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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 xmlns="http://www.w3.org/1999/xhtml" lang="EN">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Extensible Markup Language (XML) 1.0 (Fifth Edition)</title>
<style type="text/css">
code {
font-family: monospace;
}
div.constraint,
div.issue,
div.note,
div.notice {
margin-left: 2em;
}
ol.enumar {
list-style-type: decimal;
}
ol.enumla {
list-style-type: lower-alpha;
}
ol.enumlr {
list-style-type: lower-roman;
}
ol.enumua {
list-style-type: upper-alpha;
}
ol.enumur {
list-style-type: upper-roman;
}
div.exampleInner pre {
margin-left: 1em;
margin-top: 0em;
margin-bottom: 0em;
}
div.exampleOuter {
border: 4px double gray;
margin: 0em;
padding: 0em;
}
div.exampleInner {
background-color: #d5dee3;
border-top-width: 4px;
border-top-style: double;
border-top-color: #d3d3d3;
border-bottom-width: 4px;
border-bottom-style: double;
border-bottom-color: #d3d3d3;
padding: 4px;
margin: 0em;
}
div.exampleWrapper {
margin: 4px;
}
div.exampleHeader {
font-weight: bold;
margin: 4px;
}
em.rfc2119 {
text-transform: lowercase;
font-variant: small-caps;
font-style: normal;
}
</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) 1.0 (Fifth
Edition)
</h1>
<h2>
<a name="w3c-doctype" id="w3c-doctype" />W3C Recommendation 26 November
2008
</h2>
<div
id="notice-20130207"
style="border: solid black 1px; padding: 0.5em; background: #ffb"
>
<p>
<strong>Note:</strong> On 7 February 2013, this specification was
modified in place to replace broken links to RFC4646 and RFC4647.
</p>
</div>
<dl>
<dt>This version:</dt>
<dd>
<a href="http://www.w3.org/TR/2008/REC-xml-20081126/"
>http://www.w3.org/TR/2008/REC-xml-20081126/</a
>
</dd>
<dt>Latest version:</dt>
<dd>
<a href="http://www.w3.org/TR/xml/">http://www.w3.org/TR/xml/</a>
</dd>
<dt>Previous versions:</dt>
<dd>
<a href="http://www.w3.org/TR/2008/PER-xml-20080205/"
>http://www.w3.org/TR/2008/PER-xml-20080205/</a
>
<br />
<a href="http://www.w3.org/TR/2006/REC-xml-20060816/"
>http://www.w3.org/TR/2006/REC-xml-20060816/</a
>
</dd>
<dt>Editors:</dt>
<dd>
Tim Bray, Textuality and Netscape
<a href="mailto:tbray@textuality.com"><tbray@textuality.com></a>
</dd>
<dd>
Jean Paoli, Microsoft
<a href="mailto:jeanpa@microsoft.com"><jeanpa@microsoft.com></a>
</dd>
<dd>
C. M. Sperberg-McQueen, W3C
<a href="mailto:cmsmcq@w3.org"><cmsmcq@w3.org></a>
</dd>
<dd>
Eve Maler, Sun Microsystems, Inc.
<a href="mailto:elm@east.sun.com"><eve.maler@east.sun.com></a>
</dd>
<dd>François Yergeau</dd>
</dl>
<p>
Please refer to the
<a href="http://www.w3.org/XML/xml-V10-5e-errata"
><strong>errata</strong></a
>
for this document, which may include some normative corrections.
</p>
<p>
The
<a href="http://www.w3.org/XML/xml-V10-4e-errata">previous errata</a>
for this document, are also available.
</p>
<p>
See also
<a
href="http://www.w3.org/2003/03/Translations/byTechnology?technology=xml"
><strong>translations</strong></a
>.
</p>
<p>
This document is also available in these non-normative formats:
<a href="REC-xml-20081126.xml">XML</a> and <a
href="REC-xml-20081126-review.html"
>XHTML with color-coded revision indicators</a
>.
</p>
<p class="copyright">
<a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
>Copyright</a
> © 2008 <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
>
and
<a href="http://www.w3.org/Consortium/Legal/copyright-documents"
>document use</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 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/Core/">XML Core Working Group</a> as part
of the <a href="http://www.w3.org/XML/Activity">XML Activity</a>. The
English version of this specification is the only normative version.
However, for translations of this document, see
<a
href="http://www.w3.org/2003/03/Translations/byTechnology?technology=xml"
>http://www.w3.org/2003/03/Translations/byTechnology?technology=xml</a
>.
</p>
<p>
This document is a
<a href="http://www.w3.org/2005/10/Process-20051014/tr.html#q74"
>W3C Recommendation</a
>. This fifth edition is <em>not</em> a new version of XML. As a
convenience to readers, it incorporates the changes dictated by the
accumulated errata (available at
<a href="http://www.w3.org/XML/xml-V10-4e-errata"
>http://www.w3.org/XML/xml-V10-4e-errata</a
>) to the
<a href="http://www.w3.org/TR/2006/REC-xml-20060816/"
>Fourth Edition of XML 1.0, dated 16 August 2006</a
>. In particular, erratum
<a href="http://www.w3.org/XML/xml-V10-4e-errata#E09">[E09]</a> relaxes
the restrictions on element and attribute names, thereby providing in
XML 1.0 the major end user benefit currently achievable only by using
XML 1.1. As a consequence, many possible documents which were not
well-formed according to previous editions of this specification are now
well-formed, and previously invalid documents using the newly-allowed
name characters in, for example, ID attributes, are now valid.
</p>
<p>
This edition supersedes the previous
<a href="http://www.w3.org/TR/2006/REC-xml-20060816/"
>W3C Recommendation of 16 August 2006</a
>.
</p>
<p>
Please report errors in this document to the public
<a href="mailto:xml-editor@w3.org">xml-editor@w3.org</a> mail list;
public
<a href="http://lists.w3.org/Archives/Public/xml-editor/">archives</a>
are available. For the convenience of readers, an
<a href="REC-xml-20081126-review.html"
>XHTML version with color-coded revision indicators</a
>
is also provided; this version highlights each change due to an erratum
published in the
<a href="http://www.w3.org/XML/xml-V10-4e-errata">errata list</a> for
the previous edition, together with a link to the particular erratum in
that list. Most of the errata in the list provide a rationale for the
change. The errata list for this fifth edition is available at
<a href="http://www.w3.org/XML/xml-V10-5e-errata"
>http://www.w3.org/XML/xml-V10-5e-errata</a
>.
</p>
<p>
An implementation report is available at
<a href="http://www.w3.org/XML/2008/01/xml10-5e-implementation.html"
>http://www.w3.org/XML/2008/01/xml10-5e-implementation.html</a
>. A <a href="http://www.w3.org/XML/Test/">Test Suite</a> is maintained
to help assessing conformance to this specification.
</p>
<p>
This document has been reviewed by W3C Members, by software developers,
and by other W3C groups and interested parties, and is endorsed by the
Director as a W3C Recommendation. It is a stable document and may be
used as reference material or cited 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>
W3C maintains a
<a
href="http://www.w3.org/2002/08/xmlcore-IPR-statements"
rel="disclosure"
>public list of any patent disclosures</a
>
made in connection with the deliverables of the group; that page also
includes instructions for disclosing a patent. An individual who has
actual knowledge of a patent which the individual believes contains
<a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential"
>Essential Claim(s)</a
>
must disclose the information in accordance with
<a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure"
>section 6 of the W3C Patent Policy</a
>.
</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 />
2 <a href="#sec-documents">Documents</a><br />
2.1
<a href="#sec-well-formed">Well-Formed XML Documents</a><br />
2.2 <a href="#charsets">Characters</a><br />
2.3
<a href="#sec-common-syn">Common Syntactic Constructs</a><br />
2.4
<a href="#syntax">Character Data and Markup</a><br />
2.5 <a href="#sec-comments">Comments</a><br />
2.6 <a href="#sec-pi">Processing Instructions</a
><br />
2.7 <a href="#sec-cdata-sect">CDATA Sections</a
><br />
2.8
<a href="#sec-prolog-dtd">Prolog and Document Type Declaration</a><br />
2.9
<a href="#sec-rmd">Standalone Document Declaration</a><br />
2.10
<a href="#sec-white-space">White Space Handling</a><br />
2.11
<a href="#sec-line-ends">End-of-Line Handling</a><br />
2.12
<a href="#sec-lang-tag">Language Identification</a><br />
3 <a href="#sec-logical-struct">Logical Structures</a><br />
3.1
<a href="#sec-starttags">Start-Tags, End-Tags, and Empty-Element Tags</a
><br />
3.2
<a href="#elemdecls">Element Type Declarations</a><br />
3.2.1
<a href="#sec-element-content">Element Content</a><br />
3.2.2
<a href="#sec-mixed-content">Mixed Content</a><br />
3.3
<a href="#attdecls">Attribute-List Declarations</a><br />
3.3.1
<a href="#sec-attribute-types">Attribute Types</a><br />
3.3.2
<a href="#sec-attr-defaults">Attribute Defaults</a><br />
3.3.3
<a href="#AVNormalize">Attribute-Value Normalization</a><br />
3.4
<a href="#sec-condition-sect">Conditional Sections</a><br />
4 <a href="#sec-physical-struct">Physical Structures</a><br />
4.1
<a href="#sec-references">Character and Entity References</a><br />
4.2
<a href="#sec-entity-decl">Entity Declarations</a><br />
4.2.1
<a href="#sec-internal-ent">Internal Entities</a><br />
4.2.2
<a href="#sec-external-ent">External Entities</a><br />
4.3 <a href="#TextEntities">Parsed Entities</a
><br />
4.3.1
<a href="#sec-TextDecl">The Text Declaration</a><br />
4.3.2
<a href="#wf-entities">Well-Formed Parsed Entities</a><br />
4.3.3
<a href="#charencoding">Character Encoding in Entities</a><br />
4.4
<a href="#entproc">XML Processor Treatment of Entities and References</a
><br />
4.4.1
<a href="#not-recognized">Not Recognized</a><br />
4.4.2
<a href="#included">Included</a><br />
4.4.3
<a href="#include-if-valid">Included If Validating</a><br />
4.4.4
<a href="#forbidden">Forbidden</a><br />
4.4.5
<a href="#inliteral">Included in Literal</a><br />
4.4.6
<a href="#notify">Notify</a><br />
4.4.7
<a href="#bypass">Bypassed</a><br />
4.4.8
<a href="#as-PE">Included as PE</a><br />
4.4.9
<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="#CharClasses">Character Classes</a><br />
C <a href="#sec-xml-and-sgml">XML and SGML</a> (Non-Normative)<br />
D
<a href="#sec-entexpand"
>Expansion of Entity and Character References</a
>
(Non-Normative)<br />
E
<a href="#determinism">Deterministic Content Models</a>
(Non-Normative)<br />
F
<a href="#sec-guessing">Autodetection of Character Encodings</a>
(Non-Normative)<br />
F.1
<a href="#sec-guessing-no-ext-info"
>Detection Without External Encoding Information</a
><br />
F.2
<a href="#sec-guessing-with-ext-info"
>Priorities in the Presence of External Encoding Information</a
><br />
G <a href="#sec-xml-wg">W3C XML Working Group</a> (Non-Normative)<br />
H
<a href="#sec-core-wg">W3C XML Core Working Group</a>
(Non-Normative)<br />
I <a href="#prod-notes">Production Notes</a> (Non-Normative)<br />
J
<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 class="enumar">
<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
<span>BCP 47</span> <a href="#RFC1766">[IETF BCP 47]</a>
<span
>and the Language Subtag Registry
<a href="#IANA-LANGCODES">[IANA-LANGCODES]</a></span
>
for language identification tags), provides all the information
necessary to understand XML Version 1.0 and construct computer
programs to process it.
