XML Bible (2nd Edition)/XML_Bible_Second_Edition_Hungry_Minds_2001.iso/pc/specs/REC-xml-20001006.xml

Extensible Markup Language | 2001-03-12 | 202KB | 3,278 lines

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<!ENTITY http-ident "http://www.w3.org/TR/2000/REC-xml">
<!ENTITY draft.month "October">
<!ENTITY draft.day "6">
<!ENTITY iso6.doc.date "20001006">
<!ENTITY draft.year "2000">
<!ENTITY versionOfXML "1.0">
<!ENTITY pio "'<?xml'">
<!ENTITY doc.date "10 February 1998">
<!ENTITY w3c.doc.date "02-Feb-1998">
<!ENTITY WebSGML "WebSGML Adaptations Annex to ISO 8879">
<!ENTITY pic "'?>'">
<!ENTITY br "\n">
<!ENTITY cellback "#c0d9c0">
<!ENTITY mdash "--">
<!ENTITY com "--">
<!ENTITY como "--">
<!ENTITY comc "--">
<!ENTITY hcro "&#x">
<!ENTITY nbsp " ">
<!ENTITY magicents "<code>amp</code>,
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<code>gt</code>,
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<!ENTITY doc.audience "public review and discussion">
<!ENTITY doc.distribution "may be distributed freely, as long as
all text and legal notices remain intact">
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<spec w3c-doctype="rec">
<!--
Notes on preparation of the Second Edition:

- Worked from http://www.w3.org/XML/xml-19980210-errata.
- Changed DTD reference to point to V2.1 of XMLspec.
- Moved version number from <title> to <version> element and
  added "second edition" wording.  Mentioned edition information
  in status.
- Removed bgcolor="&cellback;" attributes from all <td>
  elements because that attribute is not in the current table model.
- Reversed status and abstract, so that abstract is first, according
  to W3C guidelines.
- Changed some <emph>s to <titleref>s in bibliography.
- Changed some <code>s to <at> etc. throughout; where used <attval>,
  removed existing <quote>s because the stylesheet produces them.
- Removed some spurious spaces.
- Added affiliation markup to the original member list.
- Added commas between individual <thisver> elements, because
  whitespace is now significant there.
- Moved <eg>s, <scrap>s, and lists outside of <p>s for cleaner HTML
  conversion.
- Revised Status section to reflect new status.
- Fixed all titleref hrefs so they get transformed properly; at
  next revision, these all probably need to be changed to some
  other markup.
- Incorporated all errata (barring obsoleted and invalid ones);
  added links to the errata document with <loc role="erratumref">
  elements; used diff="{add|chg|del}" attribute.  This version
  expects that the official HTML output will have diff="del"
  elements suppressed.
-->
<header>
<title>Extensible Markup Language (XML)</title>
<version>1.0 (Second Edition)</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-ident;-&iso6.doc.date;">&http-ident;-&iso6.doc.date;</loc>
(<loc href="&http-ident;-&iso6.doc.date;.html">XHTML</loc>, <loc href="&http-ident;-&iso6.doc.date;.xml">XML</loc>, <loc
href="&http-ident;-&iso6.doc.date;.pdf">PDF</loc>, <loc href="&http-ident;-&iso6.doc.date;-review.html">XHTML
review version</loc> with color-coded revision indicators)</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/2000/WD-xml-2e-20000814"> http://www.w3.org/TR/2000/WD-xml-2e-20000814</loc>
<loc href="http://www.w3.org/TR/1998/REC-xml-19980210"> http://www.w3.org/TR/1998/REC-xml-19980210</loc><!--
<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 role="1e"><name>Tim Bray</name><affiliation>Textuality and Netscape</affiliation>
<email href="mailto:[e-mail]">[e-mail]</email></author>
<author role="1e"><name>Jean Paoli</name><affiliation>Microsoft</affiliation>
<email href="mailto:[e-mail]">[e-mail]</email></author>
<author role="1e" diff="chg"><name>C. M. Sperberg-McQueen</name><affiliation>University
of Illinois at Chicago and Text Encoding Initiative</affiliation><email href="mailto:[e-mail]">[e-mail]</email>
</author>
<author role="2e" diff="add"><name>Eve Maler</name><affiliation>Sun Microsystems,
Inc.</affiliation><email href="mailto:[e-mail]">[e-mail]</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>. <phrase diff="add"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E100">[E100]</loc>
The English version of this specification is the only normative version. However,
for translations of this document, see <loc href="http://www.w3.org/XML/#trans">http://www.w3.org/XML/#trans</loc>. </phrase>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 diff="del"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E66">[E66]</loc>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 diff="add">This second edition is <emph>not</emph> a new version of XML (first published 10 February 1998);
it merely incorporates the changes dictated by the first-edition errata (available
at <loc href="http://www.w3.org/XML/xml-19980210-errata">http://www.w3.org/XML/xml-19980210-errata</loc>)
as a convenience to readers. The errata list for this second edition is available
