result/valid/REC-xml-19980210.xml - platform/external/libxml2 - Gitiles

 <?xml version="1.0" encoding="ISO-8859-1" standalone="no"?>
 <!DOCTYPE spec SYSTEM "dtds/spec.dtd" [
 <!-- LAST TOUCHED BY: Tim Bray, 8 February 1997 --><!-- The words 'FINAL EDIT' in comments mark places where changes
 need to be made after approval of the document by the ERB, before
 publication.  --><!ENTITY XML.version "1.0">
 <!ENTITY doc.date "10 February 1998">
 <!ENTITY iso6.doc.date "19980210">
 <!ENTITY w3c.doc.date "02-Feb-1998">
 <!ENTITY draft.day "10">
 <!ENTITY draft.month "February">
 <!ENTITY draft.year "1998">
 <!ENTITY WebSGML "WebSGML Adaptations Annex to ISO 8879">
 <!ENTITY lt "<">
 <!ENTITY gt ">">
 <!ENTITY xmlpio "'&lt;?xml'">
 <!ENTITY pic "'?>'">
 <!ENTITY br "\n">
 <!ENTITY cellback "#c0d9c0">
 <!ENTITY mdash "--">
 <!-- &#x2014, but nsgmls doesn't grok hex --><!ENTITY com "--">
 <!ENTITY como "--">
 <!ENTITY comc "--">
 <!ENTITY hcro "&amp;#x">
 <!-- <!ENTITY nbsp " "> --><!ENTITY nbsp "&#160;">
 <!ENTITY magicents "<code>amp</code>,
 <code>lt</code>,
 <code>gt</code>,
 <code>apos</code>,
 <code>quot</code>">
 <!-- audience and distribution status:  for use at publication time --><!ENTITY doc.audience "public review and discussion">
 <!ENTITY doc.distribution "may be distributed freely, as long as
 all text and legal notices remain intact">
 ]>
 <!-- for Panorama *-->
 <?VERBATIM "eg" ?>
 <spec>
 <header>
 <title>Extensible Markup Language (XML) 1.0</title>
 <version/>
 <w3c-designation>REC-xml-&iso6.doc.date;</w3c-designation>
 <w3c-doctype>W3C Recommendation</w3c-doctype>
 <pubdate><day>&draft.day;</day><month>&draft.month;</month><year>&draft.year;</year></pubdate>

 <publoc>
 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;">
 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;</loc>
 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.xml">
 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.xml</loc>
 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.html">
 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.html</loc>
 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.pdf">
 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.pdf</loc>
 <loc href="http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.ps">
 http://www.w3.org/TR/1998/REC-xml-&iso6.doc.date;.ps</loc>
 </publoc>
 <latestloc>
 <loc href="http://www.w3.org/TR/REC-xml">
 http://www.w3.org/TR/REC-xml</loc>
 </latestloc>
 <prevlocs>
 <loc href="http://www.w3.org/TR/PR-xml-971208">
 http://www.w3.org/TR/PR-xml-971208</loc>
 <!--
 <loc  href='http://www.w3.org/TR/WD-xml-961114'>
 http://www.w3.org/TR/WD-xml-961114</loc>
 <loc  href='http://www.w3.org/TR/WD-xml-lang-970331'>
 http://www.w3.org/TR/WD-xml-lang-970331</loc>
 <loc  href='http://www.w3.org/TR/WD-xml-lang-970630'>
 http://www.w3.org/TR/WD-xml-lang-970630</loc>
 <loc  href='http://www.w3.org/TR/WD-xml-970807'>
 http://www.w3.org/TR/WD-xml-970807</loc>
 <loc  href='http://www.w3.org/TR/WD-xml-971117'>
 http://www.w3.org/TR/WD-xml-971117</loc>-->
 </prevlocs>
 <authlist>
 <author><name>Tim Bray</name>
 <affiliation>Textuality and Netscape</affiliation>
 <email href="mailto:tbray@textuality.com">tbray@textuality.com</email></author>
 <author><name>Jean Paoli</name>
 <affiliation>Microsoft</affiliation>
 <email href="mailto:jeanpa@microsoft.com">jeanpa@microsoft.com</email></author>
 <author><name>C. M. Sperberg-McQueen</name>
 <affiliation>University of Illinois at Chicago</affiliation>
 <email href="mailto:cmsmcq@uic.edu">cmsmcq@uic.edu</email></author>
 </authlist>
 <abstract>
 <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>
 </abstract>
 <status>
 <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 <loc href="http://www.w3.org/XML">http://www.w3.org/XML</loc>.  A list of
 current W3C Recommendations and other technical documents can be found
 at <loc href="http://www.w3.org/TR">http://www.w3.org/TR</loc>.
 </p>
 <p>This specification uses the term URI, which is defined by <bibref ref="Berners-Lee"/>, a work in progress expected to update <bibref ref="RFC1738"/> and <bibref ref="RFC1808"/>.
 </p>
 <p>The list of known errors in this specification is
 available at
 <loc href="http://www.w3.org/XML/xml-19980210-errata">http://www.w3.org/XML/xml-19980210-errata</loc>.</p>
 <p>Please report errors in this document to
 <loc href="mailto:xml-editor@w3.org">xml-editor@w3.org</loc>.
 </p>
 </status>


 <pubstmt>
 <p>Chicago, Vancouver, Mountain View, et al.:
 World-Wide Web Consortium, XML Working Group, 1996, 1997.</p>
 </pubstmt>
 <sourcedesc>
 <p>Created in electronic form.</p>
 </sourcedesc>
 <langusage>
 <language id="EN">English</language>
 <language id="ebnf">Extended Backus-Naur Form (formal grammar)</language>
 </langusage>
 <revisiondesc>
 <slist>
 <sitem>1997-12-03 : CMSMcQ : yet further changes</sitem>
 <sitem>1997-12-02 : TB : further changes (see TB to XML WG,
 2 December 1997)</sitem>
 <sitem>1997-12-02 : CMSMcQ : deal with as many corrections and
 comments from the proofreaders as possible:
 entify hard-coded document date in pubdate element,
 change expansion of entity WebSGML,
 update status description as per Dan Connolly (am not sure
 about refernece to Berners-Lee et al.),
 add 'The' to abstract as per WG decision,
 move Relationship to Existing Standards to back matter and
 combine with References,
 re-order back matter so normative appendices come first,
 re-tag back matter so informative appendices are tagged informdiv1,
 remove XXX XXX from list of 'normative' specs in prose,
 move some references from Other References to Normative References,
 add RFC 1738, 1808, and 2141 to Other References (they are not
 normative since we do not require the processor to enforce any
 rules based on them),
 add reference to 'Fielding draft' (Berners-Lee et al.),
 move notation section to end of body,
 drop URIchar non-terminal and use SkipLit instead,
 lose stray reference to defunct nonterminal 'markupdecls',
 move reference to Aho et al. into appendix (Tim's right),
 add prose note saying that hash marks and fragment identifiers are
 NOT part of the URI formally speaking, and are NOT legal in
 system identifiers (processor 'may' signal an error).
 Work through:
 Tim Bray reacting to James Clark,
 Tim Bray on his own,
 Eve Maler,

 NOT DONE YET:
 change binary / text to unparsed / parsed.
 handle James's suggestion about &lt; in attriubte values
 uppercase hex characters,
 namechar list,
 </sitem>
 <sitem>1997-12-01 : JB : add some column-width parameters</sitem>
 <sitem>1997-12-01 : CMSMcQ : begin round of changes to incorporate
 recent WG decisions and other corrections:
 binding sources of character encoding info (27 Aug / 3 Sept),
 correct wording of Faust quotation (restore dropped line),
 drop SDD from EncodingDecl,
 change text at version number 1.0,
 drop misleading (wrong!) sentence about ignorables and extenders,
 modify definition of PCData to make bar on msc grammatical,
 change grammar's handling of internal subset (drop non-terminal markupdecls),
 change definition of includeSect to allow conditional sections,
 add integral-declaration constraint on internal subset,
 drop misleading / dangerous sentence about relationship of
 entities with system storage objects,
 change table body tag to htbody as per EM change to DTD,
 add rule about space normalization in public identifiers,
 add description of how to generate our name-space rules from
 Unicode character database (needs further work!).
 </sitem>
 <sitem>1997-10-08 : TB : Removed %-constructs again, new rules
 for PE appearance.</sitem>
 <sitem>1997-10-01 : TB : Case-sensitive markup; cleaned up
 element-type defs, lotsa little edits for style</sitem>
 <sitem>1997-09-25 : TB : Change to elm's new DTD, with
 substantial detail cleanup as a side-effect</sitem>
 <sitem>1997-07-24 : CMSMcQ : correct error (lost *) in definition
 of ignoreSectContents (thanks to Makoto Murata)</sitem>
 <sitem>Allow all empty elements to have end-tags, consistent with
 SGML TC (as per JJC).</sitem>
 <sitem>1997-07-23 : CMSMcQ : pre-emptive strike on pending corrections:
 introduce the term 'empty-element tag', note that all empty elements
 may use it, and elements declared EMPTY must use it.
 Add WFC requiring encoding decl to come first in an entity.
 Redefine notations to point to PIs as well as binary entities.
 Change autodetection table by removing bytes 3 and 4 from
 examples with Byte Order Mark.
 Add content model as a term and clarify that it applies to both
 mixed and element content.
 </sitem>
 <sitem>1997-06-30 : CMSMcQ : change date, some cosmetic changes,
 changes to productions for choice, seq, Mixed, NotationType,
 Enumeration.  Follow James Clark's suggestion and prohibit
 conditional sections in internal subset.  TO DO:  simplify
 production for ignored sections as a result, since we don't
 need to worry about parsers which don't expand PErefs finding
 a conditional section.</sitem>
 <sitem>1997-06-29 : TB : various edits</sitem>
 <sitem>1997-06-29 : CMSMcQ : further changes:
 Suppress old FINAL EDIT comments and some dead material.
 Revise occurrences of % in grammar to exploit Henry Thompson's pun,
 especially markupdecl and attdef.
 Remove RMD requirement relating to element content (?).
 </sitem>
 <sitem>1997-06-28 : CMSMcQ : Various changes for 1 July draft:
 Add text for draconian error handling (introduce
 the term Fatal Error).
 RE deleta est (changing wording from
 original announcement to restrict the requirement to validating
 parsers).
 Tag definition of validating processor and link to it.
 Add colon as name character.
 Change def of %operator.
 Change standard definitions of lt, gt, amp.
 Strip leading zeros from #x00nn forms.</sitem>
 <sitem>1997-04-02 : CMSMcQ : final corrections of editorial errors
 found in last night's proofreading.  Reverse course once more on
 well-formed:   Webster's Second hyphenates it, and that's enough
 for me.</sitem>
 <sitem>1997-04-01 : CMSMcQ : corrections from JJC, EM, HT, and self</sitem>
 <sitem>1997-03-31 : Tim Bray : many changes</sitem>
 <sitem>1997-03-29 : CMSMcQ : some Henry Thompson (on entity handling),
 some Charles Goldfarb, some ERB decisions (PE handling in miscellaneous
 declarations.  Changed Ident element to accept def attribute.
 Allow normalization of Unicode characters.  move def of systemliteral
 into section on literals.</sitem>
 <sitem>1997-03-28 : CMSMcQ : make as many corrections as possible, from
 Terry Allen, Norbert Mikula, James Clark, Jon Bosak, Henry Thompson,
 Paul Grosso, and self.  Among other things:  give in on "well formed"
 (Terry is right), tentatively rename QuotedCData as AttValue
 and Literal as EntityValue to be more informative, since attribute
 values are the <emph>only</emph> place QuotedCData was used, and
 vice versa for entity text and Literal. (I'd call it Entity Text,
 but 8879 uses that name for both internal and external entities.)</sitem>
 <sitem>1997-03-26 : CMSMcQ : resynch the two forks of this draft, reapply
 my changes dated 03-20 and 03-21.  Normalize old 'may not' to 'must not'
 except in the one case where it meant 'may or may not'.</sitem>
 <sitem>1997-03-21 : TB : massive changes on plane flight from Chicago
 to Vancouver</sitem>
 <sitem>1997-03-21 : CMSMcQ : correct as many reported errors as possible.
 </sitem>
 <sitem>1997-03-20 : CMSMcQ : correct typos listed in CMSMcQ hand copy of spec.</sitem>
 <sitem>1997-03-20 : CMSMcQ : cosmetic changes preparatory to revision for
 WWW conference April 1997:  restore some of the internal entity
 references (e.g. to docdate, etc.), change character xA0 to &amp;nbsp;
 and define nbsp as &amp;#160;, and refill a lot of paragraphs for
 legibility.</sitem>
 <sitem>1996-11-12 : CMSMcQ : revise using Tim's edits:
 Add list type of NUMBERED and change most lists either to
 BULLETS or to NUMBERED.
 Suppress QuotedNames, Names (not used).
 Correct trivial-grammar doc type decl.
 Rename 'marked section' as 'CDATA section' passim.
 Also edits from James Clark:
 Define the set of characters from which [^abc] subtracts.
 Charref should use just [0-9] not Digit.
 Location info needs cleaner treatment:  remove?  (ERB
 question).
 One example of a PI has wrong pic.
 Clarify discussion of encoding names.
 Encoding failure should lead to unspecified results; don't
 prescribe error recovery.
 Don't require exposure of entity boundaries.
 Ignore white space in element content.
 Reserve entity names of the form u-NNNN.
 Clarify relative URLs.
 And some of my own:
 Correct productions for content model:  model cannot
 consist of a name, so "elements ::= cp" is no good.
 </sitem>
 <sitem>1996-11-11 : CMSMcQ : revise for style.
 Add new rhs to entity declaration, for parameter entities.</sitem>
 <sitem>1996-11-10 : CMSMcQ : revise for style.
 Fix / complete section on names, characters.
 Add sections on parameter entities, conditional sections.
 Still to do:  Add compatibility note on deterministic content models.
 Finish stylistic revision.</sitem>
 <sitem>1996-10-31 : TB : Add Entity Handling section</sitem>
 <sitem>1996-10-30 : TB : Clean up term &amp; termdef.  Slip in
 ERB decision re EMPTY.</sitem>
 <sitem>1996-10-28 : TB : Change DTD.  Implement some of Michael's
 suggestions.  Change comments back to //.  Introduce language for
 XML namespace reservation.  Add section on white-space handling.
 Lots more cleanup.</sitem>
 <sitem>1996-10-24 : CMSMcQ : quick tweaks, implement some ERB
 decisions.  Characters are not integers.  Comments are /* */ not //.
 Add bibliographic refs to 10646, HyTime, Unicode.
 Rename old Cdata as MsData since it's <emph>only</emph> seen
 in marked sections.  Call them attribute-value pairs not
 name-value pairs, except once.  Internal subset is optional, needs
 '?'.  Implied attributes should be signaled to the app, not
 have values supplied by processor.</sitem>
 <sitem>1996-10-16 : TB : track down &amp; excise all DSD references;
 introduce some EBNF for entity declarations.</sitem>
 <sitem>1996-10-?? : TB : consistency check, fix up scraps so
 they all parse, get formatter working, correct a few productions.</sitem>
 <sitem>1996-10-10/11 : CMSMcQ : various maintenance, stylistic, and
 organizational changes:
 Replace a few literals with xmlpio and
 pic entities, to make them consistent and ensure we can change pic
 reliably when the ERB votes.
 Drop paragraph on recognizers from notation section.
 Add match, exact match to terminology.
 Move old 2.2 XML Processors and Apps into intro.
 Mention comments, PIs, and marked sections in discussion of
 delimiter escaping.
 Streamline discussion of doctype decl syntax.
 Drop old section of 'PI syntax' for doctype decl, and add
 section on partial-DTD summary PIs to end of Logical Structures
 section.
 Revise DSD syntax section to use Tim's subset-in-a-PI
 mechanism.</sitem>
 <sitem>1996-10-10 : TB : eliminate name recognizers (and more?)</sitem>
 <sitem>1996-10-09 : CMSMcQ : revise for style, consistency through 2.3
 (Characters)</sitem>
 <sitem>1996-10-09 : CMSMcQ : re-unite everything for convenience,
 at least temporarily, and revise quickly</sitem>
 <sitem>1996-10-08 : TB : first major homogenization pass</sitem>
 <sitem>1996-10-08 : TB : turn "current" attribute on div type into
 CDATA</sitem>
 <sitem>1996-10-02 : TB : remould into skeleton + entities</sitem>
 <sitem>1996-09-30 : CMSMcQ : add a few more sections prior to exchange
                             with Tim.</sitem>
 <sitem>1996-09-20 : CMSMcQ : finish transcribing notes.</sitem>
 <sitem>1996-09-19 : CMSMcQ : begin transcribing notes for draft.</sitem>
 <sitem>1996-09-13 : CMSMcQ : made outline from notes of 09-06,
 do some housekeeping</sitem>
 </slist>
 </revisiondesc>
 </header>
 <body>
 <div1 id="sec-intro">
 <head>Introduction</head>
 <p>Extensible Markup Language, abbreviated XML, describes a class of
 data objects called <termref def="dt-xml-doc">XML documents</termref> 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 <bibref ref="ISO8879"/>.
 By construction, XML documents
 are conforming SGML documents.
 </p>
 <p>XML documents are made up of storage units called <termref def="dt-entity">entities</termref>, which contain either parsed
 or unparsed data.
 Parsed data is made up of <termref def="dt-character">characters</termref>,
 some
 of which form <termref def="dt-chardata">character data</termref>,
 and some of which form <termref def="dt-markup">markup</termref>.
 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><termdef id="dt-xml-proc" term="XML Processor">A software module
 called an <term>XML processor</term> is used to read XML documents
 and provide access to their content and structure.</termdef> <termdef id="dt-app" term="Application">It is assumed that an XML processor is
 doing its work on behalf of another module, called the
 <term>application</term>.</termdef> 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>

 <div2 id="sec-origin-goals">
 <head>Origin and Goals</head>
 <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:<olist>
 <item><p>XML shall be straightforwardly usable over the
 Internet.</p></item>
 <item><p>XML shall support a wide variety of applications.</p></item>
 <item><p>XML shall be compatible with SGML.</p></item>
 <item><p>It shall be easy to write programs which process XML
 documents.</p></item>
 <item><p>The number of optional features in XML is to be kept to the
 absolute minimum, ideally zero.</p></item>
 <item><p>XML documents should be human-legible and reasonably
 clear.</p></item>
 <item><p>The XML design should be prepared quickly.</p></item>
 <item><p>The design of XML shall be formal and concise.</p></item>
 <item><p>XML documents shall be easy to create.</p></item>
 <item><p>Terseness in XML markup is of minimal importance.</p></item></olist>
 </p>
 <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 &XML.version;
 and construct computer programs to process it.</p>
 <p>This version of the XML specification
 <!-- is for &doc.audience;.-->
 &doc.distribution;.</p>