</p>
<p>
This version of the XML specification may be distributed freely, as
long as all text and legal notices remain intact.
</p>
</div>
<div class="div2">
<h3>
<a name="sec-terminology" id="sec-terminology" />1.2 Terminology
</h3>
<p>
The terminology used to describe XML documents is defined in the
body of this specification. 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, 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. 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. 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 are
identical. Characters with multiple possible representations in
ISO/IEC 10646 (e.g. characters with both precomposed and
base+diacritic forms) match only if they have the same
representation in both strings. No case folding is performed.
(Of strings and rules in the grammar:) A string matches a
grammatical production if it belongs to the language generated
by that production. (Of content and content models:) An element
matches its declaration when it conforms in the fashion
described in the constraint
<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>
<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. In addition, the XML document is
<a title="Validity" href="#dt-valid">valid</a> if it meets certain
further constraints.]
</p>
<p>
Each XML document has both a logical and a physical structure.
Physically, the document is composed of units called
<a title="Entity" href="#dt-entity">entities</a>. An entity may
<a title="Entity Reference" href="#dt-entref">refer</a> to other
entities to cause their inclusion in the document. A document begins
in a "root" or
<a title="Document Entity" href="#dt-docent">document entity</a>.
Logically, the document is composed of declarations, elements,
comments, character references, and processing instructions, all of
which are indicated in the document by explicit markup. The logical
and physical structures
<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 class="enumar">
<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>*</code
>
</td>
</tr>
</tbody>
</table>
<p>
Matching the <a href="#NT-document">document</a> production implies
that:
</p>
<ol class="enumar">
<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
ISO/IEC 10646:2000 <a href="#ISO10646">[ISO/IEC 10646]</a>. Legal
characters are tab, carriage return, line feed, and the legal
characters of Unicode and ISO/IEC 10646. The versions of these
standards cited in
<a href="#sec-existing-stds"><b>A.1 Normative References</b></a>
were current at the time this document was prepared. New characters
may be added to these standards by amendments or new editions.
Consequently, XML processors
<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
>#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] |
[#x10000-#x10FFFF]</code
>
</td>
<td>
<i
>/* any Unicode character, excluding the surrogate blocks,
FFFE, and FFFF. */</i
>
</td>
</tr>
</tbody>
</table>
<p>
The mechanism for encoding character code points into bit patterns
may vary from entity to entity. All XML processors
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
accept the UTF-8 and UTF-16 encodings of Unicode
<span><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 section <span>2.3</span> of
<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-#xFD<span>E</span>F],
[#x1FFFE-#x1FFFF], [#x2FFFE-#x2FFFF], [#x3FFFE-#x3FFFF],
[#x4FFFE-#x4FFFF], [#x5FFFE-#x5FFFF], [#x6FFFE-#x6FFFF],
[#x7FFFE-#x7FFFF], [#x8FFFE-#x8FFFF], [#x9FFFE-#x9FFFF],
[#xAFFFE-#xAFFFF], [#xBFFFE-#xBFFFF], [#xCFFFE-#xCFFFF],
[#xDFFFE-#xDFFFF], [#xEFFFE-#xEFFFF], [#xFFFFE-#xFFFFF],
[#x10FFFE-#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>
An <a href="#NT-Nmtoken">Nmtoken</a> (name token) is any mixture of
name characters.
</p>
<p>
[<a name="dt-name" id="dt-name" title="Name">Definition</a>: A
<a href="#NT-Name">Name</a> is an
<a href="#NT-Nmtoken">Nmtoken</a> with a restricted set of initial
characters.] Disallowed initial characters for
<a href="#NT-Name">Names</a> include digits, diacritics, the full
stop and the hyphen.
</p>
<p>
Names beginning with the string "<code>xml</code>", or with 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>
The first character of a <a href="#NT-Name">Name</a>
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be
a <a href="#NT-NameStartChar">NameStartChar</a>, and any other
characters
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be
<a href="#NT-NameChar">NameChars</a>; 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>J 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="d0e804" id="d0e804" />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="d0e888" id="d0e888" />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
>'"' ([^%&"] |
<a href="#NT-PEReference">PEReference</a> |
<a href="#NT-Reference">Reference</a>)* '"'
</code>
</td>
</tr>
<tr valign="baseline">
<td />
<td />
<td />
<td>
<code
>| "'" ([^%&'] |
<a href="#NT-PEReference">PEReference</a> |
<a href="#NT-Reference">Reference</a>)* "'"</code
>
</td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td>
<a
name="NT-AttValue"
id="NT-AttValue"
/>[10]
</td>
<td><code>AttValue</code></td>
<td> ::= </td>
<td>
<code
>'"' ([^<&"] |
<a href="#NT-Reference">Reference</a>)* '"'
</code>
</td>
</tr>
<tr valign="baseline">
<td />
<td />
<td />
<td>
<code
>| "'" ([^<&'] |
<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><</code> in the literal (e.g.,
<code><!ENTITY mylt "<"></code>), it is strongly advised
to avoid this practice since any reference to that entity will
cause a well-formedness error.
</p>
</div>
</div>
<div class="div2">
<h3><a name="syntax" 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 (&) and the left angle bracket (<)
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
appear in their literal form, except 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;</code>
" and "
<code>&lt;</code>
" respectively. The right angle bracket (>) may be represented
using the string "
<code>&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 either "
<code>&gt;</code>
" or a character reference when it appears in the string "
<code>]]></code>
" in content, when that string is not marking the end of a
<a title="CDATA Section" href="#dt-cdsection">CDATA section</a>.
</p>
<p>
In the content of elements, character data is any string of
characters which does not contain the start-delimiter of any markup
and does not include the CDATA-section-close delimiter, "
<code>]]></code>
". In a CDATA section, character data is any string of characters
not including the CDATA-section-close delimiter, "
<code>]]></code>
".
</p>
<p>
To allow attribute values to contain both single and double quotes,
the apostrophe or single-quote character (') may be represented as "
<code>&apos;</code>
", and the double-quote character (") as "
<code>&quot;</code>
".
</p>
<h5><a name="d0e1106" id="d0e1106" />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
>[^<&]* - ([^<&]* ']]>'
[^<&]*)</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> may appear anywhere in a document outside other
<a title="Markup" href="#dt-markup">markup</a>; in addition, they
may appear within the document type declaration at places allowed by
the grammar. They are not part of the document's
<a title="Character Data" href="#dt-chardata">character data</a>; an
XML processor
<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
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
be recognized within comments.
</p>
<h5><a name="d0e1149" id="d0e1149" />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
>'<!--' ((<a href="#NT-Char">Char</a> - '-') | ('-' (<a
href="#NT-Char"
>Char</a
>
- '-')))* '-->'</code
>
</td>
</tr>
</tbody>
</table>
<p>An example of a comment:</p>
<div class="exampleInner">
<pre>
<!-- declarations for <head> & <body> --></pre
>
</div>
<p>
Note that the grammar does not allow a comment ending in
<code>---></code>. The following example is
<em>not</em> well-formed.
</p>
<div class="exampleInner"><pre><!-- B+, B, or B---></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="d0e1188" id="d0e1188" />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
>'<?' <a href="#NT-PITarget">PITarget</a> (<a
href="#NT-S"
>S</a
>
(<a href="#NT-Char">Char</a>* - (<a href="#NT-Char">Char</a
>* '?>' <a href="#NT-Char">Char</a>*)))? '?>'</code
>
</td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td>
<a
name="NT-PITarget"
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 may
be used for formal declaration of PI targets. Parameter entity
references
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
be 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> may occur anywhere character data may
occur; they are used to escape blocks of text containing characters
which would otherwise be recognized as markup. CDATA sections begin
with the string "
<code><![CDATA[</code>
" and end with the string "
<code>]]></code>
":]
</p>
<h5><a name="d0e1271" id="d0e1271" />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>'<![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
>* ']]>' <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>']]>'</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>&lt;</code>
" and "
<code>&amp;</code>
". CDATA sections cannot nest.
</p>
<p>
An example of a CDATA section, in which "
<code><greeting></code>
" and "
<code></greeting></code>
" are recognized as
<a title="Character Data" href="#dt-chardata">character data</a>,
not <a title="Markup" href="#dt-markup">markup</a>:
</p>
<div class="exampleInner">
<pre>
<![CDATA[<greeting>Hello, world!</greeting>]]> </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 documents
<em class="rfc2119" title="Keyword in RFC 2119 context">SHOULD</em>
begin with an <b>XML declaration</b> which specifies the version of
XML being used.] For example, the following is a complete XML
document,
<a title="Well-Formed" href="#dt-wellformed">well-formed</a> but not
<a title="Validity" href="#dt-valid">valid</a>:
</p>
<div class="exampleInner">
<pre>
<?xml version="1.0"?>
<greeting>Hello, world!</greeting> </pre
>
</div>
<p>and so is this:</p>
<div class="exampleInner">
<pre><greeting>Hello, world!</greeting></pre>
</div>
<p>
The function of the markup in an XML document is to describe its
storage and logical structure and to associate attribute name-value
pairs with its logical structures. XML provides a mechanism, the
<a title="Document Type Declaration" href="#dt-doctype"
>document type declaration</a
>, to define constraints on the logical structure and to support the
use of predefined storage units. [<a
name="dt-valid"
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
>'<?xml' <a href="#NT-VersionInfo">VersionInfo</a>
<a href="#NT-EncodingDecl">EncodingDecl</a>?
