byTechnology?technology=xml11</a>.
</p><p>Documentation of intellectual property possibly relevant to this recommendation
may be found at the Working Group's public
<a href="http://www.w3.org/2002/08/xmlcore-IPR-statements">IPR disclosure page</a>.</p><p>An implementation report for XML 1.1 is available at <a href="http://www.w3.org/XML/2002/09/xml11-implementation.html">http://www.w3.org/XML/2002/09/xml11-implementation.html</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. The errata list for this edition is available
at <a href="http://www.w3.org/XML/xml-V11-1e-errata">http://www.w3.org/XML/xml-V11-1e-errata</a>.</p><p>A <a href="http://www.w3.org/XML/Test/">Test Suite</a> is maintained to help assessing conformance to this specification.</p></div><div class="toc"> <h2><a name="contents" id="contents" />Table of Contents</h2><p class="toc">1 <a href="#sec-intro">Introduction</a><br />     1.1 <a href="#sec-origin-goals">Origin and Goals</a><br />     1.2 <a href="#sec-terminology">Terminology</a><br />     1.3 <a href="#sec-xml11">Rationale and list of changes for XML 1.1</a><br /> 2 <a href="#sec-documents">Documents</a><br />     2.1 <a href="#sec-well-formed">Well-Formed XML Documents</a><br />     2.2 <a href="#charsets">Characters</a><br />     2.3 <a href="#sec-common-syn">Common Syntactic Constructs</a><br />     2.4 <a href="#syntax">Character Data and Markup</a><br />     2.5 <a href="#sec-comments">Comments</a><br />     2.6 <a href="#sec-pi">Processing Instructions</a><br />     2.7 <a href="#sec-cdata-sect">CDATA Sections</a><br />     2.8 <a href="#sec-prolog-dtd">Prolog and Document Type Declaration</a><br />     2.9 <a href="#sec-rmd">Standalone Document Declaration</a><br />     2.10 <a href="#sec-white-space">White Space Handling</a><br />     2.11 <a href="#sec-line-ends">End-of-Line Handling</a><br />     2.12 <a href="#sec-lang-tag">Language Identification</a><br />     2.13 <a href="#sec-normalization-checking">Normalization Checking</a><br /> 3 <a href="#sec-logical-struct">Logical Structures</a><br />     3.1 <a href="#sec-starttags">Start-Tags, End-Tags, and Empty-Element Tags</a><br />     3.2 <a href="#elemdecls">Element Type Declarations</a><br />         3.2.1 <a href="#sec-element-content">Element Content</a><br />         3.2.2 <a href="#sec-mixed-content">Mixed Content</a><br />     3.3 <a href="#attdecls">Attribute-List Declarations</a><br />         3.3.1 <a href="#sec-attribute-types">Attribute Types</a><br />         3.3.2 <a href="#sec-attr-defaults">Attribute Defaults</a><br />         3.3.3 <a href="#AVNormalize">Attribute-Value Normalization</a><br />     3.4 <a href="#sec-condition-sect">Conditional Sections</a><br /> 4 <a href="#sec-physical-struct">Physical Structures</a><br />     4.1 <a href="#sec-references">Character and Entity References</a><br />     4.2 <a href="#sec-entity-decl">Entity Declarations</a><br />         4.2.1 <a href="#sec-internal-ent">Internal Entities</a><br />         4.2.2 <a href="#sec-external-ent">External Entities</a><br />     4.3 <a href="#TextEntities">Parsed Entities</a><br />         4.3.1 <a href="#sec-TextDecl">The Text Declaration</a><br />         4.3.2 <a href="#wf-entities">Well-Formed Parsed Entities</a><br />         4.3.3 <a href="#charencoding">Character Encoding in Entities</a><br />         4.3.4 <a href="#sec-version-info">Version Information in Entities</a><br />     4.4 <a href="#entproc">XML Processor Treatment of Entities and References</a><br />         4.4.1 <a href="#not-recognized">Not Recognized</a><br />         4.4.2 <a href="#included">Included</a><br />         4.4.3 <a href="#include-if-valid">Included If Validating</a><br />         4.4.4 <a href="#forbidden">Forbidden</a><br />         4.4.5 <a href="#inliteral">Included in Literal</a><br />         4.4.6 <a href="#notify">Notify</a><br />         4.4.7 <a href="#bypass">Bypassed</a><br />         4.4.8 <a href="#as-PE">Included as PE</a><br />         4.4.9 <a href="#error">Error</a><br />     4.5 <a href="#intern-replacement">Construction of Entity Replacement Text</a><br />     4.6 <a href="#sec-predefined-ent">Predefined Entities</a><br />     4.7 <a href="#Notations">Notation Declarations</a><br />     4.8 <a href="#sec-doc-entity">Document Entity</a><br /> 5 <a href="#sec-conformance">Conformance</a><br />     5.1 <a href="#proc-types">Validating and Non-Validating Processors</a><br />     5.2 <a href="#safe-behavior">Using XML Processors</a><br /> 6 <a href="#sec-notation">Notation</a><br /> </p> <h3><a name="appendices" id="appendices" />Appendices</h3><p class="toc">A <a href="#sec-bibliography">References</a><br />     A.1 <a href="#sec-existing-stds">Normative References</a><br />     A.2 <a href="#null">Other References</a><br /> B <a href="#sec-CharNorm">Definitions for Character Normalization</a><br /> C <a href="#sec-entexpand">Expansion of Entity and Character References</a> (Non-Normative)<br /> D <a href="#determinism">Deterministic Content Models</a> (Non-Normative)<br /> E <a href="#sec-guessing">Autodetection of Character Encodings</a> (Non-Normative)<br />     E.1 <a href="#sec-guessing-no-ext-info">Detection Without External Encoding Information</a><br />     E.2 <a href="#sec-guessing-with-ext-info">Priorities in the Presence of External Encoding Information</a><br /> F <a href="#sec-xml-wg">W3C XML Working Group</a> (Non-Normative)<br /> G <a href="#sec-core-wg">W3C XML Core Working Group</a> (Non-Normative)<br /> H <a href="#prod-notes">Production Notes</a> (Non-Normative)<br /> I <a href="#sec-suggested-names">Suggestions for XML Names</a> (Non-Normative)<br /> </p></div><hr /><div class="body"><div class="div1"> <h2><a name="sec-intro" id="sec-intro" />1 Introduction</h2><p>Extensible Markup Language, abbreviated XML, describes a class of data
objects called <a title="XML Document" href="#dt-xml-doc">XML documents</a> and partially
describes the behavior of computer programs which process them. XML is an
application profile or restricted form of SGML, the Standard Generalized Markup
Language <a href="#ISO8879">[ISO 8879]</a>. By construction, XML documents are conforming
SGML documents.</p><p>XML documents are made up of storage units called <a title="Entity" href="#dt-entity">entities</a>,
which contain either parsed or unparsed data. Parsed data is made up of <a title="Character" href="#dt-character">characters</a>, some of which form <a title="Character Data" href="#dt-chardata">character
data</a>, and some of which form <a title="Markup" href="#dt-markup">markup</a>.
Markup encodes a description of the document's storage layout and logical
structure. XML provides a mechanism to impose constraints on the storage layout
and logical structure.</p><p>[<a name="dt-xml-proc" id="dt-xml-proc" title="XML Processor">Definition</a>: A software module called
an <b>XML processor</b> is used to read XML documents and provide access
to their content and structure.] [<a name="dt-app" id="dt-app" title="Application">Definition</a>: It
is assumed that an XML processor is doing its work on behalf of another module,
called the <b>application</b>.] This specification describes
the required behavior of an XML processor in terms of how it must read XML
data and the information it must provide to the application.</p><div class="div2"> <h3><a name="sec-origin-goals" id="sec-origin-goals" />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 Working Group's contact with
the W3C.</p><p>The design goals for XML are:</p><ol type="1"><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
<a href="#Unicode">[Unicode]</a> and ISO/IEC 10646 <a href="#ISO10646">[ISO/IEC 10646]</a>
for characters, Internet RFC 3066 <a href="#RFC1766">[IETF RFC 3066]</a> for
language identification tags, ISO 639 <a href="#ISO639">[ISO 639]</a>
for language name codes, and ISO 3166 <a href="#ISO3166">[ISO 3166]</a> for
country name codes), provides all the information necessary to
understand XML Version 1.1 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" id="sec-terminology" />1.2 Terminology</h3><p>The terminology used to describe XML documents is defined in the body of
this specification. <span class="mustard">The key words <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">REQUIRED</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">SHALL</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">SHALL NOT</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD NOT</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">RECOMMENDED</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em>, and <em class="rfc2119" title="Keyword in RFC 2119 context">OPTIONAL</em>, when <em class="rfc2119" title="Keyword in RFC 2119 context">EMPHASIZED</em>, are to be interpreted as described in <a href="#rfc2119">[IETF RFC 2119]</a>. In addition, </span>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">error</dt><dd><p>[<a name="dt-error" id="dt-error" title="Error">Definition</a>: A violation of the rules of this specification;
results are undefined. <span class="mustard">Unless otherwise specified, failure to observe a prescription of this specification indicated by one of the keywords <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">REQUIRED</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em>, <em class="rfc2119" title="Keyword in RFC 2119 context">SHALL</em> and <em class="rfc2119" title="Keyword in RFC 2119 context">SHALL NOT</em> is an error.</span>  Conforming software <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> detect and report an error
and <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> recover from it.]</p></dd><dt class="label">fatal error</dt><dd><p>[<a name="dt-fatal" id="dt-fatal" title="Fatal Error">Definition</a>: An error which a conforming <a title="XML Processor" href="#dt-xml-proc">XML processor</a> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> detect and report to the application.
After encountering a fatal error, the processor <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> continue processing the
data to search for further errors and <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> report such errors to the application.
In order to support correction of errors, the processor <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> continue normal processing (i.e., it <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> continue to pass character
data and information about the document's logical structure to the application
in the normal way).]</p></dd><dt class="label">at user option</dt><dd><p>[<a name="dt-atuseroption" id="dt-atuseroption" title="At user option">Definition</a>: Conforming software
<em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> or <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> (depending on the modal verb in the sentence) behave as described;
if it does, it <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> provide users a means to enable or disable the behavior
described.]</p></dd><dt class="label">validity constraint</dt><dd><p>[<a name="dt-vc" id="dt-vc" title="Validity constraint">Definition</a>: A rule which applies to
all <a title="Validity" href="#dt-valid">valid</a> XML documents. Violations of validity
constraints are errors; they <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>, at user option, be reported by <a title="Validating Processor" href="#dt-validating">validating XML processors</a>.]</p></dd><dt class="label">well-formedness constraint</dt><dd><p>[<a name="dt-wfc" id="dt-wfc" title="Well-formedness constraint">Definition</a>: A rule which applies
to all <a title="Well-Formed" href="#dt-wellformed">well-formed</a> XML documents. Violations
of well-formedness constraints are <a title="Fatal Error" href="#dt-fatal">fatal errors</a>.]</p></dd><dt class="label">match</dt><dd><p>[<a name="dt-match" id="dt-match" title="match">Definition</a>: (Of strings or names:) Two strings
or names being compared <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be identical. Characters with multiple possible
representations in Unicode (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 <b>[VC: <a href="#elementvalid">Element Valid</a>]</b>.]</p></dd><dt class="label">for compatibility</dt><dd><p>[<a name="dt-compat" id="dt-compat" title="For Compatibility">Definition</a>: Marks
a sentence describing a feature of XML included solely to ensure
that XML remains compatible with SGML.]</p></dd><dt class="label">for interoperability</dt><dd><p>[<a name="dt-interop" id="dt-interop" title="For interoperability">Definition</a>: Marks
a sentence describing a non-binding recommendation included to increase
the chances that XML documents can be processed by the existing installed
base of SGML processors which predate the WebSGML Adaptations Annex to ISO 8879.]</p></dd></dl><p></p></div><div class="div2"> <h3><a name="sec-xml11" id="sec-xml11" />1.3 Rationale and list of changes for XML 1.1</h3><p>The W3C's XML 1.0 Recommendation was first issued in 1998, and
despite the issuance of many errata culminating in a Third Edition
of 2004, has remained (by intention) unchanged with respect to what
is well-formed XML and what is not. This stability has been
extremely useful for interoperability. However, the Unicode
Standard on which XML 1.0 relies for character specifications has
not remained static, evolving from version 2.0 to version 4.0 and
beyond. Characters not present in Unicode 2.0 may already be used
in XML 1.0 character data. However, they are not allowed in XML
names such as element type names, attribute names, enumerated
attribute values, processing instruction targets, and so on. In
addition, some characters that should have been permitted in XML
names were not, due to oversights and inconsistencies in Unicode
2.0.</p><p>The overall philosophy of names has changed since XML 1.0.
Whereas XML 1.0 provided a rigid definition of names, wherein
everything that was not permitted was forbidden, XML 1.1 names are
designed so that everything that is not forbidden (for a specific
reason) is permitted. Since Unicode will continue to grow past
version 4.0, further changes to XML can be avoided by allowing
almost any character, including those not yet assigned, in
names.</p><p>In addition, XML 1.0 attempts to adapt to the line-end
conventions of various modern operating systems, but discriminates
against the conventions used on IBM and IBM-compatible mainframes.
As a result, XML documents on mainframes are not plain text files
according to the local conventions. XML 1.0 documents generated on
mainframes must either violate the local line-end conventions, or
employ otherwise unnecessary translation phases before parsing and
after generation. Allowing straightforward interoperability is
particularly important when data stores are shared between
mainframe and non-mainframe systems (as opposed to being copied
from one to the other). Therefore XML 1.1 adds NEL (#x85) to the
list of line-end characters. For completeness, the Unicode line
separator character, #x2028, is also supported.
</p><p>Finally, there is considerable demand to define a standard representation
of arbitrary Unicode characters in XML documents. Therefore, XML 1.1
allows the use of character references to the control characters #x1 through
#x1F, most of which are forbidden in XML 1.0. For reasons of robustness,
however, these characters still cannot be used directly in documents. In
order to improve the robustness of character encoding detection, the additional
control characters #x7F through #x9F, which were freely allowed in XML 1.0
documents, now must also appear only as character references. (Whitespace
characters are of course exempt.) The minor sacrifice of backward compatibility
is considered not significant. Due to potential problems with APIs,
#x0 is still forbidden both directly and as a character reference.
</p><p>Finally, XML 1.1 defines a set of constraints called "full
normalization" on XML documents, which document creators
<em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> adhere to, and document processors
<em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> verify.  Using fully normalized documents
ensures that identity comparisons of names, attribute values, and
character content can be made correctly by simple binary comparison of
Unicode strings.</p><p>A new XML version, rather than a set of errata to XML 1.0, is
being created because the changes affect the definition of
well-formed documents. XML 1.0 processors must continue to reject
documents that contain new characters in XML names, new line-end
conventions, and references to control characters. The distinction between XML 1.0 and XML 1.1 documents
is indicated by the version number information in the XML
declaration at the start of each document.