 </div2>


 <div2 id="sec-terminology">
 <head>Terminology</head>

 <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:
 <glist>
 <gitem>
 <label>may</label>
 <def><p><termdef id="dt-may" term="May">Conforming documents and XML
 processors are permitted to but need not behave as
 described.</termdef></p></def>
 </gitem>
 <gitem>
 <label>must</label>
 <def><p>Conforming documents and XML processors
 are required to behave as described; otherwise they are in error.
 <!-- do NOT change this! this is what defines a violation of
 a 'must' clause as 'an error'. -MSM -->
 </p></def>
 </gitem>
 <gitem>
 <label>error</label>
 <def><p><termdef id="dt-error" term="Error">A violation of the rules of this
 specification; results are
 undefined.  Conforming software may detect and report an error and may
 recover from it.</termdef></p></def>
 </gitem>
 <gitem>
 <label>fatal error</label>
 <def><p><termdef id="dt-fatal" term="Fatal Error">An error
 which a conforming <termref def="dt-xml-proc">XML processor</termref>
 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).
 </termdef></p></def>
 </gitem>
 <gitem>
 <label>at user option</label>
 <def><p>Conforming software may or must (depending on the modal verb in the
 sentence) behave as described; if it does, it must
 provide users a means to enable or disable the behavior
 described.</p></def>
 </gitem>
 <gitem>
 <label>validity constraint</label>
 <def><p>A rule which applies to all
 <termref def="dt-valid">valid</termref> XML documents.
 Violations of validity constraints are errors; they must, at user option,
 be reported by
 <termref def="dt-validating">validating XML processors</termref>.</p></def>
 </gitem>
 <gitem>
 <label>well-formedness constraint</label>
 <def><p>A rule which applies to all <termref def="dt-wellformed">well-formed</termref> XML documents.
 Violations of well-formedness constraints are
 <termref def="dt-fatal">fatal errors</termref>.</p></def>
 </gitem>

 <gitem>
 <label>match</label>
 <def><p><termdef id="dt-match" term="match">(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
 <specref ref="elementvalid"/>.
 </termdef>
 </p></def>
 </gitem>
 <gitem>
 <label>for compatibility</label>
 <def><p><termdef id="dt-compat" term="For Compatibility">A feature of
 XML included solely to ensure that XML remains compatible with SGML.
 </termdef></p></def>
 </gitem>
 <gitem>
 <label>for interoperability</label>
 <def><p><termdef id="dt-interop" term="For interoperability">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;.</termdef></p></def>
 </gitem>
 </glist>
 </p>
 </div2>


 </div1>
 <!-- &Docs; -->

 <div1 id="sec-documents">
 <head>Documents</head>

 <p><termdef id="dt-xml-doc" term="XML Document">
 A data object is an
 <term>XML document</term> if it is
 <termref def="dt-wellformed">well-formed</termref>, as
 defined in this specification.
 A well-formed XML document may in addition be
 <termref def="dt-valid">valid</termref> if it meets certain further
 constraints.</termdef></p>

 <p>Each XML document has both a logical and a physical structure.
 Physically, the document is composed of units called <termref def="dt-entity">entities</termref>.  An entity may <termref def="dt-entref">refer</termref> to other entities to cause their
 inclusion in the document. A document begins in a "root"  or <termref def="dt-docent">document entity</termref>.
 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 <specref ref="wf-entities"/>.
 </p>

 <div2 id="sec-well-formed">
 <head>Well-Formed XML Documents</head>

 <p><termdef id="dt-wellformed" term="Well-Formed">
 A textual object is
 a well-formed XML document if:</termdef>
 <olist>
 <item><p>Taken as a whole, it
 matches the production labeled <nt def="NT-document">document</nt>.</p></item>
 <item><p>It
 meets all the well-formedness constraints given in this specification.</p>
 </item>
 <item><p>Each of the <termref def="dt-parsedent">parsed entities</termref>
 which is referenced directly or indirectly within the document is
 <titleref href="wf-entities">well-formed</titleref>.</p></item>
 </olist></p>
 <p>
 <scrap lang="ebnf" id="document">
 <head>Document</head>
 <prod id="NT-document"><lhs>document</lhs>
 <rhs><nt def="NT-prolog">prolog</nt>
 <nt def="NT-element">element</nt>
 <nt def="NT-Misc">Misc</nt>*</rhs></prod>
 </scrap>
 </p>
 <p>Matching the <nt def="NT-document">document</nt> production
 implies that:
 <olist>
 <item><p>It contains one or more
 <termref def="dt-element">elements</termref>.</p>
 </item>
 <!--* N.B. some readers (notably JC) find the following
 paragraph awkward and redundant.  I agree it's logically redundant:
 it *says* it is summarizing the logical implications of
 matching the grammar, and that means by definition it's
 logically redundant.  I don't think it's rhetorically
 redundant or unnecessary, though, so I'm keeping it.  It
 could however use some recasting when the editors are feeling
 stronger. -MSM *-->
 <item><p><termdef id="dt-root" term="Root Element">There is  exactly
 one element, called the <term>root</term>, or document element,  no
 part of which appears in the <termref def="dt-content">content</termref> of any other element.</termdef>
 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.
 </p></item>
 </olist>
 </p>
 <p><termdef id="dt-parentchild" term="Parent/Child">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
 <term>parent</term> of <code>C</code>, and <code>C</code> as a
 <term>child</term> of <code>P</code>.</termdef></p></div2>

 <div2 id="charsets">
 <head>Characters</head>

 <p><termdef id="dt-text" term="Text">A parsed entity contains
 <term>text</term>, a sequence of
 <termref def="dt-character">characters</termref>,
 which may represent markup or character data.</termdef>
 <termdef id="dt-character" term="Character">A <term>character</term>
 is an atomic unit of text as specified by
 ISO/IEC 10646 <bibref ref="ISO10646"/>.
 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 <bibref ref="Unicode"/>, is discouraged.
 </termdef>
 <scrap lang="ebnf" id="char32">
 <head>Character Range</head>
 <prodgroup pcw2="4" pcw4="17.5" pcw5="11">
 <prod id="NT-Char"><lhs>Char</lhs>
 <rhs>#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD]
 | [#x10000-#x10FFFF]</rhs>
 <com>any Unicode character, excluding the
 surrogate blocks, FFFE, and FFFF.</com> </prod>
 </prodgroup>
 </scrap>
 </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 <specref ref="charencoding"/>.
 </p>
 <!--
 <p>Regardless of the specific encoding used, any character in the ISO/IEC
 10646 character set may be referred to by the decimal or hexadecimal
 equivalent of its
 UCS-4 code value.
 </p>-->
 </div2>

 <div2 id="sec-common-syn">
 <head>Common Syntactic Constructs</head>

 <p>This section defines some symbols used widely in the grammar.</p>
 <p><nt def="NT-S">S</nt> (white space) consists of one or more space (#x20)
 characters, carriage returns, line feeds, or tabs.

 <scrap lang="ebnf" id="white">
 <head>White Space</head>
 <prodgroup pcw2="4" pcw4="17.5" pcw5="11">
 <prod id="NT-S"><lhs>S</lhs>
 <rhs>(#x20 | #x9 | #xD | #xA)+</rhs>
 </prod>
 </prodgroup>
 </scrap></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 <specref ref="CharClasses"/>.</p>
 <p><termdef id="dt-name" term="Name">A <term>Name</term> 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.</termdef>
 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>
 <note>
 <p>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>
 </note>
 <p>An
 <nt def="NT-Nmtoken">Nmtoken</nt> (name token) is any mixture of
 name characters.
 <scrap lang="ebnf">
 <head>Names and Tokens</head>
 <prod id="NT-NameChar"><lhs>NameChar</lhs>
 <rhs><nt def="NT-Letter">Letter</nt>
 | <nt def="NT-Digit">Digit</nt>
 | '.' | '-' | '_' | ':'
 | <nt def="NT-CombiningChar">CombiningChar</nt>
 | <nt def="NT-Extender">Extender</nt></rhs>
 </prod>
 <prod id="NT-Name"><lhs>Name</lhs>
 <rhs>(<nt def="NT-Letter">Letter</nt> | '_' | ':')
 (<nt def="NT-NameChar">NameChar</nt>)*</rhs></prod>
 <prod id="NT-Names"><lhs>Names</lhs>
 <rhs><nt def="NT-Name">Name</nt>
 (<nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt>)*</rhs></prod>
 <prod id="NT-Nmtoken"><lhs>Nmtoken</lhs>
 <rhs>(<nt def="NT-NameChar">NameChar</nt>)+</rhs></prod>
 <prod id="NT-Nmtokens"><lhs>Nmtokens</lhs>
 <rhs><nt def="NT-Nmtoken">Nmtoken</nt> (<nt def="NT-S">S</nt> <nt def="NT-Nmtoken">Nmtoken</nt>)*</rhs></prod>
 </scrap>
 </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
 (<nt def="NT-EntityValue">EntityValue</nt>),
 the values of attributes (<nt def="NT-AttValue">AttValue</nt>),
 and external identifiers
 (<nt def="NT-SystemLiteral">SystemLiteral</nt>).
 Note that a <nt def="NT-SystemLiteral">SystemLiteral</nt>
 can be parsed without scanning for markup.
 <scrap lang="ebnf">
 <head>Literals</head>
 <prod id="NT-EntityValue"><lhs>EntityValue</lhs>
 <rhs>'"'
 ([^%&amp;"]
 | <nt def="NT-PEReference">PEReference</nt>
 | <nt def="NT-Reference">Reference</nt>)*
 '"'
 </rhs>
 <rhs>|&nbsp;
 "'"
 ([^%&amp;']
 | <nt def="NT-PEReference">PEReference</nt>
 | <nt def="NT-Reference">Reference</nt>)*
 "'"</rhs>
 </prod>
 <prod id="NT-AttValue"><lhs>AttValue</lhs>
 <rhs>'"'
 ([^&lt;&amp;"]
 | <nt def="NT-Reference">Reference</nt>)*
 '"'
 </rhs>
 <rhs>|&nbsp;
 "'"
 ([^&lt;&amp;']
 | <nt def="NT-Reference">Reference</nt>)*
 "'"</rhs>
 </prod>
 <prod id="NT-SystemLiteral"><lhs>SystemLiteral</lhs>
 <rhs>('"' [^"]* '"') |&nbsp;("'" [^']* "'")
 </rhs>
 </prod>
 <prod id="NT-PubidLiteral"><lhs>PubidLiteral</lhs>
 <rhs>'"' <nt def="NT-PubidChar">PubidChar</nt>*
 '"'
 | "'" (<nt def="NT-PubidChar">PubidChar</nt> - "'")* "'"</rhs>
 </prod>
 <prod id="NT-PubidChar"><lhs>PubidChar</lhs>
 <rhs>#x20 | #xD | #xA
 |&nbsp;[a-zA-Z0-9]
 |&nbsp;[-'()+,./:=?;!*#@$_%]</rhs>
 </prod>
 </scrap>
 </p>

 </div2>

 <div2 id="syntax">
 <head>Character Data and Markup</head>

 <p><termref def="dt-text">Text</termref> consists of intermingled
 <termref def="dt-chardata">character
 data</termref> and markup.
 <termdef id="dt-markup" term="Markup"><term>Markup</term> takes the form of
 <termref def="dt-stag">start-tags</termref>,
 <termref def="dt-etag">end-tags</termref>,
 <termref def="dt-empty">empty-element tags</termref>,
 <termref def="dt-entref">entity references</termref>,
 <termref def="dt-charref">character references</termref>,
 <termref def="dt-comment">comments</termref>,
 <termref def="dt-cdsection">CDATA section</termref> delimiters,
 <termref def="dt-doctype">document type declarations</termref>, and
 <termref def="dt-pi">processing instructions</termref>.
 </termdef>
 </p>
 <p><termdef id="dt-chardata" term="Character Data">All text that is not markup
 constitutes the <term>character data</term> of
 the document.</termdef></p>
 <p>The ampersand character (&amp;) and the left angle bracket (&lt;)
 may appear in their literal form <emph>only</emph> when used as markup
 delimiters, or within a <termref def="dt-comment">comment</termref>, a
 <termref def="dt-pi">processing instruction</termref>,
 or a <termref def="dt-cdsection">CDATA section</termref>.

 They are also legal within the <termref def="dt-litentval">literal entity
 value</termref> of an internal entity declaration; see
 <specref ref="wf-entities"/>.
 <!-- FINAL EDIT:  restore internal entity decl or leave it out. -->
 If they are needed elsewhere,
 they must be <termref def="dt-escape">escaped</termref>
 using either <termref def="dt-charref">numeric character references</termref>
 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, <termref def="dt-compat">for
 compatibility</termref>,
 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 <termref def="dt-cdsection">CDATA section</termref>.
 </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>".
 <scrap lang="ebnf">
 <head>Character Data</head>
 <prod id="NT-CharData">
 <lhs>CharData</lhs>
 <rhs>[^&lt;&amp;]* - ([^&lt;&amp;]* ']]&gt;' [^&lt;&amp;]*)</rhs>
 </prod>
 </scrap>
 </p>
 </div2>

 <div2 id="sec-comments">
 <head>Comments</head>

 <p><termdef id="dt-comment" term="Comment"><term>Comments</term> may
 appear anywhere in a document outside other
 <termref def="dt-markup">markup</termref>; in addition,
 they may appear within the document type declaration
 at places allowed by the grammar.
 They are not part of the document's <termref def="dt-chardata">character
 data</termref>; an XML
 processor may, but need not, make it possible for an application to
 retrieve the text of comments.
 <termref def="dt-compat">For compatibility</termref>, the string
 "<code>--</code>" (double-hyphen) must not occur within
 comments.
 <scrap lang="ebnf">
 <head>Comments</head>
 <prod id="NT-Comment"><lhs>Comment</lhs>
 <rhs>'&lt;!--'
 ((<nt def="NT-Char">Char</nt> - '-')
 | ('-' (<nt def="NT-Char">Char</nt> - '-')))*
 '--&gt;'</rhs>
 </prod>
 </scrap>
 </termdef></p>
 <p>An example of a comment:
 <eg>&lt;!&como; declarations for &lt;head&gt; &amp; &lt;body&gt; &comc;&gt;</eg>
 </p>
 </div2>

 <div2 id="sec-pi">
 <head>Processing Instructions</head>

 <p><termdef id="dt-pi" term="Processing instruction"><term>Processing
 instructions</term> (PIs) allow documents to contain instructions
 for applications.

 <scrap lang="ebnf">
 <head>Processing Instructions</head>
 <prod id="NT-PI"><lhs>PI</lhs>
 <rhs>'&lt;?' <nt def="NT-PITarget">PITarget</nt>
 (<nt def="NT-S">S</nt>
 (<nt def="NT-Char">Char</nt>* -
 (<nt def="NT-Char">Char</nt>* &pic; <nt def="NT-Char">Char</nt>*)))?
 &pic;</rhs></prod>
 <prod id="NT-PITarget"><lhs>PITarget</lhs>
 <rhs><nt def="NT-Name">Name</nt> -
 (('X' | 'x') ('M' | 'm') ('L' | 'l'))</rhs>
 </prod>
 </scrap></termdef>
 PIs are not part of the document's <termref def="dt-chardata">character
 data</termref>, but must be passed through to the application. The
 PI begins with a target (<nt def="NT-PITarget">PITarget</nt>) 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 <termref def="dt-notation">Notation</termref> mechanism
 may be used for
 formal declaration of PI targets.
 </p>
 </div2>

 <div2 id="sec-cdata-sect">
 <head>CDATA Sections</head>

 <p><termdef id="dt-cdsection" term="CDATA Section"><term>CDATA sections</term>
 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>":
 <scrap lang="ebnf">
 <head>CDATA Sections</head>
 <prod id="NT-CDSect"><lhs>CDSect</lhs>
 <rhs><nt def="NT-CDStart">CDStart</nt>
 <nt def="NT-CData">CData</nt>
 <nt def="NT-CDEnd">CDEnd</nt></rhs></prod>
 <prod id="NT-CDStart"><lhs>CDStart</lhs>
 <rhs>'&lt;![CDATA['</rhs>
 </prod>
 <prod id="NT-CData"><lhs>CData</lhs>
 <rhs>(<nt def="NT-Char">Char</nt>* -
 (<nt def="NT-Char">Char</nt>* ']]&gt;' <nt def="NT-Char">Char</nt>*))
 </rhs>
 </prod>
 <prod id="NT-CDEnd"><lhs>CDEnd</lhs>
 <rhs>']]&gt;'</rhs>
 </prod>
 </scrap>

 Within a CDATA section, only the <nt def="NT-CDEnd">CDEnd</nt> 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.</termdef>
 </p>

 <p>An example of a CDATA section, in which "<code>&lt;greeting&gt;</code>" and
 "<code>&lt;/greeting&gt;</code>"
 are recognized as <termref def="dt-chardata">character data</termref>, not
 <termref def="dt-markup">markup</termref>:
 <eg>&lt;![CDATA[&lt;greeting&gt;Hello, world!&lt;/greeting&gt;]]&gt;</eg>
 </p>
 </div2>

 <div2 id="sec-prolog-dtd">
 <head>Prolog and Document Type Declaration</head>

 <p><termdef id="dt-xmldecl" term="XML Declaration">XML documents
 may, and should,
 begin with an <term>XML declaration</term> which specifies
 the version of
 XML being used.</termdef>
 For example, the following is a complete XML document, <termref def="dt-wellformed">well-formed</termref> but not
 <termref def="dt-valid">valid</termref>:
 <eg><![CDATA[<?xml version="1.0"?>
 <greeting>Hello, world!</greeting>
 ]]></eg>
 and so is this:
 <eg><![CDATA[<greeting>Hello, world!</greeting>
 ]]></eg>
 </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 <termref def="dt-doctype">document type declaration</termref>, to define
 constraints on the logical structure and to support the use of
 predefined storage units.