<a href="#NT-SDDecl">SDDecl</a>? <a href="#NT-S">S</a>?
'?>'</code
>
</td>
</tr>
<tr valign="baseline">
<td>
<a
name="NT-VersionInfo"
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.' [0-9]+</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>
Even though the <a href="#NT-VersionNum">VersionNum</a> production
matches any version number of the form '1.x', XML 1.0 documents
<em class="rfc2119" title="Keyword in RFC 2119 context"
>SHOULD NOT</em
>
specify a version number other than '1.0'.
</p>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>
When an XML 1.0 processor encounters a document that specifies a
1.x version number other than '1.0', it will process it as a 1.0
document. This means that an XML 1.0 processor will accept 1.x
documents provided they do not use any non-1.0 features.
</p>
</div>
<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 may be contained in whole or in part within
<a title="Parameter entity" href="#dt-PE">parameter entities</a>, as
described in the well-formedness and validity constraints below. For
further information, see
<a href="#sec-physical-struct"><b>4 Physical Structures</b></a
>.
</p>
<h5><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
>'<!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>?)? '>'</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 may be made up in whole or in part of the
<a title="Replacement Text" href="#dt-repltext">replacement text</a>
of <a title="Parameter entity" href="#dt-PE">parameter entities</a>.
The productions later in this specification for individual
nonterminals (<a href="#NT-elementdecl">elementdecl</a>,
<a href="#NT-AttlistDecl">AttlistDecl</a>, and so on) describe the
declarations <em>after</em> all the parameter entities have been
<a title="Include" href="#dt-include">included</a>.
</p>
<p>
Parameter entity references are recognized anywhere in the DTD
(internal and external subsets and external parameter entities),
except in literals, processing instructions, comments, and the
contents of ignored conditional sections (see
<a href="#sec-condition-sect"><b>3.4 Conditional Sections</b></a
>). They are also recognized in entity value literals. The use of
parameter entities in the internal subset is restricted as described
below.
</p>
<div class="constraint">
<p class="prefix">
<a name="vc-roottype" 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
>
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
occur within markup declarations; they may occur where markup
declarations can occur. (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 may conditionally be ignored by
using the
<a title="conditional section" href="#dt-cond-section"
>conditional section</a
>
construct; this is not allowed in the internal subset but is allowed
in external parameter entities referenced in the internal subset.
</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>
<?xml version="1.0"?>
<!DOCTYPE greeting SYSTEM "hello.dtd">
<greeting>Hello, world!</greeting> </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>
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE greeting [
<!ELEMENT greeting (#PCDATA)>
]>
<greeting>Hello, world!</greeting></pre
>
</div>
<p>
If both the external and internal subsets are used, the internal
subset
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be
considered to occur before the external subset. This has the effect
that entity and attribute-list declarations in the internal subset
take precedence over those in the external subset.
</p>
</div>
<div class="div2">
<h3>
<a name="sec-rmd" 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 may appear
as a component of the XML declaration, signals whether or not there
are such declarations which appear external to the
<a title="Document Entity" href="#dt-docent">document entity</a> or
in parameter entities. [<a
name="dt-extmkpdecl"
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>
<a href="#NT-S">S</a> 'standalone'
<a href="#NT-Eq">Eq</a> (("'" ('yes' | 'no') "'") | ('"'
('yes' | 'no') '"'))
</code>
</td>
<td>
<a href="#vc-check-rmd"
>[VC: Standalone Document Declaration]</a
>
</td>
</tr>
</tbody>
</table>
<p>
In a standalone document declaration, the value "yes" indicates that
there are no
<a title="External Markup Declaration" href="#dt-extmkpdecl"
>external markup declarations</a
>
which affect the information passed from the XML processor to the
application. The value "no" indicates that there are or may be such
external markup declarations. Note that the standalone document
declaration only denotes the presence of external
<em>declarations</em>; the presence, in a document, of references to
external <em>entities</em>, when those entities are internally
declared, does not change its standalone status.
</p>
<p>
If there are no external markup declarations, the standalone
document declaration has no meaning. If there are external markup
declarations but there is no standalone document declaration, the
value "no" is assumed.
</p>
<p>
Any XML document for which <code>standalone="no"</code> holds can be
converted algorithmically to a standalone document, which may be
desirable for some network delivery applications.
</p>
<div class="constraint">
<p class="prefix">
<a name="vc-check-rmd" 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><?xml version="1.0" standalone='yes'?></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> may be attached to an element to signal an
intention that in that element, white space should be preserved by
applications. In valid documents, this attribute, like any other,
<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 Values" href="#dt-enumerated"
>enumerated type</a
>
whose values are one or both of "default" and "preserve". For
example:
</p>
<div class="exampleInner">
<pre>
<!ATTLIST poem xml:space (default|preserve) 'preserve'>
<!ATTLIST pre xml:space (preserve) #FIXED 'preserve'></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 overridden with another instance of the
<code>xml:space</code> attribute. 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.
</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
<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 normalized all line breaks in external parsed
entities (including the document entity) on input, before parsing,
by translating both the two-character sequence #xD #xA and any #xD
that is not followed by #xA to a single #xA character.
</p>
</div>
<div class="div2">
<h3>
<a name="sec-lang-tag" 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> may be inserted in documents to specify the
language used in the contents and attribute values of any element in
an XML document. In valid documents, this attribute, like any other,
<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 BCP 47]</a>,
<cite>Tags for the Identification of Languages</cite>; in addition,
the empty string may be specified.
</p>
<p>(Productions 33 through 38 have been removed.)</p>
<p>For example:</p>
<div class="exampleInner">
<pre>
<p xml:lang="en">The quick brown fox jumps over the lazy dog.</p>
<p xml:lang="en-GB">What colour is it?</p>
<p xml:lang="en-US">What color is it?</p>
<sp who="Faust" desc='leise' xml:lang="de">
<l>Habe nun, ach! Philosophie,</l>
<l>Juristerei, und Medizin</l>
<l>und leider auch Theologie</l>
<l>durchaus studiert mit heißem Bemüh'n.</l>
</sp></pre
>
</div>
<p>
The language specified by <code>xml:lang</code> applies to the
element where it is specified (including the values of its
attributes), and to all elements in its content unless overridden
with another instance of <code>xml:lang</code>. 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. Applications determine which of an element's attribute
values and which parts of its character content, if any, are treated
as language-dependent values described by <code>xml:lang</code>.
</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 CDATA #IMPLIED</pre></div>
<p>
but specific default values may also be given, if appropriate. In a
collection of French poems for English students, with glosses and
notes in English, the <code>xml:lang</code> attribute might be
declared this way:
</p>
<div class="exampleInner">
<pre>
<!ATTLIST poem xml:lang CDATA 'fr'>
<!ATTLIST gloss xml:lang CDATA 'en'>
<!ATTLIST note xml:lang CDATA 'en'></pre
>
</div>
</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 may have a set of attribute
specifications.] Each attribute specification has a
<a title="Attribute Name" href="#dt-attrname">name</a> and a
<a title="Attribute Value" href="#dt-attrval">value</a>.
</p>
<h5><a name="d0e2130" id="d0e2130" />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 application 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 class="enumar">
<li>
<p>
The declaration matches <b>EMPTY</b> and the element has no
<a title="Content" href="#dt-content">content</a> (not even
entity references, comments, PIs or white space).
</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, comments and PIs
(i.e. markup matching production [27]
<a href="#NT-Misc">Misc</a>) between the start-tag and the first
child element, between child elements, or between the last child
element and the end-tag. Note that a CDATA section containing
only white space or a reference to an entity whose replacement
text is character references expanding to white space do not
match the nonterminal <a href="#NT-S">S</a>, and hence cannot
appear in these positions; 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.
</p>
</li>
<li>
<p>
The declaration matches <a href="#NT-Mixed">Mixed</a>, and the
content (after replacing any entity references with their
replacement text) consists of
<a title="Character Data" href="#dt-chardata">character data</a>
(including
<a title="CDATA Section" href="#dt-cdsection">CDATA sections</a
>), <a title="Comment" href="#dt-comment">comments</a>,
<a title="Processing instruction" href="#dt-pi">PIs</a> and
<a title="Parent/Child" href="#dt-parentchild"
>child elements</a
>
whose types match names in the content model.
</p>
</li>
<li>
<p>
The declaration matches <b>ANY</b>, and the content (after
replacing any entity references with their replacement text)
consists of character data,
<a title="CDATA Section" href="#dt-cdsection">CDATA sections</a
>, <a title="Comment" href="#dt-comment">comments</a>,
<a title="Processing instruction" href="#dt-pi">PIs</a> and
<a title="Parent/Child" href="#dt-parentchild"
>child elements</a
>
whose types 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="d0e2259" id="d0e2259" />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
>'<' <a href="#NT-Name">Name</a> (<a href="#NT-S">S</a>
<a href="#NT-Attribute">Attribute</a>)*
<a href="#NT-S">S</a>? '>'</code
>
</td>
<td><a href="#uniqattspec">[WFC: Unique Att Spec]</a></td>
</tr>
<tr valign="baseline">
<td>
<a
name="NT-Attribute"
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 < 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>
An attribute name
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
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
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
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><</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><</code>.
</p>
</div>
<p>An example of a start-tag:</p>
<div class="exampleInner">
<pre><termdef id="dt-dog" term="dog"></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="d0e2403" id="d0e2403" />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
>'</' <a href="#NT-Name">Name</a> <a href="#NT-S">S</a>?
'>'</code
>
</td>
</tr>
</tbody>
</table>
<p>An example of an end-tag:</p>
<div class="exampleInner"><pre></termdef></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="d0e2433" id="d0e2433" />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="d0e2480" id="d0e2480" />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
>'<' <a href="#NT-Name">Name</a> (<a href="#NT-S">S</a>
<a href="#NT-Attribute">Attribute</a>)*
<a href="#NT-S">S</a>? '/>'</code
>
</td>
<td><a href="#uniqattspec">[WFC: Unique Att Spec]</a></td>
</tr>
</tbody>
</table>
<p>
Empty-element tags may be used for any element which has no content,
whether or not it is declared using the keyword <b>EMPTY</b>.
<a title="For interoperability" href="#dt-interop"
>For interoperability</a
>, the empty-element tag
<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>
<IMG align="left"
src="http://www.w3.org/Icons/WWW/w3c_home" />
<br></br>
<br/></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> may,
for <a title="Validity" href="#dt-valid">validation</a> purposes, be
constrained using element type and attribute-list declarations. An
element type declaration constrains the element's
<a title="Content" href="#dt-content">content</a>.