</p></div></div><div class="div1"> <h2><a name="sec-documents" id="sec-documents" />2 Documents</h2><p>[<a name="dt-xml-doc" id="dt-xml-doc" title="XML Document">Definition</a>:  A data object is an <b>XML
document</b> if it is <a title="Well-Formed" href="#dt-wellformed">well-formed</a>,
as defined in this specification. A well-formed XML document <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> <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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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" id="sec-well-formed" />2.1 Well-Formed XML Documents</h3><p>[<a name="dt-wellformed" id="dt-wellformed" title="Well-Formed">Definition</a>:  A textual object is a <b>well-formed</b>
XML document if:]</p><ol type="1"><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><a
name="document" id="document" />Document</h5><table class="scrap"
summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-document"
id="NT-document"
/>[1]   </td><td><code>document</code></td><td>   ::=   </td><td><code><a
href="#NT-prolog">prolog</a> <a href="#NT-element">element</a> <a
href="#NT-Misc">Misc</a>* - <a href="#NT-Char">Char</a>* <a
href="#NT-RestrictedChar">RestrictedChar</a> <a href="#NT-Char">Char</a>*</code></td></tr></tbody></table><p>Matching the <a href="#NT-document">document</a> production implies that:</p><ol type="1"><li><p>It contains one or more <a title="Element" href="#dt-element">elements</a>.</p></li><li><p>[<a name="dt-root" id="dt-root" title="Root Element">Definition</a>: There is exactly one element,
called the <b>root</b>, or document element, no part of which appears
in the <a title="Content" href="#dt-content">content</a> of any other element.] For
all other elements, if the <a title="Start-Tag" href="#dt-stag">start-tag</a> is in
the content of another element, the <a title="End Tag" href="#dt-etag">end-tag</a>
is in the content of the same element. More simply stated, the elements,
delimited by start- and end-tags, nest properly within each other.</p></li></ol><p>[<a name="dt-parentchild" id="dt-parentchild" title="Parent/Child">Definition</a>: As a consequence of this,
for each non-root element <code>C</code> in the document, there is one other element <code>P</code>
in the document such that <code>C</code> is in the content of <code>P</code>, but
is not in the content of any other element that is in the content of <code>P</code>. <code>P</code>
is referred to as the <b>parent</b> of <code>C</code>, and <code>C</code> as
a <b>child</b> of <code>P</code>.]</p></div><div class="div2"> <h3><a name="charsets" id="charsets" />2.2 Characters</h3><p>[<a name="dt-text" id="dt-text" title="Text">Definition</a>: A parsed entity contains <b>text</b>,
a sequence of <a title="Character" href="#dt-character">characters</a>, which may
represent markup or character data.] [<a name="dt-character" id="dt-character" title="Character">Definition</a>: A <b>character</b>
is an atomic unit of text as specified by <span>ISO/IEC 10646 <a href="#ISO10646">[ISO/IEC 10646]</a></span>. 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
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> accept any character in the range specified for <a href="#NT-Char">Char</a>.]</p> <h5><a name="char32" id="char32" />Character Range</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-Char" id="NT-Char" />[2]   </td><td><code>Char</code></td><td>   ::=   </td><td><code>[#x1-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]</code></td><td><i>/* any Unicode character, excluding the surrogate blocks, FFFE, and FFFF. */</i></td></tr><tr valign="baseline"><td><a name="NT-RestrictedChar" id="NT-RestrictedChar" />[2a]   </td><td><code>RestrictedChar</code></td><td>   ::=   </td><td><code>[#x1-#x8] | [#xB-#xC] | [#xE-#x1F] | [#x7F-#x84] | [#x86-#x9F]</code></td></tr></tbody></table><p>The mechanism for encoding character code points into bit patterns <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em>
vary from entity to entity. All XML processors <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> accept the UTF-8 and UTF-16
encodings of <span> Unicode
<a href="#Unicode">[Unicode]</a></span>;
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 class="note"><p class="prefix"><b>Note:</b></p><p>Document authors are encouraged to avoid
"compatibility characters", as defined
in Unicode <a href="#Unicode">[Unicode]</a>.
The characters defined in the following ranges are also
discouraged. They are either control characters or permanently undefined Unicode
characters:</p><div class="exampleInner"><pre>
[#x7F-#x84], [#x86-#x9F], [#xFDD0-#xFDDF],
[#1FFFE-#x1FFFF], [#2FFFE-#x2FFFF], [#3FFFE-#x3FFFF],
[#4FFFE-#x4FFFF], [#5FFFE-#x5FFFF], [#6FFFE-#x6FFFF],
[#7FFFE-#x7FFFF], [#8FFFE-#x8FFFF], [#9FFFE-#x9FFFF],
[#AFFFE-#xAFFFF], [#BFFFE-#xBFFFF], [#CFFFE-#xCFFFF],
[#DFFFE-#xDFFFF], [#EFFFE-#xEFFFF], [#FFFFE-#xFFFFF],
[#10FFFE-#x10FFFF].</pre></div></div></div><div class="div2"> <h3><a name="sec-common-syn" id="sec-common-syn" />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><a name="white" id="white" />White Space</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-S" id="NT-S" />[3]   </td><td><code>S</code></td><td>   ::=   </td><td><code>(#x20 | #x9 | #xD | #xA)+</code></td></tr></tbody></table><div class="note"><p class="prefix"><b>Note:</b></p><p>The presence of #xD in the above production is
maintained purely for backward compatibility with the
<a href="http://www.w3.org/TR/1998/REC-xml-19980210">First Edition</a>.
As explained in <a href="#sec-line-ends"><b>2.11 End-of-Line Handling</b></a>,
all #xD characters literally present in an XML document
are either removed or replaced by #xA characters before
any other processing is done. The only way to get a #xD character to match this production is to
use a character reference in an entity value literal.</p></div><p>[<a name="dt-name" id="dt-name" title="Name">Definition</a>: A <b>Name</b> is a token beginning
with a letter or one of a few punctuation characters, and continuing with
letters, digits, hyphens, underscores, colons, or full stops, together known
as name characters.] Names beginning with the string "<code>xml</code>",
or <span>with</span> 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><p>The first character of a Name <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be a NameStartChar, and any
other characters <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be NameChars; this mechanism is used to
prevent names from beginning with European (ASCII) digits or with
basic combining characters. Almost all characters are permitted in
names, except those which either are or reasonably could be used as
delimiters. The intention is to be inclusive rather than exclusive,
so that writing systems not yet encoded in Unicode can be used in
XML names. See <a href="#sec-suggested-names"><b>I Suggestions for XML Names</b></a> for suggestions on the creation of
names.</p><p>Document authors are encouraged to use names which are
meaningful words or combinations of words in natural languages, and
to avoid symbolic or white space characters in names. Note that
COLON, HYPHEN-MINUS, FULL STOP (period), LOW LINE (underscore), and
MIDDLE DOT are explicitly permitted.</p><p>The ASCII symbols and punctuation marks, along with a fairly
large group of Unicode symbol characters, are excluded from names
because they are more useful as delimiters in contexts where XML
names are used outside XML documents; providing this group gives
those contexts hard guarantees about what <em>cannot</em> be part of
an XML name. The character #x037E, GREEK QUESTION MARK, is excluded
because when normalized it becomes a semicolon, which could change
the meaning of entity references.</p> <h5><a name="IDABN1S" id="IDABN1S" />Names and Tokens</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-NameStartChar" id="NT-NameStartChar" />[4]   </td><td><code>NameStartChar</code></td><td>   ::=   </td><td><code>":" | [A-Z] | "_" | [a-z] | [#xC0-#xD6] | [#xD8-#xF6] | [#xF8-#x2FF] | [#x370-#x37D] | [#x37F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF]</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-NameChar" id="NT-NameChar" />[4a]   </td><td><code>NameChar</code></td><td>   ::=   </td><td><code><a href="#NT-NameStartChar">NameStartChar</a> | "-" | "." | [0-9] | #xB7 | [#x0300-#x036F] | [#x203F-#x2040]</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Name" id="NT-Name" />[5]   </td><td><code>Name</code></td><td>   ::=   </td><td><code><a href="#NT-NameStartChar">NameStartChar</a> (<a href="#NT-NameChar">NameChar</a>)*</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Names" id="NT-Names" />[6]   </td><td><code>Names</code></td><td>   ::=   </td><td><code><a href="#NT-Name">Name</a> (#x20 <a href="#NT-Name">Name</a>)*</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Nmtoken" id="NT-Nmtoken" />[7]   </td><td><code>Nmtoken</code></td><td>   ::=   </td><td><code>(<a href="#NT-NameChar">NameChar</a>)+</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Nmtokens" id="NT-Nmtokens" />[8]   </td><td><code>Nmtokens</code></td><td>   ::=   </td><td><code><a href="#NT-Nmtoken">Nmtoken</a> (#x20 <a href="#NT-Nmtoken">Nmtoken</a>)*</code></td></tr></tbody></table><div class="note"><p class="prefix"><b>Note:</b></p><p>The <a href="#NT-Names">Names</a>
and <a href="#NT-Nmtokens">Nmtokens</a> productions are used to define the validity
of tokenized attribute values after normalization (see <a href="#sec-attribute-types"><b>3.3.1 Attribute Types</b></a>).</p></div><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><a name="IDAFR1S" id="IDAFR1S" />Literals</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-EntityValue" id="NT-EntityValue" />[9]   </td><td><code>EntityValue</code></td><td>   ::=   </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><code>|  "'" ([^%&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" id="NT-AttValue" />[10]   </td><td><code>AttValue</code></td><td>   ::=   </td><td><code>'"' ([^&lt;&amp;"] | <a href="#NT-Reference">Reference</a>)*
'"' </code></td></tr><tr valign="baseline"><td /><td /><td /><td><code>|  "'" ([^&lt;&amp;'] | <a href="#NT-Reference">Reference</a>)*
"'"</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-SystemLiteral" id="NT-SystemLiteral" />[11]   </td><td><code>SystemLiteral</code></td><td>   ::=   </td><td><code>('"' [^"]* '"') | ("'" [^']* "'") </code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PubidLiteral" id="NT-PubidLiteral" />[12]   </td><td><code>PubidLiteral</code></td><td>   ::=   </td><td><code>'"' <a href="#NT-PubidChar">PubidChar</a>* '"'
| "'" (<a href="#NT-PubidChar">PubidChar</a> - "'")* "'"</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PubidChar" id="NT-PubidChar" />[13]   </td><td><code>PubidChar</code></td><td>   ::=   </td><td><code>#x20 | #xD | #xA | [a-zA-Z0-9] | [-'()+,./:=?;!*#@$_%]</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 a general entity consisting of a single explicit <code>&lt;</code> in the literal
(e.g., <code>&lt;!ENTITY mylt "&lt;"&gt;</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" id="syntax" />2.4 Character Data and Markup</h3><p><a title="Text" href="#dt-text">Text</a> consists of intermingled <a title="Character Data" href="#dt-chardata">character data</a> and markup. [<a name="dt-markup" id="dt-markup" title="Markup">Definition</a>: <b>Markup</b> takes the form of <a title="Start-Tag" href="#dt-stag">start-tags</a>, <a title="End Tag" href="#dt-etag">end-tags</a>, <a title="Empty" href="#dt-empty">empty-element tags</a>, <a title="Entity Reference" href="#dt-entref">entity references</a>, <a title="Character Reference" href="#dt-charref">character
references</a>, <a title="Comment" href="#dt-comment">comments</a>, <a title="CDATA Section" href="#dt-cdsection">CDATA section</a> delimiters, <a title="Document Type Declaration" href="#dt-doctype">document
type declarations</a>, <a title="Processing instruction" href="#dt-pi">processing instructions</a>, <a href="#NT-XMLDecl">XML declarations</a>, <a href="#NT-TextDecl">text declarations</a>,
and any white space that is at the top level of the document entity (that
is, outside the document element and not inside any other markup).]</p><p>[<a name="dt-chardata" id="dt-chardata" title="Character Data">Definition</a>: All text that is not markup
constitutes the <b>character data</b> of the document.]</p><p>The ampersand character (&amp;) and the left angle bracket (&lt;) <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em></span> appear
in their literal form<span class="mustard">, except</span> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 (&gt;) <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> be represented using the string "<code>&amp;gt;</code>",
and <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>, <a title="For Compatibility" href="#dt-compat">for compatibility</a>, be escaped
using <span>either</span> "<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 or the
CDATA-section-close delimiter,
"<code>]]&gt;</code>".
In a CDATA section,
character data is any string of characters not including the CDATA-section-close
delimiter.</p><p>To allow attribute values to contain both single and double quotes, the
apostrophe or single-quote character (') <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> be represented as "<code>&amp;apos;</code>",
and the double-quote character (") as "<code>&amp;quot;</code>".</p> <h5><a name="IDASZ1S" id="IDASZ1S" />Character Data</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-CharData" id="NT-CharData" />[14]   </td><td><code>CharData</code></td><td>   ::=   </td><td><code>[^&lt;&amp;]* - ([^&lt;&amp;]* ']]&gt;' [^&lt;&amp;]*)</code></td></tr></tbody></table></div><div class="div2"> <h3><a name="sec-comments" id="sec-comments" />2.5 Comments</h3><p>[<a name="dt-comment" id="dt-comment" title="Comment">Definition</a>: <b>Comments</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> appear
anywhere in a document outside other <a title="Markup" href="#dt-markup">markup</a>;
in addition, they <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em>, 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)
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> occur within comments.] Parameter
entity references <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> be</span> recognized within comments.</p> <h5><a name="IDAL11S" id="IDAL11S" />Comments</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-Comment" id="NT-Comment" />[15]   </td><td><code>Comment</code></td><td>   ::=   </td><td><code>'&lt;!--' ((<a href="#NT-Char">Char</a> - '-') | ('-'
(<a href="#NT-Char">Char</a> - '-')))* '--&gt;'</code></td></tr></tbody></table><p>An example of a comment:</p><div class="exampleInner"><pre>&lt;!-- declarations for &lt;head&gt; &amp; &lt;body&gt; --&gt;</pre></div><p>Note
that the grammar does not allow a comment ending in <code>---&gt;</code>. The
following example is <em>not</em> well-formed.</p><div class="exampleInner"><pre>&lt;!-- B+, B, or B---&gt;</pre></div></div><div class="div2"> <h3><a name="sec-pi" id="sec-pi" />2.6 Processing Instructions</h3><p>[<a name="dt-pi" id="dt-pi" title="Processing instruction">Definition</a>: <b>Processing instructions</b>
(PIs) allow documents to contain instructions for applications.]</p> <h5><a name="IDAD31S" id="IDAD31S" />Processing Instructions</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-PI" id="NT-PI" />[16]   </td><td><code>PI</code></td><td>   ::=   </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>* '?&gt;' <a href="#NT-Char">Char</a>*)))? '?&gt;'</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PITarget" id="NT-PITarget" />[17]   </td><td><code>PITarget</code></td><td>   ::=   </td><td><code><a href="#NT-Name">Name</a> - (('X' | 'x') ('M' |
'm') ('L' | 'l'))</code></td></tr></tbody></table><p>PIs are not part of the document's <a title="Character Data" href="#dt-chardata">character
data</a>, but <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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
<em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> be used for formal declaration of PI targets. Parameter
entity references <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> be</span> recognized within processing instructions.</p></div><div class="div2"> <h3><a name="sec-cdata-sect" id="sec-cdata-sect" />2.7 CDATA Sections</h3><p>[<a name="dt-cdsection" id="dt-cdsection" title="CDATA Section">Definition</a>: <b>CDATA sections</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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><a name="IDAOA2S" id="IDAOA2S" />CDATA Sections</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-CDSect" id="NT-CDSect" />[18]   </td><td><code>CDSect</code></td><td>   ::=   </td><td><code><a href="#NT-CDStart">CDStart</a> <a href="#NT-CData">CData</a> <a href="#NT-CDEnd">CDEnd</a></code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-CDStart" id="NT-CDStart" />[19]   </td><td><code>CDStart</code></td><td>   ::=   </td><td><code>'&lt;![CDATA['</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-CData" id="NT-CData" />[20]   </td><td><code>CData</code></td><td>   ::=   </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" id="NT-CDEnd" />[21]   </td><td><code>CDEnd</code></td><td>   ::=   </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&gt;</code>"
and "<code>&lt;/greeting&gt;</code>" are recognized as <a title="Character Data" href="#dt-chardata">character data</a>, not <a title="Markup" href="#dt-markup">markup</a>:</p><div class="exampleInner"><pre>&lt;![CDATA[&lt;greeting&gt;Hello, world!&lt;/greeting&gt;]]&gt; </pre></div></div><div class="div2"> <h3><a name="sec-prolog-dtd" id="sec-prolog-dtd" />2.8 Prolog and Document Type Declaration</h3><p>[<a name="dt-xmldecl" id="dt-xmldecl" title="XML Declaration">Definition</a>: XML 1.1 documents <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
begin with an <b>XML declaration</b> which specifies the version of
XML being used.] For example, the following is a complete XML 1.1 document, <a title="Well-Formed" href="#dt-wellformed">well-formed</a> but not <a title="Validity" href="#dt-valid">valid</a>:</p><div class="exampleInner"><pre>&lt;?xml version="1.1"?&gt;
&lt;greeting&gt;Hello, world!&lt;/greeting&gt; </pre></div><p>but the following is an XML 1.0 document because it
does not have an XML declaration:</p><div class="exampleInner"><pre>&lt;greeting&gt;Hello, world!&lt;/greeting&gt;</pre></div><p>The function of the markup in an XML document is to describe its storage and
logical structure and to associate <span>attribute
name-value</span> pairs with its logical structures. XML provides a mechanism, the
<a title="Document Type Declaration" href="#dt-doctype">document
type declaration</a>, to define constraints on the logical structure
and to support the use of predefined storage units. [<a name="dt-valid" id="dt-valid" title="Validity">Definition</a>: An XML document is <b>valid</b> if it has an associated
document type declaration and if the document complies with the constraints
expressed in it.]</p><p>The document type declaration <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> appear before the first <a title="Element" href="#dt-element">element</a>
in the document.</p> <h5><a name="xmldoc" id="xmldoc" />Prolog</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-prolog" id="NT-prolog" />[22]   </td><td><code>prolog</code></td><td>   ::=   </td><td><code><a href="#NT-XMLDecl">XMLDecl</a> <a href="#NT-Misc">Misc</a>*
(<a href="#NT-doctypedecl">doctypedecl</a> <a href="#NT-Misc">Misc</a>*)?</code></td></tr><tr valign="baseline"><td><a name="NT-XMLDecl" id="NT-XMLDecl" />[23]   </td><td><code>XMLDecl</code></td><td>   ::=   </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>?'?&gt;'</code></td></tr><tr valign="baseline"><td><a name="NT-VersionInfo" id="NT-VersionInfo" />[24]   </td><td><code>VersionInfo</code></td><td>   ::=   </td><td><code><a href="#NT-S">S</a> 'version' <a href="#NT-Eq">Eq</a>
("'" <a href="#NT-VersionNum">VersionNum</a> "'" | '"' <a href="#NT-VersionNum">VersionNum</a>
'"')</code></td></tr><tr valign="baseline"><td><a name="NT-Eq" id="NT-Eq" />[25]   </td><td><code>Eq</code></td><td>   ::=   </td><td><code><a href="#NT-S">S</a>? '=' <a href="#NT-S">S</a>?</code></td></tr><tr valign="baseline"><td><a name="NT-VersionNum" id="NT-VersionNum" />[26]   </td><td><code>VersionNum</code></td><td>   ::=   </td><td><code>'1.1'</code></td></tr><tr valign="baseline"><td><a name="NT-Misc" id="NT-Misc" />[27]   </td><td><code>Misc</code></td><td>   ::=   </td><td><code><a href="#NT-Comment">Comment</a> | <a href="#NT-PI">PI</a>
| <a href="#NT-S">S</a></code></td></tr></tbody></table><p>[<a name="dt-doctype" id="dt-doctype" title="Document Type Declaration">Definition</a>: The XML <b>document
type declaration</b> contains or points to <a title="markup declaration" href="#dt-markupdecl">markup
declarations</a> that provide a grammar for a class of documents. This
grammar is known as a document type definition, or <b>DTD</b>. The document
type declaration can point to an external subset (a special kind of <a title="External Entity" href="#dt-extent">external entity</a>) containing markup declarations,
or can contain the markup declarations directly in an internal subset, or
can do both. The DTD for a document consists of both subsets taken together.]</p><p>[<a name="dt-markupdecl" id="dt-markupdecl" title="markup declaration">Definition</a>:  A <b>markup declaration</b>
is an <a title="Element Type declaration" href="#dt-eldecl">element type declaration</a>, an <a title="Attribute-List Declaration" href="#dt-attdecl">attribute-list declaration</a>, an <a title="entity declaration" href="#dt-entdecl">entity
declaration</a>, or a <a title="Notation Declaration" href="#dt-notdecl">notation declaration</a>.]
