discontinued / server · Files

REC-xml-19980210 174 KB
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<!doctype html public '-//W3C//DTD HTML 4.0 Transitional//EN' 'http://www.w3.org/TR/REC-html40-971218/loose.dtd'><HTML><HEAD><meta name='GENERATOR' content='XML/XH/Lark'><link rel='STYLESHEET' type='text/css' href='/StyleSheets/TR/rec.css'><TITLE>Extensible Markup Language (XML) 1.0</TITLE></HEAD><BODY BACKGROUND='/Icons/Backgrounds/recbg.jpg'>

<H3 align='right'><A HREF='http://www.w3.org/'><IMG border='0' align='left' alt='W3C'  src='http://www.w3.org/Icons/WWW/w3c_home'></A>REC-xml-19980210</H3><br><H1 align='center'>Extensible Markup Language (XML) 1.0</H1>

<h3 align='center'>W3C Recommendation 
10-February-1998 </h3>

<DL><DT>This version:</DT>
<dd><A HREF='http://www.w3.org/TR/1998/REC-xml-19980210'>
http://www.w3.org/TR/1998/REC-xml-19980210</A>
<dd><A HREF='http://www.w3.org/TR/1998/REC-xml-19980210.xml'>
http://www.w3.org/TR/1998/REC-xml-19980210.xml</A>
<dd><A HREF='http://www.w3.org/TR/1998/REC-xml-19980210.html'>
http://www.w3.org/TR/1998/REC-xml-19980210.html</A>
<dd><A HREF='http://www.w3.org/TR/1998/REC-xml-19980210.pdf'>
http://www.w3.org/TR/1998/REC-xml-19980210.pdf</A>
<dd><A HREF='http://www.w3.org/TR/1998/REC-xml-19980210.ps'>
http://www.w3.org/TR/1998/REC-xml-19980210.ps</A>

<DT>Latest version:</DT>
<dd><A HREF='http://www.w3.org/TR/REC-xml'>
http://www.w3.org/TR/REC-xml</A>

<DT>Previous version:</DT>
<dd><A HREF='http://www.w3.org/TR/PR-xml-971208'>
http://www.w3.org/TR/PR-xml-971208</A>


<dt>Editors:</dt>
<DD>Tim Bray
 (Textuality and Netscape) 
<A HREF='mailto:tbray@textuality.com'>&lt;tbray@textuality.com&gt;</A></DD>
<DD>Jean Paoli
 (Microsoft) 
<A HREF='mailto:jeanpa@microsoft.com'>&lt;jeanpa@microsoft.com&gt;</A></DD>
<DD>C. M. Sperberg-McQueen
 (University of Illinois at Chicago) 
<A HREF='mailto:cmsmcq@uic.edu'>&lt;cmsmcq@uic.edu&gt;</A></DD>
</dl>
<H2>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>

<h2>Status of this document</h2>
<P>This document has been reviewed by W3C Members and
other interested parties and has been endorsed by the
Director as a W3C Recommendation. It is a stable
document and may be used as reference material or cited
as a normative reference from another document. W3C's
role in making the Recommendation is to draw attention
to the specification and to promote its widespread
deployment. This enhances the functionality and
interoperability of the Web.</P>
<P>
This document specifies a syntax created by subsetting an existing,
widely used international text processing standard (Standard
Generalized Markup Language, ISO 8879:1986(E) as amended and
corrected) for use on the World Wide Web.  It is a product of the W3C
XML Activity, details of which can be found at <A HREF='http://www.w3.org/XML'>http://www.w3.org/XML</A>.  A list of
current W3C Recommendations and other technical documents can be found
at <A HREF='http://www.w3.org/TR'>http://www.w3.org/TR</A>.
</P>
<P>This specification uses the term URI, which is defined by <A href='#Berners-Lee'>[Berners-Lee et al.]</A>, a work in progress expected to update <A href='#RFC1738'>[IETF RFC1738]</A> and <A href='#RFC1808'>[IETF RFC1808]</A>. 
</P>
<P>The list of known errors in this specification is 
available at 
<A HREF='http://www.w3.org/XML/xml-19980210-errata'>http://www.w3.org/XML/xml-19980210-errata</A>.</P>
<P>Please report errors in this document to 
<A HREF='mailto:xml-editor@w3.org'>xml-editor@w3.org</A>.
</P>







<H1>Extensible Markup Language (XML) 1.0</H1><H1></H1><h2>Table of Contents</h2>1. <A HREF='#sec-intro'>Introduction</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;1.1 <A HREF='#sec-origin-goals'>Origin and Goals</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;1.2 <A HREF='#sec-terminology'>Terminology</A><BR>
2. <A HREF='#sec-documents'>Documents</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.1 <A HREF='#sec-well-formed'>Well-Formed XML Documents</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.2 <A HREF='#charsets'>Characters</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.3 <A HREF='#sec-common-syn'>Common Syntactic Constructs</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.4 <A HREF='#syntax'>Character Data and Markup</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.5 <A HREF='#sec-comments'>Comments</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.6 <A HREF='#sec-pi'>Processing Instructions</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.7 <A HREF='#sec-cdata-sect'>CDATA Sections</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.8 <A HREF='#sec-prolog-dtd'>Prolog and Document Type Declaration</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.9 <A HREF='#sec-rmd'>Standalone Document Declaration</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.10 <A HREF='#sec-white-space'>White Space Handling</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.11 <A HREF='#sec-line-ends'>End-of-Line Handling</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;2.12 <A HREF='#sec-lang-tag'>Language Identification</A><BR>
3. <A HREF='#sec-logical-struct'>Logical Structures</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;3.1 <A HREF='#sec-starttags'>Start-Tags, End-Tags, and Empty-Element Tags</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;3.2 <A HREF='#elemdecls'>Element Type Declarations</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.2.1 <A HREF='#sec-element-content'>Element Content</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.2.2 <A HREF='#sec-mixed-content'>Mixed Content</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;3.3 <A HREF='#attdecls'>Attribute-List Declarations</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.3.1 <A HREF='#sec-attribute-types'>Attribute Types</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.3.2 <A HREF='#sec-attr-defaults'>Attribute Defaults</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.3.3 <A HREF='#AVNormalize'>Attribute-Value Normalization</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;3.4 <A HREF='#sec-condition-sect'>Conditional Sections</A><BR>
4. <A HREF='#sec-physical-struct'>Physical Structures</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;4.1 <A HREF='#sec-references'>Character and Entity References</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;4.2 <A HREF='#sec-entity-decl'>Entity Declarations</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.2.1 <A HREF='#sec-internal-ent'>Internal Entities</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.2.2 <A HREF='#sec-external-ent'>External Entities</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;4.3 <A HREF='#TextEntities'>Parsed Entities</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.3.1 <A HREF='#sec-TextDecl'>The Text Declaration</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.3.2 <A HREF='#wf-entities'>Well-Formed Parsed Entities</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.3.3 <A HREF='#charencoding'>Character Encoding in Entities</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;4.4 <A HREF='#entproc'>XML Processor Treatment of Entities and References</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.1 <A HREF='#not-recognized'>Not Recognized</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.2 <A HREF='#included'>Included</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.3 <A HREF='#include-if-valid'>Included If Validating</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.4 <A HREF='#forbidden'>Forbidden</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.5 <A HREF='#inliteral'>Included in Literal</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.6 <A HREF='#notify'>Notify</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.7 <A HREF='#bypass'>Bypassed</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4.8 <A HREF='#as-PE'>Included as PE</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;4.5 <A HREF='#intern-replacement'>Construction of Internal Entity Replacement Text</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;4.6 <A HREF='#sec-predefined-ent'>Predefined Entities</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;4.7 <A HREF='#Notations'>Notation Declarations</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;4.8 <A HREF='#sec-doc-entity'>Document Entity</A><BR>
5. <A HREF='#sec-conformance'>Conformance</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;5.1 <A HREF='#proc-types'>Validating and Non-Validating Processors</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;5.2 <A HREF='#safe-behavior'>Using XML Processors</A><BR>
6. <A HREF='#sec-notation'>Notation</A><BR>
<h3>Appendices</h3>A. <A HREF='#sec-bibliography'>References</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;A.1 <A HREF='#sec-existing-stds'>Normative References</A><BR>
&nbsp;&nbsp;&nbsp;&nbsp;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 (Non-Normative)</A><BR>
D. <A HREF='#sec-entexpand'>Expansion of Entity and Character References (Non-Normative)</A><BR>
E. <A HREF='#determinism'>Deterministic Content Models (Non-Normative)</A><BR>
F. <A HREF='#sec-guessing'>Autodetection of Character Encodings (Non-Normative)</A><BR>
G. <A HREF='#sec-xml-wg'>W3C XML Working Group (Non-Normative)</A><BR>

<HR>
 


<H2><A NAME='sec-intro'>1. Introduction</a></h2>
<P>Extensible Markup Language, abbreviated XML, describes a class of
data objects called <A 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 href='#dt-entity'>entities</A>, which contain either parsed
or unparsed data.
Parsed data is made up of <A href='#dt-character'>characters</A>,
some 
of which form <A href='#dt-chardata'>character data</A>, 
and some of which form <A 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'></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'></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>
 


<H3><A NAME='sec-origin-goals'>1.1 Origin and Goals</a></h3>
<P>XML was developed by an XML Working Group (originally known as the
SGML Editorial Review Board) formed under the auspices of the World
Wide Web Consortium (W3C) in 1996.
It was chaired by Jon Bosak of Sun
Microsystems with the active participation of an XML Special
Interest Group (previously known as the SGML Working Group) also
organized by the W3C. The membership of the XML Working Group is given
in an appendix. Dan Connolly served as the WG's contact with the W3C.
</P>
<P>The design goals for XML are:<OL>
<LI>XML shall be straightforwardly usable over the
Internet.</LI>
<LI>XML shall support a wide variety of applications.</LI>
<LI>XML shall be compatible with SGML.</LI>
<LI>It shall be easy to write programs which process XML
documents.</LI>
<LI>The number of optional features in XML is to be kept to the
absolute minimum, ideally zero.</LI>
<LI>XML documents should be human-legible and reasonably
clear.</LI>
<LI>The XML design should be prepared quickly.</LI>
<LI>The design of XML shall be formal and concise.</LI>
<LI>XML documents shall be easy to create.</LI>
<LI>Terseness in XML markup is of minimal importance.</LI></OL>


<P>This specification, 
together with associated standards
(Unicode and ISO/IEC 10646 for characters,
Internet RFC 1766 for language identification tags, 
ISO 639 for language name codes, and 
ISO 3166 for country name codes),
provides all the information necessary to understand 
XML Version 1.0
and construct computer programs to process it.</P>
<P>This version of the XML specification

may be distributed freely, as long as
all text and legal notices remain intact.</P>


 


 


<H3><A NAME='sec-terminology'>1.2 Terminology</a></h3>
 
<P>The terminology used to describe XML documents is defined in the body of
this specification.
The terms defined in the following list are used in building those
definitions and in describing the actions of an XML processor:
<DL>

<DT><B>may</B></DT>
<DD><a name='dt-may'></a>Conforming documents and XML
processors are permitted to but need not behave as
described.</DD>



<DT><B>must</B></DT>
<DD>Conforming documents and XML processors 
are required to behave as described; otherwise they are in error.

</DD>



<DT><B>error</B></DT>
<DD><a name='dt-error'></a>A violation of the rules of this
specification; results are
undefined.  Conforming software may detect and report an error and may
recover from it.</DD>



<DT><B>fatal error</B></DT>
<DD><a name='dt-fatal'></a>An error
which a conforming <A href='#dt-xml-proc'>XML processor</A>
must detect and report to the application.
After encountering a fatal error, the
processor may continue
processing the data to search for further errors and may report such
errors to the application.  In order to support correction of errors,
the processor may make unprocessed data from the document (with
intermingled character data and markup) available to the application.
Once a fatal error is detected, however, the processor must not
continue normal processing (i.e., it must not
continue to pass character data and information about the document's
logical structure to the application in the normal way).
</DD>



<DT><B>at user option</B></DT>
<DD>Conforming software may or must (depending on the modal verb in the
sentence) behave as described; if it does, it must
provide users a means to enable or disable the behavior
described.</DD>



<DT><B>validity constraint</B></DT>
<DD>A rule which applies to all 
<A href='#dt-valid'>valid</A> XML documents.
Violations of validity constraints are errors; they must, at user option, 
be reported by 
<A href='#dt-validating'>validating XML processors</A>.</DD>



<DT><B>well-formedness constraint</B></DT>
<DD>A rule which applies to all <A href='#dt-wellformed'>well-formed</A> XML documents.
Violations of well-formedness constraints are 
<A href='#dt-fatal'>fatal errors</A>.</DD>




<DT><B>match</B></DT>
<DD><a name='dt-match'></a>(Of strings or names:) 
Two strings or names being compared must be identical.
Characters with multiple possible representations in ISO/IEC 10646 (e.g.
characters with 
both precomposed and base+diacritic forms) match only if they have the
same representation in both strings.
At user option, processors may normalize such characters to
some canonical form.
No case folding is performed. 
(Of strings and rules in the grammar:)  
A string matches a grammatical production if it belongs to the
language generated by that production.
(Of content and content models:)
An element matches its declaration when it conforms
in the fashion described in the constraint
"<A href='#elementvalid'>Element Valid</A>".

</DD>



<DT><B>for compatibility</B></DT>
<DD><a name='dt-compat'></a>A feature of
XML included solely to ensure that XML remains compatible with SGML.
</DD>



<DT><B>for interoperability</B></DT>
<DD><a name='dt-interop'></a>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.</DD>


</DL>




 


 


<H2><A NAME='sec-documents'>2. Documents</a></h2>
 
<P><a name='dt-xml-doc'></a>
A data object is an
<b>XML document</b> if it is
<A href='#dt-wellformed'>well-formed</A>, as
defined in this specification.
A well-formed XML document may in addition be
<A 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 href='#dt-entity'>entities</A>.  An entity may <A href='#dt-entref'>refer</A> to other entities to cause their
inclusion in the document. A document begins in a "root"  or <A href='#dt-docent'>document entity</A>.
Logically, the document is composed of declarations, elements, 
comments,
character references, and
processing
instructions, all of which are indicated in the document by explicit
markup.
The logical and physical structures must nest properly, as described  
in "<A href='#wf-entities'>4.3.2&nbsp;Well-Formed Parsed Entities</A>".
</P>
 


<H3><A NAME='sec-well-formed'>2.1 Well-Formed XML Documents</a></h3>
 
<P><a name='dt-wellformed'></a>
A textual object is 
a well-formed XML document if:
<OL>
<LI>Taken as a whole, it
matches the production labeled <code><a href='#NT-document'>document</A></code>.</LI>
<LI>It
meets all the well-formedness constraints given in this specification.
</LI>
<LI>Each of the <A href='#dt-parsedent'>parsed entities</A> 
which is referenced directly or indirectly within the document is
<A href='#wf-entities'>well-formed</A>.</LI>
</OL>

<P>
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Document</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-document'></a>[1]&nbsp;</td><td align='right'><font><code>document</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-prolog'>prolog</A> 
<a href='#NT-element'>element</A> 
<a href='#NT-Misc'>Misc</A>*</code></font></td></tr>
</table>
</td></tr></table>
<p>
</P>
<P>Matching the <code><a href='#NT-document'>document</A></code> production 
implies that:
<OL>
<LI>It contains one or more
<A href='#dt-element'>elements</A>.
</LI>

<LI><a name='dt-root'></a>There is  exactly
one element, called the <b>root</b>, or document element,  no
part of which appears in the <A href='#dt-content'>content</A> of any other element.
For all other elements, if the start-tag is in the content of another
element, the end-tag is in the content of the same element.  More
simply stated, the elements, delimited by start- and end-tags, nest
properly within each other.
</LI>
</OL>


<P><a name='dt-parentchild'></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>
 


<H3><A NAME='charsets'>2.2 Characters</a></h3>
 
<P><a name='dt-text'></a>A parsed entity contains
<b>text</b>, a sequence of 
<A href='#dt-character'>characters</A>, 
which may represent markup or character data. 
<a name='dt-character'></a>A <b>character</b> 
is an atomic unit of text as specified by
ISO/IEC 10646 <A href='#ISO10646'>[ISO/IEC 10646]</A>.
Legal characters are tab, carriage return, line feed, and the legal
graphic characters of Unicode and ISO/IEC 10646.
The use of "compatibility characters", as defined in section 6.8
of <A href='#Unicode'>[Unicode]</A>, is discouraged.
 
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Character Range</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-Char'></a>[2]&nbsp;</td><td align='right'><font><code>Char</code></font></td> 
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>#x9 |&nbsp;#xA |&nbsp;#xD |&nbsp;[#x20-#xD7FF] |&nbsp;[#xE000-#xFFFD] 
|&nbsp;[#x10000-#x10FFFF]</code></font></td> 
<td align='center'><font><code> /* </code></font></td><td align='left'><font><code>any Unicode character, excluding the
surrogate blocks, FFFE, and FFFF. */</code></font></td> </tr>

</table>
</td></tr></table>
<p>
</P>

<P>The mechanism for encoding character code points into bit patterns may
vary from entity to entity. All XML processors must accept the UTF-8
and UTF-16 encodings of 10646; the mechanisms for signaling which of
the two is in use, or for bringing other encodings into play, are
discussed later, in "<A href='#charencoding'>4.3.3&nbsp;Character Encoding in Entities</A>".
</P>


 


<H3><A NAME='sec-common-syn'>2.3 Common Syntactic Constructs</a></h3>
 
<P>This section defines some symbols used widely in the grammar.</P>
<P><code><a href='#NT-S'>S</A></code> (white space) consists of one or more space (#x20)
characters, carriage returns, line feeds, or tabs.