</p>
<p>
Element type declarations often constrain which element types can
appear as
<a title="Parent/Child" href="#dt-parentchild">children</a> of the
element. At user option, an XML processor
<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="d0e2553" id="d0e2553" />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
>'<!ELEMENT' <a href="#NT-S">S</a>
<a href="#NT-Name">Name</a>
<a href="#NT-S">S</a>
<a href="#NT-contentspec">contentspec</a>
<a href="#NT-S">S</a>? '>'</code
>
</td>
<td>
<a href="#EDUnique">[VC: Unique Element Type Declaration]</a>
</td>
</tr>
<tr valign="baseline">
<td>
<a
name="NT-contentspec"
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>
An element type
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
be declared more than once.
</p>
</div>
<p>Examples of element type declarations:</p>
<div class="exampleInner">
<pre>
<!ELEMENT br EMPTY>
<!ELEMENT p (#PCDATA|emph)* >
<!ELEMENT %name.para; %content.para; >
<!ELEMENT container ANY></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="d0e2638" id="d0e2638" />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 may appear as a
<a title="Parent/Child" href="#dt-parentchild">child</a>. Any
content particle in a choice list may appear in the
<a title="Element content" href="#dt-elemcontent"
>element content</a
>
at the location where the choice list appears in the grammar;
content particles occurring in a sequence list
<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 the content model allows an element to match
more than one occurrence of an element type in the content model.
For more information, see
<a href="#determinism"><b>E Deterministic Content Models</b></a
>.
</p>
<div class="constraint">
<p class="prefix">
<a name="vc-PEinGroup" 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>
<!ELEMENT spec (front, body, back?)>
<!ELEMENT div1 (head, (p | list | note)*, div2*)>
<!ELEMENT dictionary-body (%div.mix; | %dict.mix;)*></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 may contain
character data, optionally interspersed with
<a title="Parent/Child" href="#dt-parentchild">child</a>
elements.] In this case, the types of the child elements may be
constrained, but not their order or their number of occurrences:
</p>
<h5><a name="d0e2826" id="d0e2826" />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>
<!ELEMENT p (#PCDATA|a|ul|b|i|em)*>
<!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* >
<!ELEMENT b (#PCDATA)></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
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
appear outside of
<a title="Start-Tag" href="#dt-stag">start-tags</a> and
<a title="empty-element tag" href="#dt-eetag">empty-element tags</a
>; thus, the productions used to recognize them appear in
<a href="#sec-starttags"
><b>3.1 Start-Tags, End-Tags, and Empty-Element Tags</b></a
>. Attribute-list declarations may be used:
</p>
<ul>
<li>
<p>
To define the set of attributes pertaining to a given element
type.
</p>
</li>
<li><p>To establish type constraints for these attributes.</p></li>
<li>
<p>
To provide
<a title="Attribute Default" href="#dt-default"
>default values</a
>
for attributes.
</p>
</li>
</ul>
<p>
[<a
name="dt-attdecl"
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="d0e2926" id="d0e2926" />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
>'<!ATTLIST' <a href="#NT-S">S</a>
<a href="#NT-Name">Name</a>
<a href="#NT-AttDef">AttDef</a>* <a href="#NT-S">S</a>?
'>'</code
>
</td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td>
<a name="NT-AttDef" 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 may choose to provide at most one attribute-list
declaration for a given element type, at most one attribute
definition for a given attribute name in an attribute-list
declaration, and at least one attribute definition in each
attribute-list declaration. For interoperability, an XML processor
<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 are more
constrained. The validity constraints noted in the grammar are
applied after the attribute value has been normalized as described
in
<a href="#AVNormalize"
><b>3.3.3 Attribute-Value Normalization</b></a
>.
</p>
<h5><a name="d0e3004" id="d0e3004" />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>
An element type
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
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 Values"
>Definition</a
>:
<b>Enumerated attributes</b>
have a list of allowed values in their declaration ]. They
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
take one of those values. There are two kinds of enumerated
attribute types:
</p>
<h5><a name="d0e3200" id="d0e3200" />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>
An element type
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
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 is to react if a declared
attribute is absent in a document.
</p>
<h5><a name="d0e3369" id="d0e3369" />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' <a href="#NT-S">S</a>)?
<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 < in Attribute Values]</a
>
</td>
</tr>
<tr valign="baseline">
<td />
<td />
<td />
<td />
<td>
<a href="#FixedAttr">[VC: Fixed Attribute Default]</a>
</td>
</tr>
<tr valign="baseline">
<td />
<td />
<td />
<td />
<td>
<a href="#NoExternalRefs"
>[WFC: No External Entity References]</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
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.]
</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: Attribute Default Value Syntactically
Correct</b
>
</p>
<p>
The declared default value
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST</em
>
meet the syntactic constraints of the declared attribute type.
That is, the default value of an attribute:
</p>
<ul>
<li>
<p>
of type IDREF or ENTITY must match the
<a href="#NT-Name">Name</a> production;
</p>
</li>
<li>
<p>
of type IDREFS or ENTITIES must match the
<a href="#NT-Names">Names</a> production;
</p>
</li>
<li>
<p>
of type NMTOKEN must match the
<a href="#NT-Nmtoken">Nmtoken</a> production;
</p>
</li>
<li>
<p>
of type NMTOKENS must match the
<a href="#NT-Nmtokens">Nmtokens</a> production;
</p>
</li>
<li>
<p>
of an
<a href="#NT-EnumeratedType">enumerated type</a> (either a
<a href="#NT-NotationType">NOTATION</a> type or an
<a href="#NT-Enumeration">enumeration</a>) must match one of
the enumerated values.
</p>
</li>
</ul>
<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) will be reported by a validating parser only if an
element without a specification for this attribute actually
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>
<!ATTLIST termdef
id ID #REQUIRED
name CDATA #IMPLIED>
<!ATTLIST list
type (bullets|ordered|glossary) "ordered">
<!ATTLIST form
method CDATA #FIXED "POST"></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 class="enumar">
<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
<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.
</p>
<p>
Following are examples of attribute normalization. Given the
following declarations:
</p>
<div class="exampleInner">
<pre>
<!ENTITY d "&#xD;">
<!ENTITY a "&#xA;">
<!ENTITY da "&#xD;&#xA;"></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">
<thead>
<tr>
<th>Attribute specification</th>
<th>a is NMTOKENS</th>
<th>a is CDATA</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<div class="exampleInner">
<pre>
a="
xyz"</pre
>
</div>
</td>
<td>
<div class="exampleInner"><pre>x y z</pre></div>
</td>
<td>
<div class="exampleInner"><pre>#x20 #x20 x y z</pre></div>
</td>
</tr>
<tr>
<td>
<div class="exampleInner">
<pre>
a="&d;&d;A&a;&#x20;&a;B&da;"</pre
>
</div>
</td>
<td>
<div class="exampleInner"><pre>A #x20 B</pre></div>
</td>
<td>
<div class="exampleInner">
<pre>#x20 #x20 A #x20 #x20 #x20 B #x20 #x20</pre>
</div>
</td>
</tr>
<tr>
<td>
<div class="exampleInner">
<pre>
a=
"&#xd;&#xd;A&#xa;&#xa;B&#xd;&#xa;"</pre
>
</div>
</td>
<td>
<div class="exampleInner">
<pre>#xD #xD A #xA #xA B #xD #xA</pre>
</div>
</td>
<td>
<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
>
or of external parameter entities which are included in, or excluded
from, the logical structure of the DTD based on the keyword which
governs them.]
</p>
<h5><a name="d0e3658" id="d0e3658" />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
>'<![' <a href="#NT-S">S</a>? 'INCLUDE'
<a href="#NT-S">S</a>? '['
<a href="#NT-extSubsetDecl">extSubsetDecl</a> ']]>'
</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
>'<![' <a href="#NT-S">S</a>? 'IGNORE'
<a href="#NT-S">S</a>? '['
<a href="#NT-ignoreSectContents">ignoreSectContents</a>*
']]>'</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> ('<!['
<a href="#NT-ignoreSectContents">ignoreSectContents</a>
']]>' <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>*
('<![' | ']]>') <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><![</code>", "<code>[</code>", or
"<code>]]></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
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be
processed as part of the DTD. If the keyword of the conditional
section is <b>IGNORE</b>, then the contents of the conditional
section
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
<em class="rfc2119" title="Keyword in RFC 2119 context">NOT</em> be
processed as 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
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be
ignored. The contents of an ignored conditional section
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be
parsed by ignoring all characters after the "<code>[</code>"
following the keyword, except conditional section starts
"<code><![</code>" and ends "<code>]]></code>", until the
matching conditional section end is found. Parameter entity
references
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
be 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>
<!ENTITY % draft 'INCLUDE' >
<!ENTITY % final 'IGNORE' >
<![%draft;[
<!ELEMENT book (comments*, title, body, supplements?)>
]]>
<![%final;[
<!ELEMENT book (title, body, supplements?)>
]]></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="d0e3895" id="d0e3895" />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>'&#' [0-9]+ ';' </code></td>
</tr>
<tr valign="baseline">
<td />
<td />
<td />
<td><code>| '&#x' [0-9a-fA-F]+ ';'</code></td>
<td><a href="#wf-Legalchar">[WFC: Legal Character]</a></td>
</tr>
</tbody>
</table>
<div class="constraint">
<p class="prefix">
<a name="wf-Legalchar" 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>&#x</code>
", the digits and letters up to the terminating
<code>;</code> provide a hexadecimal representation of the
character's code point in ISO/IEC 10646. If it begins just with "
<code>&#</code>
", the digits up to the terminating <code>;</code> provide a decimal
representation of the character's code point.
</p>
<p>
[<a name="dt-entref" 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>&</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="d0e3966" id="d0e3966" />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>'&' <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>
Note that non-validating processors are
<a href="#include-if-valid"><cite>not obligated to</cite></a> read
and process entity declarations occurring in parameter entities or
in the external subset; 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 parameter entity
references<span
>, if the document is not standalone (either
"<code>standalone='no'</code>" is specified or there is no
standalone declaration), then</span
>
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
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
appear outside 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 <key>less-than</key> (&#x3C;) to save options.