These declarations <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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><a name="dtd" id="dtd" />Document Type Definition</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-doctypedecl" id="NT-doctypedecl" />[28]   </td><td><code>doctypedecl</code></td><td>   ::=   </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-intSubset">intSubset</a> ']' <a href="#NT-S">S</a>?)? '&gt;'</code></td><td><a href="#vc-roottype">[VC: Root Element Type]</a></td></tr><tr valign="baseline"><td /><td /><td /><td /><td><a href="#ExtSubset">[WFC: External Subset]</a></td></tr><tr valign="baseline"><td><a name="NT-DeclSep" id="NT-DeclSep" />[28a]   </td><td><code>DeclSep</code></td><td>   ::=   </td><td><code><a href="#NT-PEReference">PEReference</a> | <a href="#NT-S">S</a></code></td><td><a href="#PE-between-Decls">[WFC: PE Between Declarations]</a></td></tr><tr valign="baseline"><td><a name="NT-intSubset" id="NT-intSubset" />[28b]   </td><td><code>intSubset</code></td><td>   ::=   </td><td><code>(<a href="#NT-markupdecl">markupdecl</a> | <a href="#NT-DeclSep">DeclSep</a>)*</code></td></tr><tr valign="baseline"><td><a name="NT-markupdecl" id="NT-markupdecl" />[29]   </td><td><code>markupdecl</code></td><td>   ::=   </td><td><code><a href="#NT-elementdecl">elementdecl</a> | <a href="#NT-AttlistDecl">AttlistDecl</a> | <a href="#NT-EntityDecl">EntityDecl</a>
| <a href="#NT-NotationDecl">NotationDecl</a> | <a href="#NT-PI">PI</a> | <a href="#NT-Comment">Comment</a></code></td><td><a href="#vc-PEinMarkupDecl">[VC: Proper Declaration/PE Nesting]</a></td></tr><tr valign="baseline"><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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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" id="vc-roottype" /><b>Validity constraint: Root Element Type</b></p><p>The <a href="#NT-Name">Name</a>
in the document type declaration <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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" id="vc-PEinMarkupDecl" /><b>Validity constraint: Proper Declaration/PE Nesting</b></p><p>Parameter-entity <a title="Replacement Text" href="#dt-repltext">replacement text</a> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be contained in the same replacement text.</p></div><div class="constraint"><p class="prefix"><a name="wfc-PEinInternalSubset" id="wfc-PEinInternalSubset" /><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> <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> occur within markup declarations; they <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> occur where markup declarations can occur</span>.
(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" id="ExtSubset" /><b>Well-formedness constraint: External Subset</b></p><p>The external subset, if any, <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the production for <a href="#NT-extSubset">extSubset</a>.</p></div><div class="constraint"><p class="prefix"><a name="PE-between-Decls" id="PE-between-Decls" /><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> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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<span> but is
allowed in external parameter entities referenced in the internal subset</span>.</p> <h5><a name="ext-Subset" id="ext-Subset" />External Subset</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-extSubset" id="NT-extSubset" />[30]   </td><td><code>extSubset</code></td><td>   ::=   </td><td><code><a href="#NT-TextDecl">TextDecl</a>? <a href="#NT-extSubsetDecl">extSubsetDecl</a></code></td></tr><tr valign="baseline"><td><a name="NT-extSubsetDecl" id="NT-extSubsetDecl" />[31]   </td><td><code>extSubsetDecl</code></td><td>   ::=   </td><td><code>( <a href="#NT-markupdecl">markupdecl</a> | <a href="#NT-conditionalSect">conditionalSect</a> | <a href="#NT-DeclSep">DeclSep</a>)*</code></td></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><div class="exampleInner"><pre>&lt;?xml version="1.1"?&gt;
&lt;!DOCTYPE greeting SYSTEM "hello.dtd"&gt;
&lt;greeting&gt;Hello, world!&lt;/greeting&gt; </pre></div><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><div class="exampleInner"><pre>&lt;?xml version="1.1" encoding="UTF-8" ?&gt;
&lt;!DOCTYPE greeting [
&lt;!ELEMENT greeting (#PCDATA)&gt;
]&gt;
&lt;greeting&gt;Hello, world!&lt;/greeting&gt;</pre></div><p>If both the external and internal subsets are used, the internal subset
<span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be</span> 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><p>XML 1.1 processors <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> accept XML 1.0
documents as well. If a document is well-formed or valid XML 1.0, and provided it
does not contain any control characters
in the range [#x7F-#x9F] other than as character escapes, it may be
made well-formed or valid XML 1.1 respectively simply by changing the
version number.</p></div><div class="div2"> <h3><a name="sec-rmd" id="sec-rmd" />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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> appear as a component of the XML declaration, signals whether or
not there are such declarations which appear external to the <a title="Document Entity" href="#dt-docent">document
entity</a>
or in parameter entities. [<a name="dt-extmkpdecl" id="dt-extmkpdecl" title="External Markup Declaration">Definition</a>: An <b>external
markup declaration</b> is defined as a markup declaration occurring in
the external subset or in a parameter entity (external or internal, the latter
being included because non-validating processors are not required to read
them).]</p> <h5><a name="fulldtd" id="fulldtd" />Standalone Document Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-SDDecl" id="NT-SDDecl" />[32]   </td><td><code>SDDecl</code></td><td>   ::=   </td><td><code>#x20+ '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" id="vc-check-rmd" /><b>Validity constraint: Standalone Document Declaration</b></p><p>The
standalone document declaration <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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
tokenized types, where the
attribute appears in the document with a value such that
<a href="#AVNormalize"><cite>normalization</cite></a>
will produce a different value from that which would be produced
in the absence of the declaration, 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><div class="exampleInner"><pre>&lt;?xml version="1.1" standalone='yes'?&gt;</pre></div></div><div class="div2"> <h3><a name="sec-white-space" id="sec-white-space" />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> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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> <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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, <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be <a title="Attribute-List Declaration" href="#dt-attdecl">declared</a>
if it is used. When declared, it <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be given as an <a title="Enumerated Attribute&#xA;Values" href="#dt-enumerated">enumerated
type</a> whose values
are one or both of "default" and "preserve".
For example:</p><div class="exampleInner"><pre>&lt;!ATTLIST poem  xml:space (default|preserve) 'preserve'&gt;
&lt;!ATTLIST pre xml:space (preserve) #FIXED 'preserve'&gt;</pre></div><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 <span>overridden</span> with
another instance of the <code>xml:space</code> attribute. <span>This specification does not give meaning to any value of <code>xml:space</code> other than "default" and "preserve". It is an error for other values to be specified; the XML processor <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> report the error or <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> recover by ignoring the attribute specification or by reporting the (erroneous) value to the application. Applications may ignore or reject erroneous values.</span></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" id="sec-line-ends" />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
<span><a title="XML Processor" href="#dt-xml-proc">XML
processor</a> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> behave as if it</span> normalized all line breaks in external parsed
entities (including the document entity) on input, before parsing, by translating

<span>all of the following to a single #xA character:</span></p><ol type="1"><li><p>the two-character sequence #xD #xA</p></li><li><p>the two-character sequence #xD #x85</p></li><li><p>the single character #x85</p></li><li><p>the single character #x2028</p></li><li><p>any #xD character that is not immediately followed by #xA or #x85.</p></li></ol><p>  The characters #x85 and #x2028 cannot be reliably recognized and
translated until an entity's encoding declaration (if present) has
been read.  Therefore, it is a fatal error to use them within the XML
declaration or text declaration.
</p></div><div class="div2"> <h3><a name="sec-lang-tag" id="sec-lang-tag" />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> <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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, <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 3066]</a>, <cite>Tags
for the Identification of Languages</cite>, or its successor<span>; in addition, the empty string <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> be specified</span>.</p><p>(Productions 33 through 38 have been removed.)</p><p>For example:</p><div class="exampleInner"><pre>&lt;p xml:lang="en"&gt;The quick brown fox jumps over the lazy dog.&lt;/p&gt;
&lt;p xml:lang="en-GB"&gt;What colour is it?&lt;/p&gt;
&lt;p xml:lang="en-US"&gt;What color is it?&lt;/p&gt;
&lt;sp who="Faust" desc='leise' xml:lang="de"&gt;
&lt;l&gt;Habe nun, ach! Philosophie,&lt;/l&gt;
&lt;l&gt;Juristerei, und Medizin&lt;/l&gt;
&lt;l&gt;und leider auch Theologie&lt;/l&gt;
&lt;l&gt;durchaus studiert mit hei&amp;#xDF;em Bem&amp;#xFC;h'n.&lt;/l&gt;
&lt;/sp&gt;</pre></div><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. <span>In particular, the empty value of <code>xml:lang</code> is used on an element B to override a specification of <code>xml:lang</code> on an enclosing element A, without specifying another language. Within B, it is considered that there is no language information available, just as if <code>xml:lang</code> had not been specified on B or any of its ancestors.</span></p><div class="note"><p class="prefix"><b>Note:</b></p><p>Language information may also be provided by external transport protocols (e.g. HTTP or
MIME). When available, this information may be used by XML applications, but the more local
information provided by <code>xml:lang</code> should be considered to override it.
</p></div><p>A simple declaration for <code>xml:lang</code> might take the form</p><div class="exampleInner"><pre>xml:lang <span>CDATA</span> #IMPLIED</pre></div><p>but specific default values <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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><div class="exampleInner"><pre>&lt;!ATTLIST poem   xml:lang <span>CDATA</span> 'fr'&gt;
&lt;!ATTLIST gloss  xml:lang <span>CDATA</span> 'en'&gt;
&lt;!ATTLIST note   xml:lang <span>CDATA</span> 'en'&gt;</pre></div></div><div class="div2"> <h3><a name="sec-normalization-checking" id="sec-normalization-checking" />2.13 Normalization Checking</h3><p>All XML <a title="Text Entity" href="#dt-parsedent"> parsed
entities</a> (including <a title="Document Entity" href="#dt-docent"> document
entities</a>) <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> be <a title="fully normalized" href="#dt-fullnorm">fully
normalized</a> as per the definition of
<a href="#sec-CharNorm"><b>B Definitions for Character Normalization</b></a> supplemented by the following definitions of
<em><a name="dt-relconst" id="dt-relconst" />relevant constructs</em> for XML:</p><ol type="1"><li><p>The <a title="Replacement Text" href="#dt-repltext">
replacement text</a> of all <a title="Text Entity" href="#dt-parsedent">parsed
entities</a></p></li><li><p>All text matching, in context, one of the following
productions:</p><ol type="a"><li><p><a href="#NT-CData">
CData</a></p></li><li><p><a href="#NT-CharData">
CharData</a></p></li><li><p><a href="#NT-content">
content</a></p></li><li><p><a href="#NT-Name"> Name</a></p></li><li><p><a href="#NT-Nmtoken">
Nmtoken</a></p></li></ol></li></ol><p>However, a document is still well-formed even if it is not
<a title="fully normalized" href="#dt-fullnorm">fully normalized</a>.
XML processors <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> provide a user option to verify that the document being
processed is in <a title="fully normalized" href="#dt-fullnorm">fully normalized</a> form, and report to the application whether
it is or not. The option to not verify <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> be chosen only when the
input text is <a title="certified" href="#dt-certified">certified</a>,
as defined by <a href="#sec-CharNorm"><b>B Definitions for Character Normalization</b></a>.</p><p>The verification of full normalization <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be carried out as if by
first verifying that the entity is in <a title="include-normalized" href="#dt-inclnorm">include-normalized</a>
form as defined by <a href="#sec-CharNorm"><b>B Definitions for Character Normalization</b></a> and by then verifying that none of the relevant
constructs listed above begins (after character references are
expanded) with a <a title="composing character" href="#dt-compchar">composing character</a> as defined by
<a href="#sec-CharNorm"><b>B Definitions for Character Normalization</b></a>.
Non-validating processors <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> ignore possible
denormalizations that would be caused by inclusion of external
entities that they do not read.</p><div class="note"><p class="prefix"><b>Note:</b></p><p>The <a title="composing character" href="#dt-compchar">composing character</a> are all
Unicode characters of non-zero combining class, plus a small number
of class-zero characters that nevertheless take part as a
non-initial character in certain Unicode canonical
decompositions.  Since these characters are meant to follow
base characters, restricting relevant constructs (including
content) from beginning with a <a title="composing character" href="#dt-compchar">composing character</a> does not
meaningfully diminish the expressiveness of XML.</p></div><p>If, while verifying full normalization, a processor encounters
characters for which it cannot determine the normalization
properties (i.e., characters introduced in a version of Unicode <a href="#Unicode">[Unicode]</a>
later than the one used in the implementation of the processor),
then the processor <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em>, at user option, ignore any possible
denormalizations caused by these characters. The option to ignore
those denormalizations <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD NOT</em> be chosen by applications when
reliability or security are critical.</p><p> XML processors <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> transform the input to be in
<a title="fully normalized" href="#dt-fullnorm">fully normalized</a> form.
XML applications that create XML 1.1 output
from either XML 1.1 or XML 1.0 input <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> ensure that the output
is <a title="fully normalized" href="#dt-fullnorm">fully normalized</a>; it is not necessary for internal processing
forms to be <a title="fully normalized" href="#dt-fullnorm">fully normalized</a>.</p><p>The purpose of this section is to strongly encourage XML
processors to ensure that the creators of XML documents have
properly normalized them, so that XML applications can make tests
such as identity comparisons of strings without having to worry
about the different possible "spellings" of strings which
Unicode allows.
</p><p>When entities are in a non-Unicode encoding, if the processor
transcodes them to Unicode, it <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> use a normalizing transcoder.