</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
White Space</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-S'></a>[3]&nbsp;</td><td align='right'><font><code>S</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>(#x20 |&nbsp;#x9 |&nbsp;#xD |&nbsp;#xA)+</code></font></td>
</tr>

</table>
</td></tr></table>
<p></P>
<P>Characters are classified for convenience as letters, digits, or other
characters.  Letters consist of an alphabetic or syllabic 
base character possibly
followed by one or more combining characters, or of an ideographic
character.  
Full definitions of the specific characters in each class
are given in "<A href='#CharClasses'>B.&nbsp;Character Classes</A>".</P>
<P><a name='dt-name'></a>A <b>Name</b> is a token
beginning with a letter or one of a few punctuation characters, and continuing
with letters, digits, hyphens, underscores, colons, or full stops, together
known as name characters.
Names beginning with the string "<CODE>xml</CODE>", or any string
which would match <CODE>(('X'|'x') ('M'|'m') ('L'|'l'))</CODE>, are
reserved for standardization in this or future versions of this
specification.
</P>

<P><b>Note:</b> The colon character within XML names is reserved for experimentation with
name spaces.  
Its meaning is expected to be
standardized at some future point, at which point those documents 
using the colon for experimental purposes may need to be updated.
(There is no guarantee that any name-space mechanism
adopted for XML will in fact use the colon as a name-space delimiter.)
In practice, this means that authors should not use the colon in XML
names except as part of name-space experiments, but that XML processors
should accept the colon as a name character.</P>

<P>An
<code><a href='#NT-Nmtoken'>Nmtoken</A></code> (name token) is any mixture of
name characters.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Names and Tokens</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-NameChar'></a>[4]&nbsp;</td><td align='right'><font><code>NameChar</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-Letter'>Letter</A> 
|&nbsp;<a href='#NT-Digit'>Digit</A> 
|&nbsp;'.' |&nbsp;'-' |&nbsp;'_' |&nbsp;':'
|&nbsp;<a href='#NT-CombiningChar'>CombiningChar</A> 
|&nbsp;<a href='#NT-Extender'>Extender</A></code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-Name'></a>[5]&nbsp;</td><td align='right'><font><code>Name</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>(<a href='#NT-Letter'>Letter</A> |&nbsp;'_' |&nbsp;':')
(<a href='#NT-NameChar'>NameChar</A>)*</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Names'></a>[6]&nbsp;</td><td align='right'><font><code>Names</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-Name'>Name</A> 
(<a href='#NT-S'>S</A> <a href='#NT-Name'>Name</A>)*</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Nmtoken'></a>[7]&nbsp;</td><td align='right'><font><code>Nmtoken</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>(<a href='#NT-NameChar'>NameChar</A>)+</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Nmtokens'></a>[8]&nbsp;</td><td align='right'><font><code>Nmtokens</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-Nmtoken'>Nmtoken</A> (<a href='#NT-S'>S</A> <a href='#NT-Nmtoken'>Nmtoken</A>)*</code></font></td></tr>
</table>
</td></tr></table>
<p>
</P>
<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
(<code><a href='#NT-EntityValue'>EntityValue</A></code>),
the values of attributes (<code><a href='#NT-AttValue'>AttValue</A></code>), 
and external identifiers 
(<code><a href='#NT-SystemLiteral'>SystemLiteral</A></code>).  
Note that a <code><a href='#NT-SystemLiteral'>SystemLiteral</A></code>
can be parsed without scanning for markup.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Literals</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-EntityValue'></a>[9]&nbsp;</td><td align='right'><font><code>EntityValue</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'"' 
([^%&amp;"] 
|&nbsp;<a href='#NT-PEReference'>PEReference</A> 
|&nbsp;<a href='#NT-Reference'>Reference</A>)*
'"' 
</code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|  
"'" 
([^%&amp;'] 
|&nbsp;<a href='#NT-PEReference'>PEReference</A> 
|&nbsp;<a href='#NT-Reference'>Reference</A>)* 
"'"</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-AttValue'></a>[10]&nbsp;</td><td align='right'><font><code>AttValue</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'"' 
([^&lt;&amp;"] 
|&nbsp;<a href='#NT-Reference'>Reference</A>)* 
'"' 
</code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|  
"'" 
([^&lt;&amp;'] 
|&nbsp;<a href='#NT-Reference'>Reference</A>)* 
"'"</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-SystemLiteral'></a>[11]&nbsp;</td><td align='right'><font><code>SystemLiteral</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>('"' [^"]* '"') | ("'" [^']* "'")
</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-PubidLiteral'></a>[12]&nbsp;</td><td align='right'><font><code>PubidLiteral</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'"' <a href='#NT-PubidChar'>PubidChar</A>* 
'"' 
|&nbsp;"'" (<a href='#NT-PubidChar'>PubidChar</A> - "'")* "'"</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-PubidChar'></a>[13]&nbsp;</td><td align='right'><font><code>PubidChar</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>#x20 |&nbsp;#xD |&nbsp;#xA 
| [a-zA-Z0-9]
| [-'()+,./:=?;!*#@$_%]</code></font></td>
</tr>
</table>
</td></tr></table>
<p>
</P>





<H3><A NAME='syntax'>2.4 Character Data and Markup</a></h3>
 
<P><A href='#dt-text'>Text</A> consists of intermingled 
<A href='#dt-chardata'>character
data</A> and markup.
<a name='dt-markup'></a><b>Markup</b> takes the form of
<A href='#dt-stag'>start-tags</A>,
<A href='#dt-etag'>end-tags</A>,
<A href='#dt-empty'>empty-element tags</A>,
<A href='#dt-entref'>entity references</A>,
<A href='#dt-charref'>character references</A>,
<A href='#dt-comment'>comments</A>,
<A href='#dt-cdsection'>CDATA section</A> delimiters,
<A href='#dt-doctype'>document type declarations</A>, and
<A href='#dt-pi'>processing instructions</A>.

</P>
<P><a name='dt-chardata'></a>All text that is not markup
constitutes the <b>character data</b> of
the document.</P>
<P>The ampersand character (&amp;) and the left angle bracket (&lt;)
may appear in their literal form <EM>only</EM> when used as markup
delimiters, or within a <A href='#dt-comment'>comment</A>, a
<A href='#dt-pi'>processing instruction</A>, 
or a <A href='#dt-cdsection'>CDATA section</A>.  

They are also legal within the <A href='#dt-litentval'>literal entity
value</A> of an internal entity declaration; see
"<A href='#wf-entities'>4.3.2&nbsp;Well-Formed Parsed Entities</A>".

If they are needed elsewhere,
they must be <A href='#dt-escape'>escaped</A>
using either <A href='#dt-charref'>numeric character references</A>
or the strings
"<CODE>&amp;amp;</CODE>" and "<CODE>&amp;lt;</CODE>" respectively. 
The right angle
bracket (&gt;) may be represented using the string
"<CODE>&amp;gt;</CODE>", and must, <A href='#dt-compat'>for
compatibility</A>, 
be escaped using
"<CODE>&amp;gt;</CODE>" or a character reference 
when it appears in the string
"<CODE>]]&gt;</CODE>"
in content, 
when that string is not marking the end of 
a <A href='#dt-cdsection'>CDATA section</A>. 
</P>
<P>
In the content of elements, character data 
is any string of characters which does
not contain the start-delimiter of any markup.  
In a CDATA section, character data
is any string of characters not including the CDATA-section-close
delimiter, "<CODE>]]&gt;</CODE>".</P>
<P>
To allow attribute values to contain both single and double quotes, the
apostrophe or single-quote character (') may be represented as
"<CODE>&amp;apos;</CODE>", and the double-quote character (") as
"<CODE>&amp;quot;</CODE>".
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Character Data</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'>
<td align='right'><a name='NT-CharData'></a>[14]&nbsp;</td><td align='right'><font><code>CharData</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>[^&lt;&amp;]* - ([^&lt;&amp;]* ']]&gt;' [^&lt;&amp;]*)</code></font></td>
</tr>
</table>
</td></tr></table>
<p>
</P>

 


<H3><A NAME='sec-comments'>2.5 Comments</a></h3>
 
<P><a name='dt-comment'></a><b>Comments</b> may 
appear anywhere in a document outside other 
<A 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 href='#dt-chardata'>character
data</A>; an XML
processor may, but need not, make it possible for an application to
retrieve the text of comments.
<A href='#dt-compat'>For compatibility</A>, the string
"<CODE>--</CODE>" (double-hyphen) must not occur within
comments.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Comments</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-Comment'></a>[15]&nbsp;</td><td align='right'><font><code>Comment</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;!--'
((<a href='#NT-Char'>Char</A> - '-') 
|&nbsp;('-' (<a href='#NT-Char'>Char</A> - '-')))* 
'--&gt;'</code></font></td>
</tr>
</table>
</td></tr></table>
<p>
</P>
<P>An example of a comment:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!--&nbsp;declarations&nbsp;for&nbsp;&lt;head&gt;&nbsp;&amp;&nbsp;&lt;body&gt;&nbsp;--&gt;</font></code></td></tr></table><p>
</P>

 


<H3><A NAME='sec-pi'>2.6 Processing Instructions</a></h3>
 
<P><a name='dt-pi'></a><b>Processing
instructions</b> (PIs) allow documents to contain instructions
for applications.
 
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Processing Instructions</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-PI'></a>[16]&nbsp;</td><td align='right'><font><code>PI</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;?' <a href='#NT-PITarget'>PITarget</A> 
(<a href='#NT-S'>S</A> 
(<a href='#NT-Char'>Char</A>* - 
(<a href='#NT-Char'>Char</A>* '?&gt;' <a href='#NT-Char'>Char</A>*)))?
'?&gt;'</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-PITarget'></a>[17]&nbsp;</td><td align='right'><font><code>PITarget</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-Name'>Name</A> - 
(('X' |&nbsp;'x') ('M' |&nbsp;'m') ('L' |&nbsp;'l'))</code></font></td>
</tr>
</table>
</td></tr></table>
<p>
PIs are not part of the document's <A href='#dt-chardata'>character
data</A>, but must be passed through to the application. The
PI begins with a target (<code><a href='#NT-PITarget'>PITarget</A></code>) 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 href='#dt-notation'>Notation</A> mechanism
may be used for
formal declaration of PI targets.
</P>

 


<H3><A NAME='sec-cdata-sect'>2.7 CDATA Sections</a></h3>
 
<P><a name='dt-cdsection'></a><b>CDATA sections</b>
may occur 
anywhere character data may occur; they are
used to escape blocks of text containing characters which would
otherwise be recognized as markup.  CDATA sections begin with the
string "<CODE>&lt;![CDATA[</CODE>" and end with the string
"<CODE>]]&gt;</CODE>":
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
CDATA Sections</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-CDSect'></a>[18]&nbsp;</td><td align='right'><font><code>CDSect</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-CDStart'>CDStart</A> 
<a href='#NT-CData'>CData</A> 
<a href='#NT-CDEnd'>CDEnd</A></code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-CDStart'></a>[19]&nbsp;</td><td align='right'><font><code>CDStart</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;![CDATA['</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-CData'></a>[20]&nbsp;</td><td align='right'><font><code>CData</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>(<a href='#NT-Char'>Char</A>* - 
(<a href='#NT-Char'>Char</A>* ']]&gt;' <a href='#NT-Char'>Char</A>*))
</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-CDEnd'></a>[21]&nbsp;</td><td align='right'><font><code>CDEnd</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>']]&gt;'</code></font></td>
</tr>
</table>
</td></tr></table>
<p>

Within a CDATA section, only the <code><a href='#NT-CDEnd'>CDEnd</A></code> string is
recognized as markup, so that left angle brackets and ampersands may occur in
their literal form; they need not (and cannot) be escaped using
"<CODE>&amp;lt;</CODE>" and "<CODE>&amp;amp;</CODE>".  CDATA sections
cannot nest.
</P>

<P>An example of a CDATA section, in which "<CODE>&lt;greeting&gt;</CODE>" and 
"<CODE>&lt;/greeting&gt;</CODE>"
are recognized as <A href='#dt-chardata'>character data</A>, not
<A href='#dt-markup'>markup</A>:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;![CDATA[&lt;greeting&gt;Hello,&nbsp;world!&lt;/greeting&gt;]]&gt;</font></code></td></tr></table><p>
</P>

 


<H3><A NAME='sec-prolog-dtd'>2.8 Prolog and Document Type Declaration</a></h3>
 
<P><a name='dt-xmldecl'></a>XML documents 
may, and should, 
begin with an <b>XML declaration</b> which specifies
the version of
XML being used.
For example, the following is a complete XML document, <A href='#dt-wellformed'>well-formed</A> but not
<A href='#dt-valid'>valid</A>:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;?xml&nbsp;version="1.0"?&gt;<BR>&lt;greeting&gt;Hello,&nbsp;world!&lt;/greeting&gt;<BR></font></code></td></tr></table><p>
and so is this:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;greeting&gt;Hello,&nbsp;world!&lt;/greeting&gt;<BR></font></code></td></tr></table><p>
</P>

<P>The version number "<CODE>1.0</CODE>" should be used to indicate
conformance to this version of this specification; it is an error
for a document to use the value "<CODE>1.0</CODE>" 
if it does not conform to this version of this specification.
It is the intent
of the XML working group to give later versions of this specification
numbers other than "<CODE>1.0</CODE>", but this intent does not
indicate a
commitment to produce any future versions of XML, nor if any are produced, to
use any particular numbering scheme.
Since future versions are not ruled out, this construct is provided 
as a means to allow the possibility of automatic version recognition, should
it become necessary.
Processors may signal an error if they receive documents labeled with 
versions they do not support. 
</P>
<P>The function of the markup in an XML document is to describe its
storage and logical structure and to associate attribute-value pairs
with its logical structures.  XML provides a mechanism, the <A 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'></a>An XML document is 
<b>valid</b> if it has an associated document type
declaration and if the document
complies with the constraints expressed in it.</P>
<P>The document type declaration must appear before
the first <A href='#dt-element'>element</A> in the document.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Prolog</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-prolog'></a>[22]&nbsp;</td><td align='right'><font><code>prolog</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><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></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-XMLDecl'></a>[23]&nbsp;</td><td align='right'><font><code>XMLDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;?xml' 
<a href='#NT-VersionInfo'>VersionInfo</A> 
<a href='#NT-EncodingDecl'>EncodingDecl</A>? 
<a href='#NT-SDDecl'>SDDecl</A>? 
<a href='#NT-S'>S</A>? 
'?&gt;'</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-VersionInfo'></a>[24]&nbsp;</td><td align='right'><font><code>VersionInfo</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-S'>S</A> 'version' <a href='#NT-Eq'>Eq</A> 
(' <a href='#NT-VersionNum'>VersionNum</A> ' 
|&nbsp;" <a href='#NT-VersionNum'>VersionNum</A> ")</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-Eq'></a>[25]&nbsp;</td><td align='right'><font><code>Eq</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-S'>S</A>? '=' <a href='#NT-S'>S</A>?</code></font></td></tr>
<tr valign='top'>
<td align='right'><a name='NT-VersionNum'></a>[26]&nbsp;</td><td align='right'><font><code>VersionNum</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>([a-zA-Z0-9_.:] |&nbsp;'-')+</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-Misc'></a>[27]&nbsp;</td><td align='right'><font><code>Misc</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-Comment'>Comment</A> |&nbsp;<a href='#NT-PI'>PI</A> |&nbsp;
<a href='#NT-S'>S</A></code></font></td></tr>

</table>
</td></tr></table>
<p></P>

<P><a name='dt-doctype'></a>The XML
<b>document type declaration</b> 
contains or points to 
<A 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 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'></a>
A <b>markup declaration</b> is 
an <A href='#dt-eldecl'>element type declaration</A>, 
an <A href='#dt-attdecl'>attribute-list declaration</A>, 
an <A href='#dt-entdecl'>entity declaration</A>, or
a <A href='#dt-notdecl'>notation declaration</A>.

These declarations may be contained in whole or in part
within <A href='#dt-PE'>parameter entities</A>,
as described in the well-formedness and validity constraints below.
For fuller information, see
"<A href='#sec-physical-struct'>4.&nbsp;Physical Structures</A>".</P>

<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Document Type Definition</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-doctypedecl'></a>[28]&nbsp;</td><td align='right'><font><code>doctypedecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;!DOCTYPE' <a href='#NT-S'>S</A> 
<a href='#NT-Name'>Name</A> (<a href='#NT-S'>S</A> 
<a href='#NT-ExternalID'>ExternalID</A>)? 
<a href='#NT-S'>S</A>? ('[' 
(<a href='#NT-markupdecl'>markupdecl</A> 
|&nbsp;<a href='#NT-PEReference'>PEReference</A> 
|&nbsp;<a href='#NT-S'>S</A>)*
']' 
<a href='#NT-S'>S</A>?)? '&gt;'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#vc-roottype'>Root Element Type</A> ]</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-markupdecl'></a>[29]&nbsp;</td><td align='right'><font><code>markupdecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-elementdecl'>elementdecl</A> 
|&nbsp;<a href='#NT-AttlistDecl'>AttlistDecl</A> 
|&nbsp;<a href='#NT-EntityDecl'>EntityDecl</A> 
|&nbsp;<a href='#NT-NotationDecl'>NotationDecl</A> 
|&nbsp;<a href='#NT-PI'>PI</A> 
|&nbsp;<a href='#NT-Comment'>Comment</A>
</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#vc-PEinMarkupDecl'>Proper Declaration/PE Nesting</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#wfc-PEinInternalSubset'>PEs in Internal Subset</A> ]</code></font></td>
</tr>


</table>
</td></tr></table>


<P>The markup declarations may be made up in whole or in part of
the <A href='#dt-repltext'>replacement text</A> of 
<A href='#dt-PE'>parameter entities</A>.
The productions later in this specification for
individual nonterminals (<code><a href='#NT-elementdecl'>elementdecl</A></code>,
<code><a href='#NT-AttlistDecl'>AttlistDecl</A></code>, and so on) describe 
the declarations <EM>after</EM> all the parameter entities have been 
<A href='#dt-include'>included</A>.</P>

<A NAME='vc-roottype'></A><P><b>Validity Constraint: 
Root Element Type</b><br>

The <code><a href='#NT-Name'>Name</A></code> in the document type declaration must
match the element type of the <A href='#dt-root'>root element</A>.