This document was prepared on &docdate; and
is classified &security-level;.</pre
>
</div>
<p>Example of a parameter-entity reference:</p>
<div class="exampleInner">
<pre>
<!-- declare the parameter entity "ISOLat2"... -->
<!ENTITY % ISOLat2
SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" >
<!-- ... now reference it. -->
%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="d0e4163" id="d0e4163" />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
>'<!ENTITY' <a href="#NT-S">S</a>
<a href="#NT-Name">Name</a>
<a href="#NT-S">S</a>
<a href="#NT-EntityDef">EntityDef</a>
<a href="#NT-S">S</a>? '>'</code
>
</td>
</tr>
<tr valign="baseline">
<td>
<a name="NT-PEDecl" id="NT-PEDecl" />[72]
</td>
<td><code>PEDecl</code></td>
<td> ::= </td>
<td>
<code
>'<!ENTITY' <a href="#NT-S">S</a> '%'
<a href="#NT-S">S</a>
<a href="#NT-Name">Name</a>
<a href="#NT-S">S</a>
<a href="#NT-PEDef">PEDef</a>
<a href="#NT-S">S</a>? '>'</code
>
</td>
</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>
<!ENTITY Pub-Status "This is a pre-release of the
specification."></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="d0e4313" id="d0e4313" />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 meant to be converted to
a URI reference (as defined in
<a href="#rfc3986">[IETF RFC 3986]</a>), as part of the process of
dereferencing it 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. This is
defined to be the external entity containing the '<' which
starts the declaration, at the point when it is parsed as a
declaration. 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
>. Attempts to retrieve the resource identified by a URI may 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.
</p>
<p>
System identifiers (and other XML strings meant to be used as URI
references) may contain characters that, according to
<a href="#rfc3986">[IETF RFC 3986]</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 '<' #x3C, '>' #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 class="enumar">
<li>
<p>
Each character to be escaped is represented in UTF-8
<span><a href="#Unicode">[Unicode]</a></span> as one or more
bytes.
</p>
</li>
<li>
<p>
The resulting bytes 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>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>
In a future edition of this specification, the XML Core Working
Group intends to replace the preceding paragraph and list of
steps with a normative reference to an upcoming revision of IETF
RFC 3987, which will define "Legacy Extended IRIs (LEIRIs)".
When this revision is available, it is the intent of the XML
Core WG to use it to replace language similar to the above in
any future revisions of XML-related specifications under its
purview.
</p>
</div>
<p>
[<a name="dt-pubid" id="dt-pubid" title="Public identifier"
>Definition</a
>: In addition to a system identifier, an external identifier may
include a <b>public identifier</b>.] An XML processor attempting
to retrieve the entity's content may use any combination of the
public and system identifiers as well as additional information
outside the scope of this specification 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>
<!ENTITY open-hatch
SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml">
<!ENTITY open-hatch
PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN"
"http://www.textuality.com/boilerplate/OpenHatch.xml">
<!ENTITY hatch-pic
SYSTEM "../grafix/OpenHatch.gif"
NDATA gif ></pre
>
</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="d0e4481" id="d0e4481" />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
>'<?xml' <a href="#NT-VersionInfo">VersionInfo</a>?
<a href="#NT-EncodingDecl">EncodingDecl</a>
<a href="#NT-S">S</a>? '?>'</code
>
</td>
</tr>
</tbody>
</table>
<p>
The text declaration
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
be provided literally, not by reference to a parsed entity. The
text declaration
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
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>
<div class="note">
<p class="prefix"><b>Note:</b></p>
<p>
Only parsed entities that are referenced directly or indirectly
within the document are required to be well-formed.
</p>
</div>
<h5>
<a name="d0e4524" id="d0e4524" />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>
</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 general 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 may 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
<span
>related character encodings, including but not limited to
UTF-16BE, UTF-16LE, or CESU-8.</span
>
</p>
<p>
Entities encoded in UTF-16
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
and entities encoded in UTF-8
<em class="rfc2119" title="Keyword in RFC 2119 context">MAY</em>
begin with the Byte Order Mark described by Annex H of
<a href="#ISO10646-2000">[ISO/IEC 10646:2000]</a>, section
<span>16.8</span> of <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>
If the replacement text of an external entity is to begin with the
character U+FEFF, and no text declaration is present, then a Byte
Order Mark MUST be present, whether the entity is encoded in UTF-8
or UTF-16.
</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="d0e4623" id="d0e4623" />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
byte sequences that are not legal in that encoding. Specifically,
it is a fatal error if an entity encoded in UTF-8 contains any
<span>ill-formed</span> code unit sequences, as defined in
<span>section 3.9 of </span> Unicode
<span><a href="#Unicode">[Unicode]</a></span
>. Unless an encoding is determined by a higher-level protocol, 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>
<?xml encoding='UTF-8'?>
<?xml encoding='EUC-JP'?></pre
>
</div>
</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">
<tbody align="center">
<tr>
<td rowspan="2" />
<td colspan="4" align="center" valign="bottom">Entity Type</td>
<td rowspan="2" align="center">Character</td>
</tr>
<tr align="center" valign="bottom">
<td>Parameter</td>
<td>Internal General</td>
<td>External Parsed General</td>
<td>Unparsed</td>
</tr>
<tr align="center" valign="middle">
<td align="right">Reference in Content</td>
<td>
<a href="#not-recognized"><cite>Not recognized</cite></a>
</td>
<td>
<a href="#included"><cite>Included</cite></a>
</td>
<td>
<a href="#include-if-valid"
><cite>Included if validating</cite></a
>
</td>
<td>
<a href="#forbidden"><cite>Forbidden</cite></a>
</td>
<td>
<a href="#included"><cite>Included</cite></a>
</td>
</tr>
<tr align="center" valign="middle">
<td align="right">Reference in Attribute Value</td>
<td>
<a href="#not-recognized"><cite>Not recognized</cite></a>
</td>
<td>
<a href="#inliteral"><cite>Included in literal</cite></a>
</td>
<td>
<a href="#forbidden"><cite>Forbidden</cite></a>
</td>
<td>
<a href="#forbidden"><cite>Forbidden</cite></a>
</td>
<td>
<a href="#included"><cite>Included</cite></a>
</td>
</tr>
<tr align="center" valign="middle">
<td align="right">Occurs as Attribute Value</td>
<td>
<a href="#not-recognized"><cite>Not recognized</cite></a>
</td>
<td>
<a href="#forbidden"><cite>Forbidden</cite></a>
</td>
<td>
<a href="#forbidden"><cite>Forbidden</cite></a>
</td>
<td>
<a href="#notify"><cite>Notify</cite></a>
</td>
<td>
<a href="#not-recognized"><cite>Not recognized</cite></a>
</td>
</tr>
<tr align="center" valign="middle">
<td align="right">Reference in EntityValue</td>
<td>
<a href="#inliteral"><cite>Included in literal</cite></a>
</td>
<td>
<a href="#bypass"><cite>Bypassed</cite></a>
</td>
<td>
<a href="#bypass"><cite>Bypassed</cite></a>
</td>
<td>
<a href="#error"><cite>Error</cite></a>
</td>
<td>
<a href="#included"><cite>Included</cite></a>
</td>
</tr>
<tr align="center" valign="middle">
<td align="right">Reference in DTD</td>
<td>
<a href="#as-PE"><cite>Included as PE</cite></a>
</td>
<td>
<a href="#forbidden"><cite>Forbidden</cite></a>
</td>
<td>
<a href="#forbidden"><cite>Forbidden</cite></a>
</td>
<td>
<a href="#forbidden"><cite>Forbidden</cite></a>
</td>
<td>
<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 may contain both
<a title="Character Data" href="#dt-chardata">character data</a>
and (except for parameter entities)
<a title="Markup" href="#dt-markup">markup</a>, which
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
be recognized in the usual way. (The string "
<code>AT&amp;T;</code>
" expands to "
<code>AT&T;</code>
" and the remaining ampersand is not recognized as an
entity-reference delimiter.) A character reference is
<b>included</b> when the indicated character is processed in place
of the reference itself.
</p>
</div>
<div class="div3">
<h4>
<a name="include-if-valid" 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
>, except in the <a href="#NT-EntityValue">EntityValue</a> in
an entity declaration.
</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
>
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
be 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
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
always be treated as a normal data character and
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
terminate the literal. For example, this is well-formed:
</p>
<div class="exampleInner">
<pre>
<!ENTITY % YN '"Yes"' >
<!ENTITY WhatHeSaid "He said %YN;" ></pre
>
</div>
<p>while this is not:</p>
<div class="exampleInner">
<pre>
<!ENTITY EndAttr "27'" >
<element attribute='a-&EndAttr;></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
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
be 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
>
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
be 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
<em class="rfc2119" title="Keyword in RFC 2119 context"
>MUST NOT</em
>
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
>: For an internal entity, 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
>: For an internal entity, 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 whitespace) 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>) may 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> (or
<a title="" href="#inliteral">included in literal</a>) 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>
<!ENTITY % pub "&#xc9;ditions Gallimard" >
<!ENTITY rights "All rights reserved" >
<!ENTITY book "La Peste: Albert Camus,
&#xA9; 1947 %pub;. &rights;" ></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. &rights;</pre
>
</div>
<p>
The general-entity reference "
<code>&rights;</code>
" would be expanded should the reference "
<code>&book;</code>
" appear in the document's content or an attribute value.
</p>
<p>
These simple rules may have complex interactions; for a detailed
discussion of a difficult example, see
<a href="#sec-entexpand"
><b>D Expansion of Entity and Character References</b></a
>.
</p>
</div>
<div class="div2">
<h3>
<a name="sec-predefined-ent" 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 may both be used to
<b>escape</b> the left angle bracket, ampersand, and other
delimiters. A set of general entities (<code>amp</code>,
<code>lt</code>, <code>gt</code>, <code>apos</code>,
<code>quot</code>) is specified for this purpose. Numeric character
references may also be used; they are expanded immediately when
recognized and
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em> be
treated as character data, so the numeric character references "
<code>&#60;</code>
" and "
<code>&#38;</code>
" may be used to escape <code><</code> and
<code>&</code> when they occur in character data.]
</p>
<p>
All XML processors
<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
<em class="rfc2119" title="Keyword in RFC 2119 context"
>OPTIONAL</em
>
but harmless). For example:
</p>
<div class="exampleInner">
<pre>
<!ENTITY lt "&#38;#60;">
<!ENTITY gt "&#62;">
<!ENTITY amp "&#38;#38;">
<!ENTITY apos "&#39;">
<!ENTITY quot "&#34;"></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="Unparsed Entity" href="#dt-unparsed">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="d0e5457" id="d0e5457" />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
>'<!NOTATION' <a href="#NT-S">S</a>
<a href="#NT-Name">Name</a>
<a href="#NT-S">S</a> (<a href="#NT-ExternalID"
>ExternalID</a
>
| <a href="#NT-PublicID">PublicID</a>)
<a href="#NT-S">S</a>? '>'</code
>
</td>
<td>
<a href="#UniqueNotationName">[VC: Unique Notation Name]</a>
</td>
</tr>
</tbody>
<tbody>
<tr valign="baseline">
<td>
<a
name="NT-PublicID"
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>
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.