</p></div></div><div class="div1"> <h2><a name="sec-logical-struct" id="sec-logical-struct" />3 Logical Structures</h2><p>[<a name="dt-element" id="dt-element" title="Element">Definition</a>: Each <a title="XML Document" href="#dt-xml-doc">XML
document</a> contains one or more <b>elements</b>, the boundaries
of which are either delimited by <a title="Start-Tag" href="#dt-stag">start-tags</a>
and <a title="End Tag" href="#dt-etag">end-tags</a>, or, for <a title="Empty" href="#dt-empty">empty</a>
elements, by an <a title="empty-element tag" href="#dt-eetag">empty-element tag</a>. Each
element has a type, identified by name, sometimes called its "generic
identifier" (GI), and <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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><a name="IDATJ3S" id="IDATJ3S" />Element</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-element" id="NT-element" />[39]   </td><td><code>element</code></td><td>   ::=   </td><td><code><a href="#NT-EmptyElemTag">EmptyElemTag</a></code></td></tr><tr valign="baseline"><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><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" id="GIMatch" /><b>Well-formedness constraint: Element Type Match</b></p><p>The <a href="#NT-Name">Name</a>
in an element's end-tag <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the element type in the start-tag.</p></div><div class="constraint"><p class="prefix"><a name="elementvalid" id="elementvalid" /><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 type="1"><li><p>The declaration matches <b>EMPTY</b> and the element has no <a title="Content" href="#dt-content">content</a> <span>(not even entity
references, comments, PIs or white space)</span>.</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<span>, comments and
PIs (i.e. markup matching production [27] <a href="#NT-Misc">Misc</a>)</span> 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 <span>or a reference
to an entity whose replacement text is character references expanding to white
space</span> <span>do</span> not
match the nonterminal <a href="#NT-S">S</a>, and
hence cannot appear in these positions<span>; however, a
reference to an internal entity with a literal value consisting of character
references expanding to white space does match <a href="#NT-S">S</a>, since its
replacement text is the white space resulting from expansion of the character
references</span>.</p></li><li><p>The declaration matches <a href="#NT-Mixed">Mixed</a> and the content
<span>(after replacing
any entity references with their replacement text)</span> consists of
<a title="Character Data" href="#dt-chardata">character data</a><span>,
<a title="Comment" href="#dt-comment">comments</a>, <a title="Processing instruction" href="#dt-pi">PIs</a></span> 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
<span>content
<span>(after replacing
any entity references with their replacement text)</span>
consists of character data and <a title="Parent/Child" href="#dt-parentchild">child elements</a>
whose types</span>
have been declared.</p></li></ol></div><div class="div2"> <h3><a name="sec-starttags" id="sec-starttags" />3.1 Start-Tags, End-Tags, and Empty-Element Tags</h3><p>[<a name="dt-stag" id="dt-stag" title="Start-Tag">Definition</a>: The beginning of every non-empty
XML element is marked by a <b>start-tag</b>.]</p> <h5><a name="IDA3O3S" id="IDA3O3S" />Start-tag</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-STag" id="NT-STag" />[40]   </td><td><code>STag</code></td><td>   ::=   </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>? '&gt;'</code></td><td><a href="#uniqattspec">[WFC: Unique Att Spec]</a></td></tr><tr valign="baseline"><td><a name="NT-Attribute" id="NT-Attribute" />[41]   </td><td><code>Attribute</code></td><td>   ::=   </td><td><code><a href="#NT-Name">Name</a> <a href="#NT-Eq">Eq</a> <a href="#NT-AttValue">AttValue</a></code></td><td><a href="#ValueType">[VC: Attribute Value Type]</a></td></tr><tr valign="baseline"><td /><td /><td /><td /><td><a href="#NoExternalRefs">[WFC: No External Entity References]</a></td></tr><tr valign="baseline"><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 name="dt-attr" id="dt-attr" title="Attribute">Definition</a>:  The <a href="#NT-Name">Name</a>-<a href="#NT-AttValue">AttValue</a>
pairs are referred to as the <b>attribute specifications</b> of the
element], [<a name="dt-attrname" id="dt-attrname" title="Attribute Name">Definition</a>: with the <a href="#NT-Name">Name</a> in each pair referred to as the <b>attribute name</b>]
and [<a name="dt-attrval" id="dt-attrval" title="Attribute Value">Definition</a>: the content of the <a href="#NT-AttValue">AttValue</a> (the text between the <code>'</code> or <code>"</code>
delimiters) as the <b>attribute value</b>.]  Note
that the order of attribute specifications in a start-tag or empty-element
tag is not significant.</p><div class="constraint"><p class="prefix"><a name="uniqattspec" id="uniqattspec" /><b>Well-formedness constraint: Unique Att Spec</b></p><p><span class="mustard">An attribute name
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em></span> appear more than once in the same start-tag or empty-element tag.</p></div><div class="constraint"><p class="prefix"><a name="ValueType" id="ValueType" /><b>Validity constraint: Attribute Value Type</b></p><p>The attribute <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
have been declared; the value <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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" id="NoExternalRefs" /><b>Well-formedness constraint: No External Entity References</b></p><p>Attribute
values <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em></span> contain direct or indirect entity references to external entities.</p></div><div class="constraint"><p class="prefix"><a name="CleanAttrVals" id="CleanAttrVals" /><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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> contain a <code>&lt;</code>.</p></div><p>An example of a start-tag:</p><div class="exampleInner"><pre>&lt;termdef id="dt-dog" term="dog"&gt;</pre></div><p>[<a name="dt-etag" id="dt-etag" title="End Tag">Definition</a>: The end of every element that begins
with a start-tag <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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><a name="IDA3U3S" id="IDA3U3S" />End-tag</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-ETag" id="NT-ETag" />[42]   </td><td><code>ETag</code></td><td>   ::=   </td><td><code>'&lt;/' <a href="#NT-Name">Name</a> <a href="#NT-S">S</a>?
'&gt;'</code></td></tr></tbody></table><p>An example of an end-tag:</p><div class="exampleInner"><pre>&lt;/termdef&gt;</pre></div><p>[<a name="dt-content" id="dt-content" title="Content">Definition</a>: The <a title="Text" href="#dt-text">text</a>
between the start-tag and end-tag is called the element's <b>content</b>:]</p> <h5><a name="IDAKW3S" id="IDAKW3S" />Content of Elements</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-content" id="NT-content" />[43]   </td><td><code>content</code></td><td>   ::=   </td><td><code><a href="#NT-CharData">CharData</a>? ((<a href="#NT-element">element</a>
| <a href="#NT-Reference">Reference</a> | <a href="#NT-CDSect">CDSect</a>
| <a href="#NT-PI">PI</a> | <a href="#NT-Comment">Comment</a>) <a href="#NT-CharData">CharData</a>?)*</code></td></tr></tbody></table><p>[<a name="dt-empty" id="dt-empty" title="Empty">Definition</a>: An element
with no <a href="#NT-content">content</a> is said to be <b>empty</b>.] The representation
of an empty element is either a start-tag immediately followed by an end-tag,
or an empty-element tag. [<a name="dt-eetag" id="dt-eetag" title="empty-element tag">Definition</a>: An <b>empty-element
tag</b> takes a special form:]</p> <h5><a name="IDARY3S" id="IDARY3S" />Tags for Empty Elements</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-EmptyElemTag" id="NT-EmptyElemTag" />[44]   </td><td><code>EmptyElemTag</code></td><td>   ::=   </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>? '/&gt;'</code></td><td><a href="#uniqattspec">[WFC: Unique Att Spec]</a></td></tr></tbody></table><p>Empty-element tags <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em>
be used, and <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> only be used, for elements which are declared
EMPTY.</p><p>Examples of empty elements:</p><div class="exampleInner"><pre>&lt;IMG align="left"
src="http://www.w3.org/Icons/WWW/w3c_home" /&gt;
&lt;br&gt;&lt;/br&gt;
&lt;br/&gt;</pre></div></div><div class="div2"> <h3><a name="elemdecls" id="elemdecls" />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> <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em>, 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> issue a warning when a declaration mentions an
element type for which no declaration is provided, but this is not an error.</p><p>[<a name="dt-eldecl" id="dt-eldecl" title="Element Type declaration">Definition</a>: An <b>element
type declaration</b> takes the form:]</p> <h5><a name="IDAV13S" id="IDAV13S" />Element Type Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-elementdecl" id="NT-elementdecl" />[45]   </td><td><code>elementdecl</code></td><td>   ::=   </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>?
'&gt;'</code></td><td><a href="#EDUnique">[VC: Unique Element Type Declaration]</a></td></tr><tr valign="baseline"><td><a name="NT-contentspec" id="NT-contentspec" />[46]   </td><td><code>contentspec</code></td><td>   ::=   </td><td><code>'EMPTY' | 'ANY' | <a href="#NT-Mixed">Mixed</a>
| <a href="#NT-children">children</a></code></td></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" id="EDUnique" /><b>Validity constraint: Unique Element Type Declaration</b></p><p><span class="mustard">An element
type <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em></span> be declared more than once.</p></div><p>Examples of element type declarations:</p><div class="exampleInner"><pre>&lt;!ELEMENT br EMPTY&gt;
&lt;!ELEMENT p (#PCDATA|emph)* &gt;
&lt;!ELEMENT %name.para; %content.para; &gt;
&lt;!ELEMENT container ANY&gt;</pre></div><div class="div3"> <h4><a name="sec-element-content" id="sec-element-content" />3.2.1 Element Content</h4><p>[<a name="dt-elemcontent" id="dt-elemcontent" title="Element content">Definition</a>: An element <a title="Start-Tag" href="#dt-stag">type</a> has <b>element content</b> when elements
of that type <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> contain only <a title="Parent/Child" href="#dt-parentchild">child</a>
elements (no character data), optionally separated by white space (characters
matching the nonterminal <a href="#NT-S">S</a>).] [<a name="dt-content-model" id="dt-content-model" title="Content model">Definition</a>: In this case, the constraint includes a <b>content
model</b>, a simple grammar governing the allowed types of the
child elements and the order in which they are allowed to appear.]
The grammar is built on content particles (<a href="#NT-cp">cp</a>s), which
consist of names, choice lists of content particles, or sequence lists of
content particles:</p> <h5><a name="IDAP53S" id="IDAP53S" />Element-content Models</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-children" id="NT-children" />[47]   </td><td><code>children</code></td><td>   ::=   </td><td><code>(<a href="#NT-choice">choice</a> | <a href="#NT-seq">seq</a>)
('?' | '*' | '+')?</code></td></tr><tr valign="baseline"><td><a name="NT-cp" id="NT-cp" />[48]   </td><td><code>cp</code></td><td>   ::=   </td><td><code>(<a href="#NT-Name">Name</a> | <a href="#NT-choice">choice</a>
| <a href="#NT-seq">seq</a>) ('?' | '*' | '+')?</code></td></tr><tr valign="baseline"><td><a name="NT-choice" id="NT-choice" />[49]   </td><td><code>choice</code></td><td>   ::=   </td><td><code>'(' <a href="#NT-S">S</a>? <a href="#NT-cp">cp</a> ( <a href="#NT-S">S</a>? '|' <a href="#NT-S">S</a>? <a href="#NT-cp">cp</a> )+ <a href="#NT-S">S</a>? ')'</code></td><td><a href="#vc-PEinGroup">[VC: Proper Group/PE Nesting]</a></td></tr><tr valign="baseline"><td><a name="NT-seq" id="NT-seq" />[50]   </td><td><code>seq</code></td><td>   ::=   </td><td><code>'(' <a href="#NT-S">S</a>? <a href="#NT-cp">cp</a> ( <a href="#NT-S">S</a>? ',' <a href="#NT-S">S</a>? <a href="#NT-cp">cp</a> )* <a href="#NT-S">S</a>? ')'</code></td><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
<em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> appear as a <a title="Parent/Child" href="#dt-parentchild">child</a>. Any content
particle in a choice list <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
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 <span>the content model
allows an element to match more than one occurrence of an element type in the
content model</span>. For more information, see <a href="#determinism"><b>D Deterministic Content Models</b></a>.</p><div class="constraint"><p class="prefix"><a name="vc-PEinGroup" id="vc-PEinGroup" /><b>Validity constraint: Proper Group/PE Nesting</b></p><p>Parameter-entity <a title="Replacement Text" href="#dt-repltext">replacement text</a> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> contain at
least one non-blank character, and neither the first nor last non-blank character
of the replacement text <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> be a connector (<code>|</code> or <code>,</code>).</p></div><p>Examples of element-content models:</p><div class="exampleInner"><pre>&lt;!ELEMENT spec (front, body, back?)&gt;
&lt;!ELEMENT div1 (head, (p | list | note)*, div2*)&gt;
&lt;!ELEMENT dictionary-body (%div.mix; | %dict.mix;)*&gt;</pre></div></div><div class="div3"> <h4><a name="sec-mixed-content" id="sec-mixed-content" />3.2.2 Mixed Content</h4><p>[<a name="dt-mixed" id="dt-mixed" title="Mixed Content">Definition</a>: An element <a title="Start-Tag" href="#dt-stag">type</a>
has <b>mixed content</b> when elements of that type <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> be constrained,
but not their order or their number of occurrences:</p> <h5><a name="IDAUHCU" id="IDAUHCU" />Mixed-content Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-Mixed" id="NT-Mixed" />[51]   </td><td><code>Mixed</code></td><td>   ::=   </td><td><code>'(' <a href="#NT-S">S</a>? '#PCDATA' (<a href="#NT-S">S</a>?
'|' <a href="#NT-S">S</a>? <a href="#NT-Name">Name</a>)* <a href="#NT-S">S</a>?