</P>

<A NAME='vc-PEinMarkupDecl'></A><P><b>Validity Constraint: 
Proper Declaration/PE Nesting</b><br>
Parameter-entity 
<A href='#dt-repltext'>replacement text</A> must be properly nested
with markup declarations. 
That is to say, if either the first character
or the last character of a markup
declaration (<code><a href='#NT-markupdecl'>markupdecl</A></code> above)
is contained in the replacement text for a 
<A href='#dt-PERef'>parameter-entity reference</A>,
both must be contained in the same replacement text.
</P>
<A NAME='wfc-PEinInternalSubset'></A><P><b>Well-Formedness Constraint: 
PEs in Internal Subset</b><br>
In the internal DTD subset, 
<A href='#dt-PERef'>parameter-entity references</A>
can occur only where markup declarations can occur, not
within markup declarations.  (This does not apply to
references that occur in
external parameter entities or to the external subset.)

</P>
<P>
Like the internal subset, the external subset and 
any external parameter entities referred to in the DTD 
must consist of a series of complete markup declarations of the types 
allowed by the non-terminal symbol
<code><a href='#NT-markupdecl'>markupdecl</A></code>, interspersed with white space
or <A href='#dt-PERef'>parameter-entity references</A>.
However, portions of the contents
of the 
external subset or of external parameter entities may conditionally be ignored
by using 
the <A href='#dt-cond-section'>conditional section</A>
construct; this is not allowed in the internal subset.

</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
External Subset</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-extSubset'></a>[30]&nbsp;</td><td align='right'><font><code>extSubset</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-TextDecl'>TextDecl</A>?
<a href='#NT-extSubsetDecl'>extSubsetDecl</A></code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-extSubsetDecl'></a>[31]&nbsp;</td><td align='right'><font><code>extSubsetDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>(
<a href='#NT-markupdecl'>markupdecl</A> 
|&nbsp;<a href='#NT-conditionalSect'>conditionalSect</A> 
|&nbsp;<a href='#NT-PEReference'>PEReference</A> 
|&nbsp;<a href='#NT-S'>S</A>
)*</code></font></td>
</tr>

</table>
</td></tr></table>
<p></P>
<P>The external subset and external parameter entities also differ 
from the internal subset in that in them,
<A href='#dt-PERef'>parameter-entity references</A>
are permitted <EM>within</EM> markup declarations,
not only <EM>between</EM> markup declarations.</P>
<P>An example of an XML document with a document type declaration:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;?xml&nbsp;version="1.0"?&gt;<BR>&lt;!DOCTYPE&nbsp;greeting&nbsp;SYSTEM&nbsp;"hello.dtd"&gt;<BR>&lt;greeting&gt;Hello,&nbsp;world!&lt;/greeting&gt;<BR></font></code></td></tr></table><p>
The <A href='#dt-sysid'>system identifier</A> 
"<CODE>hello.dtd</CODE>" gives the URI of a DTD for the document.</P>
<P>The declarations can also be given locally, as in this 
example:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;?xml&nbsp;version="1.0"&nbsp;encoding="UTF-8"&nbsp;?&gt;<BR>&lt;!DOCTYPE&nbsp;greeting&nbsp;[<BR>&nbsp;&nbsp;&lt;!ELEMENT&nbsp;greeting&nbsp;(#PCDATA)&gt;<BR>]&gt;<BR>&lt;greeting&gt;Hello,&nbsp;world!&lt;/greeting&gt;<BR></font></code></td></tr></table><p>
If both the external and internal subsets are used, the 
internal subset is considered to occur before the external subset.

This has the effect that entity and attribute-list declarations in the
internal subset take precedence over those in the external subset.
</P>

 


<H3><A NAME='sec-rmd'>2.9 Standalone Document Declaration</a></h3>
<P>Markup declarations can affect the content of the document,
as passed from an <A 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 href='#dt-docent'>document entity</A>.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Standalone Document Declaration</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-SDDecl'></a>[32]&nbsp;</td><td align='right'><font><code>SDDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>
<a href='#NT-S'>S</A> 
'standalone' <a href='#NT-Eq'>Eq</A> 
(("'" ('yes' |&nbsp;'no') "'") |&nbsp;('"' ('yes' |&nbsp;'no') '"'))
</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#vc-check-rmd'>Standalone Document Declaration</A> ]</code></font></td></tr>

</table>
</td></tr></table>
<p></P>
<P>
In a standalone document declaration, the value "<CODE>yes</CODE>" indicates
that there 
are no markup declarations external to the <A href='#dt-docent'>document
entity</A> (either in the DTD external subset, or in an
external parameter entity referenced from the internal subset)
which affect the information passed from the XML processor to
the application.  
The value "<CODE>no</CODE>" 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 "<CODE>no</CODE>" 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>
<A NAME='vc-check-rmd'></A><P><b>Validity Constraint: 
Standalone Document Declaration</b><br>
The standalone document declaration must have
the value "<CODE>no</CODE>" if any external markup declarations
contain declarations of:<UL>
<LI>attributes with <A 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</LI>
<LI>entities (other than <CODE>amp</CODE>,
<CODE>lt</CODE>,
<CODE>gt</CODE>,
<CODE>apos</CODE>,
<CODE>quot</CODE>), 
if <A href='#dt-entref'>references</A> to those
entities appear in the document, or
</LI>
<LI>attributes with values subject to
<A href='#AVNormalize'>normalization</A>, where the
attribute appears in the document with a value which will
change as a result of normalization, or
</LI>
<LI>
element types with <A href='#dt-elemcontent'>element content</A>, 
if white space occurs
directly within any instance of those types.
</LI>
</UL>


<P>An example XML declaration with a standalone document declaration:</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;?xml&nbsp;version="1.0"&nbsp;standalone='yes'?&gt;</font></code></td></tr></table><p></P>



<H3><A NAME='sec-white-space'>2.10 White Space Handling</a></h3>

<P>In editing XML documents, it is often convenient to use "white space"
(spaces, tabs, and blank lines, denoted by the nonterminal 
<code><a href='#NT-S'>S</A></code> in this specification) 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 href='#dt-xml-proc'>XML processor</A> 
must always pass all characters in a document that are not
markup through to the application.   A <A href='#dt-validating'>
validating XML processor</A> must also inform the application
which  of these characters constitute white space appearing
in <A href='#dt-elemcontent'>element content</A>.
</P>
<P>A special <A href='#dt-attr'>attribute</A> 
named <code>xml:space</code> may be attached to an element
to signal an intention that in that element,
white space should be preserved by applications.
In valid documents, this attribute, like any other, must be 
<A href='#dt-attdecl'>declared</A> if it is used.
When declared, it must be given as an 
<A href='#dt-enumerated'>enumerated type</A> whose only
possible values are "<CODE>default</CODE>" and "<CODE>preserve</CODE>".
For example:</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&nbsp;&nbsp;&nbsp;&nbsp;&lt;!ATTLIST&nbsp;poem&nbsp;&nbsp;&nbsp;xml:space&nbsp;(default|preserve)&nbsp;'preserve'&gt;</font></code></td></tr></table><p></P>
<P>The value "<CODE>default</CODE>" signals that applications'
default white-space processing modes are acceptable for this element; the
value "<CODE>preserve</CODE>" indicates the intent that applications preserve
all the white space.
This declared intent is considered to apply to all elements within the content
of the element where it is specified, unless overriden with another instance
of the <code>xml:space</code> attribute.
</P>
<P>The <A 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>




<H3><A NAME='sec-line-ends'>2.11 End-of-Line Handling</a></h3>
<P>XML <A 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 href='#dt-app'>applications</A>,
wherever an external parsed entity or the literal entity value
of an internal parsed entity contains either the literal 
two-character sequence "#xD#xA" or a standalone literal
#xD, an <A href='#dt-xml-proc'>XML processor</A> must 
pass to the application the single character #xA.
(This behavior can 
conveniently be produced by normalizing all 
line breaks to #xA on input, before parsing.)
</P>



<H3><A NAME='sec-lang-tag'>2.12 Language Identification</a></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 href='#dt-attr'>attribute</A> named
<code>xml:lang</code> may be inserted in
documents to specify the 
language used in the contents and attribute values 
of any element in an XML document.
In valid documents, this attribute, like any other, must be 
<A href='#dt-attdecl'>declared</A> if it is used.
The values of the attribute are language identifiers as defined
by <A href='#RFC1766'>[IETF RFC 1766]</A>, "Tags for the Identification of Languages":
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Language Identification</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-LanguageID'></a>[33]&nbsp;</td><td align='right'><font><code>LanguageID</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-Langcode'>Langcode</A> 
('-' <a href='#NT-Subcode'>Subcode</A>)*</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Langcode'></a>[34]&nbsp;</td><td align='right'><font><code>Langcode</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-ISO639Code'>ISO639Code</A> |&nbsp;
<a href='#NT-IanaCode'>IanaCode</A> |&nbsp;
<a href='#NT-UserCode'>UserCode</A></code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-ISO639Code'></a>[35]&nbsp;</td><td align='right'><font><code>ISO639Code</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>([a-z] |&nbsp;[A-Z]) ([a-z] |&nbsp;[A-Z])</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-IanaCode'></a>[36]&nbsp;</td><td align='right'><font><code>IanaCode</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>('i' |&nbsp;'I') '-' ([a-z] |&nbsp;[A-Z])+</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-UserCode'></a>[37]&nbsp;</td><td align='right'><font><code>UserCode</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>('x' |&nbsp;'X') '-' ([a-z] |&nbsp;[A-Z])+</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Subcode'></a>[38]&nbsp;</td><td align='right'><font><code>Subcode</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>([a-z] |&nbsp;[A-Z])+</code></font></td></tr>
</table>
</td></tr></table>
<p>
The <code><a href='#NT-Langcode'>Langcode</A></code> may be any of the following:
<UL>
<LI>a two-letter language code as defined by 
<A href='#ISO639'>[ISO 639]</A>, "Codes
for the representation of names of languages"</LI>
<LI>a language identifier registered with the Internet
Assigned Numbers Authority <A href='#IANA'>[IANA]</A>; these begin with the 
prefix "<CODE>i-</CODE>" (or "<CODE>I-</CODE>")</LI>
<LI>a language identifier assigned by the user, or agreed on
between parties in private use; these must begin with the
prefix "<CODE>x-</CODE>" or "<CODE>X-</CODE>" in order to ensure that they do not conflict 
with names later standardized or registered with IANA</LI>
</UL>

<P>There may be any number of <code><a href='#NT-Subcode'>Subcode</A></code> segments; if
the first 
subcode segment exists and the Subcode consists of two 
letters, then it must be a country code from 
<A href='#ISO3166'>[ISO 3166]</A>, "Codes 
for the representation of names of countries."
If the first 
subcode consists of more than two letters, it must be
a subcode for the language in question registered with IANA,
unless the <code><a href='#NT-Langcode'>Langcode</A></code> begins with the prefix 
"<CODE>x-</CODE>" or
"<CODE>X-</CODE>". </P>
<P>It is customary to give the language code in lower case, and
the country code (if any) in upper case.
Note that these values, unlike other names in XML documents,
are case insensitive.</P>
<P>For example:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;p&nbsp;xml:lang="en"&gt;The&nbsp;quick&nbsp;brown&nbsp;fox&nbsp;jumps&nbsp;over&nbsp;the&nbsp;lazy&nbsp;dog.&lt;/p&gt;<BR>&lt;p&nbsp;xml:lang="en-GB"&gt;What&nbsp;colour&nbsp;is&nbsp;it?&lt;/p&gt;<BR>&lt;p&nbsp;xml:lang="en-US"&gt;What&nbsp;color&nbsp;is&nbsp;it?&lt;/p&gt;<BR>&lt;sp&nbsp;who="Faust"&nbsp;desc='leise'&nbsp;xml:lang="de"&gt;<BR>&nbsp;&nbsp;&lt;l&gt;Habe&nbsp;nun,&nbsp;ach!&nbsp;Philosophie,&lt;/l&gt;<BR>&nbsp;&nbsp;&lt;l&gt;Juristerei,&nbsp;und&nbsp;Medizin&lt;/l&gt;<BR>&nbsp;&nbsp;&lt;l&gt;und&nbsp;leider&nbsp;auch&nbsp;Theologie&lt;/l&gt;<BR>&nbsp;&nbsp;&lt;l&gt;durchaus&nbsp;studiert&nbsp;mit&nbsp;heißem&nbsp;Bemüh'n.&lt;/l&gt;<BR>&nbsp;&nbsp;&lt;/sp&gt;</font></code></td></tr></table><p></P>

<P>The intent declared with <code>xml:lang</code> is considered to apply to
all attributes and content of the element where it is specified,
unless overridden with an instance of <code>xml:lang</code>
on another element within that content.</P>

<P>A simple declaration for <code>xml:lang</code> might take
the form
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>xml:lang&nbsp;&nbsp;NMTOKEN&nbsp;&nbsp;#IMPLIED</font></code></td></tr></table><p>
but specific default values may also be given, if appropriate.  In a
collection of French poems for English students, with glosses and
notes in English, the xml:lang attribute might be declared this way:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&nbsp;&nbsp;&nbsp;&nbsp;&lt;!ATTLIST&nbsp;poem&nbsp;&nbsp;&nbsp;xml:lang&nbsp;NMTOKEN&nbsp;'fr'&gt;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;!ATTLIST&nbsp;gloss&nbsp;&nbsp;xml:lang&nbsp;NMTOKEN&nbsp;'en'&gt;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&lt;!ATTLIST&nbsp;note&nbsp;&nbsp;&nbsp;xml:lang&nbsp;NMTOKEN&nbsp;'en'&gt;</font></code></td></tr></table><p>
</P>




 


<H2><A NAME='sec-logical-struct'>3. Logical Structures</a></h2>
 
<P><a name='dt-element'></a>Each <A href='#dt-xml-doc'>XML document</A> contains one or more
<b>elements</b>, the boundaries of which are 
either delimited by <A href='#dt-stag'>start-tags</A> 
and <A href='#dt-etag'>end-tags</A>, or, for <A href='#dt-empty'>empty</A> elements, by an <A 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 href='#dt-attrname'>name</A> and a <A href='#dt-attrval'>value</A>.
</P>

<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>Element</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-element'></a>[39]&nbsp;</td><td align='right'><font><code>element</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-EmptyElemTag'>EmptyElemTag</A></code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;<a href='#NT-STag'>STag</A> <a href='#NT-content'>content</A> 
<a href='#NT-ETag'>ETag</A></code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#GIMatch'>Element Type Match</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#elementvalid'>Element Valid</A> ]</code></font></td>
</tr>
</table>
</td></tr></table>

<P>This specification does not constrain the semantics, use, or (beyond
syntax) names of the element types and attributes, except that names
beginning with a match to <CODE>(('X'|'x')('M'|'m')('L'|'l'))</CODE>
are reserved for standardization in this or future versions of this
specification.
</P>
<A NAME='GIMatch'></A><P><b>Well-Formedness Constraint: 
Element Type Match</b><br>

The <code><a href='#NT-Name'>Name</A></code> in an element's end-tag must match 
the element type in
the start-tag.

</P>
<A NAME='elementvalid'></A><P><b>Validity Constraint: 
Element Valid</b><br>
An element is
valid if
there is a declaration matching 
<code><a href='#NT-elementdecl'>elementdecl</A></code> where the
<code><a href='#NT-Name'>Name</A></code> matches the element type, and
one of the following holds:
<OL>
<LI>The declaration matches <code>EMPTY</code> and the element has no 
<A href='#dt-content'>content</A>.</LI>
<LI>The declaration matches <code><a href='#NT-children'>children</A></code> and
the sequence of 
<A href='#dt-parentchild'>child elements</A>
belongs to the language generated by the regular expression in
the content model, with optional white space (characters 
matching the nonterminal <code><a href='#NT-S'>S</A></code>) between each pair
of child elements.</LI>
<LI>The declaration matches <code><a href='#NT-Mixed'>Mixed</A></code> and 
the content consists of <A href='#dt-chardata'>character 
data</A> and <A href='#dt-parentchild'>child elements</A>
whose types match names in the content model.</LI>
<LI>The declaration matches <code>ANY</code>, and the types
of any <A href='#dt-parentchild'>child elements</A> have
been declared.</LI>
</OL>



<H3><A NAME='sec-starttags'>3.1 Start-Tags, End-Tags, and Empty-Element Tags</a></h3>
 
<P><a name='dt-stag'></a>The beginning of every
non-empty XML element is marked by a <b>start-tag</b>.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Start-tag</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-STag'></a>[40]&nbsp;</td><td align='right'><font><code>STag</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;' <a href='#NT-Name'>Name</A> 
(<a href='#NT-S'>S</A> <a href='#NT-Attribute'>Attribute</A>)* 
<a href='#NT-S'>S</A>? '&gt;'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#uniqattspec'>Unique Att Spec</A> ]</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-Attribute'></a>[41]&nbsp;</td><td align='right'><font><code>Attribute</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-Name'>Name</A> <a href='#NT-Eq'>Eq</A> 
<a href='#NT-AttValue'>AttValue</A></code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#ValueType'>Attribute Value Type</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#NoExternalRefs'>No External Entity References</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#CleanAttrVals'>No &lt; in Attribute Values</A> ]</code></font></td></tr>

</table>
</td></tr></table>
<p>
The <code><a href='#NT-Name'>Name</A></code> in
the start- and end-tags gives the 
element's <b>type</b>.
<a name='dt-attr'></a>
The <code><a href='#NT-Name'>Name</A></code>-<code><a href='#NT-AttValue'>AttValue</A></code> pairs are
referred to as 
the <b>attribute specifications</b> of the element,
<a name='dt-attrname'></a>with the 
<code><a href='#NT-Name'>Name</A></code> in each pair
referred to as the <b>attribute name</b> and
<a name='dt-attrval'></a>the content of the
<code><a href='#NT-AttValue'>AttValue</A></code> (the text between the
<CODE>'</CODE> or <CODE>"</CODE> delimiters)
as the <b>attribute value</b>.
</P>
<A NAME='uniqattspec'></A><P><b>Well-Formedness Constraint: 
Unique Att Spec</b><br>

No attribute name may appear more than once in the same start-tag
or empty-element tag.