 <termdef id="dt-valid" term="Validity">An XML document is
 <term>valid</term> if it has an associated document type
 declaration and if the document
 complies with the constraints expressed in it.</termdef></p>
 <p>The document type declaration must appear before
 the first <termref def="dt-element">element</termref> in the document.
 <scrap lang="ebnf" id="xmldoc">
 <head>Prolog</head>
 <prodgroup pcw2="6" pcw4="17.5" pcw5="9">
 <prod id="NT-prolog"><lhs>prolog</lhs>
 <rhs><nt def="NT-XMLDecl">XMLDecl</nt>?
 <nt def="NT-Misc">Misc</nt>*
 (<nt def="NT-doctypedecl">doctypedecl</nt>
 <nt def="NT-Misc">Misc</nt>*)?</rhs></prod>
 <prod id="NT-XMLDecl"><lhs>XMLDecl</lhs>
 <rhs>&xmlpio;
 <nt def="NT-VersionInfo">VersionInfo</nt>
 <nt def="NT-EncodingDecl">EncodingDecl</nt>?
 <nt def="NT-SDDecl">SDDecl</nt>?
 <nt def="NT-S">S</nt>?
 &pic;</rhs>
 </prod>
 <prod id="NT-VersionInfo"><lhs>VersionInfo</lhs>
 <rhs><nt def="NT-S">S</nt> 'version' <nt def="NT-Eq">Eq</nt>
 (' <nt def="NT-VersionNum">VersionNum</nt> '
 | " <nt def="NT-VersionNum">VersionNum</nt> ")</rhs>
 </prod>
 <prod id="NT-Eq"><lhs>Eq</lhs>
 <rhs><nt def="NT-S">S</nt>? '=' <nt def="NT-S">S</nt>?</rhs></prod>
 <prod id="NT-VersionNum">
 <lhs>VersionNum</lhs>
 <rhs>([a-zA-Z0-9_.:] | '-')+</rhs>
 </prod>
 <prod id="NT-Misc"><lhs>Misc</lhs>
 <rhs><nt def="NT-Comment">Comment</nt> | <nt def="NT-PI">PI</nt> |
 <nt def="NT-S">S</nt></rhs></prod>
 </prodgroup>
 </scrap></p>

 <p><termdef id="dt-doctype" term="Document Type Declaration">The XML
 <term>document type declaration</term>
 contains or points to
 <termref def="dt-markupdecl">markup declarations</termref>
 that provide a grammar for a
 class of documents.
 This grammar is known as a document type definition,
 or <term>DTD</term>.
 The document type declaration can point to an external subset (a
 special kind of
 <termref def="dt-extent">external entity</termref>) 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.</termdef>
 </p>
 <p><termdef id="dt-markupdecl" term="markup declaration">
 A <term>markup declaration</term> is
 an <termref def="dt-eldecl">element type declaration</termref>,
 an <termref def="dt-attdecl">attribute-list declaration</termref>,
 an <termref def="dt-entdecl">entity declaration</termref>, or
 a <termref def="dt-notdecl">notation declaration</termref>.
 </termdef>
 These declarations may be contained in whole or in part
 within <termref def="dt-PE">parameter entities</termref>,
 as described in the well-formedness and validity constraints below.
 For fuller information, see
 <specref ref="sec-physical-struct"/>.</p>
 <scrap lang="ebnf" id="dtd">
 <head>Document Type Definition</head>
 <prodgroup pcw2="6" pcw4="17.5" pcw5="9">
 <prod id="NT-doctypedecl"><lhs>doctypedecl</lhs>
 <rhs>'&lt;!DOCTYPE' <nt def="NT-S">S</nt>
 <nt def="NT-Name">Name</nt> (<nt def="NT-S">S</nt>
 <nt def="NT-ExternalID">ExternalID</nt>)?
 <nt def="NT-S">S</nt>? ('['
 (<nt def="NT-markupdecl">markupdecl</nt>
 | <nt def="NT-PEReference">PEReference</nt>
 | <nt def="NT-S">S</nt>)*
 ']'
 <nt def="NT-S">S</nt>?)? '&gt;'</rhs>
 <vc def="vc-roottype"/>
 </prod>
 <prod id="NT-markupdecl"><lhs>markupdecl</lhs>
 <rhs><nt def="NT-elementdecl">elementdecl</nt>
 | <nt def="NT-AttlistDecl">AttlistDecl</nt>
 | <nt def="NT-EntityDecl">EntityDecl</nt>
 | <nt def="NT-NotationDecl">NotationDecl</nt>
 | <nt def="NT-PI">PI</nt>
 | <nt def="NT-Comment">Comment</nt>
 </rhs>
 <vc def="vc-PEinMarkupDecl"/>
 <wfc def="wfc-PEinInternalSubset"/>
 </prod>

 </prodgroup>
 </scrap>

 <p>The markup declarations may be made up in whole or in part of
 the <termref def="dt-repltext">replacement text</termref> of
 <termref def="dt-PE">parameter entities</termref>.
 The productions later in this specification for
 individual nonterminals (<nt def="NT-elementdecl">elementdecl</nt>,
 <nt def="NT-AttlistDecl">AttlistDecl</nt>, and so on) describe
 the declarations <emph>after</emph> all the parameter entities have been
 <termref def="dt-include">included</termref>.</p>

 <vcnote id="vc-roottype">
 <head>Root Element Type</head>
 <p>
 The <nt def="NT-Name">Name</nt> in the document type declaration must
 match the element type of the <termref def="dt-root">root element</termref>.
 </p>
 </vcnote>

 <vcnote id="vc-PEinMarkupDecl">
 <head>Proper Declaration/PE Nesting</head>
 <p>Parameter-entity
 <termref def="dt-repltext">replacement text</termref> must be properly nested
 with markup declarations.
 That is to say, if either the first character
 or the last character of a markup
 declaration (<nt def="NT-markupdecl">markupdecl</nt> above)
 is contained in the replacement text for a
 <termref def="dt-PERef">parameter-entity reference</termref>,
 both must be contained in the same replacement text.</p>
 </vcnote>
 <wfcnote id="wfc-PEinInternalSubset">
 <head>PEs in Internal Subset</head>
 <p>In the internal DTD subset,
 <termref def="dt-PERef">parameter-entity references</termref>
 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>
 </wfcnote>
 <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
 <nt def="NT-markupdecl">markupdecl</nt>, interspersed with white space
 or <termref def="dt-PERef">parameter-entity references</termref>.
 However, portions of the contents
 of the
 external subset or of external parameter entities may conditionally be ignored
 by using
 the <termref def="dt-cond-section">conditional section</termref>
 construct; this is not allowed in the internal subset.

 <scrap id="ext-Subset">
 <head>External Subset</head>
 <prodgroup pcw2="6" pcw4="17.5" pcw5="9">
 <prod id="NT-extSubset"><lhs>extSubset</lhs>
 <rhs><nt def="NT-TextDecl">TextDecl</nt>?
 <nt def="NT-extSubsetDecl">extSubsetDecl</nt></rhs></prod>
 <prod id="NT-extSubsetDecl"><lhs>extSubsetDecl</lhs>
 <rhs>(
 <nt def="NT-markupdecl">markupdecl</nt>
 | <nt def="NT-conditionalSect">conditionalSect</nt>
 | <nt def="NT-PEReference">PEReference</nt>
 | <nt def="NT-S">S</nt>
 )*</rhs>
 </prod>
 </prodgroup>
 </scrap></p>
 <p>The external subset and external parameter entities also differ
 from the internal subset in that in them,
 <termref def="dt-PERef">parameter-entity references</termref>
 are permitted <emph>within</emph> markup declarations,
 not only <emph>between</emph> markup declarations.</p>
 <p>An example of an XML document with a document type declaration:
 <eg><![CDATA[<?xml version="1.0"?>
 <!DOCTYPE greeting SYSTEM "hello.dtd">
 <greeting>Hello, world!</greeting>
 ]]></eg>
 The <termref def="dt-sysid">system identifier</termref>
 "<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:
 <eg><![CDATA[<?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE greeting [
   <!ELEMENT greeting (#PCDATA)>
 ]>
 <greeting>Hello, world!</greeting>
 ]]></eg>
 If both the external and internal subsets are used, the
 internal subset is considered to occur before the external subset.
 <!-- 'is considered to'? boo. whazzat mean? -->
 This has the effect that entity and attribute-list declarations in the
 internal subset take precedence over those in the external subset.
 </p>
 </div2>

 <div2 id="sec-rmd">
 <head>Standalone Document Declaration</head>
 <p>Markup declarations can affect the content of the document,
 as passed from an <termref def="dt-xml-proc">XML processor</termref>
 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 <termref def="dt-docent">document entity</termref>.
 <scrap lang="ebnf" id="fulldtd">
 <head>Standalone Document Declaration</head>
 <prodgroup pcw2="4" pcw4="19.5" pcw5="9">
 <prod id="NT-SDDecl"><lhs>SDDecl</lhs>
 <rhs>
 <nt def="NT-S">S</nt>
 'standalone' <nt def="NT-Eq">Eq</nt>
 (("'" ('yes' | 'no') "'") | ('"' ('yes' | 'no') '"'))
 </rhs>
 <vc def="vc-check-rmd"/></prod>
 </prodgroup>
 </scrap></p>
 <p>
 In a standalone document declaration, the value "<code>yes</code>" indicates
 that there
 are no markup declarations external to the <termref def="dt-docent">document
 entity</termref> (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 <emph>declarations</emph>; the presence, in a
 document, of
 references to external <emph>entities</emph>, 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>
 <vcnote id="vc-check-rmd">
 <head>Standalone Document Declaration</head>
 <p>The standalone document declaration must have
 the value "<code>no</code>" if any external markup declarations
 contain declarations of:</p><ulist>
 <item><p>attributes with <termref def="dt-default">default</termref> values, if
 elements to which
 these attributes apply appear in the document without
 specifications of values for these attributes, or</p></item>
 <item><p>entities (other than &magicents;),
 if <termref def="dt-entref">references</termref> to those
 entities appear in the document, or</p>
 </item>
 <item><p>attributes with values subject to
 <titleref href="AVNormalize">normalization</titleref>, where the
 attribute appears in the document with a value which will
 change as a result of normalization, or</p>
 </item>
 <item>
 <p>element types with <termref def="dt-elemcontent">element content</termref>,
 if white space occurs
 directly within any instance of those types.
 </p></item>
 </ulist>

 </vcnote>
 <p>An example XML declaration with a standalone document declaration:<eg>&lt;?xml version="&XML.version;" standalone='yes'?&gt;</eg></p>
 </div2>
 <div2 id="sec-white-space">
 <head>White Space Handling</head>

 <p>In editing XML documents, it is often convenient to use "white space"
 (spaces, tabs, and blank lines, denoted by the nonterminal
 <nt def="NT-S">S</nt> 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 <termref def="dt-xml-proc">XML processor</termref>
 must always pass all characters in a document that are not
 markup through to the application.   A <termref def="dt-validating">
 validating XML processor</termref> must also inform the application
 which  of these characters constitute white space appearing
 in <termref def="dt-elemcontent">element content</termref>.
 </p>
 <p>A special <termref def="dt-attr">attribute</termref>
 named <kw>xml:space</kw> 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
 <termref def="dt-attdecl">declared</termref> if it is used.
 When declared, it must be given as an
 <termref def="dt-enumerated">enumerated type</termref> whose only
 possible values are "<code>default</code>" and "<code>preserve</code>".
 For example:<eg><![CDATA[    <!ATTLIST poem   xml:space (default|preserve) 'preserve'>]]></eg></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 <kw>xml:space</kw> attribute.
 </p>
 <p>The <termref def="dt-root">root element</termref> 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>

 </div2>
 <div2 id="sec-line-ends">
 <head>End-of-Line Handling</head>
 <p>XML <termref def="dt-parsedent">parsed entities</termref> 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 <termref def="dt-app">applications</termref>,
 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 <termref def="dt-xml-proc">XML processor</termref> 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>
 </div2>
 <div2 id="sec-lang-tag">
 <head>Language Identification</head>
 <p>In document processing, it is often useful to
 identify the natural or formal language
 in which the content is
 written.
 A special <termref def="dt-attr">attribute</termref> named
 <kw>xml:lang</kw> 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
 <termref def="dt-attdecl">declared</termref> if it is used.
 The values of the attribute are language identifiers as defined
 by <bibref ref="RFC1766"/>, "Tags for the Identification of Languages":
 <scrap lang="ebnf">
 <head>Language Identification</head>
 <prod id="NT-LanguageID"><lhs>LanguageID</lhs>
 <rhs><nt def="NT-Langcode">Langcode</nt>
 ('-' <nt def="NT-Subcode">Subcode</nt>)*</rhs></prod>
 <prod id="NT-Langcode"><lhs>Langcode</lhs>
 <rhs><nt def="NT-ISO639Code">ISO639Code</nt> |
 <nt def="NT-IanaCode">IanaCode</nt> |
 <nt def="NT-UserCode">UserCode</nt></rhs>
 </prod>
 <prod id="NT-ISO639Code"><lhs>ISO639Code</lhs>
 <rhs>([a-z] | [A-Z]) ([a-z] | [A-Z])</rhs></prod>
 <prod id="NT-IanaCode"><lhs>IanaCode</lhs>
 <rhs>('i' | 'I') '-' ([a-z] | [A-Z])+</rhs></prod>
 <prod id="NT-UserCode"><lhs>UserCode</lhs>
 <rhs>('x' | 'X') '-' ([a-z] | [A-Z])+</rhs></prod>
 <prod id="NT-Subcode"><lhs>Subcode</lhs>
 <rhs>([a-z] | [A-Z])+</rhs></prod>
 </scrap>
 The <nt def="NT-Langcode">Langcode</nt> may be any of the following:
 <ulist>
 <item><p>a two-letter language code as defined by
 <bibref ref="ISO639"/>, "Codes
 for the representation of names of languages"</p></item>
 <item><p>a language identifier registered with the Internet
 Assigned Numbers Authority <bibref ref="IANA"/>; these begin with the
 prefix "<code>i-</code>" (or "<code>I-</code>")</p></item>
 <item><p>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</p></item>
 </ulist></p>
 <p>There may be any number of <nt def="NT-Subcode">Subcode</nt> segments; if
 the first
 subcode segment exists and the Subcode consists of two
 letters, then it must be a country code from
 <bibref ref="ISO3166"/>, "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 <nt def="NT-Langcode">Langcode</nt> 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:
 <eg><![CDATA[<p xml:lang="en">The quick brown fox jumps over the lazy dog.</p>
 <p xml:lang="en-GB">What colour is it?</p>
 <p xml:lang="en-US">What color is it?</p>
 <sp who="Faust" desc='leise' xml:lang="de">
   <l>Habe nun, ach! Philosophie,</l>
   <l>Juristerei, und Medizin</l>
   <l>und leider auch Theologie</l>
   <l>durchaus studiert mit heißem Bemüh'n.</l>
   </sp>]]></eg></p>
 <!--<p>The xml:lang value is considered to apply both to the contents of an
 element and
 (unless otherwise via attribute default values) to the
 values of all of its attributes with free-text (CDATA) values.  -->
 <p>The intent declared with <kw>xml:lang</kw> is considered to apply to
 all attributes and content of the element where it is specified,
 unless overridden with an instance of <kw>xml:lang</kw>
 on another element within that content.</p>
 <!--
 If no
 value is specified for xml:lang on an element, and no default value is
 defined for it in the DTD, then the xml:lang attribute of any element
 takes the same value it has in the parent element, if any.  The two
 technical terms in the following example both have the same effective
 value for xml:lang:

   <p xml:lang="en">Here the keywords are
   <term xml:lang="en">shift</term> and
   <term>reduce</term>. ...</p>

 The application, not the XML processor, is responsible for this '
 inheritance' of attribute values.
 -->
 <p>A simple declaration for <kw>xml:lang</kw> might take
 the form
 <eg>xml:lang  NMTOKEN  #IMPLIED</eg>
 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:
 <eg><![CDATA[    <!ATTLIST poem   xml:lang NMTOKEN 'fr'>
     <!ATTLIST gloss  xml:lang NMTOKEN 'en'>
     <!ATTLIST note   xml:lang NMTOKEN 'en'>]]></eg>
 </p>

 </div2>
 </div1>
 <!-- &Elements; -->

 <div1 id="sec-logical-struct">
 <head>Logical Structures</head>

 <p><termdef id="dt-element" term="Element">Each <termref def="dt-xml-doc">XML document</termref> contains one or more
 <term>elements</term>, the boundaries of which are
 either delimited by <termref def="dt-stag">start-tags</termref>
 and <termref def="dt-etag">end-tags</termref>, or, for <termref def="dt-empty">empty</termref> elements, by an <termref def="dt-eetag">empty-element tag</termref>. Each element has a type,
 identified by name, sometimes called its "generic
 identifier" (GI), and may have a set of
 attribute specifications.</termdef>  Each attribute specification
 has a <termref def="dt-attrname">name</termref> and a <termref def="dt-attrval">value</termref>.
 </p>
 <scrap lang="ebnf"><head>Element</head>
 <prod id="NT-element"><lhs>element</lhs>
 <rhs><nt def="NT-EmptyElemTag">EmptyElemTag</nt></rhs>
 <rhs>| <nt def="NT-STag">STag</nt> <nt def="NT-content">content</nt>
 <nt def="NT-ETag">ETag</nt></rhs>
 <wfc def="GIMatch"/>
 <vc def="elementvalid"/>
 </prod>
 </scrap>
 <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>
 <wfcnote id="GIMatch">
 <head>Element Type Match</head>
 <p>
 The <nt def="NT-Name">Name</nt> in an element's end-tag must match
 the element type in
 the start-tag.
 </p>
 </wfcnote>
 <vcnote id="elementvalid">
 <head>Element Valid</head>
 <p>An element is
 valid if
 there is a declaration matching
 <nt def="NT-elementdecl">elementdecl</nt> where the
 <nt def="NT-Name">Name</nt> matches the element type, and
 one of the following holds:</p>
 <olist>
 <item><p>The declaration matches <kw>EMPTY</kw> and the element has no
 <termref def="dt-content">content</termref>.</p></item>
 <item><p>The declaration matches <nt def="NT-children">children</nt> and
 the sequence of
 <termref def="dt-parentchild">child elements</termref>
 belongs to the language generated by the regular expression in
 the content model, with optional white space (characters
 matching the nonterminal <nt def="NT-S">S</nt>) between each pair
 of child elements.</p></item>
 <item><p>The declaration matches <nt def="NT-Mixed">Mixed</nt> and
 the content consists of <termref def="dt-chardata">character
 data</termref> and <termref def="dt-parentchild">child elements</termref>
 whose types match names in the content model.</p></item>
 <item><p>The declaration matches <kw>ANY</kw>, and the types
 of any <termref def="dt-parentchild">child elements</termref> have
 been declared.</p></item>
 </olist>
 </vcnote>