')*' </code></td></tr><tr valign="baseline"><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><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" id="vc-MixedChildrenUnique" /><b>Validity constraint: No Duplicate Types</b></p><p>The
same name <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> appear more than once in a single mixed-content declaration.</p></div><p>Examples of mixed content declarations:</p><div class="exampleInner"><pre>&lt;!ELEMENT p (#PCDATA|a|ul|b|i|em)*&gt;
&lt;!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* &gt;
&lt;!ELEMENT b (#PCDATA)&gt;</pre></div></div></div><div class="div2"> <h3><a name="attdecls" id="attdecls" />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
<span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> appear outside of</span> <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
<em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> be used:</p><ul><li><p>To define the set of attributes pertaining to a given element type.</p></li><li><p>To establish type constraints for these attributes.</p></li><li><p>To provide <a title="Attribute Default" href="#dt-default">default values</a> for
attributes.</p></li></ul><p>[<a name="dt-attdecl" id="dt-attdecl" title="Attribute-List Declaration">Definition</a>: <b>Attribute-list
declarations</b> specify the name, data type, and default value (if any)
of each attribute associated with a given element type:]</p> <h5><a name="IDADMCU" id="IDADMCU" />Attribute-list Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-AttlistDecl" id="NT-AttlistDecl" />[52]   </td><td><code>AttlistDecl</code></td><td>   ::=   </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>? '&gt;'</code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-AttDef" id="NT-AttDef" />[53]   </td><td><code>AttDef</code></td><td>   ::=   </td><td><code><a href="#NT-S">S</a> <a href="#NT-Name">Name</a> <a href="#NT-S">S</a> <a href="#NT-AttType">AttType</a> <a href="#NT-S">S</a> <a href="#NT-DefaultDecl">DefaultDecl</a></code></td></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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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" id="sec-attribute-types" />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 <span><a href="#AVNormalize"><b>3.3.3 Attribute-Value Normalization</b></a></span>.</p> <h5><a name="IDAPPCU" id="IDAPPCU" />Attribute Types</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-AttType" id="NT-AttType" />[54]   </td><td><code>AttType</code></td><td>   ::=   </td><td><code><a href="#NT-StringType">StringType</a> | <a href="#NT-TokenizedType">TokenizedType</a>
| <a href="#NT-EnumeratedType">EnumeratedType</a></code></td></tr><tr valign="baseline"><td><a name="NT-StringType" id="NT-StringType" />[55]   </td><td><code>StringType</code></td><td>   ::=   </td><td><code>'CDATA'</code></td></tr><tr valign="baseline"><td><a name="NT-TokenizedType" id="NT-TokenizedType" />[56]   </td><td><code>TokenizedType</code></td><td>   ::=   </td><td><code>'ID'</code></td><td><a href="#id">[VC: ID]</a></td></tr><tr valign="baseline"><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><a href="#id-default">[VC: ID Attribute Default]</a></td></tr><tr valign="baseline"><td /><td /><td /><td><code>| 'IDREF'</code></td><td><a href="#idref">[VC: IDREF]</a></td></tr><tr valign="baseline"><td /><td /><td /><td><code>| 'IDREFS'</code></td><td><a href="#idref">[VC: IDREF]</a></td></tr><tr valign="baseline"><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><code>| 'ENTITIES'</code></td><td><a href="#entname">[VC: Entity Name]</a></td></tr><tr valign="baseline"><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><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" id="id" /><b>Validity constraint: ID</b></p><p>Values of type <b>ID</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the <a href="#NT-Name">Name</a> production. A name <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> appear more than once
in an XML document as a value of this type; i.e., ID values <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> uniquely
identify the elements which bear them.</p></div><div class="constraint"><p class="prefix"><a name="one-id-per-el" id="one-id-per-el" /><b>Validity constraint: One ID per Element Type</b></p><p><span class="mustard">An element
type <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em></span> have more than one ID attribute specified.</p></div><div class="constraint"><p class="prefix"><a name="id-default" id="id-default" /><b>Validity constraint: ID Attribute Default</b></p><p>An ID attribute
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> have a declared default of <b>#IMPLIED</b> or <b>#REQUIRED</b>.</p></div><div class="constraint"><p class="prefix"><a name="idref" id="idref" /><b>Validity constraint: IDREF</b></p><p>Values of type <b>IDREF</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
match the <a href="#NT-Name">Name</a> production, and values of type <b>IDREFS</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match <a href="#NT-Names">Names</a>; each <a href="#NT-Name">Name</a> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the value of an ID attribute on some element in the XML document;
i.e. <b>IDREF</b> values <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the value of some ID attribute.</p></div><div class="constraint"><p class="prefix"><a name="entname" id="entname" /><b>Validity constraint: Entity Name</b></p><p>Values of type <b>ENTITY</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the <a href="#NT-Name">Name</a> production, values of type <b>ENTITIES</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match <a href="#NT-Names">Names</a>; each <a href="#NT-Name">Name</a> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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" id="nmtok" /><b>Validity constraint: Name Token</b></p><p>Values of type <b>NMTOKEN</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the <a href="#NT-Nmtoken">Nmtoken</a> production; values of type <b>NMTOKENS</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match <a href="#NT-Nmtokens">Nmtokens</a>.</p></div><p>[<a name="dt-enumerated" id="dt-enumerated" title="Enumerated Attribute&#xA;Values">Definition</a>: <b>Enumerated attributes</b> <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em></span> take one of a list of values
provided in the declaration]. There are two kinds of enumerated types:</p> <h5><a name="IDAHXCU" id="IDAHXCU" />Enumerated Attribute Types</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-EnumeratedType" id="NT-EnumeratedType" />[57]   </td><td><code>EnumeratedType</code></td><td>   ::=   </td><td><code><a href="#NT-NotationType">NotationType</a>
| <a href="#NT-Enumeration">Enumeration</a></code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-NotationType" id="NT-NotationType" />[58]   </td><td><code>NotationType</code></td><td>   ::=   </td><td><code>'NOTATION' <a href="#NT-S">S</a> '(' <a href="#NT-S">S</a>? <a href="#NT-Name">Name</a> (<a href="#NT-S">S</a>? '|' <a href="#NT-S">S</a>? <a href="#NT-Name">Name</a>)* <a href="#NT-S">S</a>? ')' </code></td><td><a href="#notatn">[VC: Notation Attributes]</a></td></tr><tr valign="baseline"><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><a href="#NoNotationEmpty">[VC: No Notation on Empty Element]</a></td></tr><tr valign="baseline"><td /><td /><td /><td /><td><a href="#NoDuplicateTokens">[VC: No Duplicate
Tokens]</a></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-Enumeration" id="NT-Enumeration" />[59]   </td><td><code>Enumeration</code></td><td>   ::=   </td><td><code>'(' <a href="#NT-S">S</a>? <a href="#NT-Nmtoken">Nmtoken</a>
(<a href="#NT-S">S</a>? '|' <a href="#NT-S">S</a>? <a href="#NT-Nmtoken">Nmtoken</a>)* <a href="#NT-S">S</a>? ')'</code></td><td><a href="#enum">[VC: Enumeration]</a></td></tr><tr valign="baseline"><td /><td /><td /><td /><td><a href="#NoDuplicateTokens">[VC: No Duplicate
Tokens]</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" id="notatn" /><b>Validity constraint: Notation Attributes</b></p><p>Values of this type
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match one of the <a href="#Notations"><cite>notation</cite></a> names
included in the declaration; all notation names in the declaration <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be
declared.</p></div><div class="constraint"><p class="prefix"><a name="OneNotationPer" id="OneNotationPer" /><b>Validity constraint: One Notation Per Element Type</b></p><p><span class="mustard">An element type <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em></span> have more than one <b>NOTATION</b>
attribute specified.</p></div><div class="constraint"><p class="prefix"><a name="NoNotationEmpty" id="NoNotationEmpty" /><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> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> be declared on an element
declared <b>EMPTY</b>.</p></div><div class="constraint"><p class="prefix"><a name="NoDuplicateTokens" id="NoDuplicateTokens" /><b>Validity constraint: No Duplicate
Tokens</b></p><p>The notation names in a single <a href="#NT-NotationType">NotationType</a>
attribute declaration, as well as the <a href="#NT-Nmtoken">NmToken</a>s in a single
<a href="#NT-Enumeration">Enumeration</a> attribute declaration, <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> all be distinct.</p></div><div class="constraint"><p class="prefix"><a name="enum" id="enum" /><b>Validity constraint: Enumeration</b></p><p>Values of this type <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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> <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD NOT</em> 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" id="sec-attr-defaults" />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 <em class="rfc2119" title="Keyword in RFC 2119 context">REQUIRED</em>, and if not, how an XML processor
<span>is
to</span> react if a declared attribute is absent in a document.</p> <h5><a name="IDAR4CU" id="IDAR4CU" />Attribute Defaults</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-DefaultDecl" id="NT-DefaultDecl" />[60]   </td><td><code>DefaultDecl</code></td><td>   ::=   </td><td><code>'#REQUIRED' | '#IMPLIED' </code></td></tr><tr valign="baseline"><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><a href="#defattrvalid">[VC: Attribute
Default Value Syntactically Correct]</a></td></tr><tr valign="baseline"><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><a href="#FixedAttr">[VC: Fixed Attribute Default]</a></td></tr></tbody></table><p>In an attribute declaration, <b>#REQUIRED</b> means that the attribute
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> always be provided, <b>#IMPLIED</b> that no default value is provided.
[<a name="dt-default" id="dt-default" title="Attribute Default">Definition</a>: If
the declaration is neither <b>#REQUIRED</b> nor <b>#IMPLIED</b>, then
the <a href="#NT-AttValue">AttValue</a> value contains the declared <b>default</b>
value; the <b>#FIXED</b> keyword states that the attribute <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> always have
the default value.
When an XML processor encounters
an <span>element
without a specification for an attribute for which it has read a default
value declaration, it <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> report the attribute with the declared default
value to the application</span>.]</p><div class="constraint"><p class="prefix"><a name="RequiredAttr" id="RequiredAttr" /><b>Validity constraint: Required Attribute</b></p><p>If the default
declaration is the keyword <b>#REQUIRED</b>, then the attribute <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be
specified for all elements of the type in the attribute-list declaration.</p></div><div class="constraint"><p class="prefix"><a name="defattrvalid" id="defattrvalid" /><b>Validity constraint: <span>Attribute
Default Value Syntactically Correct</span></b></p><p>The declared default value <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> meet the <span>syntactic</span>
constraints of the declared attribute type.</p><p>Note that only the
syntactic constraints of the type are required here; other constraints (e.g.
that the value be the name of a declared unparsed entity, for an attribute of
type ENTITY) may come into play if the declared default value is actually used
(an element without a specification for this attribute occurs).</p></div><div class="constraint"><p class="prefix"><a name="FixedAttr" id="FixedAttr" /><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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the default value.</p></div><p>Examples of attribute-list declarations:</p><div class="exampleInner"><pre>&lt;!ATTLIST termdef
id      ID      #REQUIRED
name    CDATA   #IMPLIED&gt;
&lt;!ATTLIST list
type    (bullets|ordered|glossary)  "ordered"&gt;
&lt;!ATTLIST form
method  CDATA   #FIXED "POST"&gt;</pre></div></div><div class="div3"> <h4><a name="AVNormalize" id="AVNormalize" />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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 type="1"><li><p>All line breaks <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> be treated
by a non-validating processor as if declared <b>CDATA</b>.</p><p>It
is an error if an
<span><a title="Attribute Value" href="#dt-attrval">attribute
value</a> contains a <a title="Entity Reference" href="#dt-entref">reference</a> to an
entity for which no declaration has been read.</span></p><p>Following are examples of attribute normalization. Given the following
declarations:</p><div class="exampleInner"><pre>&lt;!ENTITY d "&amp;#xD;"&gt;
&lt;!ENTITY a "&amp;#xA;"&gt;
&lt;!ENTITY da "&amp;#xD;&amp;#xA;"&gt;</pre></div><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" summary="Attribute normalization summary"><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"><div class="exampleInner"><pre>a="
xyz"</pre></div></td><td rowspan="1" colspan="1"><div class="exampleInner"><pre>x y z</pre></div></td><td rowspan="1" colspan="1"><div class="exampleInner"><pre>#x20 #x20 x y z</pre></div></td></tr><tr><td rowspan="1" colspan="1"><div class="exampleInner"><pre>a="&amp;d;&amp;d;A&amp;a;<span>&amp;#x20;</span>&amp;a;B&amp;da;"</pre></div></td><td rowspan="1" colspan="1"><div class="exampleInner"><pre>A #x20 B</pre></div></td><td rowspan="1" colspan="1"><div class="exampleInner"><pre>#x20 #x20 A #x20 <span>#x20</span> #x20 B #x20 #x20</pre></div></td></tr><tr><td rowspan="1" colspan="1"><div class="exampleInner"><pre>a=
"&amp;#xd;&amp;#xd;A&amp;#xa;&amp;#xa;B&amp;#xd;&amp;#xa;"</pre></div></td><td rowspan="1" colspan="1"><div class="exampleInner"><pre>#xD #xD A #xA #xA B #xD #xA</pre></div></td><td rowspan="1" colspan="1"><div class="exampleInner"><pre>#xD #xD A #xA #xA B #xD #xA</pre></div></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" id="sec-condition-sect" />3.4 Conditional Sections</h3><p>[<a name="dt-cond-section" id="dt-cond-section" title="conditional section">Definition</a>: <b>Conditional
sections</b> are portions of the <a title="Document Type Declaration" href="#dt-doctype">document type
declaration external subset</a> <span>or
of external parameter entities </span>which are included in, or excluded from,
the logical structure of the DTD based on the keyword which governs them.]</p> <h5><a name="IDAMHDU" id="IDAMHDU" />Conditional Section</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-conditionalSect" id="NT-conditionalSect" />[61]   </td><td><code>conditionalSect</code></td><td>   ::=   </td><td><code><a href="#NT-includeSect">includeSect</a> | <a href="#NT-ignoreSect">ignoreSect</a></code></td></tr><tr valign="baseline"><td><a name="NT-includeSect" id="NT-includeSect" />[62]   </td><td><code>includeSect</code></td><td>   ::=   </td><td><code>'&lt;![' S? 'INCLUDE' S? '[' <a href="#NT-extSubsetDecl">extSubsetDecl</a>
']]&gt;' </code></td><td><a href="#condsec-nesting">[VC: Proper Conditional Section/PE Nesting]</a></td></tr><tr valign="baseline"><td><a name="NT-ignoreSect" id="NT-ignoreSect" />[63]   </td><td><code>ignoreSect</code></td><td>   ::=   </td><td><code>'&lt;![' S? 'IGNORE' S? '[' <a href="#NT-ignoreSectContents">ignoreSectContents</a>*
']]&gt;'</code></td><td><a href="#condsec-nesting">[VC: Proper Conditional Section/PE Nesting]</a></td></tr><tr valign="baseline"><td><a name="NT-ignoreSectContents" id="NT-ignoreSectContents" />[64]   </td><td><code>ignoreSectContents</code></td><td>   ::=   </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" id="NT-Ignore" />[65]   </td><td><code>Ignore</code></td><td>   ::=   </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" id="condsec-nesting" /><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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
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 <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be considered</span> part of the DTD. If the keyword of
the conditional section is <b>IGNORE</b>, then the contents of the conditional
section <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be considered as</span> 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 <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be</span> ignored. The contents
of an ignored conditional section <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be</span> 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 <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> be</span> recognized in this
process.</p><p>If the keyword of the conditional section is a parameter-entity reference,
the parameter entity <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be replaced by its content before the processor
decides whether to include or ignore the conditional section.</p><p>An example:</p><div class="exampleInner"><pre>&lt;!ENTITY % draft 'INCLUDE' &gt;
&lt;!ENTITY % final 'IGNORE' &gt;
&lt;![%draft;[
&lt;!ELEMENT book (comments*, title, body, supplements?)&gt;
]]&gt;
&lt;![%final;[
&lt;!ELEMENT book (title, body, supplements?)&gt;
]]&gt;</pre></div></div></div><div class="div1"> <h2><a name="sec-physical-struct" id="sec-physical-struct" />4 Physical Structures</h2><p>[<a name="dt-entity" id="dt-entity" title="Entity">Definition</a>: An XML document may consist of one
or many storage units. These
are called <b>entities</b>; they all have <b>content</b> and are
all (except for the <a title="Document Entity" href="#dt-docent">document entity</a> and
the <a title="Document Type Declaration" href="#dt-doctype">external DTD subset</a>) identified by
entity <b>name</b>.] Each XML document has one entity
called the <a title="Document Entity" href="#dt-docent">document entity</a>, which serves
as the starting point for the <a title="XML Processor" href="#dt-xml-proc">XML processor</a>
and may contain the whole document.</p><p>Entities may be either parsed or unparsed. [<a name="dt-parsedent" id="dt-parsedent" title="Text Entity">Definition</a>: The contents of a <b>parsed
entity</b> are referred to as its <a title="Replacement Text" href="#dt-repltext">replacement
text</a>; this <a title="Text" href="#dt-text">text</a> is considered an
integral part of the document.]</p><p>[<a name="dt-unparsed" id="dt-unparsed" title="Unparsed Entity">Definition</a>: An <b>unparsed entity</b>
is a resource whose contents may or may not be <a title="Text" href="#dt-text">text</a>,
and if text, may
be other than XML. Each unparsed entity has an associated <a title="Notation" href="#dt-notation">notation</a>, identified by name. Beyond a requirement
that an XML processor make the identifiers for the entity and notation available
to the application, XML places no constraints on the contents of unparsed
entities.]</p><p>Parsed entities are invoked by name using entity references; unparsed entities
by name, given in the value of <b>ENTITY</b> or <b>ENTITIES</b> attributes.</p><p>[<a name="gen-entity" id="gen-entity" title="general entity">Definition</a>: <b>General entities</b>
are entities for use within the document content. In this specification, general
entities are sometimes referred to with the unqualified term <em>entity</em>
when this leads to no ambiguity.] [<a name="dt-PE" id="dt-PE" title="Parameter entity">Definition</a>: <b>Parameter
entities</b> are parsed entities for use within the DTD.]
These two types of entities use different forms of reference and are recognized
in different contexts. Furthermore, they occupy different namespaces; a parameter
entity and a general entity with the same name are two distinct entities.</p><div class="div2"> <h3><a name="sec-references" id="sec-references" />4.1 Character and Entity References</h3><p>[<a name="dt-charref" id="dt-charref" title="Character Reference">Definition</a>:  A <b>character
reference</b> refers to a specific character in the ISO/IEC 10646 character
set, for example one not directly accessible from available input devices.]</p> <h5><a name="IDAFYDU" id="IDAFYDU" />Character Reference</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-CharRef" id="NT-CharRef" />[66]   </td><td><code>CharRef</code></td><td>   ::=   </td><td><code>'&amp;#' [0-9]+ ';' </code></td></tr><tr valign="baseline"><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" id="wf-Legalchar" /><b>Well-formedness constraint: Legal Character</b></p><p>Characters referred
to using character references <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the production for <a 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 name="dt-entref" id="dt-entref" title="Entity Reference">Definition</a>: An <b>entity reference</b>
refers to the content of a named entity.] [<a name="dt-GERef" id="dt-GERef" title="General Entity Reference">Definition</a>: References to parsed general entities use
ampersand (<code>&amp;</code>) and semicolon (<code>;</code>) as delimiters.] [<a name="dt-PERef" id="dt-PERef" title="Parameter-entity reference">Definition</a>: <b>Parameter-entity references</b>
use percent-sign (<code>%</code>) and semicolon (<code>;</code>) as delimiters.]</p> <h5><a name="IDAS0DU" id="IDAS0DU" />Entity Reference</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-Reference" id="NT-Reference" />[67]   </td><td><code>Reference</code></td><td>   ::=   </td><td><code><a href="#NT-EntityRef">EntityRef</a> | <a href="#NT-CharRef">CharRef</a></code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-EntityRef" id="NT-EntityRef" />[68]   </td><td><code>EntityRef</code></td><td>   ::=   </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><a href="#vc-entdeclared">[VC: Entity Declared]</a></td></tr><tr valign="baseline"><td /><td /><td /><td /><td><a href="#textent">[WFC: Parsed Entity]</a></td></tr><tr valign="baseline"><td /><td /><td /><td /><td><a href="#norecursion">[WFC: No Recursion]</a></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PEReference" id="NT-PEReference" />[69]   </td><td><code>PEReference</code></td><td>   ::=   </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><a href="#norecursion">[WFC: No Recursion]</a></td></tr><tr valign="baseline"><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" id="wf-entdeclared" /><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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> <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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> precede any reference to it which appears
in a default value in an attribute-list declaration.</p><p><span>Note
that non-validating processors are <a href="#include-if-valid"><cite>not
obligated to</cite></a> to read and process entity declarations occurring in parameter entities or in
the external subset</span>; 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" id="vc-entdeclared" /><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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> <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 <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> precede any reference to it. Similarly,
the declaration of a general entity <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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" id="textent" /><b>Well-formedness constraint: Parsed Entity</b></p><p>An entity reference <em class="rfc2119" title="Keyword in RFC 2119 context">MUST
NOT</em> 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" id="norecursion" /><b>Well-formedness constraint: No Recursion</b></p><p>A parsed entity <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> contain a recursive reference to itself, either directly or indirectly.</p></div><div class="constraint"><p class="prefix"><a name="indtd" id="indtd" /><b>Well-formedness constraint: In DTD</b></p><p>Parameter-entity references <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> appear outside</span>
the <a title="Document Type Declaration" href="#dt-doctype">DTD</a>.</p></div><p>Examples of character and entity references:</p><div class="exampleInner"><pre>Type &lt;key&gt;less-than&lt;/key&gt; (&amp;#x3C;) to save options.