</P>
<A NAME='ValueType'></A><P><b>Validity Constraint: 
Attribute Value Type</b><br>

The attribute must have been declared; the value must be of the type 
declared for it.
(For attribute types, see "<A href='#attdecls'>3.3&nbsp;Attribute-List Declarations</A>".)

</P>
<A NAME='NoExternalRefs'></A><P><b>Well-Formedness Constraint: 
No External Entity References</b><br>

Attribute values cannot contain direct or indirect entity references 
to external entities.

</P>
<A NAME='CleanAttrVals'></A><P><b>Well-Formedness Constraint: 
No <CODE>&lt;</CODE> in Attribute Values</b><br>
The <A href='#dt-repltext'>replacement text</A> of any entity
referred to directly or indirectly in an attribute
value (other than "<CODE>&amp;lt;</CODE>") must not contain
a <CODE>&lt;</CODE>.
</P>
<P>An example of a start-tag:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;termdef&nbsp;id="dt-dog"&nbsp;term="dog"&gt;</font></code></td></tr></table><p></P>
<P><a name='dt-etag'></a>The end of every element 
that begins with a start-tag must
be marked by an <b>end-tag</b>
containing a name that echoes the element's type as given in the
start-tag:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
End-tag</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-ETag'></a>[42]&nbsp;</td><td align='right'><font><code>ETag</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;/' <a href='#NT-Name'>Name</A> 
<a href='#NT-S'>S</A>? '&gt;'</code></font></td></tr>

</table>
</td></tr></table>
<p>
</P>
<P>An example of an end-tag:</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;/termdef&gt;</font></code></td></tr></table><p></P>
<P><a name='dt-content'></a>The 
<A href='#dt-text'>text</A> between the start-tag and
end-tag is called the element's
<b>content</b>:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Content of Elements</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-content'></a>[43]&nbsp;</td><td align='right'><font><code>content</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>(<a href='#NT-element'>element</A> |&nbsp;<a href='#NT-CharData'>CharData</A> 
|&nbsp;<a href='#NT-Reference'>Reference</A> |&nbsp;<a href='#NT-CDSect'>CDSect</A> 
|&nbsp;<a href='#NT-PI'>PI</A> |&nbsp;<a href='#NT-Comment'>Comment</A>)*</code></font></td>
</tr>

</table>
</td></tr></table>
<p>
</P>
<P><a name='dt-empty'></a>If an element is <b>empty</b>,
it must be represented either by a start-tag immediately followed
by an end-tag or by an empty-element tag.
<a name='dt-eetag'></a>An 
<b>empty-element tag</b> takes a special form:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Tags for Empty Elements</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-EmptyElemTag'></a>[44]&nbsp;</td><td align='right'><font><code>EmptyElemTag</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;' <a href='#NT-Name'>Name</A> (<a href='#NT-S'>S</A> 
<a href='#NT-Attribute'>Attribute</A>)* <a href='#NT-S'>S</A>? 
'/&gt;'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#uniqattspec'>Unique Att Spec</A> ]</code></font></td>
</tr>

</table>
</td></tr></table>
<p>
</P>
<P>Empty-element tags may be used for any element which has no
content, whether or not it is declared using the keyword
<code>EMPTY</code>.
<A href='#dt-interop'>For interoperability</A>, the empty-element
tag must be used, and can only be used, for elements which are
<A href='#dt-eldecl'>declared</A> <code>EMPTY</code>.</P>
<P>Examples of empty elements:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;IMG&nbsp;align="left"<BR>&nbsp;src="http://www.w3.org/Icons/WWW/w3c_home"&nbsp;/&gt;<BR>&lt;br&gt;&lt;/br&gt;<BR>&lt;br/&gt;</font></code></td></tr></table><p></P>

 


<H3><A NAME='elemdecls'>3.2 Element Type Declarations</a></h3>
 
<P>The <A href='#dt-element'>element</A> structure of an
<A href='#dt-xml-doc'>XML document</A> may, for 
<A href='#dt-valid'>validation</A> purposes, 
be constrained
using element type and attribute-list declarations.
An element type declaration constrains the element's
<A href='#dt-content'>content</A>.
</P>

<P>Element type declarations often constrain which element types can
appear as <A href='#dt-parentchild'>children</A> of the element.
At user option, an XML processor may issue a warning
when a declaration mentions an element type for which no declaration
is provided, but this is not an error.</P>
<P><a name='dt-eldecl'></a>An <b>element
type declaration</b> takes the form:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Element Type Declaration</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-elementdecl'></a>[45]&nbsp;</td><td align='right'><font><code>elementdecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;!ELEMENT' <a href='#NT-S'>S</A> 
<a href='#NT-Name'>Name</A> 
<a href='#NT-S'>S</A> 
<a href='#NT-contentspec'>contentspec</A>
<a href='#NT-S'>S</A>? '&gt;'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#EDUnique'>Unique Element Type Declaration</A> ]</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-contentspec'></a>[46]&nbsp;</td><td align='right'><font><code>contentspec</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'EMPTY' 
|&nbsp;'ANY' 
|&nbsp;<a href='#NT-Mixed'>Mixed</A> 
|&nbsp;<a href='#NT-children'>children</A>
</code></font></td>
</tr>

</table>
</td></tr></table>
<p>
where the <code><a href='#NT-Name'>Name</A></code> gives the element type 
being declared.
</P>

<A NAME='EDUnique'></A><P><b>Validity Constraint: 
Unique Element Type Declaration</b><br>

No element type may be declared more than once.

</P>

<P>Examples of element type declarations:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ELEMENT&nbsp;br&nbsp;EMPTY&gt;<BR>&lt;!ELEMENT&nbsp;p&nbsp;(#PCDATA|emph)*&nbsp;&gt;<BR>&lt;!ELEMENT&nbsp;%name.para;&nbsp;%content.para;&nbsp;&gt;<BR>&lt;!ELEMENT&nbsp;container&nbsp;ANY&gt;</font></code></td></tr></table><p></P>
 


<H4><A NAME='sec-element-content'>3.2.1 Element Content</a></h4>
 
<P><a name='dt-elemcontent'></a>An element <A href='#dt-stag'>type</A> has
<b>element content</b> when elements of that
type must contain only <A href='#dt-parentchild'>child</A> 
elements (no character data), optionally separated by 
white space (characters matching the nonterminal 
<code><a href='#NT-S'>S</A></code>).

In this case, the
constraint includes a content model, 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 (<code><a href='#NT-cp'>cp</A></code>s), which consist of names, 
choice lists of content particles, or
sequence lists of content particles:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Element-content Models</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-children'></a>[47]&nbsp;</td><td align='right'><font><code>children</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>(<a href='#NT-choice'>choice</A> 
|&nbsp;<a href='#NT-seq'>seq</A>) 
('?' |&nbsp;'*' |&nbsp;'+')?</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-cp'></a>[48]&nbsp;</td><td align='right'><font><code>cp</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>(<a href='#NT-Name'>Name</A> 
|&nbsp;<a href='#NT-choice'>choice</A> 
|&nbsp;<a href='#NT-seq'>seq</A>) 
('?' |&nbsp;'*' |&nbsp;'+')?</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-choice'></a>[49]&nbsp;</td><td align='right'><font><code>choice</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'(' <a href='#NT-S'>S</A>? cp 
( <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></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#vc-PEinGroup'>Proper Group/PE Nesting</A> ]</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-seq'></a>[50]&nbsp;</td><td align='right'><font><code>seq</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'(' <a href='#NT-S'>S</A>? cp 
( <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></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#vc-PEinGroup'>Proper Group/PE Nesting</A> ]</code></font></td></tr>


</table>
</td></tr></table>
<p>
where each <code><a href='#NT-Name'>Name</A></code> is the type of an element which may
appear as a <A href='#dt-parentchild'>child</A>.  
Any content
particle in a choice list may appear in the <A href='#dt-elemcontent'>element content</A> at the location where
the choice list appears in the grammar;
content particles occurring in a sequence list must each
appear in the <A href='#dt-elemcontent'>element content</A> in the
order given in the list.  
The optional character following a name or list governs
whether the element or the content particles in the list may occur one
or more (<CODE>+</CODE>), zero or more (<CODE>*</CODE>), or zero or 
one times (<CODE>?</CODE>).  
The absence of such an operator means that the element or content particle
must appear exactly once.
This syntax
and meaning are identical to those used in the productions in this
specification.</P>
<P>
The content of an element matches a content model if and only if it is
possible to trace out a path through the content model, obeying the
sequence, choice, and repetition operators and matching each element in
the content against an element type in the content model.  <A href='#dt-compat'>For compatibility</A>, it is an error
if an element in the document can
match more than one occurrence of an element type in the content model.
For more information, see "<A href='#determinism'>E.&nbsp;Deterministic Content Models</A>".


</P>
<A NAME='vc-PEinGroup'></A><P><b>Validity Constraint: 
Proper Group/PE Nesting</b><br>
Parameter-entity 
<A href='#dt-repltext'>replacement text</A> must be properly nested
with parenthetized groups.
That is to say, if either of the opening or closing parentheses
in a <code><a href='#NT-choice'>choice</A></code>, <code><a href='#NT-seq'>seq</A></code>, or
<code><a href='#NT-Mixed'>Mixed</A></code> construct 
is contained in the replacement text for a 
<A href='#dt-PERef'>parameter entity</A>,
both must be contained in the same replacement text.
<A href='#dt-interop'>For interoperability</A>, 
if a parameter-entity reference appears in a 
<code><a href='#NT-choice'>choice</A></code>, <code><a href='#NT-seq'>seq</A></code>, or
<code><a href='#NT-Mixed'>Mixed</A></code> construct, its replacement text
should not be empty, and 
neither the first nor last non-blank
character of the replacement text should be a connector 
(<CODE>|</CODE> or <CODE>,</CODE>).

</P>
<P>Examples of element-content models:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ELEMENT&nbsp;spec&nbsp;(front,&nbsp;body,&nbsp;back?)&gt;<BR>&lt;!ELEMENT&nbsp;div1&nbsp;(head,&nbsp;(p&nbsp;|&nbsp;list&nbsp;|&nbsp;note)*,&nbsp;div2*)&gt;<BR>&lt;!ELEMENT&nbsp;dictionary-body&nbsp;(%div.mix;&nbsp;|&nbsp;%dict.mix;)*&gt;</font></code></td></tr></table><p></P>




<H4><A NAME='sec-mixed-content'>3.2.2 Mixed Content</a></h4>
 
<P><a name='dt-mixed'></a>An element 
<A href='#dt-stag'>type</A> has 
<b>mixed content</b> when elements of that type may contain
character data, optionally interspersed with
<A 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>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Mixed-content Declaration</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-Mixed'></a>[51]&nbsp;</td><td align='right'><font><code>Mixed</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><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></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;'(' <a href='#NT-S'>S</A>? '#PCDATA' <a href='#NT-S'>S</A>? ')'
</code></font></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#vc-PEinGroup'>Proper Group/PE Nesting</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#vc-MixedChildrenUnique'>No Duplicate Types</A> ]</code></font></td>
</tr>


</table>
</td></tr></table>
<p>
where the <code><a href='#NT-Name'>Name</A></code>s give the types of elements
that may appear as children.
</P>
<A NAME='vc-MixedChildrenUnique'></A><P><b>Validity Constraint: 
No Duplicate Types</b><br>
The same name must not appear more than once in a single mixed-content
declaration.
</P>
<P>Examples of mixed content declarations:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ELEMENT&nbsp;p&nbsp;(#PCDATA|a|ul|b|i|em)*&gt;<BR>&lt;!ELEMENT&nbsp;p&nbsp;(#PCDATA&nbsp;|&nbsp;%font;&nbsp;|&nbsp;%phrase;&nbsp;|&nbsp;%special;&nbsp;|&nbsp;%form;)*&nbsp;&gt;<BR>&lt;!ELEMENT&nbsp;b&nbsp;(#PCDATA)&gt;</font></code></td></tr></table><p></P>


 


<H3><A NAME='attdecls'>3.3 Attribute-List Declarations</a></h3>
 
<P><A href='#dt-attr'>Attributes</A> are used to associate
name-value pairs with <A href='#dt-element'>elements</A>.
Attribute specifications may appear only within <A href='#dt-stag'>start-tags</A>
and <A href='#dt-eetag'>empty-element tags</A>; 
thus, the productions used to
recognize them appear in "<A href='#sec-starttags'>3.1&nbsp;Start-Tags, End-Tags, and Empty-Element Tags</A>".  
Attribute-list
declarations may be used:
<UL>
<LI>To define the set of attributes pertaining to a given
element type.</LI>
<LI>To establish type constraints for these
attributes.</LI>
<LI>To provide <A href='#dt-default'>default values</A>
for attributes.</LI>
</UL>


<P><a name='dt-attdecl'></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>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Attribute-list Declaration</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-AttlistDecl'></a>[52]&nbsp;</td><td align='right'><font><code>AttlistDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;!ATTLIST' <a href='#NT-S'>S</A> 
<a href='#NT-Name'>Name</A> 
<a href='#NT-AttDef'>AttDef</A>*
<a href='#NT-S'>S</A>? '&gt;'</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-AttDef'></a>[53]&nbsp;</td><td align='right'><font><code>AttDef</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><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></font></td>
</tr>
</table>
</td></tr></table>
<p>
The <code><a href='#NT-Name'>Name</A></code> in the
<code><a href='#NT-AttlistDecl'>AttlistDecl</A></code> rule is the type of an element.  At
user option, an XML processor may issue a warning if attributes are
declared for an element type not itself declared, but this is not an
error.  The <code><a href='#NT-Name'>Name</A></code> in the 
<code><a href='#NT-AttDef'>AttDef</A></code> rule is
the name of the attribute.</P>
<P>
When more than one <code><a href='#NT-AttlistDecl'>AttlistDecl</A></code> 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 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, and at least one attribute definition
in each attribute-list declaration.
For interoperability, an XML processor may at user option
issue a warning when more than one attribute-list declaration is
provided for a given element type, or more than one attribute definition
is provided 
for a given attribute, but this is not an error.
</P>



<H4><A NAME='sec-attribute-types'>3.3.1 Attribute Types</a></h4>
 
<P>XML attribute types are of three kinds:  a string type, a
set of tokenized types, and enumerated types.  The string type may take
any literal string as a value; the tokenized types have varying lexical
and semantic constraints, as noted:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Attribute Types</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-AttType'></a>[54]&nbsp;</td><td align='right'><font><code>AttType</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-StringType'>StringType</A> 
|&nbsp;<a href='#NT-TokenizedType'>TokenizedType</A> 
|&nbsp;<a href='#NT-EnumeratedType'>EnumeratedType</A>
</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-StringType'></a>[55]&nbsp;</td><td align='right'><font><code>StringType</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'CDATA'</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-TokenizedType'></a>[56]&nbsp;</td><td align='right'><font><code>TokenizedType</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'ID'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#id'>ID</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#one-id-per-el'>One ID per Element Type</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#id-default'>ID Attribute Default</A> ]</code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;'IDREF'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#idref'>IDREF</A> ]</code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;'IDREFS'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#idref'>IDREF</A> ]</code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;'ENTITY'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#entname'>Entity Name</A> ]</code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;'ENTITIES'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#entname'>Entity Name</A> ]</code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;'NMTOKEN'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#nmtok'>Name Token</A> ]</code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;'NMTOKENS'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#nmtok'>Name Token</A> ]</code></font></td></tr>

</table>
</td></tr></table>
<p>
</P>
<A NAME='id'></A><P><b>Validity Constraint: 
ID</b><br>

Values of type <code>ID</code> must match the 
<code><a href='#NT-Name'>Name</A></code> production.  
A name must not appear more than once in
an XML document as a value of this type; i.e., ID values must uniquely
identify the elements which bear them.   

</P>
<A NAME='one-id-per-el'></A><P><b>Validity Constraint: 
One ID per Element Type</b><br>
No element type may have more than one ID attribute specified.
</P>
<A NAME='id-default'></A><P><b>Validity Constraint: 
ID Attribute Default</b><br>
An ID attribute must have a declared default of <code>#IMPLIED</code> or
<code>#REQUIRED</code>.
</P>
<A NAME='idref'></A><P><b>Validity Constraint: 
IDREF</b><br>

Values of type <code>IDREF</code> must match
the <code><a href='#NT-Name'>Name</A></code> production, and
values of type <code>IDREFS</code> must match
<code><a href='#NT-Names'>Names</A></code>; 
each <code><a href='#NT-Name'>Name</A></code> must match the value of an ID attribute on 
some element in the XML document; i.e. <code>IDREF</code> values must 
match the value of some ID attribute. 