 <div2 id="sec-starttags">
 <head>Start-Tags, End-Tags, and Empty-Element Tags</head>

 <p><termdef id="dt-stag" term="Start-Tag">The beginning of every
 non-empty XML element is marked by a <term>start-tag</term>.
 <scrap lang="ebnf">
 <head>Start-tag</head>
 <prodgroup pcw2="6" pcw4="15" pcw5="11.5">
 <prod id="NT-STag"><lhs>STag</lhs>
 <rhs>'&lt;' <nt def="NT-Name">Name</nt>
 (<nt def="NT-S">S</nt> <nt def="NT-Attribute">Attribute</nt>)*
 <nt def="NT-S">S</nt>? '&gt;'</rhs>
 <wfc def="uniqattspec"/>
 </prod>
 <prod id="NT-Attribute"><lhs>Attribute</lhs>
 <rhs><nt def="NT-Name">Name</nt> <nt def="NT-Eq">Eq</nt>
 <nt def="NT-AttValue">AttValue</nt></rhs>
 <vc def="ValueType"/>
 <wfc def="NoExternalRefs"/>
 <wfc def="CleanAttrVals"/></prod>
 </prodgroup>
 </scrap>
 The <nt def="NT-Name">Name</nt> in
 the start- and end-tags gives the
 element's <term>type</term>.</termdef>
 <termdef id="dt-attr" term="Attribute">
 The <nt def="NT-Name">Name</nt>-<nt def="NT-AttValue">AttValue</nt> pairs are
 referred to as
 the <term>attribute specifications</term> of the element</termdef>,
 <termdef id="dt-attrname" term="Attribute Name">with the
 <nt def="NT-Name">Name</nt> in each pair
 referred to as the <term>attribute name</term></termdef> and
 <termdef id="dt-attrval" term="Attribute Value">the content of the
 <nt def="NT-AttValue">AttValue</nt> (the text between the
 <code>'</code> or <code>"</code> delimiters)
 as the <term>attribute value</term>.</termdef>
 </p>
 <wfcnote id="uniqattspec">
 <head>Unique Att Spec</head>
 <p>
 No attribute name may appear more than once in the same start-tag
 or empty-element tag.
 </p>
 </wfcnote>
 <vcnote id="ValueType">
 <head>Attribute Value Type</head>
 <p>
 The attribute must have been declared; the value must be of the type
 declared for it.
 (For attribute types, see <specref ref="attdecls"/>.)
 </p>
 </vcnote>
 <wfcnote id="NoExternalRefs">
 <head>No External Entity References</head>
 <p>
 Attribute values cannot contain direct or indirect entity references
 to external entities.
 </p>
 </wfcnote>
 <wfcnote id="CleanAttrVals">
 <head>No <code>&lt;</code> in Attribute Values</head>
 <p>The <termref def="dt-repltext">replacement text</termref> 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></wfcnote>
 <p>An example of a start-tag:
 <eg>&lt;termdef id="dt-dog" term="dog"&gt;</eg></p>
 <p><termdef id="dt-etag" term="End Tag">The end of every element
 that begins with a start-tag must
 be marked by an <term>end-tag</term>
 containing a name that echoes the element's type as given in the
 start-tag:
 <scrap lang="ebnf">
 <head>End-tag</head>
 <prodgroup pcw2="6" pcw4="15" pcw5="11.5">
 <prod id="NT-ETag"><lhs>ETag</lhs>
 <rhs>'&lt;/' <nt def="NT-Name">Name</nt>
 <nt def="NT-S">S</nt>? '&gt;'</rhs></prod>
 </prodgroup>
 </scrap>
 </termdef></p>
 <p>An example of an end-tag:<eg>&lt;/termdef&gt;</eg></p>
 <p><termdef id="dt-content" term="Content">The
 <termref def="dt-text">text</termref> between the start-tag and
 end-tag is called the element's
 <term>content</term>:
 <scrap lang="ebnf">
 <head>Content of Elements</head>
 <prodgroup pcw2="6" pcw4="15" pcw5="11.5">
 <prod id="NT-content"><lhs>content</lhs>
 <rhs>(<nt def="NT-element">element</nt> | <nt def="NT-CharData">CharData</nt>
 | <nt def="NT-Reference">Reference</nt> | <nt def="NT-CDSect">CDSect</nt>
 | <nt def="NT-PI">PI</nt> | <nt def="NT-Comment">Comment</nt>)*</rhs>
 </prod>
 </prodgroup>
 </scrap>
 </termdef></p>
 <p><termdef id="dt-empty" term="Empty">If an element is <term>empty</term>,
 it must be represented either by a start-tag immediately followed
 by an end-tag or by an empty-element tag.</termdef>
 <termdef id="dt-eetag" term="empty-element tag">An
 <term>empty-element tag</term> takes a special form:
 <scrap lang="ebnf">
 <head>Tags for Empty Elements</head>
 <prodgroup pcw2="6" pcw4="15" pcw5="11.5">
 <prod id="NT-EmptyElemTag"><lhs>EmptyElemTag</lhs>
 <rhs>'&lt;' <nt def="NT-Name">Name</nt> (<nt def="NT-S">S</nt>
 <nt def="NT-Attribute">Attribute</nt>)* <nt def="NT-S">S</nt>?
 '/&gt;'</rhs>
 <wfc def="uniqattspec"/>
 </prod>
 </prodgroup>
 </scrap>
 </termdef></p>
 <p>Empty-element tags may be used for any element which has no
 content, whether or not it is declared using the keyword
 <kw>EMPTY</kw>.
 <termref def="dt-interop">For interoperability</termref>, the empty-element
 tag must be used, and can only be used, for elements which are
 <termref def="dt-eldecl">declared</termref> <kw>EMPTY</kw>.</p>
 <p>Examples of empty elements:
 <eg>&lt;IMG align="left"
  src="http://www.w3.org/Icons/WWW/w3c_home" /&gt;
 &lt;br&gt;&lt;/br&gt;
 &lt;br/&gt;</eg></p>
 </div2>

 <div2 id="elemdecls">
 <head>Element Type Declarations</head>

 <p>The <termref def="dt-element">element</termref> structure of an
 <termref def="dt-xml-doc">XML document</termref> may, for
 <termref def="dt-valid">validation</termref> purposes,
 be constrained
 using element type and attribute-list declarations.
 An element type declaration constrains the element's
 <termref def="dt-content">content</termref>.
 </p>

 <p>Element type declarations often constrain which element types can
 appear as <termref def="dt-parentchild">children</termref> 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><termdef id="dt-eldecl" term="Element Type declaration">An <term>element
 type declaration</term> takes the form:
 <scrap lang="ebnf">
 <head>Element Type Declaration</head>
 <prodgroup pcw2="5.5" pcw4="18" pcw5="9">
 <prod id="NT-elementdecl"><lhs>elementdecl</lhs>
 <rhs>'&lt;!ELEMENT' <nt def="NT-S">S</nt>
 <nt def="NT-Name">Name</nt>
 <nt def="NT-S">S</nt>
 <nt def="NT-contentspec">contentspec</nt>
 <nt def="NT-S">S</nt>? '&gt;'</rhs>
 <vc def="EDUnique"/></prod>
 <prod id="NT-contentspec"><lhs>contentspec</lhs>
 <rhs>'EMPTY'
 | 'ANY'
 | <nt def="NT-Mixed">Mixed</nt>
 | <nt def="NT-children">children</nt>
 </rhs>
 </prod>
 </prodgroup>
 </scrap>
 where the <nt def="NT-Name">Name</nt> gives the element type
 being declared.</termdef>
 </p>

 <vcnote id="EDUnique">
 <head>Unique Element Type Declaration</head>
 <p>
 No element type may be declared more than once.
 </p>
 </vcnote>

 <p>Examples of element type declarations:
 <eg>&lt;!ELEMENT br EMPTY&gt;
 &lt;!ELEMENT p (#PCDATA|emph)* &gt;
 &lt;!ELEMENT %name.para; %content.para; &gt;
 &lt;!ELEMENT container ANY&gt;</eg></p>

 <div3 id="sec-element-content">
 <head>Element Content</head>

 <p><termdef id="dt-elemcontent" term="Element content">An element <termref def="dt-stag">type</termref> has
 <term>element content</term> when elements of that
 type must contain only <termref def="dt-parentchild">child</termref>
 elements (no character data), optionally separated by
 white space (characters matching the nonterminal
 <nt def="NT-S">S</nt>).
 </termdef>
 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 (<nt def="NT-cp">cp</nt>s), which consist of names,
 choice lists of content particles, or
 sequence lists of content particles:
 <scrap lang="ebnf">
 <head>Element-content Models</head>
 <prodgroup pcw2="5.5" pcw4="16" pcw5="11">
 <prod id="NT-children"><lhs>children</lhs>
 <rhs>(<nt def="NT-choice">choice</nt>
 | <nt def="NT-seq">seq</nt>)
 ('?' | '*' | '+')?</rhs></prod>
 <prod id="NT-cp"><lhs>cp</lhs>
 <rhs>(<nt def="NT-Name">Name</nt>
 | <nt def="NT-choice">choice</nt>
 | <nt def="NT-seq">seq</nt>)
 ('?' | '*' | '+')?</rhs></prod>
 <prod id="NT-choice"><lhs>choice</lhs>
 <rhs>'(' <nt def="NT-S">S</nt>? cp
 ( <nt def="NT-S">S</nt>? '|' <nt def="NT-S">S</nt>? <nt def="NT-cp">cp</nt> )*
 <nt def="NT-S">S</nt>? ')'</rhs>
 <vc def="vc-PEinGroup"/></prod>
 <prod id="NT-seq"><lhs>seq</lhs>
 <rhs>'(' <nt def="NT-S">S</nt>? cp
 ( <nt def="NT-S">S</nt>? ',' <nt def="NT-S">S</nt>? <nt def="NT-cp">cp</nt> )*
 <nt def="NT-S">S</nt>? ')'</rhs>
 <vc def="vc-PEinGroup"/></prod>

 </prodgroup>
 </scrap>
 where each <nt def="NT-Name">Name</nt> is the type of an element which may
 appear as a <termref def="dt-parentchild">child</termref>.
 Any content
 particle in a choice list may appear in the <termref def="dt-elemcontent">element content</termref> at the location where
 the choice list appears in the grammar;
 content particles occurring in a sequence list must each
 appear in the <termref def="dt-elemcontent">element content</termref> 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.  <termref def="dt-compat">For compatibility</termref>, 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 <specref ref="determinism"/>.
 <!-- appendix <specref ref="determinism"/>. -->
 <!-- appendix on deterministic content models. -->
 </p>
 <vcnote id="vc-PEinGroup">
 <head>Proper Group/PE Nesting</head>
 <p>Parameter-entity
 <termref def="dt-repltext">replacement text</termref> must be properly nested
 with parenthetized groups.
 That is to say, if either of the opening or closing parentheses
 in a <nt def="NT-choice">choice</nt>, <nt def="NT-seq">seq</nt>, or
 <nt def="NT-Mixed">Mixed</nt> construct
 is contained in the replacement text for a
 <termref def="dt-PERef">parameter entity</termref>,
 both must be contained in the same replacement text.</p>
 <p><termref def="dt-interop">For interoperability</termref>,
 if a parameter-entity reference appears in a
 <nt def="NT-choice">choice</nt>, <nt def="NT-seq">seq</nt>, or
 <nt def="NT-Mixed">Mixed</nt> 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>
 </vcnote>
 <p>Examples of element-content models:
 <eg>&lt;!ELEMENT spec (front, body, back?)&gt;
 &lt;!ELEMENT div1 (head, (p | list | note)*, div2*)&gt;
 &lt;!ELEMENT dictionary-body (%div.mix; | %dict.mix;)*&gt;</eg></p>
 </div3>

 <div3 id="sec-mixed-content">
 <head>Mixed Content</head>

 <p><termdef id="dt-mixed" term="Mixed Content">An element
 <termref def="dt-stag">type</termref> has
 <term>mixed content</term> when elements of that type may contain
 character data, optionally interspersed with
 <termref def="dt-parentchild">child</termref> elements.</termdef>
 In this case, the types of the child elements
 may be constrained, but not their order or their number of occurrences:
 <scrap lang="ebnf">
 <head>Mixed-content Declaration</head>
 <prodgroup pcw2="5.5" pcw4="16" pcw5="11">
 <prod id="NT-Mixed"><lhs>Mixed</lhs>
 <rhs>'(' <nt def="NT-S">S</nt>?
 '#PCDATA'
 (<nt def="NT-S">S</nt>?
 '|'
 <nt def="NT-S">S</nt>?
 <nt def="NT-Name">Name</nt>)*
 <nt def="NT-S">S</nt>?
 ')*' </rhs>
 <rhs>| '(' <nt def="NT-S">S</nt>? '#PCDATA' <nt def="NT-S">S</nt>? ')'
 </rhs><vc def="vc-PEinGroup"/>
 <vc def="vc-MixedChildrenUnique"/>
 </prod>

 </prodgroup>
 </scrap>
 where the <nt def="NT-Name">Name</nt>s give the types of elements
 that may appear as children.
 </p>
 <vcnote id="vc-MixedChildrenUnique">
 <head>No Duplicate Types</head>
 <p>The same name must not appear more than once in a single mixed-content
 declaration.
 </p></vcnote>
 <p>Examples of mixed content declarations:
 <eg>&lt;!ELEMENT p (#PCDATA|a|ul|b|i|em)*&gt;
 &lt;!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* &gt;
 &lt;!ELEMENT b (#PCDATA)&gt;</eg></p>
 </div3>
 </div2>

 <div2 id="attdecls">
 <head>Attribute-List Declarations</head>

 <p><termref def="dt-attr">Attributes</termref> are used to associate
 name-value pairs with <termref def="dt-element">elements</termref>.
 Attribute specifications may appear only within <termref def="dt-stag">start-tags</termref>
 and <termref def="dt-eetag">empty-element tags</termref>;
 thus, the productions used to
 recognize them appear in <specref ref="sec-starttags"/>.
 Attribute-list
 declarations may be used:
 <ulist>
 <item><p>To define the set of attributes pertaining to a given
 element type.</p></item>
 <item><p>To establish type constraints for these
 attributes.</p></item>
 <item><p>To provide <termref def="dt-default">default values</termref>
 for attributes.</p></item>
 </ulist>
 </p>
 <p><termdef id="dt-attdecl" term="Attribute-List Declaration">
 <term>Attribute-list declarations</term> specify the name, data type, and default
 value (if any) of each attribute associated with a given element type:
 <scrap lang="ebnf">
 <head>Attribute-list Declaration</head>
 <prod id="NT-AttlistDecl"><lhs>AttlistDecl</lhs>
 <rhs>'&lt;!ATTLIST' <nt def="NT-S">S</nt>
 <nt def="NT-Name">Name</nt>
 <nt def="NT-AttDef">AttDef</nt>*
 <nt def="NT-S">S</nt>? '&gt;'</rhs>
 </prod>
 <prod id="NT-AttDef"><lhs>AttDef</lhs>
 <rhs><nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt>
 <nt def="NT-S">S</nt> <nt def="NT-AttType">AttType</nt>
 <nt def="NT-S">S</nt> <nt def="NT-DefaultDecl">DefaultDecl</nt></rhs>
 </prod>
 </scrap>
 The <nt def="NT-Name">Name</nt> in the
 <nt def="NT-AttlistDecl">AttlistDecl</nt> 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 <nt def="NT-Name">Name</nt> in the
 <nt def="NT-AttDef">AttDef</nt> rule is
 the name of the attribute.</termdef></p>
 <p>
 When more than one <nt def="NT-AttlistDecl">AttlistDecl</nt> 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.
 <termref def="dt-interop">For interoperability,</termref> 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>

 <div3 id="sec-attribute-types">
 <head>Attribute Types</head>

 <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:
 <scrap lang="ebnf">
 <head>Attribute Types</head>
 <prodgroup pcw4="14" pcw5="11.5">
 <prod id="NT-AttType"><lhs>AttType</lhs>
 <rhs><nt def="NT-StringType">StringType</nt>
 | <nt def="NT-TokenizedType">TokenizedType</nt>
 | <nt def="NT-EnumeratedType">EnumeratedType</nt>
 </rhs>
 </prod>
 <prod id="NT-StringType"><lhs>StringType</lhs>
 <rhs>'CDATA'</rhs>
 </prod>
 <prod id="NT-TokenizedType"><lhs>TokenizedType</lhs>
 <rhs>'ID'</rhs>
 <vc def="id"/>
 <vc def="one-id-per-el"/>
 <vc def="id-default"/>
 <rhs>| 'IDREF'</rhs>
 <vc def="idref"/>
 <rhs>| 'IDREFS'</rhs>
 <vc def="idref"/>
 <rhs>| 'ENTITY'</rhs>
 <vc def="entname"/>
 <rhs>| 'ENTITIES'</rhs>
 <vc def="entname"/>
 <rhs>| 'NMTOKEN'</rhs>
 <vc def="nmtok"/>
 <rhs>| 'NMTOKENS'</rhs>
 <vc def="nmtok"/></prod>
 </prodgroup>
 </scrap>
 </p>
 <vcnote id="id">
 <head>ID</head>
 <p>
 Values of type <kw>ID</kw> must match the
 <nt def="NT-Name">Name</nt> 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>
 </vcnote>
 <vcnote id="one-id-per-el">
 <head>One ID per Element Type</head>
 <p>No element type may have more than one ID attribute specified.</p>
 </vcnote>
 <vcnote id="id-default">
 <head>ID Attribute Default</head>
 <p>An ID attribute must have a declared default of <kw>#IMPLIED</kw> or
 <kw>#REQUIRED</kw>.</p>
 </vcnote>
 <vcnote id="idref">
 <head>IDREF</head>
 <p>
 Values of type <kw>IDREF</kw> must match
 the <nt def="NT-Name">Name</nt> production, and
 values of type <kw>IDREFS</kw> must match
 <nt def="NT-Names">Names</nt>;
 each <nt def="NT-Name">Name</nt> must match the value of an ID attribute on
 some element in the XML document; i.e. <kw>IDREF</kw> values must
 match the value of some ID attribute.
 </p>
 </vcnote>
 <vcnote id="entname">
 <head>Entity Name</head>
 <p>
 Values of type <kw>ENTITY</kw>
 must match the <nt def="NT-Name">Name</nt> production,
 values of type <kw>ENTITIES</kw> must match
 <nt def="NT-Names">Names</nt>;
 each <nt def="NT-Name">Name</nt> must
 match the
 name of an <termref def="dt-unparsed">unparsed entity</termref> declared in the
 <termref def="dt-doctype">DTD</termref>.
 </p>
 </vcnote>
 <vcnote id="nmtok">
 <head>Name Token</head>
 <p>
 Values of type <kw>NMTOKEN</kw> must match the
 <nt def="NT-Nmtoken">Nmtoken</nt> production;
 values of type <kw>NMTOKENS</kw> must
 match <termref def="NT-Nmtokens">Nmtokens</termref>.
 </p>
 </vcnote>
 <!-- why?
 <p>The XML processor must normalize attribute values before
 passing them to the application, as described in
 <specref ref="AVNormalize"/>.</p>-->
 <p><termdef id="dt-enumerated" term="Enumerated Attribute Values"><term>Enumerated attributes</term> can take one
 of a list of values provided in the declaration</termdef>. There are two
 kinds of enumerated types:
 <scrap lang="ebnf">
 <head>Enumerated Attribute Types</head>
 <prod id="NT-EnumeratedType"><lhs>EnumeratedType</lhs>
 <rhs><nt def="NT-NotationType">NotationType</nt>
 | <nt def="NT-Enumeration">Enumeration</nt>
 </rhs></prod>
 <prod id="NT-NotationType"><lhs>NotationType</lhs>
 <rhs>'NOTATION'
 <nt def="NT-S">S</nt>
 '('
 <nt def="NT-S">S</nt>?
 <nt def="NT-Name">Name</nt>
 (<nt def="NT-S">S</nt>? '|' <nt def="NT-S">S</nt>?
 <nt def="NT-Name">Name</nt>)*
 <nt def="NT-S">S</nt>? ')'
 </rhs>
 <vc def="notatn"/></prod>
 <prod id="NT-Enumeration"><lhs>Enumeration</lhs>
 <rhs>'(' <nt def="NT-S">S</nt>?
 <nt def="NT-Nmtoken">Nmtoken</nt>
 (<nt def="NT-S">S</nt>? '|'
 <nt def="NT-S">S</nt>?
 <nt def="NT-Nmtoken">Nmtoken</nt>)*
 <nt def="NT-S">S</nt>?
 ')'</rhs>
 <vc def="enum"/></prod>
 </scrap>
 A <kw>NOTATION</kw> attribute identifies a
 <termref def="dt-notation">notation</termref>, 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>