at <loc href="http://www.w3.org/XML/xml-V10-2e-errata">http://www.w3.org/XML/xml-V10-2e-errata</loc>.</p>
<p>Please report errors in this document to <loc href="mailto:[e-mail]">[e-mail]</loc><phrase
diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E101">[E101]</loc>; <loc
href="http://lists.w3.org/Archives/Public/xml-editor">archives</loc> are available</phrase>.</p>
<note diff="add">
<p>C. M. Sperberg-McQueen's affiliation has changed since the publication
of the first edition. He is now at the World Wide Web Consortium, and can
be contacted at <loc href="mailto:[e-mail]">[e-mail]</loc>.</p>
</note>
</status>
<pubstmt>
<p>Chicago, Vancouver, Mountain View, et al.: World-Wide Web Consortium, XML
Working Group, 1996, 1997, 2000.</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 < 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 &nbsp; and define nbsp
as &#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 & 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 & 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:</p>
<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>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 &versionOfXML; 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><termdef id="dt-must" term="Must">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 --></termdef></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><termdef id="dt-atuseroption" term="At user option">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.</termdef></p>
</def></gitem>
<gitem><label>validity constraint</label>
<def>
<p><termdef id="dt-vc" term="Validity constraint">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>.</termdef></p>
</def></gitem>
<gitem><label>well-formedness constraint</label>
<def>
<p><termdef id="dt-wfc" term="Well-formedness constraint">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>.</termdef></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. <phrase diff="del"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E85">[E85]</loc>At
user option, processors may normalize such characters to some canonical form. </phrase>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"><phrase diff="add"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E87">[E87]</loc>Marks
a sentence describing</phrase> 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"><phrase diff="add"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E87">[E87]</loc>Marks
a sentence describing</phrase> 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 <quote>root</quote>
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 <term>well-formed</term>
XML document if:</termdef></p>
<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 <termref
def="dt-wellformed">well-formed</termref>.</p></item>
</olist>
<scrap id="document" lang="ebnf">
<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>Matching the <nt def="NT-document">document</nt> production implies that:</p>
<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> <phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E17">[E17]</loc>For
all other elements, if the <termref def="dt-stag">start-tag</termref> is in
the content of another element, the <termref def="dt-etag">end-tag</termref>
is in the content of the same element.</phrase> More simply stated, the elements,
delimited by start- and end-tags, nest properly within each other.</p></item>
</olist>
<p><termdef id="dt-parentchild" term="Parent/Child">As a consequence of this,
for each non-root element <el>C</el> in the document, there is one other element <el>P</el>
in the document such that <el>C</el> is in the content of <el>P</el>, but
is not in the content of any other element that is in the content of <el>P</el>. <el>P</el>
is referred to as the <term>parent</term> of <el>C</el>, and <el>C</el> as
a <term>child</term> of <el>P</el>.</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"/> <phrase
diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</loc>(see
also <bibref ref="ISO10646-2000"/>)</phrase>. Legal characters are tab, carriage
return, line feed, and the legal <phrase diff="del"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E35">[E35]</loc>graphic </phrase>characters
of Unicode and ISO/IEC 10646. <phrase diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E69">[E69]</loc>The
versions of these standards cited in <specref ref="sec-existing-stds"/> were
current at the time this document was prepared. New characters may be added
to these standards by amendments or new editions. Consequently, XML processors
must accept any character in the range specified for <nt def="NT-Char">Char</nt>.</phrase>
The use of <quote>compatibility characters</quote>, as defined in section
6.8 of <bibref ref="Unicode"/> <phrase diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</loc>(see
also D21 in section 3.6 of <bibref ref="Unicode3"/>)</phrase>, is discouraged.</termdef></p>
<scrap id="char32" lang="ebnf">
<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>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.</p>