This document was prepared on &amp;docdate; and
is classified &amp;security-level;.</pre></div><p>Example of a parameter-entity reference:</p><div class="exampleInner"><pre>&lt;!-- declare the parameter entity "ISOLat2"... --&gt;
&lt;!ENTITY % ISOLat2
SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" &gt;
&lt;!-- ... now reference it. --&gt;
%ISOLat2;</pre></div></div><div class="div2"> <h3><a name="sec-entity-decl" id="sec-entity-decl" />4.2 Entity Declarations</h3><p>[<a name="dt-entdecl" id="dt-entdecl" title="entity declaration">Definition</a>:  Entities are declared
thus:]</p> <h5><a name="IDAECEU" id="IDAECEU" />Entity Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-EntityDecl" id="NT-EntityDecl" />[70]   </td><td><code>EntityDecl</code></td><td>   ::=   </td><td><code><a href="#NT-GEDecl">GEDecl</a> | <a href="#NT-PEDecl">PEDecl</a></code></td></tr><tr valign="baseline"><td><a name="NT-GEDecl" id="NT-GEDecl" />[71]   </td><td><code>GEDecl</code></td><td>   ::=   </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>?
'&gt;'</code></td></tr><tr valign="baseline"><td><a name="NT-PEDecl" id="NT-PEDecl" />[72]   </td><td><code>PEDecl</code></td><td>   ::=   </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>? '&gt;'</code></td></tr><tr valign="baseline"><td><a name="NT-EntityDef" id="NT-EntityDef" />[73]   </td><td><code>EntityDef</code></td><td>   ::=   </td><td><code><a href="#NT-EntityValue">EntityValue</a>| (<a href="#NT-ExternalID">ExternalID</a> <a href="#NT-NDataDecl">NDataDecl</a>?)</code></td></tr><tr valign="baseline"><td><a name="NT-PEDef" id="NT-PEDef" />[74]   </td><td><code>PEDef</code></td><td>   ::=   </td><td><code><a href="#NT-EntityValue">EntityValue</a> | <a href="#NT-ExternalID">ExternalID</a></code></td></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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> issue a warning if entities are declared multiple times.</p><div class="div3"> <h4><a name="sec-internal-ent" id="sec-internal-ent" />4.2.1 Internal Entities</h4><p>[<a name="dt-internent" id="dt-internent" title="Internal Entity Replacement Text">Definition</a>: If the
entity definition is an <a href="#NT-EntityValue">EntityValue</a>, the defined
entity is called an <b>internal entity</b>. There is no separate physical
storage object, and the content of the entity is given in the declaration.]
Note that some processing of entity and character references in the <a title="Literal Entity Value" href="#dt-litentval">literal entity value</a> may be required to produce
the correct <a title="Replacement Text" href="#dt-repltext">replacement text</a>: see <a href="#intern-replacement"><b>4.5 Construction of 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><div class="exampleInner"><pre>&lt;!ENTITY Pub-Status "This is a pre-release of the
specification."&gt;</pre></div></div><div class="div3"> <h4><a name="sec-external-ent" id="sec-external-ent" />4.2.2 External Entities</h4><p>[<a name="dt-extent" id="dt-extent" title="External Entity">Definition</a>: If the entity is not internal,
it is an <b>external entity</b>, declared as follows:]</p> <h5><a name="IDAUIEU" id="IDAUIEU" />External Entity Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-ExternalID" id="NT-ExternalID" />[75]   </td><td><code>ExternalID</code></td><td>   ::=   </td><td><code>'SYSTEM' <a href="#NT-S">S</a> <a href="#NT-SystemLiteral">SystemLiteral</a></code></td></tr><tr valign="baseline"><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" id="NT-NDataDecl" />[76]   </td><td><code>NDataDecl</code></td><td>   ::=   </td><td><code><a href="#NT-S">S</a> 'NDATA' <a href="#NT-S">S</a> <a href="#NT-Name">Name</a></code></td><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" id="not-declared" /><b>Validity constraint: Notation Declared</b></p><p>The <a href="#NT-Name">Name</a> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> match the declared name of a <a title="Notation" href="#dt-notation">notation</a>.</p></div><p>[<a name="dt-sysid" id="dt-sysid" title="System Identifier">Definition</a>: The <a href="#NT-SystemLiteral">SystemLiteral</a> is called the entity's <b>system
identifier</b>. It is <span>meant to be
converted to</span> a URI reference
(as defined in <a href="#rfc2396">[IETF RFC 2396]</a>, updated by <a href="#rfc2732">[IETF RFC 2732]</a>),
<span>as part of the
process of dereferencing it</span> 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. <span>This is defined to
be the external entity containing the '&lt;' which starts the declaration, at the
point when it is parsed as a declaration.</span>
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>. <span>Attempts to
retrieve the resource identified by a URI <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> be redirected at the parser
level (for example, in an entity resolver) or below (at the protocol level,
for example, via an HTTP <code>Location:</code> header). In the absence of additional
information outside the scope of this specification within the resource,
the base URI of a resource is always the URI of the actual resource returned.
In other words, it is the URI of the resource retrieved after all redirection
has occurred.</span></p><p>System
identifiers (and other XML strings meant to be used as URI references) <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> contain
characters that, according to <a href="#rfc2396">[IETF RFC 2396]</a> and <a href="#rfc2732">[IETF RFC 2732]</a>,
must be escaped before a URI can be used to retrieve the referenced resource. The
characters to be escaped are the control characters #x0 to #x1F and #x7F (most of
which cannot appear in XML), space #x20, the delimiters '&lt;' #x3C, '&gt;' #x3E and
'"' #x22, the <em>unwise</em> characters '{' #x7B, '}' #x7D, '|' #x7C, '\' #x5C, '^' #x5E and
'`' #x60, as well as all characters above #x7F. Since escaping is not always a fully
reversible process, it <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be performed only when absolutely necessary and as late
as possible in a processing chain. In particular, neither the process of converting
a relative URI to an absolute one nor the process of passing a URI reference to a
process or software component responsible for dereferencing it <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> trigger escaping.
When escaping does occur, it <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be performed as follows:</p><ol type="1"><li><p>Each
character <span>to be escaped</span>
is <span>represented in</span>
UTF-8 <span><a href="#Unicode">[Unicode]</a></span>
as one or more bytes.</p></li><li><p><span>The resulting bytes</span>
are escaped with
the URI escaping mechanism (that is, converted to <code>%</code><var>HH</var>,
where HH is the hexadecimal notation of the byte value).</p></li><li><p>The original character is replaced by the resulting character sequence.</p></li></ol><p>[<a name="dt-pubid" id="dt-pubid" title="Public identifier">Definition</a>:  In addition to a system
identifier, an external identifier <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> include a <b>public identifier</b>.]
An XML processor attempting to retrieve the entity's content <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> use
<span>any combination of
the public and system identifiers as well as additional information outside the
scope of this specification</span> to try to generate an alternative URI reference.
If the processor is unable to do so, it <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> use the URI
reference specified in the system literal. Before a match is attempted,
all strings of white space in the public identifier <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be normalized to
single space characters (#x20), and leading and trailing white space <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
be removed.</p><p>Examples of external entity declarations:</p><div class="exampleInner"><pre>&lt;!ENTITY open-hatch
SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml"&gt;
&lt;!ENTITY open-hatch
PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN"
"http://www.textuality.com/boilerplate/OpenHatch.xml"&gt;
&lt;!ENTITY hatch-pic
SYSTEM "../grafix/OpenHatch.gif"
NDATA gif &gt;</pre></div></div></div><div class="div2"> <h3><a name="TextEntities" id="TextEntities" />4.3 Parsed Entities</h3><div class="div3"> <h4><a name="sec-TextDecl" id="sec-TextDecl" />4.3.1 The Text Declaration</h4><p>External parsed entities <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> each begin with a <b>text declaration</b>.</p> <h5><a name="IDAUPEU" id="IDAUPEU" />Text Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-TextDecl" id="NT-TextDecl" />[77]   </td><td><code>TextDecl</code></td><td>   ::=   </td><td><code>'&lt;?xml' <a href="#NT-VersionInfo">VersionInfo</a>? <a href="#NT-EncodingDecl">EncodingDecl</a> <a href="#NT-S">S</a>? '?&gt;'</code></td></tr></tbody></table><p>The text declaration <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be provided literally, not by reference
to a parsed entity. <span class="mustard">The</span> text declaration
<span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em></span> 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" id="wf-entities" />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><a name="IDA2REU" id="IDA2REU" />Well-Formed External Parsed Entity</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-extParsedEnt" id="NT-extParsedEnt" />[78]   </td><td><code>extParsedEnt</code></td><td>   ::=   </td><td><code><a href="#NT-TextDecl">TextDecl</a>? <a href="#NT-content">content</a> - <a href="#NT-Char">Char</a>* <a href="#NT-RestrictedChar">RestrictedChar</a> <a href="#NT-Char">Char</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 <span>general</span>
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" id="charencoding" />4.3.3 Character Encoding in Entities</h4><p>Each external parsed entity in an XML document <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> use a different encoding
for its characters. All XML processors <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <span><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em></span> <span>and entities
encoded in UTF-8 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em></span> begin with the Byte Order Mark described in
ISO/IEC 10646 <a href="#ISO10646">[ISO/IEC 10646]</a> or Unicode <a href="#Unicode">[Unicode]</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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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><a name="IDARVEU" id="IDARVEU" />Encoding Declaration</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-EncodingDecl" id="NT-EncodingDecl" />[80]   </td><td><code>EncodingDecl</code></td><td>   ::=   </td><td><code><a href="#NT-S">S</a> 'encoding' <a href="#NT-Eq">Eq</a>
('"' <a href="#NT-EncName">EncName</a> '"' | "'" <a href="#NT-EncName">EncName</a>
"'" ) </code></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-EncName" id="NT-EncName" />[81]   </td><td><code>EncName</code></td><td>   ::=   </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>" <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> 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) <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> 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>" <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> be used for the various encoded
forms of JIS X-0208-1997. It
is <em class="rfc2119" title="Keyword in RFC 2119 context">RECOMMENDED</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> use names starting with an "x-" prefix.
XML processors <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> match character encoding names in a case-insensitive
way and <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> 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 a <a title="Fatal Error" href="#dt-fatal">fatal 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 <a title="Fatal Error" href="#dt-fatal">fatal error</a> 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 <a title="Fatal Error" href="#dt-fatal">fatal error</a> if an XML entity is determined (via default, encoding declaration,
or higher-level protocol) to be in a certain encoding but contains <span>byte</span>
sequences that are not legal in that encoding. <span>Specifically, it is a
fatal error if an entity encoded in UTF-8 contains any irregular code unit sequences,
as defined in Unicode <a href="#Unicode">[Unicode]</a>.</span> <span>Unless an encoding
is determined by a higher-level protocol, </span>it is also a <a title="Fatal Error" href="#dt-fatal">fatal error</a> 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><div class="exampleInner"><pre>&lt;?xml encoding='UTF-8'?&gt;
&lt;?xml encoding='EUC-JP'?&gt;</pre></div></div><div class="div3"> <h4><a name="sec-version-info" id="sec-version-info" />4.3.4 Version Information in Entities</h4><p>Each entity, including the <a title="Document Entity" href="#dt-docent">document entity</a>,
can be separately
declared as XML 1.0 or XML 1.1. The version declaration appearing
in the document entity determines the version of the document as a
whole. An XML 1.1 document may invoke XML 1.0 external entities, so
that otherwise duplicated versions of external entities,
particularly DTD external subsets, need not be maintained. However,
in such a case the rules of XML 1.1 are applied to the entire
document.</p><p> If an entity (including the document entity) is not labeled
with a version number, it is treated as if labeled as version
1.0.</p></div></div><div class="div2"> <h3><a name="entproc" id="entproc" />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
<em class="rfc2119" title="Keyword in RFC 2119 context">REQUIRED</em> 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" summary="Entity type/reference matrix"><tbody align="center"><tr><td rowspan="2" colspan="1"></td><td colspan="4" align="center" valign="bottom" rowspan="1">Entity
Type</td><td rowspan="2" align="center" colspan="1">Character</td></tr><tr align="center" valign="bottom"><td rowspan="1" colspan="1">Parameter</td><td rowspan="1" colspan="1">Internal General</td><td rowspan="1" colspan="1">External Parsed
General</td><td rowspan="1" colspan="1">Unparsed</td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Reference
in Content</td><td rowspan="1" colspan="1"><a href="#not-recognized"><cite>Not recognized</cite></a></td><td rowspan="1" colspan="1"><a href="#included"><cite>Included</cite></a></td><td rowspan="1" colspan="1"><a href="#include-if-valid"><cite>Included
if validating</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#included"><cite>Included</cite></a></td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Reference in Attribute Value</td><td rowspan="1" colspan="1"><a href="#not-recognized"><cite>Not recognized</cite></a></td><td rowspan="1" colspan="1"><a href="#inliteral"><cite>Included
in literal</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#included"><cite>Included</cite></a></td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Occurs as Attribute
Value</td><td rowspan="1" colspan="1"><a href="#not-recognized"><cite>Not recognized</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#notify"><cite>Notify</cite></a></td><td rowspan="1" colspan="1"><a href="#not-recognized"><cite>Not recognized</cite></a></td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Reference in EntityValue</td><td rowspan="1" colspan="1"><a href="#inliteral"><cite>Included in literal</cite></a></td><td rowspan="1" colspan="1"><a href="#bypass"><cite>Bypassed</cite></a></td><td rowspan="1" colspan="1"><a href="#bypass"><cite>Bypassed</cite></a></td><td rowspan="1" colspan="1"><a href="#error"><cite><span>Error</span></cite></a></td><td rowspan="1" colspan="1"><a href="#included"><cite>Included</cite></a></td></tr><tr align="center" valign="middle"><td align="right" rowspan="1" colspan="1">Reference in DTD</td><td rowspan="1" colspan="1"><a href="#as-PE"><cite>Included as PE</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td><td rowspan="1" colspan="1"><a href="#forbidden"><cite>Forbidden</cite></a></td></tr></tbody></table><div class="div3"> <h4><a name="not-recognized" id="not-recognized" />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" id="included" />4.4.2 Included</h4><p>[<a name="dt-include" id="dt-include" title="Include">Definition</a>: An entity is <b>included</b>
when its <a title="Replacement Text" href="#dt-repltext">replacement text</a> is retrieved
and processed, in place of the reference itself, as though it were part of
the document at the location the reference was recognized.] The replacement
text <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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" id="include-if-valid" />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
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> <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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em>, but need
not, include the entity's replacement text. If a non-validating processor
does not include the replacement text, it <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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" id="forbidden" />4.4.4 Forbidden</h4><p>The following are forbidden, and constitute <a title="Fatal Error" href="#dt-fatal">fatal
errors</a>:</p><ul><li><p>the appearance of a reference to an <a title="Unparsed Entity" href="#dt-unparsed">unparsed
entity</a><span>, except in the
<a href="#NT-EntityValue">EntityValue</a> in an entity declaration</span>.</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" id="inliteral" />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> <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be</span> 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 <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> always be</span> treated as a normal data
character and <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em></span> terminate the literal. For example, this is well-formed:</p><div class="exampleInner"><pre>&lt;!ENTITY % YN '"Yes"' &gt;
&lt;!ENTITY WhatHeSaid "He said %YN;" &gt;</pre></div><p>while this is not:</p><div class="exampleInner"><pre>&lt;!ENTITY EndAttr "27'" &gt;
&lt;element attribute='a-&amp;EndAttr;&gt;</pre></div></div><div class="div3"> <h4><a name="notify" id="notify" />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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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" id="bypass" />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 <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be</span> bypassed and left as is.</p></div><div class="div3"> <h4><a name="as-PE" id="as-PE" />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> <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be</span> 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 <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em></span> 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 class="div3"> <h4><a name="error" id="error" />4.4.9 Error</h4><p>It is an <a title="Error" href="#dt-error">error</a> for a reference to
an unparsed entity to appear in the <a href="#NT-EntityValue">EntityValue</a> in an
entity declaration.</p></div></div><div class="div2"> <h3><a name="intern-replacement" id="intern-replacement" />4.5 Construction of Entity Replacement Text</h3><p>In discussing the treatment of entities, it is useful to distinguish
two forms of the entity's value.