</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;
when <code>standalone="yes"</code>, processors
<em class="rfc2119" title="Keyword in RFC 2119 context">MUST</em>
process these declarations.
</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>
</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, may fail to be detected by a
non-validating processor. Examples include the constraints
entitled
<a href="#wf-entdeclared"><cite>Entity Declared</cite></a
>, <a href="#textent"><cite>Parsed Entity</cite></a
>, and <a href="#norecursion"><cite>No Recursion</cite></a
>, as well as some of the cases described as
<a href="#forbidden"><cite>forbidden</cite></a> in
<a href="#entproc"
><b
>4.4 XML Processor Treatment of Entities and References</b
></a
>.
</p>
</li>
<li>
<p>
The information passed from the processor to the application may
vary, depending on whether the processor reads parameter and
external entities. For example, a non-validating processor may
fail to
<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<span
>, or in the internal subset after an unread parameter entity
reference</span
>.
</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 whose number (code point) in ISO/IEC 10646
is <code>N</code>. 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="RFC1766" />IETF BCP 47</dt>
<dd>
IETF (Internet Engineering Task Force).
<cite
>BCP 47, consisting of
<a href="http://tools.ietf.org/html/rfc4646"
>RFC 4646: Tags for Identifying Languages</a
>, and
<a href="http://tools.ietf.org/html/rfc4647"
>RFC 4647: Matching of Language Tags</a
></cite
>, A. Phillips, M. Davis. 2006.
</dd>
<dt class="label">
<a name="rfc3986" id="rfc3986" />IETF RFC 3986
</dt>
<dd>
IETF (Internet Engineering Task Force).
<a href="http://www.ietf.org/rfc/rfc3986.txt"
><cite
>RFC 3986: Uniform Resource Identifier (URI): Generic
Syntax</cite
></a
>. T. Berners-Lee, R. Fielding, L. Masinter. 2005. (See
http://www.ietf.org/rfc/rfc3986.txt.)
</dd>
<dt class="label">
<a name="ISO10646" id="ISO10646" />ISO/IEC 10646
</dt>
<dd>
ISO (International Organization for Standardization).
<cite
>ISO/IEC 10646-1:2000. Information technology — Universal
Multiple-Octet Coded Character Set (UCS) — Part 1: Architecture
and Basic Multilingual Plane</cite
>
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.org/iso/home.htm"
>http://www.iso.org/iso/home.htm</a
>
for the latest version.)
</dd>
<dt class="label">
<a name="ISO10646-2000" id="ISO10646-2000" />ISO/IEC 10646:2000
</dt>
<dd>
ISO (International Organization for Standardization).
<cite
>ISO/IEC 10646-1:2000. Information technology — Universal
Multiple-Octet Coded Character Set (UCS) — Part 1: Architecture
and Basic Multilingual Plane.</cite
>
[Geneva]: International Organization for Standardization, 2000.
</dd>
<dt class="label"><a name="Unicode" id="Unicode" />Unicode</dt>
<dd>
The Unicode Consortium.
<em>The Unicode Standard, Version <span>5.0.0,</span></em>
<span
>defined by: The Unicode Standard, Version 5.0 (Boston, MA,
Addison-Wesley, 2007. ISBN 0-321-48091-0)</span
>.
</dd>
<dt class="label">
<a name="unipart15" id="unipart15" />UnicodeNormal
</dt>
<dd>
The Unicode Consortium.
<a href="http://unicode.org/reports/tr15/"
><cite>Unicode normalization forms</cite></a
>. Mark Davis and Martin Durst. 2008. (See
http://unicode.org/reports/tr15/.)
</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="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" />IANA-LANGCODES</dt>
<dd>
(Internet Assigned Numbers Authority)
<a href="http://www.iana.org/assignments/language-subtag-registry"
><cite>Registry of Language Tags</cite></a
>
(See http://www.iana.org/assignments/language-subtag-registry.)
</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/xml-names/"
><cite>Namespaces in XML</cite></a
>. Textuality, Hewlett-Packard, and Microsoft. World Wide Web
Consortium, 1999. (See http://www.w3.org/TR/xml-names/.)
</dd>
</dl>
</div>
</div>
<div class="div1">
<h2><a name="CharClasses" id="CharClasses" />B Character Classes</h2>
<p>
Because of changes to productions
<a href="#NT-NameStartChar">[4]</a> and <a href="#NT-Name">[5]</a>,
the productions in this Appendix are now orphaned and not used anymore
in determining name characters. This Appendix may be removed in a
future edition of this specification; other specifications that wish
to refer to the productions herein should do so by means of a
reference to the relevant production(s) in the
<a href="http://www.w3.org/TR/2006/REC-xml-20060816/"
>Fourth Edition</a
>
of this specification.
</p>
<p>
Following the characteristics defined in the Unicode standard,
characters are classed as base characters (among others, these contain
the alphabetic characters of the Latin alphabet), ideographic
characters, and combining characters (among others, this class
contains most diacritics). Digits and extenders are also
distinguished.
</p>
<h5><a name="CHARACTERS" id="CHARACTERS" />Characters</h5>
<table class="scrap" summary="Scrap">
<tbody>
<tr valign="baseline">
<td>
<a name="NT-Letter" id="NT-Letter" />[84]
</td>
<td><code>Letter</code></td>
<td> ::= </td>
<td>
<code>
<a href="#NT-BaseChar">BaseChar</a> |
<a href="#NT-Ideographic">Ideographic</a>
</code>
</td>
</tr>
<tr valign="baseline">
<td>
<a name="NT-BaseChar" id="NT-BaseChar" />[85]
</td>
<td><code>BaseChar</code></td>
<td> ::= </td>
<td>
<code
>[#x0041-#x005A] | [#x0061-#x007A] | [#x00C0-#x00D6]
| [#x00D8-#x00F6] | [#x00F8-#x00FF]
| [#x0100-#x0131] | [#x0134-#x013E]
| [#x0141-#x0148] | [#x014A-#x017E]
| [#x0180-#x01C3] | [#x01CD-#x01F0]
| [#x01F4-#x01F5] | [#x01FA-#x0217]
| [#x0250-#x02A8] | [#x02BB-#x02C1] | #x0386
| [#x0388-#x038A] | #x038C | [#x038E-#x03A1]
| [#x03A3-#x03CE] | [#x03D0-#x03D6] | #x03DA
| #x03DC | #x03DE | #x03E0
| [#x03E2-#x03F3] | [#x0401-#x040C]
| [#x040E-#x044F] | [#x0451-#x045C]
| [#x045E-#x0481] | [#x0490-#x04C4]
| [#x04C7-#x04C8] | [#x04CB-#x04CC]
| [#x04D0-#x04EB] | [#x04EE-#x04F5]
| [#x04F8-#x04F9] | [#x0531-#x0556] | #x0559
| [#x0561-#x0586] | [#x05D0-#x05EA]
| [#x05F0-#x05F2] | [#x0621-#x063A]
| [#x0641-#x064A] | [#x0671-#x06B7]
| [#x06BA-#x06BE] | [#x06C0-#x06CE]
| [#x06D0-#x06D3] | #x06D5 | [#x06E5-#x06E6]
| [#x0905-#x0939] | #x093D | [#x0958-#x0961]
| [#x0985-#x098C] | [#x098F-#x0990]
| [#x0993-#x09A8] | [#x09AA-#x09B0] | #x09B2
| [#x09B6-#x09B9] | [#x09DC-#x09DD]
| [#x09DF-#x09E1] | [#x09F0-#x09F1]
| [#x0A05-#x0A0A] | [#x0A0F-#x0A10]
| [#x0A13-#x0A28] | [#x0A2A-#x0A30]
| [#x0A32-#x0A33] | [#x0A35-#x0A36]
| [#x0A38-#x0A39] | [#x0A59-#x0A5C] | #x0A5E
| [#x0A72-#x0A74] | [#x0A85-#x0A8B] | #x0A8D
| [#x0A8F-#x0A91] | [#x0A93-#x0AA8]
| [#x0AAA-#x0AB0] | [#x0AB2-#x0AB3]
| [#x0AB5-#x0AB9] | #x0ABD | #x0AE0
| [#x0B05-#x0B0C] | [#x0B0F-#x0B10]
| [#x0B13-#x0B28] | [#x0B2A-#x0B30]
| [#x0B32-#x0B33] | [#x0B36-#x0B39] | #x0B3D
| [#x0B5C-#x0B5D] | [#x0B5F-#x0B61]
| [#x0B85-#x0B8A] | [#x0B8E-#x0B90]
| [#x0B92-#x0B95] | [#x0B99-#x0B9A] | #x0B9C
| [#x0B9E-#x0B9F] | [#x0BA3-#x0BA4]
| [#x0BA8-#x0BAA] | [#x0BAE-#x0BB5]
| [#x0BB7-#x0BB9] | [#x0C05-#x0C0C]
| [#x0C0E-#x0C10] | [#x0C12-#x0C28]
| [#x0C2A-#x0C33] | [#x0C35-#x0C39]
| [#x0C60-#x0C61] | [#x0C85-#x0C8C]
| [#x0C8E-#x0C90] | [#x0C92-#x0CA8]
| [#x0CAA-#x0CB3] | [#x0CB5-#x0CB9] | #x0CDE
| [#x0CE0-#x0CE1] | [#x0D05-#x0D0C]
| [#x0D0E-#x0D10] | [#x0D12-#x0D28]
| [#x0D2A-#x0D39] | [#x0D60-#x0D61]
| [#x0E01-#x0E2E] | #x0E30 | [#x0E32-#x0E33]
| [#x0E40-#x0E45] | [#x0E81-#x0E82] | #x0E84
| [#x0E87-#x0E88] | #x0E8A | #x0E8D
| [#x0E94-#x0E97] | [#x0E99-#x0E9F]
| [#x0EA1-#x0EA3] | #x0EA5 | #x0EA7
| [#x0EAA-#x0EAB] | [#x0EAD-#x0EAE] | #x0EB0