</P>
<A NAME='entname'></A><P><b>Validity Constraint: 
Entity Name</b><br>

Values of type <code>ENTITY</code> 
must match the <code><a href='#NT-Name'>Name</A></code> production,
values of type <code>ENTITIES</code> must match
<code><a href='#NT-Names'>Names</A></code>;
each <code><a href='#NT-Name'>Name</A></code> must 
match the
name of an <A href='#dt-unparsed'>unparsed entity</A> declared in the
<A href='#dt-doctype'>DTD</A>.

</P>
<A NAME='nmtok'></A><P><b>Validity Constraint: 
Name Token</b><br>

Values of type <code>NMTOKEN</code> must match the
<code><a href='#NT-Nmtoken'>Nmtoken</A></code> production;
values of type <code>NMTOKENS</code> must 
match <A href='#NT-Nmtokens'>Nmtokens</A>.

</P>

<P><a name='dt-enumerated'></a><b>Enumerated attributes</b> can take one 
of a list of values provided in the declaration. There are two
kinds of enumerated types:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Enumerated Attribute Types</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-EnumeratedType'></a>[57]&nbsp;</td><td align='right'><font><code>EnumeratedType</code></font></td> 
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-NotationType'>NotationType</A> 
|&nbsp;<a href='#NT-Enumeration'>Enumeration</A>
</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-NotationType'></a>[58]&nbsp;</td><td align='right'><font><code>NotationType</code></font></td> 
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><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></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#notatn'>Notation Attributes</A> ]</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Enumeration'></a>[59]&nbsp;</td><td align='right'><font><code>Enumeration</code></font></td> 
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><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></font></td> 
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#enum'>Enumeration</A> ]</code></font></td></tr>
</table>
</td></tr></table>
<p>
A <code>NOTATION</code> attribute identifies a 
<A 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>

<A NAME='notatn'></A><P><b>Validity Constraint: 
Notation Attributes</b><br>

Values of this type must match
one of the <A href='#Notations'>notation</A> names included in
the declaration; all notation names in the declaration must
be declared.

</P>
<A NAME='enum'></A><P><b>Validity Constraint: 
Enumeration</b><br>

Values of this type
must match one of the <code><a href='#NT-Nmtoken'>Nmtoken</A></code> tokens in the
declaration. 

</P>
<P><A href='#dt-interop'>For interoperability,</A> the same
<code><a href='#NT-Nmtoken'>Nmtoken</A></code> should not occur more than once in the
enumerated attribute types of a single element type.
</P>




<H4><A NAME='sec-attr-defaults'>3.3.2 Attribute Defaults</a></h4>
 
<P>An <A href='#dt-attdecl'>attribute declaration</A> provides
information on whether
the attribute's presence is required, and if not, how an XML processor should
react if a declared attribute is absent in a document.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Attribute Defaults</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-DefaultDecl'></a>[60]&nbsp;</td><td align='right'><font><code>DefaultDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'#REQUIRED' 
| '#IMPLIED' </code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;(('#FIXED' S)? <a href='#NT-AttValue'>AttValue</A>)</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#RequiredAttr'>Required Attribute</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#defattrvalid'>Attribute Default Legal</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#CleanAttrVals'>No &lt; in Attribute Values</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#FixedAttr'>Fixed Attribute Default</A> ]</code></font></td>
</tr>

</table>
</td></tr></table>
<p>

</P>
<P>In an attribute declaration, <code>#REQUIRED</code> means that the
attribute must always be provided, <code>#IMPLIED</code> that no default 
value is provided.

<a name='dt-default'></a>If the 
declaration
is neither <code>#REQUIRED</code> nor <code>#IMPLIED</code>, then the
<code><a href='#NT-AttValue'>AttValue</A></code> value contains the declared
<b>default</b> value; the <code>#FIXED</code> keyword states that
the attribute must always have the default value.
If a default value
is declared, when an XML processor encounters an omitted attribute, it
is to behave as though the attribute were present with 
the declared default value.</P>
<A NAME='RequiredAttr'></A><P><b>Validity Constraint: 
Required Attribute</b><br>
If the default declaration is the keyword <code>#REQUIRED</code>, then
the attribute must be specified for
all elements of the type in the attribute-list declaration.
</P>
<A NAME='defattrvalid'></A><P><b>Validity Constraint: 
Attribute Default Legal</b><br>

The declared
default value must meet the lexical constraints of the declared attribute type.

</P>
<A NAME='FixedAttr'></A><P><b>Validity Constraint: 
Fixed Attribute Default</b><br>
If an attribute has a default value declared with the 
<code>#FIXED</code> keyword, instances of that attribute must
match the default value.
</P>

<P>Examples of attribute-list declarations:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ATTLIST&nbsp;termdef<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;id&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ID&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;#REQUIRED<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;name&nbsp;&nbsp;&nbsp;&nbsp;CDATA&nbsp;&nbsp;&nbsp;#IMPLIED&gt;<BR>&lt;!ATTLIST&nbsp;list<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;type&nbsp;&nbsp;&nbsp;&nbsp;(bullets|ordered|glossary)&nbsp;&nbsp;"ordered"&gt;<BR>&lt;!ATTLIST&nbsp;form<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;method&nbsp;&nbsp;CDATA&nbsp;&nbsp;&nbsp;#FIXED&nbsp;"POST"&gt;</font></code></td></tr></table><p></P>



<H4><A NAME='AVNormalize'>3.3.3 Attribute-Value Normalization</a></h4>
<P>Before the value of an attribute is passed to the application
or checked for validity, the
XML processor must normalize it as follows:
<UL>
<LI>a character reference is processed by appending the referenced    
character to the attribute value</LI>
<LI>an entity reference is processed by recursively processing the
replacement text of the entity</LI>
<LI>a whitespace character (#x20, #xD, #xA, #x9) is processed by
appending #x20 to the normalized value, except that only a single #x20
is appended for a "#xD#xA" sequence that is part of an external
parsed entity or the literal entity value of an internal parsed
entity</LI>
<LI>other characters are processed by appending them to the normalized
value
</LI></UL>


<P>If the declared value is not CDATA, then the XML processor must
further process the normalized attribute value by discarding any
leading and trailing space (#x20) characters, and by replacing
sequences of space (#x20) characters by a single space (#x20)
character.</P>
<P>
All attributes for which no declaration has been read should be treated
by a non-validating parser as if declared
<code>CDATA</code>.
</P>




<H3><A NAME='sec-condition-sect'>3.4 Conditional Sections</a></h3>
<P><a name='dt-cond-section'></a>
<b>Conditional sections</b> are portions of the
<A href='#dt-doctype'>document type declaration external subset</A>
which are 
included in, or excluded from, the logical structure of the DTD based on
the keyword which governs them.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Conditional Section</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-conditionalSect'></a>[61]&nbsp;</td><td align='right'><font><code>conditionalSect</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-includeSect'>includeSect</A>
|&nbsp;<a href='#NT-ignoreSect'>ignoreSect</A>
</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-includeSect'></a>[62]&nbsp;</td><td align='right'><font><code>includeSect</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;![' S? 'INCLUDE' S? '[' 

<a href='#NT-extSubsetDecl'>extSubsetDecl</A>
']]&gt;'
</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-ignoreSect'></a>[63]&nbsp;</td><td align='right'><font><code>ignoreSect</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;![' S? 'IGNORE' S? '[' 
<a href='#NT-ignoreSectContents'>ignoreSectContents</A>*
']]&gt;'</code></font></td>
</tr>

<tr valign='top'><td align='right'><a name='NT-ignoreSectContents'></a>[64]&nbsp;</td><td align='right'><font><code>ignoreSectContents</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-Ignore'>Ignore</A>
('&lt;![' <a href='#NT-ignoreSectContents'>ignoreSectContents</A> ']]&gt;' 
<a href='#NT-Ignore'>Ignore</A>)*</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Ignore'></a>[65]&nbsp;</td><td align='right'><font><code>Ignore</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-Char'>Char</A>* - 
(<a href='#NT-Char'>Char</A>* ('&lt;![' |&nbsp;']]&gt;') 
<a href='#NT-Char'>Char</A>*)
</code></font></td></tr>


</table>
</td></tr></table>
<p>
</P>
<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 <code>INCLUDE</code>, then the contents of the conditional
section are part of the DTD.
If the keyword of the conditional
section is <code>IGNORE</code>, then the contents of the conditional section are
not logically part of the DTD.
Note that for reliable parsing, the contents of even ignored
conditional sections must be read in order to
detect nested conditional sections and ensure that the end of the
outermost (ignored) conditional section is properly detected.
If a conditional section with a
keyword of <code>INCLUDE</code> occurs within a larger conditional
section with a keyword of <code>IGNORE</code>, both the outer and the
inner conditional sections are ignored.</P>
<P>If the keyword of the conditional section is a 
parameter-entity reference, the parameter entity must be replaced by its
content before the processor decides whether to
include or ignore the conditional section.</P>
<P>An example:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ENTITY&nbsp;%&nbsp;draft&nbsp;'INCLUDE'&nbsp;&gt;<BR>&lt;!ENTITY&nbsp;%&nbsp;final&nbsp;'IGNORE'&nbsp;&gt;<BR>&nbsp;<BR>&lt;![%draft;[<BR>&lt;!ELEMENT&nbsp;book&nbsp;(comments*,&nbsp;title,&nbsp;body,&nbsp;supplements?)&gt;<BR>]]&gt;<BR>&lt;![%final;[<BR>&lt;!ELEMENT&nbsp;book&nbsp;(title,&nbsp;body,&nbsp;supplements?)&gt;<BR>]]&gt;<BR></font></code></td></tr></table><p>
</P>



 



 


<H2><A NAME='sec-physical-struct'>4. Physical Structures</a></h2>
 
<P><a name='dt-entity'></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 document entity, see below, and 
the <A href='#dt-doctype'>external DTD subset</A>) 
identified by <b>name</b>.

Each XML document has one entity
called the <A href='#dt-docent'>document entity</A>, which serves
as the starting point for the <A 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'></a>A <b>parsed entity's</b>
contents are referred to as its 
<A href='#dt-repltext'>replacement text</A>;
this <A href='#dt-text'>text</A> is considered an
integral part of the document.</P>

<P><a name='dt-unparsed'></a>An 
<b>unparsed entity</b> 
is a resource whose contents may or may not be
<A href='#dt-text'>text</A>, and if text, may not be XML.
Each unparsed entity
has an associated <A 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 <code>ENTITY</code>
or <code>ENTITIES</code>
attributes.</P>
<P><a name='gen-entity'></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'></a>Parameter entities 
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>



<H3><A NAME='sec-references'>4.1 Character and Entity References</a></h3>
<P><a name='dt-charref'></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>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Character Reference</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-CharRef'></a>[66]&nbsp;</td><td align='right'><font><code>CharRef</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&amp;#' [0-9]+ ';' </code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;'&amp;#x' [0-9a-fA-F]+ ';'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#wf-Legalchar'>Legal Character</A> ]</code></font></td>
</tr>
</table>
</td></tr></table>
<p>
<A NAME='wf-Legalchar'></A><P><b>Well-Formedness Constraint: 
Legal Character</b><br>
Characters referred to using character references must
match the production for
<A href='#NT-Char'>Char</A>.
</P>
If the character reference begins with "<CODE>&amp;#x</CODE>", the digits and
letters up to the terminating <CODE>;</CODE> provide a hexadecimal
representation of the character's code point in ISO/IEC 10646.
If it begins just with "<CODE>&amp;#</CODE>", the digits up to the terminating
<CODE>;</CODE> provide a decimal representation of the character's 
code point.


<P><a name='dt-entref'></a>An <b>entity
reference</b> refers to the content of a named entity.
<a name='dt-GERef'></a>References to 
parsed general entities
use ampersand (<CODE>&amp;</CODE>) and semicolon (<CODE>;</CODE>) as
delimiters.
<a name='dt-PERef'></a>
<b>Parameter-entity references</b> use percent-sign (<CODE>%</CODE>) and
semicolon 
(<CODE>;</CODE>) as delimiters.
</P>

<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Entity Reference</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-Reference'></a>[67]&nbsp;</td><td align='right'><font><code>Reference</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-EntityRef'>EntityRef</A> 
|&nbsp;<a href='#NT-CharRef'>CharRef</A></code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-EntityRef'></a>[68]&nbsp;</td><td align='right'><font><code>EntityRef</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&amp;' <a href='#NT-Name'>Name</A> ';'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#wf-entdeclared'>Entity Declared</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#vc-entdeclared'>Entity Declared</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#textent'>Parsed Entity</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#norecursion'>No Recursion</A> ]</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-PEReference'></a>[69]&nbsp;</td><td align='right'><font><code>PEReference</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'%' <a href='#NT-Name'>Name</A> ';'</code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#vc-entdeclared'>Entity Declared</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#norecursion'>No Recursion</A> ]</code></font></td>
</tr><tr valign='top'><td></td><td></td><td></td><td></td><td align='center'><font><code> [ </code></font></td><td align='left'><font><code>WFC: <a href='#indtd'>In DTD</A> ]</code></font></td>
</tr>
</table>
</td></tr></table>


<A NAME='wf-entdeclared'></A><P><b>Well-Formedness Constraint: 
Entity Declared</b><br>
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>", 
the <code><a href='#NT-Name'>Name</A></code> given in the entity reference must 
<A href='#dt-match'>match</A> that in an 
<A href='#sec-entity-decl'>entity declaration</A>, 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 parameter entity must precede any reference to it.
Similarly, the declaration of a general entity must precede any
reference to it which appears in a default value in an attribute-list
declaration.
Note that if entities are declared in the external subset or in 
external parameter entities, a non-validating processor is 
<A href='#include-if-valid'>not obligated to</A> read
and process their declarations; for such documents, the rule that
an entity must be declared is a well-formedness constraint only
if <A href='#sec-rmd'>standalone='yes'</A>.
</P>
<A NAME='vc-entdeclared'></A><P><b>Validity Constraint: 
Entity Declared</b><br>
In a document with an external subset or external parameter
entities with "<CODE>standalone='no'</CODE>",
the <code><a href='#NT-Name'>Name</A></code> given in the entity reference must <A href='#dt-match'>match</A> that in an 
<A href='#sec-entity-decl'>entity declaration</A>.
For interoperability, valid documents should declare the entities 
<CODE>amp</CODE>,
<CODE>lt</CODE>,
<CODE>gt</CODE>,
<CODE>apos</CODE>,
<CODE>quot</CODE>, in the form
specified in "<A href='#sec-predefined-ent'>4.6&nbsp;Predefined Entities</A>".
The declaration of a parameter entity must precede any reference to it.
Similarly, the declaration of a general entity must precede any
reference to it which appears in a default value in an attribute-list
declaration.
</P>

<A NAME='textent'></A><P><b>Well-Formedness Constraint: 
Parsed Entity</b><br>

An entity reference must not contain the name of an <A href='#dt-unparsed'>unparsed entity</A>. Unparsed entities may be referred
to only in <A href='#dt-attrval'>attribute values</A> declared to
be of type <code>ENTITY</code> or <code>ENTITIES</code>.

</P>
<A NAME='norecursion'></A><P><b>Well-Formedness Constraint: 
No Recursion</b><br>

A parsed entity must not contain a recursive reference to itself,
either directly or indirectly.

</P>
<A NAME='indtd'></A><P><b>Well-Formedness Constraint: 
In DTD</b><br>

Parameter-entity references may only appear in the 
<A href='#dt-doctype'>DTD</A>.