 <vcnote id="notatn">
 <head>Notation Attributes</head>
 <p>
 Values of this type must match
 one of the <titleref href="Notations">notation</titleref> names included in
 the declaration; all notation names in the declaration must
 be declared.
 </p>
 </vcnote>
 <vcnote id="enum">
 <head>Enumeration</head>
 <p>
 Values of this type
 must match one of the <nt def="NT-Nmtoken">Nmtoken</nt> tokens in the
 declaration.
 </p>
 </vcnote>
 <p><termref def="dt-interop">For interoperability,</termref> the same
 <nt def="NT-Nmtoken">Nmtoken</nt> should not occur more than once in the
 enumerated attribute types of a single element type.
 </p>
 </div3>

 <div3 id="sec-attr-defaults">
 <head>Attribute Defaults</head>

 <p>An <termref def="dt-attdecl">attribute declaration</termref> 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.
 <scrap lang="ebnf">
 <head>Attribute Defaults</head>
 <prodgroup pcw4="14" pcw5="11.5">
 <prod id="NT-DefaultDecl"><lhs>DefaultDecl</lhs>
 <rhs>'#REQUIRED'
 |&nbsp;'#IMPLIED' </rhs>
 <rhs>| (('#FIXED' S)? <nt def="NT-AttValue">AttValue</nt>)</rhs>
 <vc def="RequiredAttr"/>
 <vc def="defattrvalid"/>
 <wfc def="CleanAttrVals"/>
 <vc def="FixedAttr"/>
 </prod>
 </prodgroup>
 </scrap>

 </p>
 <p>In an attribute declaration, <kw>#REQUIRED</kw> means that the
 attribute must always be provided, <kw>#IMPLIED</kw> that no default
 value is provided.
 <!-- not any more!!
 <kw>#IMPLIED</kw> means that if the attribute is omitted
 from an element of this type,
 the XML processor must inform the application
 that no value was specified; no constraint is placed on the behavior
 of the application. -->
 <termdef id="dt-default" term="Attribute Default">If the
 declaration
 is neither <kw>#REQUIRED</kw> nor <kw>#IMPLIED</kw>, then the
 <nt def="NT-AttValue">AttValue</nt> value contains the declared
 <term>default</term> value; the <kw>#FIXED</kw> 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.</termdef></p>
 <vcnote id="RequiredAttr">
 <head>Required Attribute</head>
 <p>If the default declaration is the keyword <kw>#REQUIRED</kw>, then
 the attribute must be specified for
 all elements of the type in the attribute-list declaration.
 </p></vcnote>
 <vcnote id="defattrvalid">
 <head>Attribute Default Legal</head>
 <p>
 The declared
 default value must meet the lexical constraints of the declared attribute type.
 </p>
 </vcnote>
 <vcnote id="FixedAttr">
 <head>Fixed Attribute Default</head>
 <p>If an attribute has a default value declared with the
 <kw>#FIXED</kw> keyword, instances of that attribute must
 match the default value.
 </p></vcnote>

 <p>Examples of attribute-list declarations:
 <eg>&lt;!ATTLIST termdef
           id      ID      #REQUIRED
           name    CDATA   #IMPLIED&gt;
 &lt;!ATTLIST list
           type    (bullets|ordered|glossary)  "ordered"&gt;
 &lt;!ATTLIST form
           method  CDATA   #FIXED "POST"&gt;</eg></p>
 </div3>
 <div3 id="AVNormalize">
 <head>Attribute-Value Normalization</head>
 <p>Before the value of an attribute is passed to the application
 or checked for validity, the
 XML processor must normalize it as follows:
 <ulist>
 <item><p>a character reference is processed by appending the referenced
 character to the attribute value</p></item>
 <item><p>an entity reference is processed by recursively processing the
 replacement text of the entity</p></item>
 <item><p>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</p></item>
 <item><p>other characters are processed by appending them to the normalized
 value</p>
 </item></ulist>
 </p>
 <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
 <kw>CDATA</kw>.
 </p>
 </div3>
 </div2>
 <div2 id="sec-condition-sect">
 <head>Conditional Sections</head>
 <p><termdef id="dt-cond-section" term="conditional section">
 <term>Conditional sections</term> are portions of the
 <termref def="dt-doctype">document type declaration external subset</termref>
 which are
 included in, or excluded from, the logical structure of the DTD based on
 the keyword which governs them.</termdef>
 <scrap lang="ebnf">
 <head>Conditional Section</head>
 <prodgroup pcw2="9" pcw4="14.5">
 <prod id="NT-conditionalSect"><lhs>conditionalSect</lhs>
 <rhs><nt def="NT-includeSect">includeSect</nt>
 | <nt def="NT-ignoreSect">ignoreSect</nt>
 </rhs>
 </prod>
 <prod id="NT-includeSect"><lhs>includeSect</lhs>
 <rhs>'&lt;![' S? 'INCLUDE' S? '['

 <nt def="NT-extSubsetDecl">extSubsetDecl</nt>
 ']]&gt;'
 </rhs>
 </prod>
 <prod id="NT-ignoreSect"><lhs>ignoreSect</lhs>
 <rhs>'&lt;![' S? 'IGNORE' S? '['
 <nt def="NT-ignoreSectContents">ignoreSectContents</nt>*
 ']]&gt;'</rhs>
 </prod>

 <prod id="NT-ignoreSectContents"><lhs>ignoreSectContents</lhs>
 <rhs><nt def="NT-Ignore">Ignore</nt>
 ('&lt;![' <nt def="NT-ignoreSectContents">ignoreSectContents</nt> ']]&gt;'
 <nt def="NT-Ignore">Ignore</nt>)*</rhs></prod>
 <prod id="NT-Ignore"><lhs>Ignore</lhs>
 <rhs><nt def="NT-Char">Char</nt>* -
 (<nt def="NT-Char">Char</nt>* ('&lt;![' | ']]&gt;')
 <nt def="NT-Char">Char</nt>*)
 </rhs></prod>

 </prodgroup>
 </scrap>
 </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 <kw>INCLUDE</kw>, then the contents of the conditional
 section are part of the DTD.
 If the keyword of the conditional
 section is <kw>IGNORE</kw>, 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 <kw>INCLUDE</kw> occurs within a larger conditional
 section with a keyword of <kw>IGNORE</kw>, 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:
 <eg>&lt;!ENTITY % draft 'INCLUDE' &gt;
 &lt;!ENTITY % final 'IGNORE' &gt;

 &lt;![%draft;[
 &lt;!ELEMENT book (comments*, title, body, supplements?)&gt;
 ]]&gt;
 &lt;![%final;[
 &lt;!ELEMENT book (title, body, supplements?)&gt;
 ]]&gt;
 </eg>
 </p>
 </div2>


 <!--
 <div2 id='sec-pass-to-app'>
 <head>XML Processor Treatment of Logical Structure</head>
 <p>When an XML processor encounters a start-tag, it must make
 at least the following information available to the application:
 <ulist>
 <item>
 <p>the element type's generic identifier</p>
 </item>
 <item>
 <p>the names of attributes known to apply to this element type
 (validating processors must make available names of all attributes
 declared for the element type; non-validating processors must
 make available at least the names of the attributes for which
 values are specified.
 </p>
 </item>
 </ulist>
 </p>
 </div2>
 -->

 </div1>
 <!-- &Entities; -->

 <div1 id="sec-physical-struct">
 <head>Physical Structures</head>

 <p><termdef id="dt-entity" term="Entity">An XML document may consist
 of one or many storage units.   These are called
 <term>entities</term>; they all have <term>content</term> and are all
 (except for the document entity, see below, and
 the <termref def="dt-doctype">external DTD subset</termref>)
 identified by <term>name</term>.
 </termdef>
 Each XML document has one entity
 called the <termref def="dt-docent">document entity</termref>, which serves
 as the starting point for the <termref def="dt-xml-proc">XML
 processor</termref> and may contain the whole document.</p>
 <p>Entities may be either parsed or unparsed.
 <termdef id="dt-parsedent" term="Text Entity">A <term>parsed entity's</term>
 contents are referred to as its
 <termref def="dt-repltext">replacement text</termref>;
 this <termref def="dt-text">text</termref> is considered an
 integral part of the document.</termdef></p>

 <p><termdef id="dt-unparsed" term="Unparsed Entity">An
 <term>unparsed entity</term>
 is a resource whose contents may or may not be
 <termref def="dt-text">text</termref>, and if text, may not be XML.
 Each unparsed entity
 has an associated <termref def="dt-notation">notation</termref>, 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.</termdef>
 </p>
 <p>
 Parsed entities are invoked by name using entity references;
 unparsed entities by name, given in the value of <kw>ENTITY</kw>
 or <kw>ENTITIES</kw>
 attributes.</p>
 <p><termdef id="gen-entity" term="general entity"><term>General entities</term>
 are entities for use within the document content.
 In this specification, general entities are sometimes referred
 to with the unqualified term <emph>entity</emph> when this leads
 to no ambiguity.</termdef>
 <termdef id="dt-PE" term="Parameter entity">Parameter entities
 are parsed entities for use within the DTD.</termdef>
 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>

 <div2 id="sec-references">
 <head>Character and Entity References</head>
 <p><termdef id="dt-charref" term="Character Reference">
 A <term>character reference</term> refers to a specific character in the
 ISO/IEC 10646 character set, for example one not directly accessible from
 available input devices.
 <scrap lang="ebnf">
 <head>Character Reference</head>
 <prod id="NT-CharRef"><lhs>CharRef</lhs>
 <rhs>'&amp;#' [0-9]+ ';' </rhs>
 <rhs>| '&hcro;' [0-9a-fA-F]+ ';'</rhs>
 <wfc def="wf-Legalchar"/>
 </prod>
 </scrap>
 <wfcnote id="wf-Legalchar">
 <head>Legal Character</head>
 <p>Characters referred to using character references must
 match the production for
 <termref def="NT-Char">Char</termref>.</p>
 </wfcnote>
 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.
 </termdef>
 </p>
 <p><termdef id="dt-entref" term="Entity Reference">An <term>entity
 reference</term> refers to the content of a named entity.</termdef>
 <termdef id="dt-GERef" term="General Entity Reference">References to
 parsed general entities
 use ampersand (<code>&amp;</code>) and semicolon (<code>;</code>) as
 delimiters.</termdef>
 <termdef id="dt-PERef" term="Parameter-entity reference">
 <term>Parameter-entity references</term> use percent-sign (<code>%</code>) and
 semicolon
 (<code>;</code>) as delimiters.</termdef>
 </p>
 <scrap lang="ebnf">
 <head>Entity Reference</head>
 <prod id="NT-Reference"><lhs>Reference</lhs>
 <rhs><nt def="NT-EntityRef">EntityRef</nt>
 | <nt def="NT-CharRef">CharRef</nt></rhs></prod>
 <prod id="NT-EntityRef"><lhs>EntityRef</lhs>
 <rhs>'&amp;' <nt def="NT-Name">Name</nt> ';'</rhs>
 <wfc def="wf-entdeclared"/>
 <vc def="vc-entdeclared"/>
 <wfc def="textent"/>
 <wfc def="norecursion"/>
 </prod>
 <prod id="NT-PEReference"><lhs>PEReference</lhs>
 <rhs>'%' <nt def="NT-Name">Name</nt> ';'</rhs>
 <vc def="vc-entdeclared"/>
 <wfc def="norecursion"/>
 <wfc def="indtd"/>
 </prod>
 </scrap>

 <wfcnote id="wf-entdeclared">
 <head>Entity Declared</head>
 <p>In a document without any DTD, a document with only an internal
 DTD subset which contains no parameter entity references, or a document with
 "<code>standalone='yes'</code>",
 the <nt def="NT-Name">Name</nt> given in the entity reference must
 <termref def="dt-match">match</termref> that in an
 <titleref href="sec-entity-decl">entity declaration</titleref>, except that
 well-formed documents need not declare
 any of the following entities: &magicents;.
 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>
 <p>Note that if entities are declared in the external subset or in
 external parameter entities, a non-validating processor is
 <titleref href="include-if-valid">not obligated to</titleref> read
 and process their declarations; for such documents, the rule that
 an entity must be declared is a well-formedness constraint only
 if <titleref href="sec-rmd">standalone='yes'</titleref>.</p>
 </wfcnote>
 <vcnote id="vc-entdeclared">
 <head>Entity Declared</head>
 <p>In a document with an external subset or external parameter
 entities with "<code>standalone='no'</code>",
 the <nt def="NT-Name">Name</nt> given in the entity reference must <termref def="dt-match">match</termref> that in an
 <titleref href="sec-entity-decl">entity declaration</titleref>.
 For interoperability, valid documents should declare the entities
 &magicents;, in the form
 specified in <specref ref="sec-predefined-ent"/>.
 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>
 </vcnote>
 <!-- FINAL EDIT:  is this duplication too clumsy? -->
 <wfcnote id="textent">
 <head>Parsed Entity</head>
 <p>
 An entity reference must not contain the name of an <termref def="dt-unparsed">unparsed entity</termref>. Unparsed entities may be referred
 to only in <termref def="dt-attrval">attribute values</termref> declared to
 be of type <kw>ENTITY</kw> or <kw>ENTITIES</kw>.
 </p>
 </wfcnote>
 <wfcnote id="norecursion">
 <head>No Recursion</head>
 <p>
 A parsed entity must not contain a recursive reference to itself,
 either directly or indirectly.
 </p>
 </wfcnote>
 <wfcnote id="indtd">
 <head>In DTD</head>
 <p>
 Parameter-entity references may only appear in the
 <termref def="dt-doctype">DTD</termref>.
 </p>
 </wfcnote>
 <p>Examples of character and entity references:
 <eg>Type &lt;key&gt;less-than&lt;/key&gt; (&hcro;3C;) to save options.
 This document was prepared on &amp;docdate; and
 is classified &amp;security-level;.</eg></p>
 <p>Example of a parameter-entity reference:
 <eg><![CDATA[<!-- declare the parameter entity "ISOLat2"... -->
 <!ENTITY % ISOLat2
          SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" >
 <!-- ... now reference it. -->
 %ISOLat2;]]></eg></p>
 </div2>

 <div2 id="sec-entity-decl">
 <head>Entity Declarations</head>

 <p><termdef id="dt-entdecl" term="entity declaration">
 Entities are declared thus:
 <scrap lang="ebnf">
 <head>Entity Declaration</head>
 <prodgroup pcw2="5" pcw4="18.5">
 <prod id="NT-EntityDecl"><lhs>EntityDecl</lhs>
 <rhs><nt def="NT-GEDecl">GEDecl</nt><!--</rhs><com>General entities</com>
 <rhs>--> | <nt def="NT-PEDecl">PEDecl</nt></rhs>
 <!--<com>Parameter entities</com>-->
 </prod>
 <prod id="NT-GEDecl"><lhs>GEDecl</lhs>
 <rhs>'&lt;!ENTITY' <nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt>
 <nt def="NT-S">S</nt> <nt def="NT-EntityDef">EntityDef</nt>
 <nt def="NT-S">S</nt>? '&gt;'</rhs>
 </prod>
 <prod id="NT-PEDecl"><lhs>PEDecl</lhs>
 <rhs>'&lt;!ENTITY' <nt def="NT-S">S</nt> '%' <nt def="NT-S">S</nt>
 <nt def="NT-Name">Name</nt> <nt def="NT-S">S</nt>
 <nt def="NT-PEDef">PEDef</nt> <nt def="NT-S">S</nt>? '&gt;'</rhs>
 <!--<com>Parameter entities</com>-->
 </prod>
 <prod id="NT-EntityDef"><lhs>EntityDef</lhs>
 <rhs><nt def="NT-EntityValue">EntityValue</nt>
 <!--</rhs>
 <rhs>-->| (<nt def="NT-ExternalID">ExternalID</nt>
 <nt def="NT-NDataDecl">NDataDecl</nt>?)</rhs>
 <!-- <nt def='NT-ExternalDef'>ExternalDef</nt></rhs> -->
 </prod>
 <!-- FINAL EDIT: what happened to WFs here? -->
 <prod id="NT-PEDef"><lhs>PEDef</lhs>
 <rhs><nt def="NT-EntityValue">EntityValue</nt>
 | <nt def="NT-ExternalID">ExternalID</nt></rhs></prod>
 </prodgroup>
 </scrap>
 The <nt def="NT-Name">Name</nt> identifies the entity in an
 <termref def="dt-entref">entity reference</termref> or, in the case of an
 unparsed entity, in the value of an <kw>ENTITY</kw> or <kw>ENTITIES</kw>
 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.</termdef>
 </p>