[<a name="dt-litentval" id="dt-litentval" title="Literal Entity Value">Definition</a>: <span>For an
internal entity, </span>the <b>literal
entity value</b> is the quoted string actually present in the entity declaration,
corresponding to the non-terminal <a href="#NT-EntityValue">EntityValue</a>.] [<a name="dt-extlitentval" id="dt-extlitentval" title="Literal Entity Value">Definition</a>: For an external entity, the <b>literal
entity value</b> is the exact text contained in the entity.] [<a name="dt-repltext" id="dt-repltext" title="Replacement Text">Definition</a>: <span>For an
internal entity, </span>the <b>replacement text</b>
is the content of the entity, after replacement of character references and
parameter-entity references.] [<a name="dt-extrepltext" id="dt-extrepltext" title="Replacement Text">Definition</a>: For
an external entity, the <b>replacement text</b> is the content of the entity,
after stripping the text declaration (leaving any surrounding white space) if there
is one but without any replacement of character references or parameter-entity
references.]</p><p>The literal entity value as given in an internal entity declaration (<a href="#NT-EntityValue">EntityValue</a>) <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> contain character, parameter-entity,
and general-entity references. Such references <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be contained entirely
within the literal entity value. The actual replacement text that is <a title="Include" href="#dt-include">included</a><span> (or <a title="" href="#inliteral">included in literal</a>)</span> as described above
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> contain the <em>replacement
text</em> of any parameter entities referred to, and <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> contain the character
referred to, in place of any character references in the literal entity value;
however, general-entity references <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be left as-is, unexpanded. For example,
given the following declarations:</p><div class="exampleInner"><pre>&lt;!ENTITY % pub    "&amp;#xc9;ditions Gallimard" &gt;
&lt;!ENTITY   rights "All rights reserved" &gt;
&lt;!ENTITY   book   "La Peste: Albert Camus,
&amp;#xA9; 1947 %pub;. &amp;rights;" &gt;</pre></div><p>then the replacement text for the entity "<code>book</code>"
is:</p><div class="exampleInner"><pre>La Peste: Albert Camus,
© 1947 Éditions Gallimard. &amp;rights;</pre></div><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>C Expansion of Entity and Character References</b></a>.</p></div><div class="div2"> <h3><a name="sec-predefined-ent" id="sec-predefined-ent" />4.6 Predefined Entities</h3><p>[<a name="dt-escape" id="dt-escape" title="escape">Definition</a>: Entity and character references <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em>
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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> also be used; they are expanded
immediately when recognized and <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be treated as character data, so the
numeric character references "<code>&amp;#60;</code>" and "<code>&amp;#38;</code>" <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> be used to escape <code>&lt;</code> and <code>&amp;</code> when they occur
in character data.]</p><p>All XML processors <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> recognize these entities whether they are declared
or not. <a title="For interoperability" href="#dt-interop">For interoperability</a>, valid XML
documents <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> declare these entities, like any others, before using them. If
the entities <code>lt</code> or <code>amp</code> are declared, they <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">REQUIRED</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <span class="mustard"><em class="rfc2119" title="Keyword in RFC 2119 context">OPTIONAL</em></span> but harmless).
For example:</p><div class="exampleInner"><pre>&lt;!ENTITY lt     "&amp;#38;#60;"&gt;
&lt;!ENTITY gt     "&amp;#62;"&gt;
&lt;!ENTITY amp    "&amp;#38;#38;"&gt;
&lt;!ENTITY apos   "&amp;#39;"&gt;
&lt;!ENTITY quot   "&amp;#34;"&gt;</pre></div></div><div class="div2"> <h3><a name="Notations" id="Notations" />4.7 Notation Declarations</h3><p>[<a name="dt-notation" id="dt-notation" title="Notation">Definition</a>: <b>Notations</b> identify
by name the format of <a title="External Entity" href="#dt-extent">unparsed entities</a>,
the format of elements which bear a notation attribute, or the application
to which a <a title="Processing instruction" href="#dt-pi">processing instruction</a> is addressed.]</p><p>[<a name="dt-notdecl" id="dt-notdecl" title="Notation Declaration">Definition</a>: <b>Notation declarations</b>
provide a name for the notation, for use in entity and attribute-list declarations
and in attribute specifications, and an external identifier for the notation
which may allow an XML processor or its client application to locate a helper
application capable of processing data in the given notation.]</p> <h5><a name="IDAYTFU" id="IDAYTFU" />Notation Declarations</h5><table class="scrap" summary="Scrap"><tbody><tr valign="baseline"><td><a name="NT-NotationDecl" id="NT-NotationDecl" />[82]   </td><td><code>NotationDecl</code></td><td>   ::=   </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>? '&gt;'</code></td><td><a href="#UniqueNotationName">[VC: Unique Notation Name]</a></td></tr></tbody><tbody><tr valign="baseline"><td><a name="NT-PublicID" id="NT-PublicID" />[83]   </td><td><code>PublicID</code></td><td>   ::=   </td><td><code>'PUBLIC' <a href="#NT-S">S</a> <a href="#NT-PubidLiteral">PubidLiteral</a></code></td></tr></tbody></table><div class="constraint"><p class="prefix"><a name="UniqueNotationName" id="UniqueNotationName" /><b>Validity constraint: Unique Notation Name</b></p><p><span class="mustard">A given <a href="#NT-Name">Name</a> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> be declared in more than one notation declaration.</span></p></div><p>XML processors <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em> 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" id="sec-doc-entity" />4.8 Document Entity</h3><p>[<a name="dt-docent" id="dt-docent" title="Document Entity">Definition</a>: The <b>document entity</b>
serves as the root of the entity tree and a starting-point for an <a title="XML Processor" href="#dt-xml-proc">XML processor</a>.] This specification does
not specify how the document entity is to be located by an XML processor;
unlike other entities, the document entity has no name and might well appear
on a processor input stream without any identification at all.</p></div></div><div class="div1"> <h2><a name="sec-conformance" id="sec-conformance" />5 Conformance</h2><div class="div2"> <h3><a name="proc-types" id="proc-types" />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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> report violations of
this specification's well-formedness constraints in the content of the <a title="Document Entity" href="#dt-docent">document entity</a> and any other <a title="Text Entity" href="#dt-parsedent">parsed
entities</a> that they read.</p><p>[<a name="dt-validating" id="dt-validating" title="Validating Processor">Definition</a>: <b>Validating
processors</b> <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>,
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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> read and process the entire
DTD and all external parsed entities referenced in the document.</p><p>Non-validating processors are <em class="rfc2119" title="Keyword in RFC 2119 context">REQUIRED</em> to check only the <a title="Document Entity" href="#dt-docent">document
entity</a>, including the entire internal DTD subset, for well-formedness. [<a name="dt-use-mdecl" id="dt-use-mdecl" title="Process Declarations">Definition</a>:  While they are not required
to check the document for validity, they are <em class="rfc2119" title="Keyword in RFC 2119 context">REQUIRED</em> 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 <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> 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
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST NOT</em> <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<span>; when <code>standalone="yes"</code>, processors <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
process these declarations</span>.</p><p>Note
that when processing invalid documents with a non-validating
processor the application may not be presented with consistent
information.  For example, several requirements for uniqueness
within the document may not be met, including more than one element
with the same id, duplicate declarations of elements or notations
with the same name, etc.  In these cases the behavior of the parser
with respect to reporting such information to the application is
undefined.</p><p>XML 1.1 processors <em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be able to process both XML 1.0
and XML 1.1 documents.  Programs which generate XML <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em>
generate XML 1.0, unless one of the specific features of XML 1.1 is required.</p></div><div class="div2"> <h3><a name="safe-behavior" id="safe-behavior" />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, <span>may fail to</span> 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 <span>may fail to</span> <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 <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD NOT</em> rely on any behaviors
not required of such processors.  Applications which require DTD facilities
not related to validation (such
as the declaration of default attributes and internal entities that are
or may be specified in
external entities <em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em> use validating XML processors.</p></div></div><div class="div1"> <h2><a name="sec-notation" id="sec-notation" />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><div class="exampleInner"><pre>symbol ::= expression</pre></div><p>Symbols are written with an initial capital letter if they are the
start symbol of a regular language, otherwise with an initial lowercase
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
<span>whose</span><span> number
(code point) in</span> ISO/IEC 10646 <span>is <code>N</code></span>. The number of leading zeros in the <code>#xN</code>
form is insignificant.</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>.</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" id="sec-bibliography" />A References</h2><div class="div2"> <h3><a name="sec-existing-stds" id="sec-existing-stds" />A.1 Normative References</h3><dl><dt class="label"><a name="IANA" id="IANA" />IANA-CHARSETS</dt><dd>(Internet
Assigned Numbers Authority) <a href="http://www.iana.org/assignments/character-sets"><cite>Official Names for Character Sets</cite></a>,
ed. Keld Simonsen et al.   (See http://www.iana.org/assignments/character-sets.)</dd><dt class="label"><a name="rfc2119" id="rfc2119" />IETF RFC 2119</dt><dd>IETF
(Internet Engineering Task Force). <a href="http://www.ietf.org/rfc/rfc2119.txt"><cite>RFC 2119: Key words for use in RFCs to Indicate Requirement Levels</cite></a>.
Scott Bradner, 1997.  (See http://www.ietf.org/rfc/rfc2119.txt.)</dd><dt class="label"><a name="rfc2396" id="rfc2396" />IETF RFC 2396</dt><dd>IETF
(Internet Engineering Task Force). <a href="http://www.ietf.org/rfc/rfc2396.txt"><cite>RFC 2396: Uniform Resource Identifiers
(URI): Generic Syntax</cite></a>. T. Berners-Lee, R. Fielding, L. Masinter.
1998.  (See http://www.ietf.org/rfc/rfc2396.txt.)</dd><dt class="label"><a name="rfc2732" id="rfc2732" />IETF RFC 2732</dt><dd>IETF
(Internet Engineering Task Force). <a href="http://www.ietf.org/rfc/rfc2732.txt"><cite>RFC 2732: Format for Literal
IPv6 Addresses in URL's</cite></a>. R. Hinden, B. Carpenter, L. Masinter.
1999.  (See http://www.ietf.org/rfc/rfc2732.txt.)</dd><dt class="label"><a name="RFC1766" id="RFC1766" />IETF RFC 3066</dt><dd>IETF
(Internet Engineering Task Force). <a href="http://www.ietf.org/rfc/rfc3066.txt"><cite>RFC 3066: Tags for the Identification
of Languages</cite></a>, ed. H. Alvestrand. 2001.  (See http://www.ietf.org/rfc/rfc3066.txt.)</dd><dt class="label"><a name="ISO10646" id="ISO10646" />ISO/IEC 10646</dt><dd><span>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> and <cite>ISO/IEC 10646-2:2001.
Information technology — Universal Multiple-Octet Coded Character Set (UCS) — Part 2:
Supplementary Planes</cite>, as, from time to time, amended, replaced by a new edition or
expanded by the addition of new parts. [Geneva]: International Organization for Standardization.
(See <a href="http://www.iso.ch">http://www.iso.ch</a> for the latest version.)</span></dd><dt class="label"><a name="Unicode" id="Unicode" />Unicode</dt><dd>The Unicode Consortium. <em>The Unicode
Standard, Version 4.0.</em> Reading, Mass.: Addison-Wesley,
2003,
as updated from time to time by the publication of new versions. (See
<a href="http://www.unicode.org/unicode/standard/versions">
http://www.unicode.org/unicode/standard/versions</a> for the latest version
and additional information on versions of the standard and of the Unicode
Character Database).</dd><dt class="label"><a name="XML1.0" />XML-1.0</dt><dd>W3C.  <a href="http://www.w3.org/TR/REC-xml"><cite>Extensible Markup Language (XML) 1.0 (Third
Edition)</cite></a>.  Tim Bray, Jean Paoli, C.M. Sperberg-McQueen, Eve Maler, François Yergeau
(editors)  (See http://www.w3.org/TR/REC-xml.)</dd></dl></div><div class="div2"> <h3><a name="null" id="null" />A.2 Other References</h3><dl><dt class="label"><a name="Aho" id="Aho" />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="ABK" id="ABK" />Brüggemann-Klein</dt><dd>Brüggemann-Klein,
Anne. <a href="ftp://ftp.informatik.uni-freiburg.de/documents/papers/brueggem/habil.ps"><cite>Formal Models in Document Processing</cite></a>. Habilitationsschrift. Faculty
of Mathematics at the University of Freiburg, 1993.  (See ftp://ftp.informatik.uni-freiburg.de/documents/papers/brueggem/habil.ps.)</dd><dt class="label"><a name="ABKDW" id="ABKDW" />Brüggemann-Klein and Wood</dt><dd>Brüggemann-Klein,
Anne, and Derick Wood. <cite>Deterministic Regular Languages</cite>.
Universität Freiburg, Institut für Informatik, Bericht 38, Oktober 1991. Extended
abstract in A. Finkel, M. Jantzen, Hrsg., STACS 1992, S. 173-184. Springer-Verlag,
Berlin 1992. Lecture Notes in Computer Science 577. Full version titled <cite>One-Unambiguous
Regular Languages</cite> in Information and Computation 140 (2): 229-253,
February 1998.</dd><dt class="label"><a name="Charmod" />Charmod</dt><dd>W3C Working Draft.

<a href="http://www.w3.org/TR/2003/WD-charmod-20030822/"><cite>Character Model for the World Wide Web 1.0</cite></a>.

Martin J. Dürst, François Yergeau, Richard Ishida, Misha Wolf, Tex Texin.  (See http://www.w3.org/TR/2003/WD-charmod-20030822/.)</dd><dt class="label"><a name="Clark" id="Clark" />Clark</dt><dd>James Clark.
<a href="http://www.w3.org/TR/NOTE-sgml-xml-971215"><cite>Comparison of SGML and XML</cite></a>.  (See http://www.w3.org/TR/NOTE-sgml-xml-971215.)</dd><dt class="label"><a name="IANA-LANGCODES" id="IANA-LANGCODES" />IANA-LANGCODES</dt><dd>(Internet
Assigned Numbers Authority) <a href="http://www.iana.org/assignments/language-tags"><cite>Registry of Language Tags</cite></a>,
ed. Keld Simonsen et al.   (See http://www.iana.org/assignments/language-tags.)</dd><dt class="label"><a name="RFC2141" id="RFC2141" />IETF RFC 2141</dt><dd>IETF
(Internet Engineering Task Force). <a href="http://www.ietf.org/rfc/rfc2141.txt"><cite>RFC 2141: URN Syntax</cite></a>, ed.
R. Moats. 1997.   (See http://www.ietf.org/rfc/rfc2141.txt.)</dd><dt class="label"><a name="rfc2376" id="rfc2376" />IETF RFC 3023</dt><dd>IETF
(Internet Engineering Task Force). <a href="http://www.ietf.org/rfc/rfc3023.txt"><cite>RFC 3023: XML Media Types</cite></a>.
eds. M. Murata, S. St.Laurent, D. Kohn. 2001.  (See http://www.ietf.org/rfc/rfc3023.txt.)</dd><dt class="label"><a name="rfc2781" id="rfc2781" />IETF RFC 2781</dt><dd>IETF
(Internet Engineering Task Force). <a href="http://www.ietf.org/rfc/rfc2781.txt"><cite>RFC 2781: UTF-16, an encoding
of ISO 10646</cite></a>, ed. P. Hoffman, F. Yergeau. 2000.  (See http://www.ietf.org/rfc/rfc2781.txt.)</dd><dt class="label"><a name="ISO639" id="ISO639" />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" id="ISO3166" />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" id="ISO8879" />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" id="ISO10744" />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" id="websgml" />WEBSGML</dt><dd>ISO
(International Organization for Standardization). <a href="http://www.sgmlsource.com/8879/n0029.htm"><cite>ISO 8879:1986
TC2. Information technology — Document Description and Processing Languages</cite></a>.
[Geneva]: International Organization for Standardization, 1998.  (See http://www.sgmlsource.com/8879/n0029.htm.)</dd><dt class="label"><a name="xml-names" id="xml-names" />XML Names</dt><dd>Tim Bray,
Dave Hollander, and Andrew Layman, editors. <a href="http://www.w3.org/TR/REC-xml-names/"><cite>Namespaces in XML</cite></a>.