</P>
<P>Examples of character and entity references:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>Type&nbsp;&lt;key&gt;less-than&lt;/key&gt;&nbsp;(&amp;#x3C;)&nbsp;to&nbsp;save&nbsp;options.<BR>This&nbsp;document&nbsp;was&nbsp;prepared&nbsp;on&nbsp;&amp;docdate;&nbsp;and<BR>is&nbsp;classified&nbsp;&amp;security-level;.</font></code></td></tr></table><p></P>
<P>Example of a parameter-entity reference:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!--&nbsp;declare&nbsp;the&nbsp;parameter&nbsp;entity&nbsp;"ISOLat2"...&nbsp;--&gt;<BR>&lt;!ENTITY&nbsp;%&nbsp;ISOLat2<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;SYSTEM&nbsp;"http://www.xml.com/iso/isolat2-xml.entities"&nbsp;&gt;<BR>&lt;!--&nbsp;...&nbsp;now&nbsp;reference&nbsp;it.&nbsp;--&gt;<BR>%ISOLat2;</font></code></td></tr></table><p></P>

 


<H3><A NAME='sec-entity-decl'>4.2 Entity Declarations</a></h3>
 
<P><a name='dt-entdecl'></a>
Entities are declared thus:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Entity Declaration</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-EntityDecl'></a>[70]&nbsp;</td><td align='right'><font><code>EntityDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-GEDecl'>GEDecl</A> |&nbsp;<a href='#NT-PEDecl'>PEDecl</A></code></font></td>

</tr>
<tr valign='top'><td align='right'><a name='NT-GEDecl'></a>[71]&nbsp;</td><td align='right'><font><code>GEDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;!ENTITY' <a href='#NT-S'>S</A> <a href='#NT-Name'>Name</A> 
<a href='#NT-S'>S</A> <a href='#NT-EntityDef'>EntityDef</A> 
<a href='#NT-S'>S</A>? '&gt;'</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-PEDecl'></a>[72]&nbsp;</td><td align='right'><font><code>PEDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;!ENTITY' <a href='#NT-S'>S</A> '%' <a href='#NT-S'>S</A> 
<a href='#NT-Name'>Name</A> <a href='#NT-S'>S</A> 
<a href='#NT-PEDef'>PEDef</A> <a href='#NT-S'>S</A>? '&gt;'</code></font></td>

</tr>
<tr valign='top'><td align='right'><a name='NT-EntityDef'></a>[73]&nbsp;</td><td align='right'><font><code>EntityDef</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-EntityValue'>EntityValue</A>
|&nbsp;(<a href='#NT-ExternalID'>ExternalID</A> 
<a href='#NT-NDataDecl'>NDataDecl</A>?)</code></font></td>

</tr>

<tr valign='top'><td align='right'><a name='NT-PEDef'></a>[74]&nbsp;</td><td align='right'><font><code>PEDef</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-EntityValue'>EntityValue</A> 
|&nbsp;<a href='#NT-ExternalID'>ExternalID</A></code></font></td></tr>

</table>
</td></tr></table>
<p>
The <code><a href='#NT-Name'>Name</A></code> identifies the entity in an
<A href='#dt-entref'>entity reference</A> or, in the case of an
unparsed entity, in the value of an <code>ENTITY</code> or <code>ENTITIES</code>
attribute.
If the same entity is declared more than once, the first declaration
encountered is binding; at user option, an XML processor may issue a
warning if entities are declared multiple times.
</P>



<H4><A NAME='sec-internal-ent'>4.2.1 Internal Entities</a></h4>
 
<P><a name='dt-internent'></a>If 
the entity definition is an 
<code><a href='#NT-EntityValue'>EntityValue</A></code>,  
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 href='#dt-litentval'>literal entity value</A> may be required to
produce the correct <A href='#dt-repltext'>replacement 
text</A>: see "<A href='#intern-replacement'>4.5&nbsp;Construction of Internal Entity Replacement Text</A>".
</P>
<P>An internal entity is a <A href='#dt-parsedent'>parsed
entity</A>.</P>
<P>Example of an internal entity declaration:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ENTITY&nbsp;Pub-Status&nbsp;"This&nbsp;is&nbsp;a&nbsp;pre-release&nbsp;of&nbsp;the<BR>&nbsp;specification."&gt;</font></code></td></tr></table><p></P>

 


<H4><A NAME='sec-external-ent'>4.2.2 External Entities</a></h4>
 
<P><a name='dt-extent'></a>If the entity is not
internal, it is an <b>external
entity</b>, declared as follows:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
External Entity Declaration</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-ExternalID'></a>[75]&nbsp;</td><td align='right'><font><code>ExternalID</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'SYSTEM' <a href='#NT-S'>S</A> 
<a href='#NT-SystemLiteral'>SystemLiteral</A></code></font></td>
</tr><tr valign='top'><td align='right'></td><td></td><td></td><td align='left'><font><code>|&nbsp;'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></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-NDataDecl'></a>[76]&nbsp;</td><td align='right'><font><code>NDataDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-S'>S</A> 'NDATA' <a href='#NT-S'>S</A> 
<a href='#NT-Name'>Name</A></code></font></td>
<td align='center'><font><code> [ </code></font></td><td align='left'><font><code>VC: <a href='#not-declared'>Notation Declared</A> ]</code></font></td></tr>
</table>
</td></tr></table>
<p>
If the <code><a href='#NT-NDataDecl'>NDataDecl</A></code> is present, this is a
general <A href='#dt-unparsed'>unparsed
entity</A>; otherwise it is a parsed entity.</P>
<A NAME='not-declared'></A><P><b>Validity Constraint: 
Notation Declared</b><br>

The <code><a href='#NT-Name'>Name</A></code> must match the declared name of a
<A href='#dt-notation'>notation</A>.

</P>
<P><a name='dt-sysid'></a>The
<code><a href='#NT-SystemLiteral'>SystemLiteral</A></code> 
is called the entity's <b>system identifier</b>. It is a URI,
which may be used to retrieve the entity.
Note that the hash mark (<CODE>#</CODE>) and fragment identifier 
frequently used with URIs are not, formally, part of the URI itself; 
an XML processor may signal an error if a fragment identifier is 
given as part of a system identifier.
Unless otherwise provided by information outside the scope of this
specification (e.g. a special XML element type defined by a particular
DTD, or a processing instruction defined by a particular application
specification), relative URIs are relative to the location of the
resource within which the entity declaration occurs.
A URI might thus be relative to the 
<A href='#dt-docent'>document entity</A>, to the entity
containing the <A href='#dt-doctype'>external DTD subset</A>, 
or to some other <A href='#dt-extent'>external parameter entity</A>.
</P>
<P>An XML processor should handle a non-ASCII character in a URI by
representing the character in UTF-8 as one or more bytes, and then 
escaping these bytes with the URI escaping mechanism (i.e., by
converting each byte to %HH, where HH is the hexadecimal notation of the
byte value).</P>
<P><a name='dt-pubid'></a>
In addition to a system identifier, an external identifier may
include a <b>public identifier</b>.  
An XML processor attempting to retrieve the entity's content may use the public
identifier to try to generate an alternative URI.  If the processor
is unable to do so, it must use the URI specified in the system
literal.  Before a match is attempted, all strings
of white space in the public identifier must be normalized to single space characters (#x20),
and leading and trailing white space must be removed.</P>
<P>Examples of external entity declarations:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ENTITY&nbsp;open-hatch<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;SYSTEM&nbsp;"http://www.textuality.com/boilerplate/OpenHatch.xml"&gt;<BR>&lt;!ENTITY&nbsp;open-hatch<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;PUBLIC&nbsp;"-//Textuality//TEXT&nbsp;Standard&nbsp;open-hatch&nbsp;boilerplate//EN"<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"http://www.textuality.com/boilerplate/OpenHatch.xml"&gt;<BR>&lt;!ENTITY&nbsp;hatch-pic<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;SYSTEM&nbsp;"../grafix/OpenHatch.gif"<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;NDATA&nbsp;gif&nbsp;&gt;</font></code></td></tr></table><p></P>

 




<H3><A NAME='TextEntities'>4.3 Parsed Entities</a></h3>


<H4><A NAME='sec-TextDecl'>4.3.1 The Text Declaration</a></h4>
<P>External parsed entities may each begin with a <b>text
declaration</b>. 
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Text Declaration</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-TextDecl'></a>[77]&nbsp;</td><td align='right'><font><code>TextDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;?xml' 
<a href='#NT-VersionInfo'>VersionInfo</A>?
<a href='#NT-EncodingDecl'>EncodingDecl</A>
<a href='#NT-S'>S</A>? '?&gt;'</code></font></td>
</tr>

</table>
</td></tr></table>
<p>
</P>
<P>The text declaration must be provided literally, not
by reference to a parsed entity.
No text declaration may appear at any position other than the beginning of
an external parsed entity.</P>



<H4><A NAME='wf-entities'>4.3.2 Well-Formed Parsed Entities</a></h4>
<P>The document entity is well-formed if it matches the production labeled
<code><a href='#NT-document'>document</A></code>.
An external general 
parsed entity is well-formed if it matches the production labeled
<code><a href='#NT-extParsedEnt'>extParsedEnt</A></code>.
An external parameter
entity is well-formed if it matches the production labeled
<code><a href='#NT-extPE'>extPE</A></code>.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Well-Formed External Parsed Entity</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-extParsedEnt'></a>[78]&nbsp;</td><td align='right'><font><code>extParsedEnt</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-TextDecl'>TextDecl</A>? 
<a href='#NT-content'>content</A></code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-extPE'></a>[79]&nbsp;</td><td align='right'><font><code>extPE</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-TextDecl'>TextDecl</A>? 
<a href='#NT-extSubsetDecl'>extSubsetDecl</A></code></font></td>
</tr>
</table>
</td></tr></table>
<p>
An internal general parsed entity is well-formed if its replacement text 
matches the production labeled
<code><a href='#NT-content'>content</A></code>.
All internal parameter entities are well-formed by definition.
</P>
<P>A consequence of well-formedness in entities is that the logical 
and physical structures in an XML document are properly nested; no 
<A href='#dt-stag'>start-tag</A>,
<A href='#dt-etag'>end-tag</A>,
<A href='#dt-empty'>empty-element tag</A>,
<A href='#dt-element'>element</A>, 
<A href='#dt-comment'>comment</A>, 
<A href='#dt-pi'>processing instruction</A>, 
<A href='#dt-charref'>character
reference</A>, or
<A href='#dt-entref'>entity reference</A> 
can begin in one entity and end in another.</P>



<H4><A NAME='charencoding'>4.3.3 Character Encoding in Entities</a></h4>
 
<P>Each external parsed entity in an XML document may use a different
encoding for its characters. All XML processors must be able to read
entities in either UTF-8 or UTF-16. 

</P>
<P>Entities encoded in UTF-16 must
begin with the Byte Order Mark described by ISO/IEC 10646 Annex E and
Unicode Appendix B (the ZERO WIDTH NO-BREAK SPACE character, #xFEFF).
This is an encoding signature, not part of either the markup or the
character data of the XML document.
XML processors must be able to use this character to
differentiate between UTF-8 and UTF-16 encoded documents.</P>
<P>Although an XML processor is required to read only entities in
the UTF-8 and UTF-16 encodings, it is recognized that other encodings are
used around the world, and it may be desired for XML processors
to read entities that use them.
Parsed entities which are stored in an encoding other than
UTF-8 or UTF-16 must begin with a <A href='#TextDecl'>text
declaration</A> containing an encoding declaration:
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Encoding Declaration</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-EncodingDecl'></a>[80]&nbsp;</td><td align='right'><font><code>EncodingDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-S'>S</A>
'encoding' <a href='#NT-Eq'>Eq</A> 
('"' <a href='#NT-EncName'>EncName</A> '"' |&nbsp;
"'" <a href='#NT-EncName'>EncName</A> "'" )
</code></font></td>
</tr>
<tr valign='top'><td align='right'><a name='NT-EncName'></a>[81]&nbsp;</td><td align='right'><font><code>EncName</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>[A-Za-z] ([A-Za-z0-9._] |&nbsp;'-')*</code></font></td>
<td align='center'><font><code> /* </code></font></td><td align='left'><font><code>Encoding name contains only Latin characters */</code></font></td>
</tr>
</table>
</td></tr></table>
<p>
In the <A href='#dt-docent'>document entity</A>, the encoding
declaration is part of the <A href='#dt-xmldecl'>XML declaration</A>.
The <code><a href='#NT-EncName'>EncName</A></code> is the name of the encoding used.
</P>

<P>In an encoding declaration, the values
"<CODE>UTF-8</CODE>",
"<CODE>UTF-16</CODE>",
"<CODE>ISO-10646-UCS-2</CODE>", and
"<CODE>ISO-10646-UCS-4</CODE>" should be 
used for the various encodings and transformations of Unicode /
ISO/IEC 10646, the values
"<CODE>ISO-8859-1</CODE>",
"<CODE>ISO-8859-2</CODE>", ...
"<CODE>ISO-8859-9</CODE>" should be used for the parts of ISO 8859, and
the values
"<CODE>ISO-2022-JP</CODE>",
"<CODE>Shift_JIS</CODE>", and
"<CODE>EUC-JP</CODE>"
should be used for the various encoded forms of JIS X-0208-1997.  XML
processors may recognize other encodings; it is recommended that
character encodings registered (as <EM>charset</EM>s) 
with the Internet Assigned Numbers
Authority <A href='#IANA'>[IANA]</A>, other than those just listed, should be
referred to
using their registered names.
Note that these registered names are defined to be 
case-insensitive, so processors wishing to match against them 
should do so in a case-insensitive
way.</P>
<P>In the absence of information provided by an external
transport protocol (e.g. HTTP or MIME), 
it is an <A href='#dt-error'>error</A> for an entity including
an encoding declaration to be presented to the XML processor 
in an encoding other than that named in the declaration, 
for an encoding declaration to occur other than at the beginning 
of an external entity, 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 href='#dt-fatal'>fatal error</A> when an XML processor
encounters an entity with an encoding that it is unable to process.</P>
<P>Examples of encoding declarations:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;?xml&nbsp;encoding='UTF-8'?&gt;<BR>&lt;?xml&nbsp;encoding='EUC-JP'?&gt;</font></code></td></tr></table><p></P>




<H3><A NAME='entproc'>4.4 XML Processor Treatment of Entities and References</a></h3>
<P>The table below summarizes the contexts in which character references,
entity references, and invocations of unparsed entities might appear and the
required behavior of an <A href='#dt-xml-proc'>XML processor</A> in
each case.  
The labels in the leftmost column describe the recognition context:
<DL>
<DT><B>Reference in Content</B></DT>
<DD>as a reference
anywhere after the <A href='#dt-stag'>start-tag</A> and
before the <A href='#dt-etag'>end-tag</A> of an element; corresponds
to the nonterminal <code><a href='#NT-content'>content</A></code>.</DD>



<DT><B>Reference in Attribute Value</B></DT>
<DD>as a reference within either the value of an attribute in a 
<A href='#dt-stag'>start-tag</A>, or a default
value in an <A href='#dt-attdecl'>attribute declaration</A>;
corresponds to the nonterminal
<code><a href='#NT-AttValue'>AttValue</A></code>.</DD>


<DT><B>Occurs as Attribute Value</B></DT>
<DD>as a <code><a href='#NT-Name'>Name</A></code>, not a reference, appearing either as
the value of an 
attribute which has been declared as type <code>ENTITY</code>, or as one of
the space-separated tokens in the value of an attribute which has been
declared as type <code>ENTITIES</code>.
</DD>

<DT><B>Reference in Entity Value</B></DT>
<DD>as a reference
within a parameter or internal entity's 
<A href='#dt-litentval'>literal entity value</A> in
the entity's declaration; corresponds to the nonterminal 
<code><a href='#NT-EntityValue'>EntityValue</A></code>.</DD>

<DT><B>Reference in DTD</B></DT>
<DD>as a reference within either the internal or external subsets of the 
<A href='#dt-doctype'>DTD</A>, but outside
of an <code><a href='#NT-EntityValue'>EntityValue</A></code> or
<code><a href='#NT-AttValue'>AttValue</A></code>.</DD>


</DL>

<TABLE border='0' cellpadding='7' align='center'>

<tr><td bgcolor='#c0d9c0' rowspan='2' colspan='1'></td>
<td bgcolor='#c0d9c0' align='center' valign='bottom' colspan='4'>Entity&nbsp;Type</td>
<td bgcolor='#c0d9c0' rowspan='2' align='center'>Character</td>
</tr>
<tr align='center' valign='bottom'>
<td bgcolor='#c0d9c0'>Parameter</td>
<td bgcolor='#c0d9c0'>Internal<BR>General</td>
<td bgcolor='#c0d9c0'>External&nbsp;Parsed<BR>General</td>
<td bgcolor='#c0d9c0'>Unparsed</td>
</tr>
<tr align='center' valign='middle'>

<td bgcolor='#c0d9c0' align='right'>Reference<BR>in&nbsp;Content</td>
<td bgcolor='#c0d9c0'><A href='#not-recognized'>Not&nbsp;recognized</A></td>
<td bgcolor='#c0d9c0'><A href='#included'>Included</A></td>
<td bgcolor='#c0d9c0'><A href='#include-if-valid'>Included&nbsp;if&nbsp;validating</A></td>
<td bgcolor='#c0d9c0'><A href='#forbidden'>Forbidden</A></td>
<td bgcolor='#c0d9c0'><A href='#included'>Included</A></td>
</tr>
<tr align='center' valign='middle'>
<td bgcolor='#c0d9c0' align='right'>Reference<BR>in&nbsp;Attribute&nbsp;Value</td>
<td bgcolor='#c0d9c0'><A href='#not-recognized'>Not&nbsp;recognized</A></td>
<td bgcolor='#c0d9c0'><A href='#inliteral'>Included&nbsp;in&nbsp;literal</A></td>
<td bgcolor='#c0d9c0'><A href='#forbidden'>Forbidden</A></td>
<td bgcolor='#c0d9c0'><A href='#forbidden'>Forbidden</A></td>
<td bgcolor='#c0d9c0'><A href='#included'>Included</A></td>
</tr>
<tr align='center' valign='middle'>
<td bgcolor='#c0d9c0' align='right'>Occurs&nbsp;as<BR>Attribute&nbsp;Value</td>
<td bgcolor='#c0d9c0'><A href='#not-recognized'>Not&nbsp;recognized</A></td>
<td bgcolor='#c0d9c0'><A href='#not-recognized'>Forbidden</A></td>
<td bgcolor='#c0d9c0'><A href='#not-recognized'>Forbidden</A></td>
<td bgcolor='#c0d9c0'><A href='#notify'>Notify</A></td>
<td bgcolor='#c0d9c0'><A href='#not recognized'>Not&nbsp;recognized</A></td>
</tr>
<tr align='center' valign='middle'>
<td bgcolor='#c0d9c0' align='right'>Reference<BR>in&nbsp;EntityValue</td>
<td bgcolor='#c0d9c0'><A href='#inliteral'>Included&nbsp;in&nbsp;literal</A></td>
<td bgcolor='#c0d9c0'><A href='#bypass'>Bypassed</A></td>
<td bgcolor='#c0d9c0'><A href='#bypass'>Bypassed</A></td>
<td bgcolor='#c0d9c0'><A href='#forbidden'>Forbidden</A></td>
<td bgcolor='#c0d9c0'><A href='#included'>Included</A></td>
</tr>
<tr align='center' valign='middle'>
<td bgcolor='#c0d9c0' align='right'>Reference<BR>in&nbsp;DTD</td>
<td bgcolor='#c0d9c0'><A href='#as-PE'>Included&nbsp;as&nbsp;PE</A></td>
<td bgcolor='#c0d9c0'><A href='#forbidden'>Forbidden</A></td>
<td bgcolor='#c0d9c0'><A href='#forbidden'>Forbidden</A></td>
<td bgcolor='#c0d9c0'><A href='#forbidden'>Forbidden</A></td>
<td bgcolor='#c0d9c0'><A href='#forbidden'>Forbidden</A></td>
</tr>

</TABLE>


<H4><A NAME='not-recognized'>4.4.1 Not Recognized</a></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 <code><a href='#NT-content'>content</A></code>.
Similarly, the names of unparsed entities are not recognized except
when they appear in the value of an appropriately declared attribute.
</P>