 <div3 id="sec-internal-ent">
 <head>Internal Entities</head>

 <p><termdef id="dt-internent" term="Internal Entity Replacement Text">If
 the entity definition is an
 <nt def="NT-EntityValue">EntityValue</nt>,
 the defined entity is called an <term>internal entity</term>.
 There is no separate physical
 storage object, and the content of the entity is given in the
 declaration. </termdef>
 Note that some processing of entity and character references in the
 <termref def="dt-litentval">literal entity value</termref> may be required to
 produce the correct <termref def="dt-repltext">replacement
 text</termref>: see <specref ref="intern-replacement"/>.
 </p>
 <p>An internal entity is a <termref def="dt-parsedent">parsed
 entity</termref>.</p>
 <p>Example of an internal entity declaration:
 <eg>&lt;!ENTITY Pub-Status "This is a pre-release of the
  specification."&gt;</eg></p>
 </div3>

 <div3 id="sec-external-ent">
 <head>External Entities</head>

 <p><termdef id="dt-extent" term="External Entity">If the entity is not
 internal, it is an <term>external
 entity</term>, declared as follows:
 <scrap lang="ebnf">
 <head>External Entity Declaration</head>
 <!--
 <prod id='NT-ExternalDef'><lhs>ExternalDef</lhs>
 <rhs></prod> -->
 <prod id="NT-ExternalID"><lhs>ExternalID</lhs>
 <rhs>'SYSTEM' <nt def="NT-S">S</nt>
 <nt def="NT-SystemLiteral">SystemLiteral</nt></rhs>
 <rhs>| 'PUBLIC' <nt def="NT-S">S</nt>
 <nt def="NT-PubidLiteral">PubidLiteral</nt>
 <nt def="NT-S">S</nt>
 <nt def="NT-SystemLiteral">SystemLiteral</nt>
 </rhs>
 </prod>
 <prod id="NT-NDataDecl"><lhs>NDataDecl</lhs>
 <rhs><nt def="NT-S">S</nt> 'NDATA' <nt def="NT-S">S</nt>
 <nt def="NT-Name">Name</nt></rhs>
 <vc def="not-declared"/></prod>
 </scrap>
 If the <nt def="NT-NDataDecl">NDataDecl</nt> is present, this is a
 general <termref def="dt-unparsed">unparsed
 entity</termref>; otherwise it is a parsed entity.</termdef></p>
 <vcnote id="not-declared">
 <head>Notation Declared</head>
 <p>
 The <nt def="NT-Name">Name</nt> must match the declared name of a
 <termref def="dt-notation">notation</termref>.
 </p>
 </vcnote>
 <p><termdef id="dt-sysid" term="System Identifier">The
 <nt def="NT-SystemLiteral">SystemLiteral</nt>
 is called the entity's <term>system identifier</term>. It is a URI,
 which may be used to retrieve the entity.</termdef>
 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
 <termref def="dt-docent">document entity</termref>, to the entity
 containing the <termref def="dt-doctype">external DTD subset</termref>,
 or to some other <termref def="dt-extent">external parameter entity</termref>.
 </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><termdef id="dt-pubid" term="Public identifier">
 In addition to a system identifier, an external identifier may
 include a <term>public identifier</term>.</termdef>
 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:
 <eg>&lt;!ENTITY open-hatch
          SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml"&gt;
 &lt;!ENTITY open-hatch
          PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN"
          "http://www.textuality.com/boilerplate/OpenHatch.xml"&gt;
 &lt;!ENTITY hatch-pic
          SYSTEM "../grafix/OpenHatch.gif"
          NDATA gif &gt;</eg></p>
 </div3>

 </div2>

 <div2 id="TextEntities">
 <head>Parsed Entities</head>
 <div3 id="sec-TextDecl">
 <head>The Text Declaration</head>
 <p>External parsed entities may each begin with a <term>text
 declaration</term>.
 <scrap lang="ebnf">
 <head>Text Declaration</head>
 <prodgroup pcw4="12.5" pcw5="13">
 <prod id="NT-TextDecl"><lhs>TextDecl</lhs>
 <rhs>&xmlpio;
 <nt def="NT-VersionInfo">VersionInfo</nt>?
 <nt def="NT-EncodingDecl">EncodingDecl</nt>
 <nt def="NT-S">S</nt>? &pic;</rhs>
 </prod>
 </prodgroup>
 </scrap>
 </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>
 </div3>
 <div3 id="wf-entities">
 <head>Well-Formed Parsed Entities</head>
 <p>The document entity is well-formed if it matches the production labeled
 <nt def="NT-document">document</nt>.
 An external general
 parsed entity is well-formed if it matches the production labeled
 <nt def="NT-extParsedEnt">extParsedEnt</nt>.
 An external parameter
 entity is well-formed if it matches the production labeled
 <nt def="NT-extPE">extPE</nt>.
 <scrap lang="ebnf">
 <head>Well-Formed External Parsed Entity</head>
 <prod id="NT-extParsedEnt"><lhs>extParsedEnt</lhs>
 <rhs><nt def="NT-TextDecl">TextDecl</nt>?
 <nt def="NT-content">content</nt></rhs>
 </prod>
 <prod id="NT-extPE"><lhs>extPE</lhs>
 <rhs><nt def="NT-TextDecl">TextDecl</nt>?
 <nt def="NT-extSubsetDecl">extSubsetDecl</nt></rhs>
 </prod>
 </scrap>
 An internal general parsed entity is well-formed if its replacement text
 matches the production labeled
 <nt def="NT-content">content</nt>.
 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
 <termref def="dt-stag">start-tag</termref>,
 <termref def="dt-etag">end-tag</termref>,
 <termref def="dt-empty">empty-element tag</termref>,
 <termref def="dt-element">element</termref>,
 <termref def="dt-comment">comment</termref>,
 <termref def="dt-pi">processing instruction</termref>,
 <termref def="dt-charref">character
 reference</termref>, or
 <termref def="dt-entref">entity reference</termref>
 can begin in one entity and end in another.</p>
 </div3>
 <div3 id="charencoding">
 <head>Character Encoding in Entities</head>

 <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 <titleref href="TextDecl">text
 declaration</titleref> containing an encoding declaration:
 <scrap lang="ebnf">
 <head>Encoding Declaration</head>
 <prod id="NT-EncodingDecl"><lhs>EncodingDecl</lhs>
 <rhs><nt def="NT-S">S</nt>
 'encoding' <nt def="NT-Eq">Eq</nt>
 ('"' <nt def="NT-EncName">EncName</nt> '"' |
 "'" <nt def="NT-EncName">EncName</nt> "'" )
 </rhs>
 </prod>
 <prod id="NT-EncName"><lhs>EncName</lhs>
 <rhs>[A-Za-z] ([A-Za-z0-9._] | '-')*</rhs>
 <com>Encoding name contains only Latin characters</com>
 </prod>
 </scrap>
 In the <termref def="dt-docent">document entity</termref>, the encoding
 declaration is part of the <termref def="dt-xmldecl">XML declaration</termref>.
 The <nt def="NT-EncName">EncName</nt> is the name of the encoding used.
 </p>
 <!-- FINAL EDIT:  check name of IANA and charset names -->
 <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 <emph>charset</emph>s)
 with the Internet Assigned Numbers
 Authority <bibref ref="IANA"/>, 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 <termref def="dt-error">error</termref> 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 <termref def="dt-fatal">fatal error</termref> when an XML processor
 encounters an entity with an encoding that it is unable to process.</p>
 <p>Examples of encoding declarations:
 <eg>&lt;?xml encoding='UTF-8'?&gt;
 &lt;?xml encoding='EUC-JP'?&gt;</eg></p>
 </div3>
 </div2>
 <div2 id="entproc">
 <head>XML Processor Treatment of Entities and References</head>
 <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 <termref def="dt-xml-proc">XML processor</termref> in
 each case.
 The labels in the leftmost column describe the recognition context:
 <glist>
 <gitem><label>Reference in Content</label>
 <def><p>as a reference
 anywhere after the <termref def="dt-stag">start-tag</termref> and
 before the <termref def="dt-etag">end-tag</termref> of an element; corresponds
 to the nonterminal <nt def="NT-content">content</nt>.</p></def>
 </gitem>
 <gitem>
 <label>Reference in Attribute Value</label>
 <def><p>as a reference within either the value of an attribute in a
 <termref def="dt-stag">start-tag</termref>, or a default
 value in an <termref def="dt-attdecl">attribute declaration</termref>;
 corresponds to the nonterminal
 <nt def="NT-AttValue">AttValue</nt>.</p></def></gitem>
 <gitem>
 <label>Occurs as Attribute Value</label>
 <def><p>as a <nt def="NT-Name">Name</nt>, not a reference, appearing either as
 the value of an
 attribute which has been declared as type <kw>ENTITY</kw>, or as one of
 the space-separated tokens in the value of an attribute which has been
 declared as type <kw>ENTITIES</kw>.</p>
 </def></gitem>
 <gitem><label>Reference in Entity Value</label>
 <def><p>as a reference
 within a parameter or internal entity's
 <termref def="dt-litentval">literal entity value</termref> in
 the entity's declaration; corresponds to the nonterminal
 <nt def="NT-EntityValue">EntityValue</nt>.</p></def></gitem>
 <gitem><label>Reference in DTD</label>
 <def><p>as a reference within either the internal or external subsets of the
 <termref def="dt-doctype">DTD</termref>, but outside
 of an <nt def="NT-EntityValue">EntityValue</nt> or
 <nt def="NT-AttValue">AttValue</nt>.</p></def>
 </gitem>
 </glist></p>
 <htable border="1" cellpadding="7" align="center">
 <htbody>
 <tr><td bgcolor="&cellback;" rowspan="2" colspan="1"/>
 <td bgcolor="&cellback;" align="center" valign="bottom" colspan="4">Entity Type</td>
 <td bgcolor="&cellback;" rowspan="2" align="center">Character</td>
 </tr>
 <tr align="center" valign="bottom">
 <td bgcolor="&cellback;">Parameter</td>
 <td bgcolor="&cellback;">Internal
 General</td>
 <td bgcolor="&cellback;">External Parsed
 General</td>
 <td bgcolor="&cellback;">Unparsed</td>
 </tr>
 <tr align="center" valign="middle">

 <td bgcolor="&cellback;" align="right">Reference
 in Content</td>
 <td bgcolor="&cellback;"><titleref href="not-recognized">Not recognized</titleref></td>
 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td>
 <td bgcolor="&cellback;"><titleref href="include-if-valid">Included if validating</titleref></td>
 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td>
 </tr>
 <tr align="center" valign="middle">
 <td bgcolor="&cellback;" align="right">Reference
 in Attribute Value</td>
 <td bgcolor="&cellback;"><titleref href="not-recognized">Not recognized</titleref></td>
 <td bgcolor="&cellback;"><titleref href="inliteral">Included in literal</titleref></td>
 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td>
 </tr>
 <tr align="center" valign="middle">
 <td bgcolor="&cellback;" align="right">Occurs as
 Attribute Value</td>
 <td bgcolor="&cellback;"><titleref href="not-recognized">Not recognized</titleref></td>
 <td bgcolor="&cellback;"><titleref href="not-recognized">Forbidden</titleref></td>
 <td bgcolor="&cellback;"><titleref href="not-recognized">Forbidden</titleref></td>
 <td bgcolor="&cellback;"><titleref href="notify">Notify</titleref></td>
 <td bgcolor="&cellback;"><titleref href="not recognized">Not recognized</titleref></td>
 </tr>
 <tr align="center" valign="middle">
 <td bgcolor="&cellback;" align="right">Reference
 in EntityValue</td>
 <td bgcolor="&cellback;"><titleref href="inliteral">Included in literal</titleref></td>
 <td bgcolor="&cellback;"><titleref href="bypass">Bypassed</titleref></td>
 <td bgcolor="&cellback;"><titleref href="bypass">Bypassed</titleref></td>
 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
 <td bgcolor="&cellback;"><titleref href="included">Included</titleref></td>
 </tr>
 <tr align="center" valign="middle">
 <td bgcolor="&cellback;" align="right">Reference
 in DTD</td>
 <td bgcolor="&cellback;"><titleref href="as-PE">Included as PE</titleref></td>
 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
 <td bgcolor="&cellback;"><titleref href="forbidden">Forbidden</titleref></td>
 </tr>
 </htbody>
 </htable>
 <div3 id="not-recognized">
 <head>Not Recognized</head>
 <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 <nt def="NT-content">content</nt>.
 Similarly, the names of unparsed entities are not recognized except
 when they appear in the value of an appropriately declared attribute.
 </p>
 </div3>
 <div3 id="included">
 <head>Included</head>
 <p><termdef id="dt-include" term="Include">An entity is
 <term>included</term> when its
 <termref def="dt-repltext">replacement text</termref> 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
 <termref def="dt-chardata">character data</termref>
 and (except for parameter entities) <termref def="dt-markup">markup</termref>,
 which must be recognized in
 the usual way, except that the replacement text of entities used to escape
 markup delimiters (the entities &magicents;) 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 <term>included</term> when the indicated
 character is processed in place of the reference itself.
 </termdef></p>
 </div3>
 <div3 id="include-if-valid">
 <head>Included If Validating</head>
 <p>When an XML processor recognizes a reference to a parsed entity, in order
 to <termref def="dt-valid">validate</termref>
 the document, the processor must
 <termref def="dt-include">include</termref> its
 replacement text.
 If the entity is external, and the processor is not
 attempting to validate the XML document, the
 processor <termref def="dt-may">may</termref>, 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>
 </div3>
 <div3 id="forbidden">
 <head>Forbidden</head>
 <p>The following are forbidden, and constitute
 <termref def="dt-fatal">fatal</termref> errors:
 <ulist>
 <item><p>the appearance of a reference to an
 <termref def="dt-unparsed">unparsed entity</termref>.
 </p></item>
 <item><p>the appearance of any character or general-entity reference in the
 DTD except within an <nt def="NT-EntityValue">EntityValue</nt> or
 <nt def="NT-AttValue">AttValue</nt>.</p></item>
 <item><p>a reference to an external entity in an attribute value.</p>
 </item>
 </ulist>
 </p>
 </div3>
 <div3 id="inliteral">
 <head>Included in Literal</head>
 <p>When an <termref def="dt-entref">entity reference</termref> appears in an
 attribute value, or a parameter entity reference appears in a literal entity
 value, its <termref def="dt-repltext">replacement text</termref> 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:
 <eg><![CDATA[<!ENTITY % YN '"Yes"' >
 <!ENTITY WhatHeSaid "He said &YN;" >]]></eg>
 while this is not:
 <eg>&lt;!ENTITY EndAttr "27'" &gt;
 &lt;element attribute='a-&amp;EndAttr;&gt;</eg>
 </p></div3>
 <div3 id="notify">
 <head>Notify</head>
 <p>When the name of an <termref def="dt-unparsed">unparsed
 entity</termref> appears as a token in the
 value of an attribute of declared type <kw>ENTITY</kw> or <kw>ENTITIES</kw>,
 a validating processor must inform the
 application of the <termref def="dt-sysid">system</termref>
 and <termref def="dt-pubid">public</termref> (if any)
 identifiers for both the entity and its associated
 <termref def="dt-notation">notation</termref>.</p>
 </div3>
 <div3 id="bypass">
 <head>Bypassed</head>
 <p>When a general entity reference appears in the
 <nt def="NT-EntityValue">EntityValue</nt> in an entity declaration,
 it is bypassed and left as is.</p>
 </div3>
 <div3 id="as-PE">
 <head>Included as PE</head>
 <p>Just as with external parsed entities, parameter entities
 need only be <titleref href="include-if-valid">included if
 validating</titleref>.
 When a parameter-entity reference is recognized in the DTD
 and included, its
 <termref def="dt-repltext">replacement
 text</termref> 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>
 </div3>

 </div2>
 <div2 id="intern-replacement">
 <head>Construction of Internal Entity Replacement Text</head>
 <p>In discussing the treatment
 of internal entities, it is
 useful to distinguish two forms of the entity's value.
 <termdef id="dt-litentval" term="Literal Entity Value">The <term>literal
 entity value</term> is the quoted string actually
 present in the entity declaration, corresponding to the
 non-terminal <nt def="NT-EntityValue">EntityValue</nt>.</termdef>
 <termdef id="dt-repltext" term="Replacement Text">The <term>replacement
 text</term> is the content of the entity, after
 replacement of character references and parameter-entity
 references.
 </termdef></p>

 <p>The literal entity value
 as given in an internal entity declaration
 (<nt def="NT-EntityValue">EntityValue</nt>) 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
 <termref def="dt-include">included</termref> as described above
 must contain the <emph>replacement text</emph> 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:

 <eg><![CDATA[<!ENTITY % pub    "&#xc9;ditions Gallimard" >
 <!ENTITY   rights "All rights reserved" >
 <!ENTITY   book   "La Peste: Albert Camus,
 &#xA9; 1947 %pub;. &rights;" >]]></eg>
 then the replacement text for the entity "<code>book</code>" is:
 <eg>La Peste: Albert Camus,
 © 1947 Éditions Gallimard. &amp;rights;</eg>
 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
 <specref ref="sec-entexpand"/>.
 </p>

 </div2>
 <div2 id="sec-predefined-ent">
 <head>Predefined Entities</head>
 <p><termdef id="dt-escape" term="escape">Entity and character
 references can both be used to <term>escape</term> the left angle bracket,
 ampersand, and other delimiters.   A set of general entities
 (&magicents;) 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.</termdef></p>
 <p>All XML processors must recognize these entities whether they
 are declared or not.
 <termref def="dt-interop">For interoperability</termref>,
 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.
 <eg><![CDATA[<!ENTITY lt     "&#38;#60;">
 <!ENTITY gt     "&#62;">
 <!ENTITY amp    "&#38;#38;">
 <!ENTITY apos   "&#39;">
 <!ENTITY quot   "&#34;">
 ]]></eg>
 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>
 </div2>