Textuality, Hewlett-Packard, and Microsoft. World Wide Web Consortium, 1999.  (See http://www.w3.org/TR/REC-xml-names/.)</dd></dl></div></div><div class="div1"> <h2><a name="sec-CharNorm" id="sec-CharNorm" />B Definitions for Character Normalization</h2><p>This appendix contains the necessary definitions for character normalization.
For additional background information and examples, see <a href="#Charmod">[Charmod]</a>.</p><p>
[<a name="dt-Uni-encform" id="dt-Uni-encform" title="Unicode encoding form">Definition</a>: Text is said to be
in a <b>Unicode encoding form</b> if it is encoded in
UTF-8, UTF-16 or UTF-32.]</p><p>
[<a name="dt-legacyenc" id="dt-legacyenc" title="legacy encoding">Definition</a>: <b>Legacy encoding</b>
is taken to mean any character encoding not based on Unicode.]</p><p>
[<a name="dt-normtransc" id="dt-normtransc" title="normalizing transcoder">Definition</a>: A
<b>normalizing transcoder</b> is a transcoder that converts from a
<a title="legacy encoding" href="#dt-legacyenc">legacy encoding</a> to a
<a title="Unicode encoding form" href="#dt-Uni-encform">Unicode encoding form</a> and
ensures that the result is in Unicode Normalization Form C
(see UAX #15 <a href="#Unicode">[Unicode]</a>).]</p><p>[<a name="dt-charesc" id="dt-charesc" title="character escape">Definition</a>: A <b>character escape</b>
is a syntactic device defined in a markup or programming language that allows
one or more of:]</p><ol type="1"><li><p>expressing syntax-significant characters while disregarding
their significance in the syntax of the language, or</p></li><li><p>expressing characters not representable in the character encoding
chosen for an instance of the language, or</p></li><li><p>expressing characters in general, without use of the corresponding
character codes.</p></li></ol><p>
[<a name="dt-certified" id="dt-certified" title="certified">Definition</a>: <b>Certified</b> text
is text which satisfies at least one of the following conditions:]</p><ol type="1"><li><p>it has been confirmed through inspection that the text
is in normalized form</p></li><li><p>the source text-processing component is identified
and is known to produce only normalized text.</p></li></ol><p>
[<a name="dt-uninorm" id="dt-uninorm" title="Unicode-normalized">Definition</a>: Text is, for the purposes of
this specification, <b>Unicode-normalized</b> if it is in a
<a title="Unicode encoding form" href="#dt-Uni-encform">Unicode encoding form</a> and is in
Unicode Normalization Form C, according to a version of Unicode Standard Annex #15:
Unicode Normalization Forms <a href="#Unicode">[Unicode]</a> at least as recent as the
oldest version of the Unicode Standard that contains all the characters
actually present in the text, but no earlier
than version 3.2.]</p><p>
[<a name="dt-inclnorm" id="dt-inclnorm" title="include-normalized">Definition</a>: Text is
<b>include-normalized</b> if:]</p><ol type="1"><li><p>the text is <a title="Unicode-normalized" href="#dt-uninorm">Unicode-normalized</a>
and does not contain any <a title="character escape" href="#dt-charesc">character escapes</a>
or <a title="Include" href="#dt-include">includes</a> whose expansion would
cause the text to become no longer <a title="Unicode-normalized" href="#dt-uninorm">Unicode-normalized</a>;
or</p></li><li><p>the text is in a <a title="legacy encoding" href="#dt-legacyenc">legacy encoding</a> and, if it were transcoded
to a <a title="Unicode encoding form" href="#dt-Uni-encform">Unicode encoding form</a> by a
<a title="normalizing transcoder" href="#dt-normtransc">normalizing transcoder</a>, the resulting
text would satisfy clause 1 above.</p></li></ol><p>
[<a name="dt-compchar" id="dt-compchar" title="composing character">Definition</a>: A <b>composing character</b>
is a character that is one or both of the following:]</p><ol type="1"><li><p>the second character in the canonical decomposition mapping of
some primary composite (as defined in D3 of UAX #15 <a href="#Unicode">[Unicode]</a>), or</p></li><li><p>of non-zero canonical combining class (as defined in Unicode
<a href="#Unicode">[Unicode]</a>).</p></li></ol><p>
[<a name="dt-fullnorm" id="dt-fullnorm" title="fully normalized">Definition</a>: Text is
<b>fully-normalized</b> if:]</p><ol type="1"><li><p>the text is in a <a title="Unicode encoding form" href="#dt-Uni-encform">Unicode encoding
form</a>, is <a title="include-normalized" href="#dt-inclnorm">include-normalized</a> and
none of the <a title="" href="#dt-relconst"><span>relevant</span>
constructs</a> comprising the text begin with a
<a title="composing character" href="#dt-compchar">composing character</a> or a
character escape representing a
<a title="composing character" href="#dt-compchar">composing character</a>; or</p></li><li><p>the text is in a <a title="legacy encoding" href="#dt-legacyenc">legacy encoding</a> and,
if it were transcoded to a <a title="Unicode encoding form" href="#dt-Uni-encform">Unicode encoding form</a>
by a <a title="normalizing transcoder" href="#dt-normtransc">normalizing transcoder</a>, the resulting text
would satisfy clause 1 above.</p></li></ol></div><div class="div1"> <h2><a name="sec-entexpand" id="sec-entexpand" />C 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><div class="exampleInner"><pre>&lt;!ENTITY example "&lt;p&gt;An ampersand (&amp;#38;#38;) may be escaped
numerically (&amp;#38;#38;#38;) or with a general entity
(&amp;amp;amp;).&lt;/p&gt;" &gt;</pre></div><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><div class="exampleInner"><pre>&lt;p&gt;An ampersand (&amp;#38;) may be escaped
numerically (&amp;#38;#38;) or with a general entity
(&amp;amp;amp;).&lt;/p&gt;</pre></div><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><div class="exampleInner"><pre>An ampersand (&amp;) may be escaped
numerically (&amp;#38;) or with a general entity
(&amp;amp;).</pre></div><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><div class="exampleInner"><pre>1 &lt;?xml version='1.0'?&gt;
2 &lt;!DOCTYPE test [
3 &lt;!ELEMENT test (#PCDATA) &gt;
4 &lt;!ENTITY % xx '&amp;#37;zz;'&gt;
5 &lt;!ENTITY % zz '&amp;#60;!ENTITY tricky "error-prone" &gt;' &gt;
6 %xx;
7 ]&gt;
8 &lt;test&gt;This sample shows a &amp;tricky; method.&lt;/test&gt;</pre></div><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"
&gt;</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"
&gt;</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" id="determinism" />D Deterministic Content Models (Non-Normative)</h2><p>As
noted in <a href="#sec-element-content"><b>3.2.1 Element Content</b></a>, it is required that content
models in element type declarations be deterministic. This requirement is <a title="For Compatibility" href="#dt-compat">for compatibility</a> with SGML (which calls deterministic
content models "unambiguous"); XML processors built
using SGML systems may flag non-deterministic content models as errors.</p><p>For example, the content model <code>((b, c) | (b, d))</code> is non-deterministic,
because given an initial <code>b</code> the XML processor
cannot know which <code>b</code> in the model is being matched without looking
ahead to see which element follows the <code>b</code>. In this case, the two references
to <code>b</code> can be collapsed into a single reference, making the model read <code>(b,
(c | d))</code>. An initial <code>b</code> now clearly matches only a single name
in the content model. The processor doesn't need to look ahead to see what follows; either <code>c</code> or <code>d</code>
would be accepted.</p><p>More formally: a finite state automaton may be constructed from the content
model using the standard algorithms, e.g. algorithm 3.5 in section 3.9 of
Aho, Sethi, and Ullman <a href="#Aho">[Aho/Ullman]</a>. In many such algorithms, a follow
set is constructed for each position in the regular expression (i.e., each
leaf node in the syntax tree for the regular expression); if any position
has a follow set in which more than one following position is labeled with
the same element type name, then the content model is in error and may be
reported as an error.</p><p>Algorithms exist which allow many but not all non-deterministic content
models to be reduced automatically to equivalent deterministic models; see
Brüggemann-Klein 1991 <a href="#ABK">[Brüggemann-Klein]</a>.</p></div><div class="div1"> <h2><a name="sec-guessing" id="sec-guessing" />E 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" id="sec-guessing-no-ext-info" />E.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 must
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" summary="Encoding detection summary"><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" summary="Encoding detection summary"><tbody><tr><td rowspan="1" colspan="1"><code>00 00 00 3C</code></td><td rowspan="4" colspan="1">UCS-4 or other encoding with a 32-bit code unit and ASCII
characters encoded as ASCII values, in respectively big-endian (1234), little-endian
(4321) and two unusual byte orders (2143 and 3412). The encoding declaration
must be read to determine which of UCS-4 or other supported 32-bit encodings
applies.</td></tr><tr><td rowspan="1" colspan="1"><code>3C 00 00 00</code></td></tr><tr><td rowspan="1" colspan="1"><code>00 00 3C 00</code></td></tr><tr><td rowspan="1" colspan="1"><code>00 3C 00 00</code></td></tr><tr><td rowspan="1" colspan="1"><code>00 3C 00 3F</code></td><td rowspan="1" colspan="1">UTF-16BE or big-endian ISO-10646-UCS-2
or other encoding with a 16-bit code unit in big-endian order and ASCII characters
encoded as ASCII values (the encoding declaration must be read to determine
which)</td></tr><tr><td rowspan="1" colspan="1"><code>3C 00 3F 00</code></td><td rowspan="1" colspan="1">UTF-16LE or little-endian
ISO-10646-UCS-2 or other encoding with a 16-bit code unit in little-endian
order and ASCII characters encoded as ASCII values (the encoding declaration
must be read to determine which)</td></tr><tr><td rowspan="1" colspan="1"><code>3C 3F 78 6D</code></td><td rowspan="1" colspan="1">UTF-8, ISO 646, ASCII, some part of ISO 8859, Shift-JIS, EUC, or any other
7-bit, 8-bit, or mixed-width encoding which ensures that the characters of
ASCII have their normal positions, width, and values; the actual encoding
declaration must be read to detect which of these applies, but since all of
these encodings use the same bit patterns for the relevant ASCII characters,
the encoding declaration itself may be read reliably</td></tr><tr><td rowspan="1" colspan="1"><code>4C
6F A7 94</code></td><td rowspan="1" colspan="1">EBCDIC (in some flavor; the full encoding declaration
must be read to tell which code page is in use)</td></tr><tr><td rowspan="1" colspan="1">Other</td><td rowspan="1" colspan="1">UTF-8 without an encoding declaration, or else the data stream is mislabeled
(lacking a required encoding declaration), corrupt, fragmentary, or enclosed
in a wrapper of some kind</td></tr></tbody></table><div class="note"><p class="prefix"><b>Note:</b></p><p>In cases above which do not require reading the encoding declaration to
determine the encoding, section 4.3.3 still requires that the encoding declaration,
if present, be read and that the encoding name be checked to match the actual
encoding of the entity. Also, it is possible that new character encodings
will be invented that will make it necessary to use the encoding declaration
to determine the encoding, in cases where this is not required at present.</p></div><p>This level of autodetection is enough to read the XML encoding declaration
and parse the character-encoding identifier, which is still necessary to distinguish
the individual members of each family of encodings (e.g. to tell UTF-8 from
8859, and the parts of 8859 from each other, or to distinguish the specific
EBCDIC code page in use, and so on).</p><p>Because the contents of the encoding declaration are restricted to characters
from the ASCII repertoire (however encoded),
a processor can reliably read the entire encoding declaration as soon as it
has detected which family of encodings is in use. Since in practice, all widely
used character encodings fall into one of the categories above, the XML encoding
declaration allows reasonably reliable in-band labeling of character encodings,
even when external sources of information at the operating-system or transport-protocol
level are unreliable. Character encodings such as UTF-7
that make overloaded usage of ASCII-valued bytes may fail to be reliably detected.</p><p>Once the processor has detected the character encoding in use, it can act
appropriately, whether by invoking a separate input routine for each case,
or by calling the proper conversion function on each character of input.</p><p>Like any self-labeling system, the XML encoding declaration will not work
if any software changes the entity's character set or encoding without updating
the encoding declaration. Implementors of character-encoding routines should
be careful to ensure the accuracy of the internal and external information
used to label the entity.</p></div><div class="div2"> <h3><a name="sec-guessing-with-ext-info" id="sec-guessing-with-ext-info" />E.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 3023]</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" id="sec-xml-wg" />F 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 participants voted for its approval. The current and former members
in 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" id="sec-core-wg" />G W3C XML Core <span>Working</span> Group (Non-Normative)</h2><p>The present edition of this specification was prepared by the W3C XML Core
Working Group (WG). The participants in the WG at the time of publication of this
edition were:</p><ul><li>Leonid Arbouzov, Sun Microsystems</li><li>Mary Brady</li><li>John Cowan (<i>XML 1.1 First Edition Editor</i>) </li><li>John Evdemon, Microsoft</li><li>Andrew Fang, Arbortext</li><li>Paul Grosso, Arbortext (<i>Co-Chair</i>) </li><li>Arnaud Le Hors, IBM</li><li>Dmitry Lenkov, Oracle</li><li>Anjana Manian, Oracle</li><li>Glenn Marcy, IBM</li><li>Jonathan Marsh, Microsoft</li><li>Sandra Martinez, NIST</li><li>Liam Quin, W3C (<i>Staff Contact</i>) </li><li>Lew Shannon</li><li>Richard Tobin, University of Edinburgh</li><li>Daniel Veillard</li><li>Norman Walsh, Sun Microsystems (<i>Co-Chair</i>) </li><li>François Yergeau</li></ul></div><div class="div1"> <h2><a name="prod-notes" id="prod-notes" />H Production Notes (Non-Normative)</h2><p>This edition was encoded in a
slightly modified version of the
<a href="http://www.w3.org/2002/xmlspec/dtd/2.5/xmlspec.dtd">XMLspec DTD, 2.5</a>.
The XHTML versions were produced with a combination of the
<a href="http://www.w3.org/2002/xmlspec/xhtml/1.9/xmlspec.xsl">xmlspec.xsl</a>,
<a href="http://www.w3.org/2002/xmlspec/xhtml/1.9/diffspec.xsl">diffspec.xsl</a>,
and <a href="REC-xml-3e.xsl">REC-xml-3e.xsl</a>
XSLT stylesheets.</p></div><div class="div1"> <h2><a name="sec-suggested-names" id="sec-suggested-names" />I Suggestions for XML Names (Non-Normative)</h2><p>The following suggestions define what is believed to be best
practice in the construction of XML names used as element names,
attribute names, processing instruction targets, entity names,
notation names, and the values of attributes of type ID, and are
intended as guidance for document authors and schema designers.
All references to Unicode are understood with respect to
a particular version of the Unicode Standard greater than or equal
to 3.0; which version should be used is left to the discretion of
the document author or schema designer.</p><p>The first two suggestions are directly derived from the rules
given for identifiers in the Unicode Standard, version 3.0, and
exclude all control characters, enclosing nonspacing marks,
non-decimal numbers, private-use characters, punctuation characters
(with the noted exceptions), symbol characters, unassigned
codepoints, and white space characters. The other suggestions
are mostly derived from <a href="#XML1.0">[XML-1.0]</a> Appendix B.</p><ol type="1"><li><p>The first character of any name should have a Unicode General
Category of Ll, Lu, Lo, Lm, Lt, or Nl, or else be '_' #x5F.</p></li><li><p>Characters other than the first should have a Unicode General
Category of Ll, Lu, Lo, Lm, Lt, Mc, Mn, Nl, Nd, Pc, or Cf, or else
be one of the following: '-' #x2D, '.' #x2E, ':' #x3A or
'·' #xB7 (middle dot). Since Cf characters are not
directly visible, they should be employed with caution and only
when necessary, to avoid creating names which are distinct to XML
processors but look the same to human beings.</p></li><li><p>Ideographic characters which have a canonical decomposition
(including those in the ranges [#xF900-#xFAFF] and
[#x2F800-#x2FFFD], with 12 exceptions) should not be used in names.
</p></li><li><p>Characters which have a compatibility decomposition (those with
a "compatibility formatting tag" in field 5 of the Unicode
Character Database -- marked by field 5 beginning with a "&lt;")
should not be used in names.  This suggestion does not apply
to #x0E33 THAI CHARACTER SARA AM or #x0EB3 LAO CHARACTER AM, which
despite their compatibility decompositions are in regular use in
those scripts.</p></li><li><p>Combining characters meant for use with symbols only (including
those in the ranges [#x20D0-#x20EF] and [#x1D165-#x1D1AD]) should
not be used in names.</p></li><li><p>The interlinear annotation characters ([#xFFF9-#xFFFB) should
not be used in names.</p></li><li><p>Variation selector characters should not be used in names.</p></li><li><p>Names which are nonsensical, unpronounceable, hard to read, or
easily confusable with other names should not be employed.</p></li></ol></div></div></body></html>