<H4><A NAME='included'>4.4.2 Included</a></h4>
<P><a name='dt-include'></a>An entity is 
<b>included</b> when its 
<A 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 href='#dt-chardata'>character data</A>
and (except for parameter entities) <A href='#dt-markup'>markup</A>,
which must be recognized in
the usual way, except that the replacement text of entities used to escape
markup delimiters (the entities <CODE>amp</CODE>,
<CODE>lt</CODE>,
<CODE>gt</CODE>,
<CODE>apos</CODE>,
<CODE>quot</CODE>) is always treated as
data.  (The string "<CODE>AT&amp;amp;T;</CODE>" expands to
"<CODE>AT&amp;T;</CODE>" and the remaining ampersand is not recognized
as an entity-reference delimiter.) 
A character reference is <b>included</b> when the indicated
character is processed in place of the reference itself.
</P>



<H4><A NAME='include-if-valid'>4.4.3 Included If Validating</a></h4>
<P>When an XML processor recognizes a reference to a parsed entity, in order
to <A href='#dt-valid'>validate</A>
the document, the processor must 
<A href='#dt-include'>include</A> its
replacement text.
If the entity is external, and the processor is not
attempting to validate the XML document, the
processor <A href='#dt-may'>may</A>, but need not, 
include the entity's replacement text.
If a non-validating parser does not include the replacement text,
it must inform the application that it recognized, but did not
read, the entity.</P>
<P>This rule is based on the recognition that the automatic inclusion
provided by the SGML and XML entity mechanism, primarily designed
to support modularity in authoring, is not necessarily 
appropriate for other applications, in particular document browsing.
Browsers, for example, when encountering an external parsed entity reference,
might choose to provide a visual indication of the entity's
presence and retrieve it for display only on demand.
</P>



<H4><A NAME='forbidden'>4.4.4 Forbidden</a></h4>
<P>The following are forbidden, and constitute
<A href='#dt-fatal'>fatal</A> errors:
<UL>
<LI>the appearance of a reference to an
<A href='#dt-unparsed'>unparsed entity</A>.
</LI>
<LI>the appearance of any character or general-entity reference in the
DTD except within an <code><a href='#NT-EntityValue'>EntityValue</A></code> or 
<code><a href='#NT-AttValue'>AttValue</A></code>.</LI>
<LI>a reference to an external entity in an attribute value.
</LI>
</UL>





<H4><A NAME='inliteral'>4.4.5 Included in Literal</a></h4>
<P>When an <A href='#dt-entref'>entity reference</A> appears in an
attribute value, or a parameter entity reference appears in a literal entity
value, its <A href='#dt-repltext'>replacement text</A> is
processed in place of the reference itself as though it
were part of the document at the location the reference was recognized,
except that a single or double quote character in the replacement text
is always treated as a normal data character and will not terminate the
literal. 
For example, this is well-formed:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ENTITY&nbsp;%&nbsp;YN&nbsp;'"Yes"'&nbsp;&gt;<BR>&lt;!ENTITY&nbsp;WhatHeSaid&nbsp;"He&nbsp;said&nbsp;&amp;YN;"&nbsp;&gt;</font></code></td></tr></table><p>
while this is not:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ENTITY&nbsp;EndAttr&nbsp;"27'"&nbsp;&gt;<BR>&lt;element&nbsp;attribute='a-&amp;EndAttr;&gt;</font></code></td></tr></table><p>
</P>


<H4><A NAME='notify'>4.4.6 Notify</a></h4>
<P>When the name of an <A href='#dt-unparsed'>unparsed
entity</A> appears as a token in the
value of an attribute of declared type <code>ENTITY</code> or <code>ENTITIES</code>,
a validating processor must inform the
application of the <A href='#dt-sysid'>system</A> 
and <A href='#dt-pubid'>public</A> (if any)
identifiers for both the entity and its associated
<A href='#dt-notation'>notation</A>.</P>



<H4><A NAME='bypass'>4.4.7 Bypassed</a></h4>
<P>When a general entity reference appears in the
<code><a href='#NT-EntityValue'>EntityValue</A></code> in an entity declaration,
it is bypassed and left as is.</P>



<H4><A NAME='as-PE'>4.4.8 Included as PE</a></h4>
<P>Just as with external parsed entities, parameter entities
need only be <A href='#include-if-valid'>included if
validating</A>. 
When a parameter-entity reference is recognized in the DTD
and included, its 
<A href='#dt-repltext'>replacement
text</A> is enlarged by the attachment of one leading and one following
space (#x20) character; the intent is to constrain the replacement
text of parameter 
entities to contain an integral number of grammatical tokens in the DTD.
</P>





<H3><A NAME='intern-replacement'>4.5 Construction of Internal Entity Replacement Text</a></h3>
<P>In discussing the treatment
of internal entities, it is  
useful to distinguish two forms of the entity's value.
<a name='dt-litentval'></a>The <b>literal
entity value</b> is the quoted string actually
present in the entity declaration, corresponding to the
non-terminal <code><a href='#NT-EntityValue'>EntityValue</A></code>.
<a name='dt-repltext'></a>The <b>replacement
text</b> is the content of the entity, after
replacement of character references and parameter-entity
references.
</P>

<P>The literal entity value 
as given in an internal entity declaration
(<code><a href='#NT-EntityValue'>EntityValue</A></code>) may contain character,
parameter-entity, and general-entity references.
Such references must be contained entirely within the
literal entity value.
The actual replacement text that is 
<A href='#dt-include'>included</A> as described above
must contain the <EM>replacement text</EM> of any 
parameter entities referred to, and must contain the character
referred to, in place of any character references in the
literal entity value; however,
general-entity references must be left as-is, unexpanded.
For example, given the following declarations:

</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ENTITY&nbsp;%&nbsp;pub&nbsp;&nbsp;&nbsp;&nbsp;"&amp;#xc9;ditions&nbsp;Gallimard"&nbsp;&gt;<BR>&lt;!ENTITY&nbsp;&nbsp;&nbsp;rights&nbsp;"All&nbsp;rights&nbsp;reserved"&nbsp;&gt;<BR>&lt;!ENTITY&nbsp;&nbsp;&nbsp;book&nbsp;&nbsp;&nbsp;"La&nbsp;Peste:&nbsp;Albert&nbsp;Camus,&nbsp;<BR>&amp;#xA9;&nbsp;1947&nbsp;%pub;.&nbsp;&amp;rights;"&nbsp;&gt;</font></code></td></tr></table><p>
then the replacement text for the entity "<CODE>book</CODE>" is:
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>La&nbsp;Peste:&nbsp;Albert&nbsp;Camus,&nbsp;<BR>©&nbsp;1947&nbsp;Éditions&nbsp;Gallimard.&nbsp;&amp;rights;</font></code></td></tr></table><p>
The general-entity reference "<CODE>&amp;rights;</CODE>" would be expanded
should the reference "<CODE>&amp;book;</CODE>" appear in the document's
content or an attribute value.</P>
<P>These simple rules may have complex interactions; for a detailed
discussion of a difficult example, see
"<A href='#sec-entexpand'>D.&nbsp;Expansion of Entity and Character References</A>".
</P>




<H3><A NAME='sec-predefined-ent'>4.6 Predefined Entities</a></h3>
<P><a name='dt-escape'></a>Entity and character
references can both be used to <b>escape</b> the left angle bracket,
ampersand, and other delimiters.   A set of general entities
(<CODE>amp</CODE>,
<CODE>lt</CODE>,
<CODE>gt</CODE>,
<CODE>apos</CODE>,
<CODE>quot</CODE>) is specified for this purpose.
Numeric character references may also be used; they are
expanded immediately when recognized and must be treated as
character data, so the numeric character references
"<CODE>&amp;#60;</CODE>" and "<CODE>&amp;#38;</CODE>" may be used to 
escape <CODE>&lt;</CODE> and <CODE>&amp;</CODE> when they occur
in character data.</P>
<P>All XML processors must recognize these entities whether they
are declared or not.  
<A href='#dt-interop'>For interoperability</A>,
valid XML documents should declare these
entities, like any others, before using them.
If the entities in question are declared, they must be declared
as internal entities whose replacement text is the single
character being escaped or a character reference to
that character, as shown below.
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ENTITY&nbsp;lt&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&amp;#38;#60;"&gt;&nbsp;<BR>&lt;!ENTITY&nbsp;gt&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&amp;#62;"&gt;&nbsp;<BR>&lt;!ENTITY&nbsp;amp&nbsp;&nbsp;&nbsp;&nbsp;"&amp;#38;#38;"&gt;&nbsp;<BR>&lt;!ENTITY&nbsp;apos&nbsp;&nbsp;&nbsp;"&amp;#39;"&gt;&nbsp;<BR>&lt;!ENTITY&nbsp;quot&nbsp;&nbsp;&nbsp;"&amp;#34;"&gt;&nbsp;<BR></font></code></td></tr></table><p>
Note that the <CODE>&lt;</CODE> and <CODE>&amp;</CODE> characters
in the declarations of "<CODE>lt</CODE>" and "<CODE>amp</CODE>"
are doubly escaped to meet the requirement that entity replacement
be well-formed.
</P>




<H3><A NAME='Notations'>4.7 Notation Declarations</a></h3>
 
<P><a name='dt-notation'></a><b>Notations</b> identify by
name the format of <A href='#dt-extent'>unparsed
entities</A>, the
format of elements which bear a notation attribute, 
or the application to which  
a <A href='#dt-pi'>processing instruction</A> is
addressed.</P>
<P><a name='dt-notdecl'></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>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Notation Declarations</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>
<tr valign='top'><td align='right'><a name='NT-NotationDecl'></a>[82]&nbsp;</td><td align='right'><font><code>NotationDecl</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'&lt;!NOTATION' <a href='#NT-S'>S</A> <a href='#NT-Name'>Name</A> 
<a href='#NT-S'>S</A> 
(<a href='#NT-ExternalID'>ExternalID</A> |&nbsp;
<a href='#NT-PublicID'>PublicID</A>)
<a href='#NT-S'>S</A>? '&gt;'</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-PublicID'></a>[83]&nbsp;</td><td align='right'><font><code>PublicID</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>'PUBLIC' <a href='#NT-S'>S</A> 
<a href='#NT-PubidLiteral'>PubidLiteral</A> 
</code></font></td></tr>
</table>
</td></tr></table>
<p>
</P>
<P>XML processors must provide applications with the name and external
identifier(s) of any notation declared and referred to in an attribute
value, attribute definition, or entity declaration.  They may
additionally resolve the external identifier into the
<A 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>


 


<H3><A NAME='sec-doc-entity'>4.8 Document Entity</a></h3>
 
<P><a name='dt-docent'></a>The <b>document
entity</b> serves as the root of the entity
tree and a starting-point for an <A 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>





 


<H2><A NAME='sec-conformance'>5. Conformance</a></h2>
 


<H3><A NAME='proc-types'>5.1 Validating and Non-Validating Processors</a></h3>
<P>Conforming <A href='#dt-xml-proc'>XML processors</A> fall into two
classes: validating and non-validating.</P>
<P>Validating and non-validating processors alike must report
violations of this specification's well-formedness constraints
in the content of the
<A href='#dt-docent'>document entity</A> and any 
other <A href='#dt-parsedent'>parsed entities</A> that 
they read.</P>
<P><a name='dt-validating'></a>
<b>Validating processors</b> must report
violations of the constraints expressed by the declarations in the
<A href='#dt-doctype'>DTD</A>, and
failures to fulfill the validity constraints given
in this specification.

To accomplish this, validating XML processors must read and process the entire
DTD and all external parsed entities referenced in the document.
</P>
<P>Non-validating processors are required to check only the 
<A href='#dt-docent'>document entity</A>, including
the entire internal DTD subset, for well-formedness.
<a name='dt-use-mdecl'></a>
While they are not required to check the document for validity,
they are required to 
<b>process</b> all the declarations they read in the
internal DTD subset and in any parameter entity that they
read, up to the first reference
to a parameter entity that they do <EM>not</EM> read; that is to 
say, they must
use the information in those declarations to
<A href='#AVNormalize'>normalize</A> attribute values,
<A href='#included'>include</A> the replacement text of 
internal entities, and supply 
<A href='#sec-attr-defaults'>default attribute values</A>.

They must not <A href='#dt-use-mdecl'>process</A>
<A href='#dt-entdecl'>entity declarations</A> or 
<A href='#dt-attdecl'>attribute-list declarations</A> 
encountered after a reference to a parameter entity that is not
read, since the entity may have contained overriding declarations.
</P>



<H3><A NAME='safe-behavior'>5.2 Using XML Processors</a></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:
<UL>
<LI>Certain well-formedness errors, specifically those that require
reading external entities, may not be detected by a non-validating processor.
Examples include the constraints entitled 
<A href='#wf-entdeclared'>Entity Declared</A>, 
<A href='#wf-textent'>Parsed Entity</A>, and
<A href='#wf-norecursion'>No Recursion</A>, as well
as some of the cases described as
<A href='#forbidden'>forbidden</A> in 
"<A href='#entproc'>4.4&nbsp;XML Processor Treatment of Entities and References</A>".</LI>
<LI>The information passed from the processor to the application may
vary, depending on whether the processor reads
parameter and external entities.
For example, a non-validating processor may not 
<A href='#AVNormalize'>normalize</A> attribute values,
<A href='#included'>include</A> the replacement text of 
internal entities, or supply 
<A href='#sec-attr-defaults'>default attribute values</A>,
where doing so depends on having read declarations in 
external or parameter entities.</LI>
</UL>


<P>For maximum reliability in interoperating between different XML
processors, applications which use non-validating processors should not 
rely on any behaviors not required of such processors.
Applications which require facilities such as the use of default
attributes or internal entities which are declared in external
entities should use validating XML processors.</P>





<H2><A NAME='sec-notation'>6. Notation</a></h2>
 
<P>The formal grammar of XML is given in this specification using a simple
Extended Backus-Naur Form (EBNF) notation.  Each rule in the grammar defines
one symbol, in the form
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>symbol&nbsp;::=&nbsp;expression</font></code></td></tr></table><p></P>
<P>Symbols are written with an initial capital letter if they are
defined by a regular expression, or with an initial lower case letter 
otherwise.
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:
<DL>

<DT><B><CODE>#xN</CODE></B></DT>
<DD>where <CODE>N</CODE> is a hexadecimal integer, the
expression matches the character in ISO/IEC 10646 whose canonical
(UCS-4) 
code value, when interpreted as an unsigned binary number, has
the value indicated.  The number of leading zeros in the
<CODE>#xN</CODE> form is insignificant; the number of leading
zeros in the corresponding code value 
is governed by the character
encoding in use and is not significant for XML.</DD>



<DT><B><CODE>[a-zA-Z]</CODE>, <CODE>[#xN-#xN]</CODE></B></DT>
<DD>matches any <A href='#dt-character'>character</A> 
with a value in the range(s) indicated (inclusive).</DD>



<DT><B><CODE>[^a-z]</CODE>, <CODE>[^#xN-#xN]</CODE></B></DT>
<DD>matches any <A href='#dt-character'>character</A> 
with a value <EM>outside</EM> the
range indicated.</DD>



<DT><B><CODE>[^abc]</CODE>, <CODE>[^#xN#xN#xN]</CODE></B></DT>
<DD>matches any <A href='#dt-character'>character</A>
with a value not among the characters given.</DD>



<DT><B><CODE>"string"</CODE></B></DT>
<DD>matches a literal string <A href='#dt-match'>matching</A>
that given inside the double quotes.</DD>



<DT><B><CODE>'string'</CODE></B></DT>
<DD>matches a literal string <A href='#dt-match'>matching</A>
that given inside the single quotes.</DD>


</DL>

These symbols may be combined to match more complex patterns as follows,
where <CODE>A</CODE> and <CODE>B</CODE> represent simple expressions:
<DL>

<DT><B>(<CODE>expression</CODE>)</B></DT>
<DD><CODE>expression</CODE> is treated as a unit 
and may be combined as described in this list.</DD>



<DT><B><CODE>A?</CODE></B></DT>
<DD>matches <CODE>A</CODE> or nothing; optional <CODE>A</CODE>.</DD>



<DT><B><CODE>A B</CODE></B></DT>
<DD>matches <CODE>A</CODE> followed by <CODE>B</CODE>.</DD>



<DT><B><CODE>A | B</CODE></B></DT>
<DD>matches <CODE>A</CODE> or <CODE>B</CODE> but not both.</DD>



<DT><B><CODE>A - B</CODE></B></DT>
<DD>matches any string that matches <CODE>A</CODE> but does not match
<CODE>B</CODE>.
</DD>



<DT><B><CODE>A+</CODE></B></DT>
<DD>matches one or more occurrences of <CODE>A</CODE>.</DD>



<DT><B><CODE>A*</CODE></B></DT>
<DD>matches zero or more occurrences of <CODE>A</CODE>.</DD>



</DL>

Other notations used in the productions are:
<DL>

<DT><B><CODE>/* ... */</CODE></B></DT>
<DD>comment.</DD>



<DT><B><CODE>[ wfc: ... ]</CODE></B></DT>
<DD>well-formedness constraint; this identifies by name a 
constraint on 
<A href='#dt-wellformed'>well-formed</A> documents
associated with a production.</DD>



<DT><B><CODE>[ vc: ... ]</CODE></B></DT>
<DD>validity constraint; this identifies by name a constraint on
<A href='#dt-valid'>valid</A> documents associated with
a production.</DD>


</DL>



<HR>

<h1>Appendices</h1>

 





<H2><A NAME='sec-bibliography'>A. References</a></h2>


<H3><A NAME='sec-existing-stds'>A.1 Normative References</a></h3>

<DL>
<dt><a name='IANA'>IANA</a></dt><dd>
(Internet Assigned Numbers Authority) <EM>Official Names for 
Character Sets</EM>,
ed. Keld Simonsen et al.
See <A HREF='ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets'>ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets</A>.
</DD>