 <div2 id="Notations">
 <head>Notation Declarations</head>

 <p><termdef id="dt-notation" term="Notation"><term>Notations</term> identify by
 name the format of <termref def="dt-extent">unparsed
 entities</termref>, the
 format of elements which bear a notation attribute,
 or the application to which
 a <termref def="dt-pi">processing instruction</termref> is
 addressed.</termdef></p>
 <p><termdef id="dt-notdecl" term="Notation Declaration">
 <term>Notation declarations</term>
 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.
 <scrap lang="ebnf">
 <head>Notation Declarations</head>
 <prod id="NT-NotationDecl"><lhs>NotationDecl</lhs>
 <rhs>'&lt;!NOTATION' <nt def="NT-S">S</nt> <nt def="NT-Name">Name</nt>
 <nt def="NT-S">S</nt>
 (<nt def="NT-ExternalID">ExternalID</nt> |
 <nt def="NT-PublicID">PublicID</nt>)
 <nt def="NT-S">S</nt>? '&gt;'</rhs></prod>
 <prod id="NT-PublicID"><lhs>PublicID</lhs>
 <rhs>'PUBLIC' <nt def="NT-S">S</nt>
 <nt def="NT-PubidLiteral">PubidLiteral</nt>
 </rhs></prod>
 </scrap>
 </termdef></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
 <termref def="dt-sysid">system identifier</termref>,
 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>
 </div2>


 <div2 id="sec-doc-entity">
 <head>Document Entity</head>

 <p><termdef id="dt-docent" term="Document Entity">The <term>document
 entity</term> serves as the root of the entity
 tree and a starting-point for an <termref def="dt-xml-proc">XML
 processor</termref>.</termdef>
 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>
 </div2>


 </div1>
 <!-- &Conformance; -->

 <div1 id="sec-conformance">
 <head>Conformance</head>

 <div2 id="proc-types">
 <head>Validating and Non-Validating Processors</head>
 <p>Conforming <termref def="dt-xml-proc">XML processors</termref> 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
 <termref def="dt-docent">document entity</termref> and any
 other <termref def="dt-parsedent">parsed entities</termref> that
 they read.</p>
 <p><termdef id="dt-validating" term="Validating Processor">
 <term>Validating processors</term> must report
 violations of the constraints expressed by the declarations in the
 <termref def="dt-doctype">DTD</termref>, and
 failures to fulfill the validity constraints given
 in this specification.
 </termdef>
 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
 <termref def="dt-docent">document entity</termref>, including
 the entire internal DTD subset, for well-formedness.
 <termdef id="dt-use-mdecl" term="Process Declarations">
 While they are not required to check the document for validity,
 they are required to
 <term>process</term> 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 <emph>not</emph> read; that is to
 say, they must
 use the information in those declarations to
 <titleref href="AVNormalize">normalize</titleref> attribute values,
 <titleref href="included">include</titleref> the replacement text of
 internal entities, and supply
 <titleref href="sec-attr-defaults">default attribute values</titleref>.
 </termdef>
 They must not <termref def="dt-use-mdecl">process</termref>
 <termref def="dt-entdecl">entity declarations</termref> or
 <termref def="dt-attdecl">attribute-list declarations</termref>
 encountered after a reference to a parameter entity that is not
 read, since the entity may have contained overriding declarations.
 </p>
 </div2>
 <div2 id="safe-behavior">
 <head>Using XML Processors</head>
 <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:
 <ulist>
 <item><p>Certain well-formedness errors, specifically those that require
 reading external entities, may not be detected by a non-validating processor.
 Examples include the constraints entitled
 <titleref href="wf-entdeclared">Entity Declared</titleref>,
 <titleref href="wf-textent">Parsed Entity</titleref>, and
 <titleref href="wf-norecursion">No Recursion</titleref>, as well
 as some of the cases described as
 <titleref href="forbidden">forbidden</titleref> in
 <specref ref="entproc"/>.</p></item>
 <item><p>The information passed from the processor to the application may
 vary, depending on whether the processor reads
 parameter and external entities.
 For example, a non-validating processor may not
 <titleref href="AVNormalize">normalize</titleref> attribute values,
 <titleref href="included">include</titleref> the replacement text of
 internal entities, or supply
 <titleref href="sec-attr-defaults">default attribute values</titleref>,
 where doing so depends on having read declarations in
 external or parameter entities.</p></item>
 </ulist>
 </p>
 <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>
 </div2>
 </div1>

 <div1 id="sec-notation">
 <head>Notation</head>

 <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
 <eg>symbol ::= expression</eg></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:
 <glist>
 <gitem>
 <label><code>#xN</code></label>
 <def><p>where <code>N</code> is a hexadecimal integer, the
 expression matches the character in ISO/IEC 10646 whose canonical
 (UCS-4)
 code value, when interpreted as an unsigned binary number, has
 the value indicated.  The number of leading zeros in the
 <code>#xN</code> form is insignificant; the number of leading
 zeros in the corresponding code value
 is governed by the character
 encoding in use and is not significant for XML.</p></def>
 </gitem>
 <gitem>
 <label><code>[a-zA-Z]</code>, <code>[#xN-#xN]</code></label>
 <def><p>matches any <termref def="dt-character">character</termref>
 with a value in the range(s) indicated (inclusive).</p></def>
 </gitem>
 <gitem>
 <label><code>[^a-z]</code>, <code>[^#xN-#xN]</code></label>
 <def><p>matches any <termref def="dt-character">character</termref>
 with a value <emph>outside</emph> the
 range indicated.</p></def>
 </gitem>
 <gitem>
 <label><code>[^abc]</code>, <code>[^#xN#xN#xN]</code></label>
 <def><p>matches any <termref def="dt-character">character</termref>
 with a value not among the characters given.</p></def>
 </gitem>
 <gitem>
 <label><code>"string"</code></label>
 <def><p>matches a literal string <termref def="dt-match">matching</termref>
 that given inside the double quotes.</p></def>
 </gitem>
 <gitem>
 <label><code>'string'</code></label>
 <def><p>matches a literal string <termref def="dt-match">matching</termref>
 that given inside the single quotes.</p></def>
 </gitem>
 </glist>
 These symbols may be combined to match more complex patterns as follows,
 where <code>A</code> and <code>B</code> represent simple expressions:
 <glist>
 <gitem>
 <label>(<code>expression</code>)</label>
 <def><p><code>expression</code> is treated as a unit
 and may be combined as described in this list.</p></def>
 </gitem>
 <gitem>
 <label><code>A?</code></label>
 <def><p>matches <code>A</code> or nothing; optional <code>A</code>.</p></def>
 </gitem>
 <gitem>
 <label><code>A B</code></label>
 <def><p>matches <code>A</code> followed by <code>B</code>.</p></def>
 </gitem>
 <gitem>
 <label><code>A | B</code></label>
 <def><p>matches <code>A</code> or <code>B</code> but not both.</p></def>
 </gitem>
 <gitem>
 <label><code>A - B</code></label>
 <def><p>matches any string that matches <code>A</code> but does not match
 <code>B</code>.
 </p></def>
 </gitem>
 <gitem>
 <label><code>A+</code></label>
 <def><p>matches one or more occurrences of <code>A</code>.</p></def>
 </gitem>
 <gitem>
 <label><code>A*</code></label>
 <def><p>matches zero or more occurrences of <code>A</code>.</p></def>
 </gitem>

 </glist>
 Other notations used in the productions are:
 <glist>
 <gitem>
 <label><code>/* ... */</code></label>
 <def><p>comment.</p></def>
 </gitem>
 <gitem>
 <label><code>[ wfc: ... ]</code></label>
 <def><p>well-formedness constraint; this identifies by name a
 constraint on
 <termref def="dt-wellformed">well-formed</termref> documents
 associated with a production.</p></def>
 </gitem>
 <gitem>
 <label><code>[ vc: ... ]</code></label>
 <def><p>validity constraint; this identifies by name a constraint on
 <termref def="dt-valid">valid</termref> documents associated with
 a production.</p></def>
 </gitem>
 </glist>
 </p></div1>

 </body>
 <back>
 <!-- &SGML; -->


 <!-- &Biblio; -->
 <div1 id="sec-bibliography">

 <head>References</head>
 <div2 id="sec-existing-stds">
 <head>Normative References</head>

 <blist>
 <bibl id="IANA" key="IANA">
 (Internet Assigned Numbers Authority) <emph>Official Names for
 Character Sets</emph>,
 ed. Keld Simonsen et al.
 See <loc href="ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets">ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets</loc>.
 </bibl>

 <bibl id="RFC1766" key="IETF RFC 1766">
 IETF (Internet Engineering Task Force).
 <emph>RFC 1766:  Tags for the Identification of Languages</emph>,
 ed. H. Alvestrand.
 1995.
 </bibl>

 <bibl id="ISO639" key="ISO 639">
 (International Organization for Standardization).
 <emph>ISO 639:1988 (E).
 Code for the representation of names of languages.</emph>
 [Geneva]:  International Organization for
 Standardization, 1988.</bibl>

 <bibl id="ISO3166" key="ISO 3166">
 (International Organization for Standardization).
 <emph>ISO 3166-1:1997 (E).
 Codes for the representation of names of countries and their subdivisions
 &mdash; Part 1: Country codes</emph>
 [Geneva]:  International Organization for
 Standardization, 1997.</bibl>

 <bibl id="ISO10646" key="ISO/IEC 10646">ISO
 (International Organization for Standardization).
 <emph>ISO/IEC 10646-1993 (E).  Information technology &mdash; Universal
 Multiple-Octet Coded Character Set (UCS) &mdash; Part 1:
 Architecture and Basic Multilingual Plane.</emph>
 [Geneva]:  International Organization for
 Standardization, 1993 (plus amendments AM 1 through AM 7).
 </bibl>

 <bibl id="Unicode" key="Unicode">The Unicode Consortium.
 <emph>The Unicode Standard, Version 2.0.</emph>
 Reading, Mass.:  Addison-Wesley Developers Press, 1996.</bibl>

 </blist>

 </div2>

 <div2><head>Other References</head>

 <blist>

 <bibl id="Aho" key="Aho/Ullman">Aho, Alfred V.,
 Ravi Sethi, and Jeffrey D. Ullman.
 <emph>Compilers:  Principles, Techniques, and Tools</emph>.
 Reading:  Addison-Wesley, 1986, rpt. corr. 1988.</bibl>

 <bibl id="Berners-Lee" xml-link="simple" key="Berners-Lee et al.">
 Berners-Lee, T., R. Fielding, and L. Masinter.
 <emph>Uniform Resource Identifiers (URI):  Generic Syntax and
 Semantics</emph>.
 1997.
 (Work in progress; see updates to RFC1738.)</bibl>

 <bibl id="ABK" key="Brüggemann-Klein">Brüggemann-Klein, Anne.
 <emph>Regular Expressions into Finite Automata</emph>.
 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.

 </bibl>

 <bibl id="ABKDW" key="Brüggemann-Klein and Wood">Brüggemann-Klein, Anne,
 and Derick Wood.
 <emph>Deterministic Regular Languages</emph>.
 Universität Freiburg, Institut für Informatik,
 Bericht 38, Oktober 1991.
 </bibl>

 <bibl id="Clark" key="Clark">James Clark.
 Comparison of SGML and XML. See
 <loc href="http://www.w3.org/TR/NOTE-sgml-xml-971215">http://www.w3.org/TR/NOTE-sgml-xml-971215</loc>.
 </bibl>
 <bibl id="RFC1738" xml-link="simple" key="IETF RFC1738">
 IETF (Internet Engineering Task Force).
 <emph>RFC 1738:  Uniform Resource Locators (URL)</emph>,
 ed. T. Berners-Lee, L. Masinter, M. McCahill.
 1994.
 </bibl>

 <bibl id="RFC1808" xml-link="simple" key="IETF RFC1808">
 IETF (Internet Engineering Task Force).
 <emph>RFC 1808:  Relative Uniform Resource Locators</emph>,
 ed. R. Fielding.
 1995.
 </bibl>

 <bibl id="RFC2141" xml-link="simple" key="IETF RFC2141">
 IETF (Internet Engineering Task Force).
 <emph>RFC 2141:  URN Syntax</emph>,
 ed. R. Moats.
 1997.
 </bibl>

 <bibl id="ISO8879" key="ISO 8879">ISO
 (International Organization for Standardization).
 <emph>ISO 8879:1986(E).  Information processing &mdash; Text and Office
 Systems &mdash; Standard Generalized Markup Language (SGML).</emph>  First
 edition &mdash; 1986-10-15.  [Geneva]:  International Organization for
 Standardization, 1986.
 </bibl>


 <bibl id="ISO10744" key="ISO/IEC 10744">ISO
 (International Organization for Standardization).
 <emph>ISO/IEC 10744-1992 (E).  Information technology &mdash;
 Hypermedia/Time-based Structuring Language (HyTime).
 </emph>
 [Geneva]:  International Organization for
 Standardization, 1992.
 <emph>Extended Facilities Annexe.</emph>
 [Geneva]:  International Organization for
 Standardization, 1996.
 </bibl>