| [#x0EB2-#x0EB3] | #x0EBD | [#x0EC0-#x0EC4]
| [#x0F40-#x0F47] | [#x0F49-#x0F69]
| [#x10A0-#x10C5] | [#x10D0-#x10F6] | #x1100
| [#x1102-#x1103] | [#x1105-#x1107] | #x1109
| [#x110B-#x110C] | [#x110E-#x1112] | #x113C
| #x113E | #x1140 | #x114C | #x114E
| #x1150 | [#x1154-#x1155] | #x1159
| [#x115F-#x1161] | #x1163 | #x1165
| #x1167 | #x1169 | [#x116D-#x116E]
| [#x1172-#x1173] | #x1175 | #x119E
| #x11A8 | #x11AB | [#x11AE-#x11AF]
| [#x11B7-#x11B8] | #x11BA | [#x11BC-#x11C2]
| #x11EB | #x11F0 | #x11F9
| [#x1E00-#x1E9B] | [#x1EA0-#x1EF9]
| [#x1F00-#x1F15] | [#x1F18-#x1F1D]
| [#x1F20-#x1F45] | [#x1F48-#x1F4D]
| [#x1F50-#x1F57] | #x1F59 | #x1F5B
| #x1F5D | [#x1F5F-#x1F7D] | [#x1F80-#x1FB4]
| [#x1FB6-#x1FBC] | #x1FBE | [#x1FC2-#x1FC4]
| [#x1FC6-#x1FCC] | [#x1FD0-#x1FD3]
| [#x1FD6-#x1FDB] | [#x1FE0-#x1FEC]
| [#x1FF2-#x1FF4] | [#x1FF6-#x1FFC] | #x2126
| [#x212A-#x212B] | #x212E | [#x2180-#x2182]
| [#x3041-#x3094] | [#x30A1-#x30FA]
| [#x3105-#x312C] | [#xAC00-#xD7A3]
</code>
</td>
</tr>
<tr valign="baseline">
<td>
<a
name="NT-Ideographic"
id="NT-Ideographic"
/>[86]
</td>
<td><code>Ideographic</code></td>
<td> ::= </td>
<td>
<code
>[#x4E00-#x9FA5] | #x3007 | [#x3021-#x3029]
</code>
</td>
</tr>
<tr valign="baseline">
<td>
<a
name="NT-CombiningChar"
id="NT-CombiningChar"
/>[87]
</td>
<td><code>CombiningChar</code></td>
<td> ::= </td>
<td>
<code
>[#x0300-#x0345] | [#x0360-#x0361] | [#x0483-#x0486]
| [#x0591-#x05A1] | [#x05A3-#x05B9]
| [#x05BB-#x05BD] | #x05BF | [#x05C1-#x05C2]
| #x05C4 | [#x064B-#x0652] | #x0670
| [#x06D6-#x06DC] | [#x06DD-#x06DF]
| [#x06E0-#x06E4] | [#x06E7-#x06E8]
| [#x06EA-#x06ED] | [#x0901-#x0903] | #x093C
| [#x093E-#x094C] | #x094D | [#x0951-#x0954]
| [#x0962-#x0963] | [#x0981-#x0983] | #x09BC
| #x09BE | #x09BF | [#x09C0-#x09C4]
| [#x09C7-#x09C8] | [#x09CB-#x09CD] | #x09D7
| [#x09E2-#x09E3] | #x0A02 | #x0A3C
| #x0A3E | #x0A3F | [#x0A40-#x0A42]
| [#x0A47-#x0A48] | [#x0A4B-#x0A4D]
| [#x0A70-#x0A71] | [#x0A81-#x0A83] | #x0ABC
| [#x0ABE-#x0AC5] | [#x0AC7-#x0AC9]
| [#x0ACB-#x0ACD] | [#x0B01-#x0B03] | #x0B3C
| [#x0B3E-#x0B43] | [#x0B47-#x0B48]
| [#x0B4B-#x0B4D] | [#x0B56-#x0B57]
| [#x0B82-#x0B83] | [#x0BBE-#x0BC2]
| [#x0BC6-#x0BC8] | [#x0BCA-#x0BCD] | #x0BD7
| [#x0C01-#x0C03] | [#x0C3E-#x0C44]
| [#x0C46-#x0C48] | [#x0C4A-#x0C4D]
| [#x0C55-#x0C56] | [#x0C82-#x0C83]
| [#x0CBE-#x0CC4] | [#x0CC6-#x0CC8]
| [#x0CCA-#x0CCD] | [#x0CD5-#x0CD6]
| [#x0D02-#x0D03] | [#x0D3E-#x0D43]
| [#x0D46-#x0D48] | [#x0D4A-#x0D4D] | #x0D57
| #x0E31 | [#x0E34-#x0E3A] | [#x0E47-#x0E4E]
| #x0EB1 | [#x0EB4-#x0EB9] | [#x0EBB-#x0EBC]
| [#x0EC8-#x0ECD] | [#x0F18-#x0F19] | #x0F35
| #x0F37 | #x0F39 | #x0F3E | #x0F3F
| [#x0F71-#x0F84] | [#x0F86-#x0F8B]
| [#x0F90-#x0F95] | #x0F97 | [#x0F99-#x0FAD]
| [#x0FB1-#x0FB7] | #x0FB9 | [#x20D0-#x20DC]
| #x20E1 | [#x302A-#x302F] | #x3099
| #x309A
</code>
</td>
</tr>
<tr valign="baseline">
<td><a name="NT-Digit" id="NT-Digit" />[88] </td>
<td><code>Digit</code></td>
<td> ::= </td>
<td>
<code
>[#x0030-#x0039] | [#x0660-#x0669] | [#x06F0-#x06F9]
| [#x0966-#x096F] | [#x09E6-#x09EF]
| [#x0A66-#x0A6F] | [#x0AE6-#x0AEF]
| [#x0B66-#x0B6F] | [#x0BE7-#x0BEF]
| [#x0C66-#x0C6F] | [#x0CE6-#x0CEF]
| [#x0D66-#x0D6F] | [#x0E50-#x0E59]
| [#x0ED0-#x0ED9] | [#x0F20-#x0F29]
</code>
</td>
</tr>
<tr valign="baseline">
<td>
<a name="NT-Extender" id="NT-Extender" />[89]
</td>
<td><code>Extender</code></td>
<td> ::= </td>
<td>
<code
>#x00B7 | #x02D0 | #x02D1 | #x0387
| #x0640 | #x0E46 | #x0EC6 | #x3005
| [#x3031-#x3035] | [#x309D-#x309E]
| [#x30FC-#x30FE]
</code>
</td>
</tr>
</tbody>
</table>
<p>
The character classes defined here can be derived from the Unicode 2.0
character database as follows:
</p>
<ul>
<li>
<p>
Name start characters must have one of the categories Ll, Lu, Lo,
Lt, Nl.
</p>
</li>
<li>
<p>
Name characters other than Name-start characters must have one of
the categories Mc, Me, Mn, Lm, or Nd.
</p>
</li>
<li>
<p>
Characters in the compatibility area (i.e. with character code
greater than #xF900 and less than #xFFFE) are not allowed in XML
names.
</p>
</li>
<li>
<p>
Characters which have a font or compatibility decomposition (i.e.
those with a "compatibility formatting tag" in field 5 of the
database -- marked by field 5 beginning with a "<") are not
allowed.
</p>
</li>
<li>
<p>
The following characters are treated as name-start characters
rather than name characters, because the property file classifies
them as Alphabetic: [#x02BB-#x02C1], #x0559, #x06E5, #x06E6.
</p>
</li>
<li>
<p>
Characters #x20DD-#x20E0 are excluded (in accordance with Unicode
2.0, section 5.14).
</p>
</li>
<li>
<p>
Character #x00B7 is classified as an extender, because the
property list so identifies it.
</p>
</li>
<li>
<p>
Character #x0387 is added as a name character, because #x00B7 is
its canonical equivalent.
</p>
</li>
<li>
<p>Characters ':' and '_' are allowed as name-start characters.</p>
</li>
<li><p>Characters '-' and '.' are allowed as name characters.</p></li>
</ul>
</div>
<div class="div1">
<h2>
<a name="sec-xml-and-sgml" id="sec-xml-and-sgml" />C XML and SGML
(Non-Normative)
</h2>
<p>
XML is designed to be a subset of SGML, in that every XML document
should also be a conforming SGML document. For a detailed comparison
of the additional restrictions that XML places on documents beyond
those of SGML, see <a href="#Clark">[Clark]</a>.
</p>
</div>
<div class="div1">
<h2>
<a name="sec-entexpand" id="sec-entexpand" />D Expansion of Entity and
Character References (Non-Normative)
</h2>
<p>
This appendix contains some examples illustrating the sequence of
entity- and character-reference recognition and expansion, as
specified in
<a href="#entproc"
><b>4.4 XML Processor Treatment of Entities and References</b></a
>.
</p>
<p>If the DTD contains the declaration</p>
<div class="exampleInner">
<pre>
<!ENTITY example "<p>An ampersand (&#38;#38;) may be escaped
numerically (&#38;#38;#38;) or with a general entity
(&amp;amp;).</p>" ></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>
<p>An ampersand (&#38;) may be escaped
numerically (&#38;#38;) or with a general entity
(&amp;amp;).</p></pre
>
</div>
<p>
A reference in the document to "
<code>&example;</code>
" will cause the text to be reparsed, at which time the start- and
end-tags of the <code>p</code> element will be recognized and the
three references will be recognized and expanded, resulting in a
<code>p</code> element with the following content (all data, no
delimiters or markup):
</p>
<div class="exampleInner">
<pre>
An ampersand (&) may be escaped
numerically (&#38;) or with a general entity
(&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 <?xml version='1.0'?>
2 <!DOCTYPE test [
3 <!ELEMENT test (#PCDATA) >
4 <!ENTITY % xx '&#37;zz;'>
5 <!ENTITY % zz '&#60;!ENTITY tricky "error-prone" >' >
6 %xx;
7 ]>
8 <test>This sample shows a &tricky; method.</test></pre
>
</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>&#60;</code>
" is expanded immediately and the parameter entity "
<code>zz</code>
" is stored with the replacement text "
<code><!ENTITY tricky "error-prone" ></code>
", which is a well-formed entity declaration.
</p>
</li>
<li>
<p>
in line 6, the reference to "
<code>xx</code>
" is recognized, and the replacement text of "
<code>xx</code>
" (namely "
<code>%zz;</code>
") is parsed. The reference to "
<code>zz</code>
" is recognized in its turn, and its replacement text ("
<code><!ENTITY tricky "error-prone" ></code>
") is parsed. The general entity "
<code>tricky</code>
" has now been declared, with the replacement text "
<code>error-prone</code>
".