<dt><a name='RFC1766'>IETF RFC 1766</a></dt><dd>
IETF (Internet Engineering Task Force).
<EM>RFC 1766:  Tags for the Identification of Languages</EM>,
ed. H. Alvestrand.
1995.
</DD>

<dt><a name='ISO639'>ISO 639</a></dt><dd>
(International Organization for Standardization).
<EM>ISO 639:1988 (E).
Code for the representation of names of languages.</EM>
[Geneva]:  International Organization for
Standardization, 1988.</DD>

<dt><a name='ISO3166'>ISO 3166</a></dt><dd>
(International Organization for Standardization).
<EM>ISO 3166-1:1997 (E).
Codes for the representation of names of countries and their subdivisions 
-- Part 1: Country codes</EM>
[Geneva]:  International Organization for
Standardization, 1997.</DD>

<dt><a name='ISO10646'>ISO/IEC 10646</a></dt><dd>ISO
(International Organization for Standardization).
<EM>ISO/IEC 10646-1993 (E).  Information technology -- Universal
Multiple-Octet Coded Character Set (UCS) -- Part 1:
Architecture and Basic Multilingual Plane.</EM>
[Geneva]:  International Organization for
Standardization, 1993 (plus amendments AM 1 through AM 7).
</DD>

<dt><a name='Unicode'>Unicode</a></dt><dd>The Unicode Consortium.
<EM>The Unicode Standard, Version 2.0.</EM>
Reading, Mass.:  Addison-Wesley Developers Press, 1996.</DD>

</DL>





<H3><A NAME='null'>A.2 Other References</a></h3> 

<DL>

<dt><a name='Aho'>Aho/Ullman</a></dt><dd>Aho, Alfred V., 
Ravi Sethi, and Jeffrey D. Ullman.
<EM>Compilers:  Principles, Techniques, and Tools</EM>.
Reading:  Addison-Wesley, 1986, rpt. corr. 1988.</DD>

<dt><a name='Berners-Lee'>Berners-Lee et al.</a></dt><dd>
Berners-Lee, T., R. Fielding, and L. Masinter.
<EM>Uniform Resource Identifiers (URI):  Generic Syntax and
Semantics</EM>.
1997.
(Work in progress; see updates to RFC1738.)</DD>

<dt><a name='ABK'>Brüggemann-Klein</a></dt><dd>Brüggemann-Klein, Anne.
<EM>Regular Expressions into Finite Automata</EM>.
Extended abstract in I. Simon, Hrsg., LATIN 1992, 
S. 97-98. Springer-Verlag, Berlin 1992. 
Full Version in Theoretical Computer Science 120: 197-213, 1993.

</DD>

<dt><a name='ABKDW'>Brüggemann-Klein and Wood</a></dt><dd>Brüggemann-Klein, Anne,
and Derick Wood.
<EM>Deterministic Regular Languages</EM>.
Universität Freiburg, Institut für Informatik,
Bericht 38, Oktober 1991.
</DD>

<dt><a name='Clark'>Clark</a></dt><dd>James Clark.
Comparison of SGML and XML. See
<A HREF='http://www.w3.org/TR/NOTE-sgml-xml-971215'>http://www.w3.org/TR/NOTE-sgml-xml-971215</A>.
</DD>
<dt><a name='RFC1738'>IETF RFC1738</a></dt><dd>
IETF (Internet Engineering Task Force).
<EM>RFC 1738:  Uniform Resource Locators (URL)</EM>, 
ed. T. Berners-Lee, L. Masinter, M. McCahill.
1994.
</DD>

<dt><a name='RFC1808'>IETF RFC1808</a></dt><dd>
IETF (Internet Engineering Task Force).
<EM>RFC 1808:  Relative Uniform Resource Locators</EM>, 
ed. R. Fielding.
1995.
</DD>

<dt><a name='RFC2141'>IETF RFC2141</a></dt><dd>
IETF (Internet Engineering Task Force).
<EM>RFC 2141:  URN Syntax</EM>, 
ed. R. Moats.
1997.
</DD>

<dt><a name='ISO8879'>ISO 8879</a></dt><dd>ISO
(International Organization for Standardization).
<EM>ISO 8879:1986(E).  Information processing -- Text and Office
Systems -- Standard Generalized Markup Language (SGML).</EM>  First
edition -- 1986-10-15.  [Geneva]:  International Organization for
Standardization, 1986.
</DD>


<dt><a name='ISO10744'>ISO/IEC 10744</a></dt><dd>ISO
(International Organization for Standardization).
<EM>ISO/IEC 10744-1992 (E).  Information technology --
Hypermedia/Time-based Structuring Language (HyTime).
</EM>
[Geneva]:  International Organization for
Standardization, 1992.
<EM>Extended Facilities Annexe.</EM>
[Geneva]:  International Organization for
Standardization, 1996. 
</DD>



</DL>





<H2><A NAME='CharClasses'>B. Character Classes</a></h2>
<P>Following the characteristics defined in the Unicode standard,
characters are classed as base characters (among others, these
contain the alphabetic characters of the Latin alphabet, without
diacritics), ideographic characters, and combining characters (among
others, this class contains most diacritics); these classes combine
to form the class of letters.  Digits and extenders are
also distinguished.
</p>
<table cellpadding='5' border='1' bgcolor='#f5dcb3' width='100%'><tr align='left'><td><strong>
Characters</strong></td></tr><tr><td>
<table border='0' bgcolor='#f5dcb3'>

<tr valign='top'><td align='right'><a name='NT-Letter'></a>[84]&nbsp;</td><td align='right'><font><code>Letter</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code><a href='#NT-BaseChar'>BaseChar</A> 
|&nbsp;<a href='#NT-Ideographic'>Ideographic</A></code></font></td> </tr>
<tr valign='top'><td align='right'><a name='NT-BaseChar'></a>[85]&nbsp;</td><td align='right'><font><code>BaseChar</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><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></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Ideographic'></a>[86]&nbsp;</td><td align='right'><font><code>Ideographic</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>[#x4E00-#x9FA5]
| #x3007
| [#x3021-#x3029]
</code></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-CombiningChar'></a>[87]&nbsp;</td><td align='right'><font><code>CombiningChar</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><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></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Digit'></a>[88]&nbsp;</td><td align='right'><font><code>Digit</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><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></font></td></tr>
<tr valign='top'><td align='right'><a name='NT-Extender'></a>[89]&nbsp;</td><td align='right'><font><code>Extender</code></font></td>
<td align='center'><font><code> ::= </code></font></td><td align='left'><font><code>#x00B7
| #x02D0
| #x02D1
| #x0387
| #x0640
| #x0E46
| #x0EC6
| #x3005
| [#x3031-#x3035]
| [#x309D-#x309E]
| [#x30FC-#x30FE]
</code></font></td></tr>


</table>
</td></tr></table>
<p>
</P>
<P>The character classes defined here can be derived from the
Unicode character database as follows:
<UL>
<LI>
Name start characters must have one of the categories Ll, Lu,
Lo, Lt, Nl.
</LI>
<LI>
Name characters other than Name-start characters 
must have one of the categories Mc, Me, Mn, Lm, or Nd.
</LI>
<LI>
Characters in the compatibility area (i.e. with character code
greater than #xF900 and less than #xFFFE) are not allowed in XML
names.
</LI>
<LI>
Characters which have a font or compatibility decomposition (i.e. those
with a "compatibility formatting tag" in field 5 of the database --
marked by field 5 beginning with a "&lt;") are not allowed.
</LI>
<LI>
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.
</LI>
<LI>
Characters #x20DD-#x20E0 are excluded (in accordance with 
Unicode, section 5.14).
</LI>
<LI>
Character #x00B7 is classified as an extender, because the
property list so identifies it.
</LI>
<LI>
Character #x0387 is added as a name character, because #x00B7
is its canonical equivalent.
</LI>
<LI>
Characters ':' and '_' are allowed as name-start characters.
</LI>
<LI>
Characters '-' and '.' are allowed as name characters.
</LI>
</UL>





<H2><A NAME='sec-xml-and-sgml'>C. XML and SGML (Non-Normative)</a></h2>
 
<P>XML is designed to be a subset of SGML, in that every
<A href='#dt-valid'>valid</A> XML document should also be a
conformant 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>



<H2><A NAME='sec-entexpand'>D. Expansion of Entity and Character References (Non-Normative)</a></h2>
<P>This appendix contains some examples illustrating the
sequence of entity- and character-reference recognition and
expansion, as specified in "<A href='#entproc'>4.4&nbsp;XML Processor Treatment of Entities and References</A>".</P>
<P>
If the DTD contains the declaration 
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;!ENTITY&nbsp;example&nbsp;"&lt;p&gt;An&nbsp;ampersand&nbsp;(&amp;#38;#38;)&nbsp;may&nbsp;be&nbsp;escaped<BR>numerically&nbsp;(&amp;#38;#38;#38;)&nbsp;or&nbsp;with&nbsp;a&nbsp;general&nbsp;entity<BR>(&amp;amp;amp;).&lt;/p&gt;"&nbsp;&gt;<BR></font></code></td></tr></table><p>
then the XML processor will recognize the character references 
when it parses the entity declaration, and resolve them before 
storing the following string as the
value of the entity "<CODE>example</CODE>":
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>&lt;p&gt;An&nbsp;ampersand&nbsp;(&amp;#38;)&nbsp;may&nbsp;be&nbsp;escaped<BR>numerically&nbsp;(&amp;#38;#38;)&nbsp;or&nbsp;with&nbsp;a&nbsp;general&nbsp;entity<BR>(&amp;amp;amp;).&lt;/p&gt;<BR></font></code></td></tr></table><p>
A reference in the document to "<CODE>&amp;example;</CODE>" 
will cause the text to be reparsed, at which time the 
start- and end-tags of the "<CODE>p</CODE>" element will be recognized 
and the three references will be recognized and expanded, 
resulting in a "<CODE>p</CODE>" element with the following content
(all data, no delimiters or markup):
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>An&nbsp;ampersand&nbsp;(&amp;)&nbsp;may&nbsp;be&nbsp;escaped<BR>numerically&nbsp;(&amp;#38;)&nbsp;or&nbsp;with&nbsp;a&nbsp;general&nbsp;entity<BR>(&amp;amp;).<BR></font></code></td></tr></table><p>
</P>
<P>A more complex example will illustrate the rules and their
effects fully.  In the following example, the line numbers are
solely for reference.
</p><table cellpadding='5' border='1' bgcolor='#80ffff' width='100%'><tr><td><code><font>1&nbsp;&lt;?xml&nbsp;version='1.0'?&gt;<BR>2&nbsp;&lt;!DOCTYPE&nbsp;test&nbsp;[<BR>3&nbsp;&lt;!ELEMENT&nbsp;test&nbsp;(#PCDATA)&nbsp;&gt;<BR>4&nbsp;&lt;!ENTITY&nbsp;%&nbsp;xx&nbsp;'&amp;#37;zz;'&gt;<BR>5&nbsp;&lt;!ENTITY&nbsp;%&nbsp;zz&nbsp;'&amp;#60;!ENTITY&nbsp;tricky&nbsp;"error-prone"&nbsp;&gt;'&nbsp;&gt;<BR>6&nbsp;%xx;<BR>7&nbsp;]&gt;<BR>8&nbsp;&lt;test&gt;This&nbsp;sample&nbsp;shows&nbsp;a&nbsp;&amp;tricky;&nbsp;method.&lt;/test&gt;<BR></font></code></td></tr></table><p>
This produces the following:
<UL>
<LI>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.)</LI>
<LI>in line 5, the character reference "<CODE>&amp;#60;</CODE>" is
expanded immediately and the parameter entity "<CODE>zz</CODE>" is
stored with the replacement text 
"<CODE>&lt;!ENTITY tricky "error-prone" &gt;</CODE>",
which is a well-formed entity declaration.</LI>
<LI>in line 6, the reference to "<CODE>xx</CODE>" is recognized,
and the replacement text of "<CODE>xx</CODE>" (namely 
"<CODE>%zz;</CODE>") is parsed.  The reference to "<CODE>zz</CODE>"
is recognized in its turn, and its replacement text 
("<CODE>&lt;!ENTITY tricky "error-prone" &gt;</CODE>") is parsed.
The general entity "<CODE>tricky</CODE>" has now been
declared, with the replacement text "<CODE>error-prone</CODE>".</LI>
<LI>
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>
</LI>
</UL>


 


<H2><A NAME='determinism'>E. Deterministic Content Models (Non-Normative)</a></h2>
<P><A href='#dt-compat'>For compatibility</A>, it is
required
that content models in element type declarations be deterministic.  
</P>

<P>SGML
requires deterministic content models (it calls them
"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 parser
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 parser 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>



<H2><A NAME='sec-guessing'>F. Autodetection of Character Encodings (Non-Normative)</a></h2>
<P>The XML encoding declaration functions as an internal label on each
entity, indicating which character encoding is in use.  Before an XML
processor can read the internal label, however, it apparently has to
know what character encoding is in use--which is what the internal label
is trying to indicate.  In the general case, this is a hopeless
situation. It is not entirely hopeless in XML, however, because XML
limits the general case in two ways:  each implementation is assumed
to support only a  finite set of character encodings, and the XML
encoding declaration is restricted in position and content in order to
make it feasible to autodetect the character encoding in use in each
entity in normal cases.  Also, in many cases other sources of information
are available in addition to the XML data stream itself.  
Two cases may be distinguished, 
depending on whether the XML entity is presented to the
processor without, or with, any accompanying
(external) information.  We consider the first case first.
</P>
<P>
Because each XML entity not in UTF-8 or UTF-16 format <EM>must</EM>
begin with an XML encoding declaration, in which the first  characters
must be '<CODE>&lt;?xml</CODE>', any conforming processor can detect,
after two to four octets of input, which of the following cases apply. 
In reading this list, it may help to know that in UCS-4, '&lt;' is
"<CODE>#x0000003C</CODE>" and '?' is "<CODE>#x0000003F</CODE>", and the Byte
Order Mark required of UTF-16 data streams is "<CODE>#xFEFF</CODE>".</P>
<P>
<UL>
<LI>
<CODE>00 00 00 3C</CODE>: UCS-4, big-endian machine (1234 order)
</LI>
<LI>
<CODE>3C 00 00 00</CODE>: UCS-4, little-endian machine (4321 order)
</LI>
<LI>
<CODE>00 00 3C 00</CODE>: UCS-4, unusual octet order (2143)
</LI>
<LI>
<CODE>00 3C 00 00</CODE>: UCS-4, unusual octet order (3412)
</LI>
<LI>
<CODE>FE FF</CODE>: UTF-16, big-endian
</LI>
<LI>
<CODE>FF FE</CODE>: UTF-16, little-endian
</LI>
<LI>
<CODE>00 3C 00 3F</CODE>: UTF-16, big-endian, no Byte Order Mark
(and thus, strictly speaking, in error)
</LI>
<LI>
<CODE>3C 00 3F 00</CODE>: UTF-16, little-endian, no Byte Order Mark
(and thus, strictly speaking, in error)
</LI>
<LI>
<CODE>3C 3F 78 6D</CODE>: 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 ASCII characters, the encoding 
declaration itself may be read reliably

</LI>
<LI>
<CODE>4C 6F A7 94</CODE>: EBCDIC (in some flavor; the full
encoding declaration must be read to tell which code page is in 
use)
</LI>
<LI>
other: UTF-8 without an encoding declaration, or else 
the data stream is corrupt, fragmentary, or enclosed in
a wrapper of some kind
</LI>
</UL>


<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
ASCII characters, 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.
</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>
<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.
Rules for the relative priority of the internal label and the
MIME-type label in an external header, for example, should be part of the
RFC document defining the text/xml and application/xml MIME types. In
the interests of interoperability, however, the following rules
are recommended.
<UL>
<LI>If an XML entity is in a file, the Byte-Order Mark
and encoding-declaration PI are used (if present) to determine the
character encoding.  All other heuristics and sources of information
are solely for error recovery.
</LI>
<LI>If an XML entity is delivered with a
MIME type of text/xml, then the <CODE>charset</CODE> parameter
on the MIME type determines the
character encoding method; all other heuristics and sources of
information are solely for error recovery.
</LI>
<LI>If an XML entity is delivered 
with a
MIME type of application/xml, then the Byte-Order Mark and
encoding-declaration PI are used (if present) to determine the
character encoding.  All other heuristics and sources of
information are solely for error recovery.
</LI>
</UL>

These rules apply only in the absence of protocol-level documentation;
in particular, when the MIME types text/xml and application/xml are
defined, the recommendations of the relevant RFC will supersede
these rules.






<H2><A NAME='sec-xml-wg'>G. W3C XML Working Group (Non-Normative)</a></h2>
 
<P>This specification was prepared and approved for publication by the
W3C XML Working Group (WG).  WG approval of this specification does
not necessarily imply that all WG members voted for its approval.  
The current and former members of the XML WG are:</P>
 

Jon Bosak, Sun (Chair);
James Clark (Technical Lead);
Tim Bray, Textuality and Netscape (XML Co-editor);
Jean Paoli, Microsoft (XML Co-editor);
C. M. Sperberg-McQueen, U. of Ill. (XML
Co-editor);
Dan Connolly, W3C (W3C Liaison);
Paula Angerstein, Texcel;
Steve DeRose, INSO;
Dave Hollander, HP;
Eliot Kimber, ISOGEN;
Eve Maler, ArborText;
Tom Magliery, NCSA;
Murray Maloney, Muzmo and Grif;
Makoto Murata, Fuji Xerox Information Systems;
Joel Nava, Adobe;
Conleth O'Connell, Vignette;
Peter Sharpe, SoftQuad;
John Tigue, DataChannel