<scrap id="white" lang="ebnf">
<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>Characters are classified for convenience as letters, digits, or other
characters. <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E30">[E30]</loc>A
letter consists of an alphabetic or syllabic base character or an ideographic
character.</phrase> 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 <quote><code>xml</code></quote>,
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 diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E98">[E98]</loc>The
Namespaces in XML Recommendation <bibref ref="xml-names"/> assigns a meaning
to names containing colon characters. Therefore, authors should not use the
colon in XML names except for namespace purposes, but XML processors must
accept the colon as a name character.</p>
</note>
<p>An <nt def="NT-Nmtoken">Nmtoken</nt> (name token) is any mixture of name
characters.</p>
<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>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.</p>
<scrap lang="ebnf">
<head>Literals</head>
<prod id="NT-EntityValue">
<lhs>EntityValue</lhs><rhs>'"' ([^%&"] | <nt def="NT-PEReference">PEReference</nt>
| <nt def="NT-Reference">Reference</nt>)* '"' </rhs>
<rhs>|  "'" ([^%&'] | <nt def="NT-PEReference">PEReference</nt> | <nt
def="NT-Reference">Reference</nt>)* "'"</rhs>
</prod>
<prod id="NT-AttValue">
<lhs>AttValue</lhs><rhs>'"' ([^<&"] | <nt def="NT-Reference">Reference</nt>)*
'"' </rhs>
<rhs>|  "'" ([^<&'] | <nt def="NT-Reference">Reference</nt>)*
"'"</rhs>
</prod>
<prod id="NT-SystemLiteral">
<lhs>SystemLiteral</lhs><rhs>('"' [^"]* '"') | ("'" [^']* "'") </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 | [a-zA-Z0-9] | [-'()+,./:=?;!*#@$_%]</rhs>
</prod>
</scrap>
<note diff="add">
<p><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E72">[E72]</loc>Although
the <nt def="NT-EntityValue">EntityValue</nt> production allows the definition
of an entity consisting of a single explicit <code><</code> in the literal
(e.g., <code><!ENTITY mylt "<"></code>), it is strongly advised to avoid
this practice since any reference to that entity will cause a well-formedness
error.</p>
</note>
</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>, <termref def="dt-pi">processing instructions</termref>, <phrase
diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E89">[E89]</loc><nt
def="NT-XMLDecl">XML declarations</nt>, <nt def="NT-TextDecl">text declarations</nt>,
and any white space that is at the top level of the document entity (that
is, outside the document element and not inside any other markup).</phrase></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 (&) and the left angle bracket (<) 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>.<phrase
diff="del"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E18">[E18]</loc>They
are also legal within the <termref def="dt-litentval">literal entity value</termref>
of an internal entity declaration; see <specref ref="wf-entities"/>.</phrase> <!-- 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 <quote><code>&amp;</code></quote> and <quote><code>&lt;</code></quote>
respectively. The right angle bracket (>) may be represented using the string <quote><code>&gt;</code></quote>,
and must, <termref def="dt-compat">for compatibility</termref>, be escaped
using <quote><code>&gt;</code></quote> or a character reference when it
appears in the string <quote><code>]]></code></quote> 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, <quote><code>]]></code></quote>.</p>
<p>To allow attribute values to contain both single and double quotes, the
apostrophe or single-quote character (') may be represented as <quote><code>&apos;</code></quote>,
and the double-quote character (") as <quote><code>&quot;</code></quote>.</p>
<scrap lang="ebnf">
<head>Character Data</head>
<prod id="NT-CharData">
<lhs>CharData</lhs><rhs>[^<&]* - ([^<&]* ']]>' [^<&]*)</rhs>
</prod>
</scrap>
</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 <quote><code>--</code></quote> (double-hyphen)
must not occur within comments.</termdef> <phrase diff="add"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E63">[E63]</loc>Parameter
entity references are not recognized within comments.</phrase></p>
<scrap lang="ebnf">
<head>Comments</head>
<prod id="NT-Comment">
<lhs>Comment</lhs><rhs>'<!--' ((<nt def="NT-Char">Char</nt> - '-') | ('-'
(<nt def="NT-Char">Char</nt> - '-')))* '-->'</rhs>
</prod>
</scrap>
<p>An example of a comment:</p>
<eg><!&como; declarations for <head> & <body> &comc;></eg>
<p diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E27">[E27]</loc>Note
that the grammar does not allow a comment ending in <code>---></code>. The
following example is <emph>not</emph> well-formed.</p>
<eg diff="add"><!-- B+, B, or B---></eg>
</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.</termdef></p>
<scrap lang="ebnf">
<head>Processing Instructions</head>