</p>
</li>
<li>
<p>
in line 8, the reference to the general entity "
<code>tricky</code>
" is recognized, and it is expanded, so the full content of the
<code>test</code> element is the self-describing (and
ungrammatical) string
<em>This sample shows a error-prone method.</em>
</p>
</li>
</ul>
<p>In the following example</p>
<div class="exampleInner">
<pre>
<!DOCTYPE foo [
<!ENTITY x "&lt;">
]>
<foo attr="&x;"/></pre
>
</div>
<p>
the replacement text of x is the four characters "&lt;" because
references to general entities in entity values are
<a href="#bypass"><cite>bypassed</cite></a
>. The replacement text of lt is a character reference to the
less-than character, for example the five characters "&#60;" (see
<a href="#sec-predefined-ent"><b>4.6 Predefined Entities</b></a
>). Since neither of these contains a less-than character the result
is well-formed.
</p>
<p>If the definition of x had been</p>
<div class="exampleInner"><pre><!ENTITY x "&#60;"></pre></div>
<p>
then the document would not have been well-formed, because the
replacement text of x would be the single character "<" which is
not permitted in attribute values (see
<a href="#CleanAttrVals"
><cite>WFC: No < in Attribute Values</cite></a
>).
</p>
</div>
<div class="div1">
<h2>
<a name="determinism" id="determinism" />E Deterministic Content
Models (Non-Normative)
</h2>
<p>
As noted in
<a href="#sec-element-content"><b>3.2.1 Element Content</b></a
>, it is required that content models in element type declarations be
deterministic. This requirement is
<a title="For Compatibility" href="#dt-compat">for compatibility</a>
with SGML (which calls deterministic content models "unambiguous");
XML processors built using SGML systems may flag non-deterministic
content models as errors.
</p>
<p>
For example, the content model <code>((b, c) | (b, d))</code> is
non-deterministic, because given an initial <code>b</code> the XML
processor cannot know which <code>b</code> in the model is being
matched without looking ahead to see which element follows the
<code>b</code>. In this case, the two references to <code>b</code> can
be collapsed into a single reference, making the model read
<code>(b, (c | d))</code>. An initial <code>b</code> now clearly
matches only a single name in the content model. The processor doesn't
need to look ahead to see what follows; either <code>c</code> or
<code>d</code> would be accepted.
</p>
<p>
More formally: a finite state automaton may be constructed from the
content model using the standard algorithms, e.g. algorithm 3.5 in
section 3.9 of Aho, Sethi, and Ullman <a href="#Aho">[Aho/Ullman]</a>.
In many such algorithms, a follow set is constructed for each position
in the regular expression (i.e., each leaf node in the syntax tree for
the regular expression); if any position has a follow set in which
more than one following position is labeled with the same element type
name, then the content model is in error and may be reported as an
error.
</p>
<p>
Algorithms exist which allow many but not all non-deterministic
content models to be reduced automatically to equivalent deterministic
models; see Brüggemann-Klein 1991
<a href="#ABK">[Brüggemann-Klein]</a>.
</p>
</div>
<div class="div1">
<h2>
<a name="sec-guessing" id="sec-guessing" />F Autodetection of
Character Encodings (Non-Normative)
</h2>
<p>
The XML encoding declaration functions as an internal label on each
entity, indicating which character encoding is in use. Before an XML
processor can read the internal label, however, it apparently has to
know what character encoding is in use—which is what the internal
label is trying to indicate. In the general case, this is a hopeless
situation. It is not entirely hopeless in XML, however, because XML
limits the general case in two ways: each implementation is assumed to
support only a finite set of character encodings, and the XML encoding
declaration is restricted in position and content in order to make it
feasible to autodetect the character encoding in use in each entity in
normal cases. Also, in many cases other sources of information are
available in addition to the XML data stream itself. Two cases may be
distinguished, depending on whether the XML entity is presented to the
processor without, or with, any accompanying (external) information.
We <span>will</span> consider
<span>these cases in turn.</span>
</p>
<div class="div2">
<h3>
<a
name="sec-guessing-no-ext-info"
id="sec-guessing-no-ext-info"
/>F.1 Detection Without External Encoding Information
</h3>
<p>
Because each XML entity not accompanied by external encoding
information and not in UTF-8 or UTF-16 encoding must begin with an
XML encoding declaration, in which the first characters must be
'<code><?xml</code>', any conforming processor can detect, after
two to four octets of input, which of the following cases apply. In
reading this list, it may help to know that in UCS-4, '<' is "
<code>#x0000003C</code>
" and '?' is "
<code>#x0000003F</code>
", and the Byte Order Mark required of UTF-16 data streams is "
<code>#xFEFF</code>
". The notation
<var>##</var> is used to denote any byte value except that two
consecutive <var>##</var>s cannot be both 00.
</p>
<p>With a Byte Order Mark:</p>
<table border="1" frame="border">
<tbody>
<tr>
<td>
<code>00 00 FE FF</code>
</td>
<td>UCS-4, big-endian machine (1234 order)</td>
</tr>
<tr>
<td>
<code>FF FE 00 00</code>
</td>
<td>UCS-4, little-endian machine (4321 order)</td>
</tr>
<tr>
<td>
<code>00 00 FF FE</code>
</td>
<td>UCS-4, unusual octet order (2143)</td>
</tr>
<tr>
<td>
<code>FE FF 00 00</code>
</td>
<td>UCS-4, unusual octet order (3412)</td>
</tr>
<tr>
<td>
<code>FE FF ## ##</code>
</td>
<td>UTF-16, big-endian</td>
</tr>
<tr>
<td>
<code>FF FE ## ##</code>
</td>
<td>UTF-16, little-endian</td>
</tr>
<tr>
<td>
<code>EF BB BF</code>
</td>
<td>UTF-8</td>
</tr>
</tbody>
</table>
<p>Without a Byte Order Mark:</p>
<table border="1" frame="border">
<tbody>
<tr>
<td>
<code>00 00 00 3C</code>
</td>
<td rowspan="4">
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>
<code>3C 00 00 00</code>
</td>
</tr>
<tr>
<td>
<code>00 00 3C 00</code>
</td>
</tr>
<tr>
<td>
<code>00 3C 00 00</code>
</td>
</tr>
<tr>
<td>
<code>00 3C 00 3F</code>
</td>
<td>
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>
<code>3C 00 3F 00</code>
</td>
<td>
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>
<code>3C 3F 78 6D</code>
</td>
<td>
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>
<code>4C 6F A7 94</code>
</td>
<td>
EBCDIC (in some flavor; the full encoding declaration must be
read to tell which code page is in use)
</td>
</tr>
<tr>
<td>Other</td>
<td>
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"
/>F.2 Priorities in the Presence of External Encoding Information
</h3>
<p>
The second possible case occurs when the XML entity is accompanied
by encoding information, as in some file systems and some network
protocols. When multiple sources of information are available, their
relative priority and the preferred method of handling conflict
should be specified as part of the higher-level protocol used to
deliver XML. In particular, please refer to
<a href="#rfc2376">[IETF RFC 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" />G W3C XML Working Group
(Non-Normative)
</h2>
<p>
This specification was prepared and approved for publication by the
W3C XML Working Group (WG). WG approval of this specification does not
necessarily imply that all WG members voted for its approval. The
current and former participants of the XML WG are:
</p>
<ul>
<li>Jon Bosak, Sun (<i>Chair</i>)</li>
<li>James Clark (<i>Technical Lead</i>)</li>
<li>Tim Bray, Textuality and Netscape (<i>XML Co-editor</i>)</li>
<li>Jean Paoli, Microsoft (<i>XML Co-editor</i>)</li>
<li>C. M. Sperberg-McQueen, U. of Ill. (<i>XML Co-editor</i>)</li>
<li>Dan Connolly, W3C (<i>W3C Liaison</i>)</li>
<li>Paula Angerstein, Texcel</li>
<li>Steve DeRose, INSO</li>
<li>Dave Hollander, HP</li>
<li>Eliot Kimber, ISOGEN</li>
<li>Eve Maler, ArborText</li>
<li>Tom Magliery, NCSA</li>
<li>Murray Maloney, SoftQuad, Grif SA, Muzmo and Veo Systems</li>
<li>MURATA Makoto (FAMILY Given), Fuji Xerox Information Systems</li>
<li>Joel Nava, Adobe</li>
<li>Conleth O'Connell, Vignette</li>
<li>Peter Sharpe, SoftQuad</li>
<li>John Tigue, DataChannel</li>
</ul>
</div>
<div class="div1">
<h2>
<a name="sec-core-wg" id="sec-core-wg" />H W3C XML Core Working Group
(Non-Normative)
</h2>
<p>
The <span>fifth</span> 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>John Cowan, Google</li>
<li>Andrew Fang, PTC-Arbortext</li>
<li>Paul Grosso, PTC-Arbortext (<i>Co-Chair</i>)</li>
<li>Konrad Lanz, A-SIT</li>
<li>Glenn Marcy, IBM</li>
<li>Henry Thompson, W3C (<i>Staff Contact</i>)</li>
<li>Richard Tobin, University of Edinburgh</li>
<li>Daniel Veillard</li>
<li>Norman Walsh, Mark Logic (<i>Co-Chair</i>)</li>
<li>François Yergeau</li>
</ul>
</div>
<div class="div1">
<h2>
<a name="prod-notes" id="prod-notes" />I 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/2.10/xmlspec.dtd"
>XMLspec DTD, v2.10</a
>. The XHTML versions were produced with a combination of the
<a href="http://www.w3.org/2002/xmlspec/xhtml/1.13/xmlspec.xsl"
>xmlspec.xsl</a
>,
<a href="http://www.w3.org/2002/xmlspec/xhtml/1.13/diffspec.xsl"
>diffspec.xsl</a
>, and <a href="REC-xml.xsl">REC-xml.xsl</a> XSLT stylesheets.
</p>
</div>
<div class="div1">
<h2>
<a name="sec-suggested-names" id="sec-suggested-names" />J 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 5.0; 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 Standard Annex #31 (UAX #31) of the Unicode
Standard, version 5.0 <a href="#Unicode">[Unicode]</a>, 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
Appendix B in previous editions of this specification.
</p>
<ol class="enumar">
<li>
<p>
The first character of any name should have a Unicode property of
ID_Start, or else be '_' #x5F.
</p>
</li>
<li>
<p>
Characters other than the first should have a Unicode property of
ID_Continue, or be one of the characters listed in the table
entitled "Characters for Natural Language Identifiers" in UAX #31,
with the exception of "'" #x27 and "’" #x2019.
</p>
</li>
<li>
<p>
Characters in names should be expressed using Normalization Form C
as defined in <a href="#unipart15">[UnicodeNormal]</a>.
</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 "<") should not
be used in names. This suggestion does not apply to characters
which despite their compatibility decompositions are in regular
use in their scripts, for example #x0E33 THAI CHARACTER SARA AM or
#x0EB3 LAO CHARACTER AM.
</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>
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