 </blist>
 </div2>
 </div1>
 <div1 id="CharClasses">
 <head>Character Classes</head>
 <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.
 <scrap lang="ebnf" id="CHARACTERS">
 <head>Characters</head>
 <prodgroup pcw3="3" pcw4="15">
 <prod id="NT-Letter"><lhs>Letter</lhs>
 <rhs><nt def="NT-BaseChar">BaseChar</nt>
 | <nt def="NT-Ideographic">Ideographic</nt></rhs> </prod>
 <prod id="NT-BaseChar"><lhs>BaseChar</lhs>
 <rhs>[#x0041-#x005A]
 |&nbsp;[#x0061-#x007A]
 |&nbsp;[#x00C0-#x00D6]
 |&nbsp;[#x00D8-#x00F6]
 |&nbsp;[#x00F8-#x00FF]
 |&nbsp;[#x0100-#x0131]
 |&nbsp;[#x0134-#x013E]
 |&nbsp;[#x0141-#x0148]
 |&nbsp;[#x014A-#x017E]
 |&nbsp;[#x0180-#x01C3]
 |&nbsp;[#x01CD-#x01F0]
 |&nbsp;[#x01F4-#x01F5]
 |&nbsp;[#x01FA-#x0217]
 |&nbsp;[#x0250-#x02A8]
 |&nbsp;[#x02BB-#x02C1]
 |&nbsp;#x0386
 |&nbsp;[#x0388-#x038A]
 |&nbsp;#x038C
 |&nbsp;[#x038E-#x03A1]
 |&nbsp;[#x03A3-#x03CE]
 |&nbsp;[#x03D0-#x03D6]
 |&nbsp;#x03DA
 |&nbsp;#x03DC
 |&nbsp;#x03DE
 |&nbsp;#x03E0
 |&nbsp;[#x03E2-#x03F3]
 |&nbsp;[#x0401-#x040C]
 |&nbsp;[#x040E-#x044F]
 |&nbsp;[#x0451-#x045C]
 |&nbsp;[#x045E-#x0481]
 |&nbsp;[#x0490-#x04C4]
 |&nbsp;[#x04C7-#x04C8]
 |&nbsp;[#x04CB-#x04CC]
 |&nbsp;[#x04D0-#x04EB]
 |&nbsp;[#x04EE-#x04F5]
 |&nbsp;[#x04F8-#x04F9]
 |&nbsp;[#x0531-#x0556]
 |&nbsp;#x0559
 |&nbsp;[#x0561-#x0586]
 |&nbsp;[#x05D0-#x05EA]
 |&nbsp;[#x05F0-#x05F2]
 |&nbsp;[#x0621-#x063A]
 |&nbsp;[#x0641-#x064A]
 |&nbsp;[#x0671-#x06B7]
 |&nbsp;[#x06BA-#x06BE]
 |&nbsp;[#x06C0-#x06CE]
 |&nbsp;[#x06D0-#x06D3]
 |&nbsp;#x06D5
 |&nbsp;[#x06E5-#x06E6]
 |&nbsp;[#x0905-#x0939]
 |&nbsp;#x093D
 |&nbsp;[#x0958-#x0961]
 |&nbsp;[#x0985-#x098C]
 |&nbsp;[#x098F-#x0990]
 |&nbsp;[#x0993-#x09A8]
 |&nbsp;[#x09AA-#x09B0]
 |&nbsp;#x09B2
 |&nbsp;[#x09B6-#x09B9]
 |&nbsp;[#x09DC-#x09DD]
 |&nbsp;[#x09DF-#x09E1]
 |&nbsp;[#x09F0-#x09F1]
 |&nbsp;[#x0A05-#x0A0A]
 |&nbsp;[#x0A0F-#x0A10]
 |&nbsp;[#x0A13-#x0A28]
 |&nbsp;[#x0A2A-#x0A30]
 |&nbsp;[#x0A32-#x0A33]
 |&nbsp;[#x0A35-#x0A36]
 |&nbsp;[#x0A38-#x0A39]
 |&nbsp;[#x0A59-#x0A5C]
 |&nbsp;#x0A5E
 |&nbsp;[#x0A72-#x0A74]
 |&nbsp;[#x0A85-#x0A8B]
 |&nbsp;#x0A8D
 |&nbsp;[#x0A8F-#x0A91]
 |&nbsp;[#x0A93-#x0AA8]
 |&nbsp;[#x0AAA-#x0AB0]
 |&nbsp;[#x0AB2-#x0AB3]
 |&nbsp;[#x0AB5-#x0AB9]
 |&nbsp;#x0ABD
 |&nbsp;#x0AE0
 |&nbsp;[#x0B05-#x0B0C]
 |&nbsp;[#x0B0F-#x0B10]
 |&nbsp;[#x0B13-#x0B28]
 |&nbsp;[#x0B2A-#x0B30]
 |&nbsp;[#x0B32-#x0B33]
 |&nbsp;[#x0B36-#x0B39]
 |&nbsp;#x0B3D
 |&nbsp;[#x0B5C-#x0B5D]
 |&nbsp;[#x0B5F-#x0B61]
 |&nbsp;[#x0B85-#x0B8A]
 |&nbsp;[#x0B8E-#x0B90]
 |&nbsp;[#x0B92-#x0B95]
 |&nbsp;[#x0B99-#x0B9A]
 |&nbsp;#x0B9C
 |&nbsp;[#x0B9E-#x0B9F]
 |&nbsp;[#x0BA3-#x0BA4]
 |&nbsp;[#x0BA8-#x0BAA]
 |&nbsp;[#x0BAE-#x0BB5]
 |&nbsp;[#x0BB7-#x0BB9]
 |&nbsp;[#x0C05-#x0C0C]
 |&nbsp;[#x0C0E-#x0C10]
 |&nbsp;[#x0C12-#x0C28]
 |&nbsp;[#x0C2A-#x0C33]
 |&nbsp;[#x0C35-#x0C39]
 |&nbsp;[#x0C60-#x0C61]
 |&nbsp;[#x0C85-#x0C8C]
 |&nbsp;[#x0C8E-#x0C90]
 |&nbsp;[#x0C92-#x0CA8]
 |&nbsp;[#x0CAA-#x0CB3]
 |&nbsp;[#x0CB5-#x0CB9]
 |&nbsp;#x0CDE
 |&nbsp;[#x0CE0-#x0CE1]
 |&nbsp;[#x0D05-#x0D0C]
 |&nbsp;[#x0D0E-#x0D10]
 |&nbsp;[#x0D12-#x0D28]
 |&nbsp;[#x0D2A-#x0D39]
 |&nbsp;[#x0D60-#x0D61]
 |&nbsp;[#x0E01-#x0E2E]
 |&nbsp;#x0E30
 |&nbsp;[#x0E32-#x0E33]
 |&nbsp;[#x0E40-#x0E45]
 |&nbsp;[#x0E81-#x0E82]
 |&nbsp;#x0E84
 |&nbsp;[#x0E87-#x0E88]
 |&nbsp;#x0E8A
 |&nbsp;#x0E8D
 |&nbsp;[#x0E94-#x0E97]
 |&nbsp;[#x0E99-#x0E9F]
 |&nbsp;[#x0EA1-#x0EA3]
 |&nbsp;#x0EA5
 |&nbsp;#x0EA7
 |&nbsp;[#x0EAA-#x0EAB]
 |&nbsp;[#x0EAD-#x0EAE]
 |&nbsp;#x0EB0
 |&nbsp;[#x0EB2-#x0EB3]
 |&nbsp;#x0EBD
 |&nbsp;[#x0EC0-#x0EC4]
 |&nbsp;[#x0F40-#x0F47]
 |&nbsp;[#x0F49-#x0F69]
 |&nbsp;[#x10A0-#x10C5]
 |&nbsp;[#x10D0-#x10F6]
 |&nbsp;#x1100
 |&nbsp;[#x1102-#x1103]
 |&nbsp;[#x1105-#x1107]
 |&nbsp;#x1109
 |&nbsp;[#x110B-#x110C]
 |&nbsp;[#x110E-#x1112]
 |&nbsp;#x113C
 |&nbsp;#x113E
 |&nbsp;#x1140
 |&nbsp;#x114C
 |&nbsp;#x114E
 |&nbsp;#x1150
 |&nbsp;[#x1154-#x1155]
 |&nbsp;#x1159
 |&nbsp;[#x115F-#x1161]
 |&nbsp;#x1163
 |&nbsp;#x1165
 |&nbsp;#x1167
 |&nbsp;#x1169
 |&nbsp;[#x116D-#x116E]
 |&nbsp;[#x1172-#x1173]
 |&nbsp;#x1175
 |&nbsp;#x119E
 |&nbsp;#x11A8
 |&nbsp;#x11AB
 |&nbsp;[#x11AE-#x11AF]
 |&nbsp;[#x11B7-#x11B8]
 |&nbsp;#x11BA
 |&nbsp;[#x11BC-#x11C2]
 |&nbsp;#x11EB
 |&nbsp;#x11F0
 |&nbsp;#x11F9
 |&nbsp;[#x1E00-#x1E9B]
 |&nbsp;[#x1EA0-#x1EF9]
 |&nbsp;[#x1F00-#x1F15]
 |&nbsp;[#x1F18-#x1F1D]
 |&nbsp;[#x1F20-#x1F45]
 |&nbsp;[#x1F48-#x1F4D]
 |&nbsp;[#x1F50-#x1F57]
 |&nbsp;#x1F59
 |&nbsp;#x1F5B
 |&nbsp;#x1F5D
 |&nbsp;[#x1F5F-#x1F7D]
 |&nbsp;[#x1F80-#x1FB4]
 |&nbsp;[#x1FB6-#x1FBC]
 |&nbsp;#x1FBE
 |&nbsp;[#x1FC2-#x1FC4]
 |&nbsp;[#x1FC6-#x1FCC]
 |&nbsp;[#x1FD0-#x1FD3]
 |&nbsp;[#x1FD6-#x1FDB]
 |&nbsp;[#x1FE0-#x1FEC]
 |&nbsp;[#x1FF2-#x1FF4]
 |&nbsp;[#x1FF6-#x1FFC]
 |&nbsp;#x2126
 |&nbsp;[#x212A-#x212B]
 |&nbsp;#x212E
 |&nbsp;[#x2180-#x2182]
 |&nbsp;[#x3041-#x3094]
 |&nbsp;[#x30A1-#x30FA]
 |&nbsp;[#x3105-#x312C]
 |&nbsp;[#xAC00-#xD7A3]
 </rhs></prod>
 <prod id="NT-Ideographic"><lhs>Ideographic</lhs>
 <rhs>[#x4E00-#x9FA5]
 |&nbsp;#x3007
 |&nbsp;[#x3021-#x3029]
 </rhs></prod>
 <prod id="NT-CombiningChar"><lhs>CombiningChar</lhs>
 <rhs>[#x0300-#x0345]
 |&nbsp;[#x0360-#x0361]
 |&nbsp;[#x0483-#x0486]
 |&nbsp;[#x0591-#x05A1]
 |&nbsp;[#x05A3-#x05B9]
 |&nbsp;[#x05BB-#x05BD]
 |&nbsp;#x05BF
 |&nbsp;[#x05C1-#x05C2]
 |&nbsp;#x05C4
 |&nbsp;[#x064B-#x0652]
 |&nbsp;#x0670
 |&nbsp;[#x06D6-#x06DC]
 |&nbsp;[#x06DD-#x06DF]
 |&nbsp;[#x06E0-#x06E4]
 |&nbsp;[#x06E7-#x06E8]
 |&nbsp;[#x06EA-#x06ED]
 |&nbsp;[#x0901-#x0903]
 |&nbsp;#x093C
 |&nbsp;[#x093E-#x094C]
 |&nbsp;#x094D
 |&nbsp;[#x0951-#x0954]
 |&nbsp;[#x0962-#x0963]
 |&nbsp;[#x0981-#x0983]
 |&nbsp;#x09BC
 |&nbsp;#x09BE
 |&nbsp;#x09BF
 |&nbsp;[#x09C0-#x09C4]
 |&nbsp;[#x09C7-#x09C8]
 |&nbsp;[#x09CB-#x09CD]
 |&nbsp;#x09D7
 |&nbsp;[#x09E2-#x09E3]
 |&nbsp;#x0A02
 |&nbsp;#x0A3C
 |&nbsp;#x0A3E
 |&nbsp;#x0A3F
 |&nbsp;[#x0A40-#x0A42]
 |&nbsp;[#x0A47-#x0A48]
 |&nbsp;[#x0A4B-#x0A4D]
 |&nbsp;[#x0A70-#x0A71]
 |&nbsp;[#x0A81-#x0A83]
 |&nbsp;#x0ABC
 |&nbsp;[#x0ABE-#x0AC5]
 |&nbsp;[#x0AC7-#x0AC9]
 |&nbsp;[#x0ACB-#x0ACD]
 |&nbsp;[#x0B01-#x0B03]
 |&nbsp;#x0B3C
 |&nbsp;[#x0B3E-#x0B43]
 |&nbsp;[#x0B47-#x0B48]
 |&nbsp;[#x0B4B-#x0B4D]
 |&nbsp;[#x0B56-#x0B57]
 |&nbsp;[#x0B82-#x0B83]
 |&nbsp;[#x0BBE-#x0BC2]
 |&nbsp;[#x0BC6-#x0BC8]
 |&nbsp;[#x0BCA-#x0BCD]
 |&nbsp;#x0BD7
 |&nbsp;[#x0C01-#x0C03]
 |&nbsp;[#x0C3E-#x0C44]
 |&nbsp;[#x0C46-#x0C48]
 |&nbsp;[#x0C4A-#x0C4D]
 |&nbsp;[#x0C55-#x0C56]
 |&nbsp;[#x0C82-#x0C83]
 |&nbsp;[#x0CBE-#x0CC4]
 |&nbsp;[#x0CC6-#x0CC8]
 |&nbsp;[#x0CCA-#x0CCD]
 |&nbsp;[#x0CD5-#x0CD6]
 |&nbsp;[#x0D02-#x0D03]
 |&nbsp;[#x0D3E-#x0D43]
 |&nbsp;[#x0D46-#x0D48]
 |&nbsp;[#x0D4A-#x0D4D]
 |&nbsp;#x0D57
 |&nbsp;#x0E31
 |&nbsp;[#x0E34-#x0E3A]
 |&nbsp;[#x0E47-#x0E4E]
 |&nbsp;#x0EB1
 |&nbsp;[#x0EB4-#x0EB9]
 |&nbsp;[#x0EBB-#x0EBC]
 |&nbsp;[#x0EC8-#x0ECD]
 |&nbsp;[#x0F18-#x0F19]
 |&nbsp;#x0F35
 |&nbsp;#x0F37
 |&nbsp;#x0F39
 |&nbsp;#x0F3E
 |&nbsp;#x0F3F
 |&nbsp;[#x0F71-#x0F84]
 |&nbsp;[#x0F86-#x0F8B]
 |&nbsp;[#x0F90-#x0F95]
 |&nbsp;#x0F97
 |&nbsp;[#x0F99-#x0FAD]
 |&nbsp;[#x0FB1-#x0FB7]
 |&nbsp;#x0FB9
 |&nbsp;[#x20D0-#x20DC]
 |&nbsp;#x20E1
 |&nbsp;[#x302A-#x302F]
 |&nbsp;#x3099
 |&nbsp;#x309A
 </rhs></prod>
 <prod id="NT-Digit"><lhs>Digit</lhs>
 <rhs>[#x0030-#x0039]
 |&nbsp;[#x0660-#x0669]
 |&nbsp;[#x06F0-#x06F9]
 |&nbsp;[#x0966-#x096F]
 |&nbsp;[#x09E6-#x09EF]
 |&nbsp;[#x0A66-#x0A6F]
 |&nbsp;[#x0AE6-#x0AEF]
 |&nbsp;[#x0B66-#x0B6F]
 |&nbsp;[#x0BE7-#x0BEF]
 |&nbsp;[#x0C66-#x0C6F]
 |&nbsp;[#x0CE6-#x0CEF]
 |&nbsp;[#x0D66-#x0D6F]
 |&nbsp;[#x0E50-#x0E59]
 |&nbsp;[#x0ED0-#x0ED9]
 |&nbsp;[#x0F20-#x0F29]
 </rhs></prod>
 <prod id="NT-Extender"><lhs>Extender</lhs>
 <rhs>#x00B7
 |&nbsp;#x02D0
 |&nbsp;#x02D1
 |&nbsp;#x0387
 |&nbsp;#x0640
 |&nbsp;#x0E46
 |&nbsp;#x0EC6
 |&nbsp;#x3005
 |&nbsp;[#x3031-#x3035]
 |&nbsp;[#x309D-#x309E]
 |&nbsp;[#x30FC-#x30FE]
 </rhs></prod>

 </prodgroup>
 </scrap>
 </p>
 <p>The character classes defined here can be derived from the
 Unicode character database as follows:
 <ulist>
 <item>
 <p>Name start characters must have one of the categories Ll, Lu,
 Lo, Lt, Nl.</p>
 </item>
 <item>
 <p>Name characters other than Name-start characters
 must have one of the categories Mc, Me, Mn, Lm, or Nd.</p>
 </item>
 <item>
 <p>Characters in the compatibility area (i.e. with character code
 greater than #xF900 and less than #xFFFE) are not allowed in XML
 names.</p>
 </item>
 <item>
 <p>Characters which have a font or compatibility decomposition (i.e. those
 with a "compatibility formatting tag" in field 5 of the database --
 marked by field 5 beginning with a "&lt;") are not allowed.</p>
 </item>
 <item>
 <p>The following characters are treated as name-start characters
 rather than name characters, because the property file classifies
 them as Alphabetic:  [#x02BB-#x02C1], #x0559, #x06E5, #x06E6.</p>
 </item>
 <item>
 <p>Characters #x20DD-#x20E0 are excluded (in accordance with
 Unicode, section 5.14).</p>
 </item>
 <item>
 <p>Character #x00B7 is classified as an extender, because the
 property list so identifies it.</p>
 </item>
 <item>
 <p>Character #x0387 is added as a name character, because #x00B7
 is its canonical equivalent.</p>
 </item>
 <item>
 <p>Characters ':' and '_' are allowed as name-start characters.</p>
 </item>
 <item>
 <p>Characters '-' and '.' are allowed as name characters.</p>
 </item>
 </ulist>
 </p>
 </div1>
 <inform-div1 id="sec-xml-and-sgml">
 <head>XML and SGML</head>

 <p>XML is designed to be a subset of SGML, in that every
 <termref def="dt-valid">valid</termref> 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 <bibref ref="Clark"/>.
 </p>
 </inform-div1>
 <inform-div1 id="sec-entexpand">
 <head>Expansion of Entity and Character References</head>
 <p>This appendix contains some examples illustrating the
 sequence of entity- and character-reference recognition and
 expansion, as specified in <specref ref="entproc"/>.</p>
 <p>
 If the DTD contains the declaration
 <eg><![CDATA[<!ENTITY example "<p>An ampersand (&#38;#38;) may be escaped
 numerically (&#38;#38;#38;) or with a general entity
 (&amp;amp;).</p>" >
 ]]></eg>
 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>":
 <eg><![CDATA[<p>An ampersand (&#38;) may be escaped
 numerically (&#38;#38;) or with a general entity
 (&amp;amp;).</p>
 ]]></eg>
 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):
 <eg><![CDATA[An ampersand (&) may be escaped
 numerically (&#38;) or with a general entity
 (&amp;).
 ]]></eg>
 </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.
 <eg><![CDATA[1 <?xml version='1.0'?>
 2 <!DOCTYPE test [
 3 <!ELEMENT test (#PCDATA) >
 4 <!ENTITY % xx '&#37;zz;'>
 5 <!ENTITY % zz '&#60;!ENTITY tricky "error-prone" >' >
 6 %xx;
 7 ]>
 8 <test>This sample shows a &tricky; method.</test>
 ]]></eg>
 This produces the following:
 <ulist spacing="compact">
 <item><p>in line 4, the reference to character 37 is expanded immediately,
 and the parameter entity "<code>xx</code>" is stored in the symbol
 table with the value "<code>%zz;</code>".  Since the replacement text
 is not rescanned, the reference to parameter entity "<code>zz</code>"
 is not recognized.  (And it would be an error if it were, since
 "<code>zz</code>" is not yet declared.)</p></item>
 <item><p>in line 5, the character reference "<code>&amp;#60;</code>" is
 expanded immediately and the parameter entity "<code>zz</code>" is
 stored with the replacement text
 "<code>&lt;!ENTITY tricky "error-prone" &gt;</code>",
 which is a well-formed entity declaration.</p></item>
 <item><p>in line 6, the reference to "<code>xx</code>" is recognized,
 and the replacement text of "<code>xx</code>" (namely
 "<code>%zz;</code>") is parsed.  The reference to "<code>zz</code>"
 is recognized in its turn, and its replacement text
 ("<code>&lt;!ENTITY tricky "error-prone" &gt;</code>") is parsed.
 The general entity "<code>tricky</code>" has now been
 declared, with the replacement text "<code>error-prone</code>".</p></item>
 <item><p>
 in line 8, the reference to the general entity "<code>tricky</code>" is
 recognized, and it is expanded, so the full content of the
 "<code>test</code>" element is the self-describing (and ungrammatical) string
 <emph>This sample shows a error-prone method.</emph>
 </p></item>
 </ulist>
 </p>
 </inform-div1>
 <inform-div1 id="determinism">
 <head>Deterministic Content Models</head>
 <p><termref def="dt-compat">For compatibility</termref>, it is
 required
 that content models in element type declarations be deterministic.
 </p>
 <!-- FINAL EDIT:  WebSGML allows ambiguity? -->
 <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 <bibref ref="Aho"/>.
 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 <bibref ref="ABK"/>.</p>
 </inform-div1>
 <inform-div1 id="sec-guessing">
 <head>Autodetection of Character Encodings</head>
 <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&mdash;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 <emph>must</emph>
 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>
 <ulist>
 <item>
 <p><code>00 00 00 3C</code>: UCS-4, big-endian machine (1234 order)</p>
 </item>
 <item>
 <p><code>3C 00 00 00</code>: UCS-4, little-endian machine (4321 order)</p>
 </item>
 <item>
 <p><code>00 00 3C 00</code>: UCS-4, unusual octet order (2143)</p>
 </item>
 <item>
 <p><code>00 3C 00 00</code>: UCS-4, unusual octet order (3412)</p>
 </item>
 <item>
 <p><code>FE FF</code>: UTF-16, big-endian</p>
 </item>
 <item>
 <p><code>FF FE</code>: UTF-16, little-endian</p>
 </item>
 <item>
 <p><code>00 3C 00 3F</code>: UTF-16, big-endian, no Byte Order Mark
 (and thus, strictly speaking, in error)</p>
 </item>
 <item>
 <p><code>3C 00 3F 00</code>: UTF-16, little-endian, no Byte Order Mark
 (and thus, strictly speaking, in error)</p>
 </item>
 <item>
 <p><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
 </p>
 </item>
 <item>
 <p><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)</p>
 </item>
 <item>
 <p>other: UTF-8 without an encoding declaration, or else
 the data stream is corrupt, fragmentary, or enclosed in
 a wrapper of some kind</p>
 </item>
 </ulist>
 </p>
 <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.
 <ulist>
 <item><p>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.
 </p></item>
 <item><p>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.
 </p></item>
 <item><p>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.
 </p></item>
 </ulist>
 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.
 </p>

 </inform-div1>

 <inform-div1 id="sec-xml-wg">
 <head>W3C XML Working Group</head>

 <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>

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

 </inform-div1>
 </back>
 </spec>
 <!-- Keep this comment at the end of the file
 Local variables:
 mode: sgml
 sgml-default-dtd-file:"~/sgml/spec.ced"
 sgml-omittag:t
 sgml-shorttag:t
 End:
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