<prod id="NT-PI">
<lhs>PI</lhs><rhs>'<?' <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>
<p>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 <quote><code>XML</code></quote>, <quote><code>xml</code></quote>,
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. <phrase diff="add"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E63">[E63]</loc>Parameter
entity references are not recognized within processing instructions.</phrase></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 <quote><code><![CDATA[</code></quote>
and end with the string <quote><code>]]></code></quote>:</termdef></p>
<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>'<![CDATA['</rhs>
</prod>
<prod id="NT-CData">
<lhs>CData</lhs><rhs>(<nt def="NT-Char">Char</nt>* - (<nt def="NT-Char">Char</nt>*
']]>' <nt def="NT-Char">Char</nt>*)) </rhs>
</prod>
<prod id="NT-CDEnd">
<lhs>CDEnd</lhs><rhs>']]>'</rhs>
</prod>
</scrap>
<p>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 <quote><code>&lt;</code></quote>
and <quote><code>&amp;</code></quote>. CDATA sections cannot nest.</p>
<p>An example of a CDATA section, in which <quote><code><greeting></code></quote>
and <quote><code></greeting></code></quote> are recognized as <termref
def="dt-chardata">character data</termref>, not <termref def="dt-markup">markup</termref>:</p>
<eg><![CDATA[<greeting>Hello, world!</greeting>]]> </eg>
</div2>
<div2 id="sec-prolog-dtd">
<head>Prolog and Document Type Declaration</head>
<p><termdef id="dt-xmldecl" term="XML Declaration">XML documents <phrase diff="chg"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E107">[E107]</loc>should</phrase>
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>:</p>
<eg><![CDATA[<?xml version="1.0"?> <greeting>Hello, world!</greeting> ]]></eg>
<p>and so is this:</p>
<eg><![CDATA[<greeting>Hello, world!</greeting>]]></eg>
<p>The version number <quote><code>1.0</code></quote> should be used to indicate
conformance to this version of this specification; it is an error for a document
to use the value <quote><code>1.0</code></quote> 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 <quote><code>1.0</code></quote>,
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.</p>
<scrap id="xmldoc" lang="ebnf">
<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>&pio; <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" diff="chg">
<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>
'"')<com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E15">[E15]</loc></com></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><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 <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E14">[E14]</loc>further</phrase>
information, see <specref ref="sec-physical-struct"/>.</p>
<scrap id="dtd" lang="ebnf">
<head>Document Type Definition</head>
<prodgroup pcw2="6" pcw4="17.5" pcw5="9">
<prod id="NT-doctypedecl" diff="chg">
<lhs>doctypedecl</lhs><rhs>'<!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 diff="chg" def="NT-DeclSep">DeclSep</nt>)*
']' <nt def="NT-S">S</nt>?)? '>'</rhs><vc def="vc-roottype"/><wfc def="ExtSubset"
diff="add"/><com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</loc></com>
</prod>
<prod id="NT-DeclSep" diff="add">
<lhs>DeclSep</lhs><rhs><nt def="NT-PEReference">PEReference</nt> | <nt def="NT-S">S</nt></rhs>
<wfc def="PE-between-Decls" diff="add"/><com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</loc></com>
</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 diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E82">[E82]</loc>Note
that it is possible to construct a well-formed document containing a <nt def="NT-doctypedecl">doctypedecl</nt>
that neither points to an external subset nor contains an internal subset.</p>
<p>The markup declarations may be made up in whole or in part of the <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>
<p diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E75">[E75]</loc>Parameter
entity references are recognized anywhere in the DTD (internal and external
subsets and external parameter entities), except in literals, processing instructions,
comments, and the contents of ignored conditional sections (see <specref ref="sec-condition-sect"/>).
They are also recognized in entity value literals. The use of parameter entities
in the internal subset is restricted as described below.</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>
<wfcnote id="ExtSubset" diff="add"><head><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</loc>External
Subset</head><p>The external subset, if any, must match the production for <nt
def="NT-extSubset">extSubset</nt>.</p>
</wfcnote>
<wfcnote id="PE-between-Decls" diff="add"><head><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</loc>PE
Between Declarations</head><p>The replacement text of a parameter entity reference
in a <nt def="NT-DeclSep">DeclSep</nt> must match the production <nt def="NT-extSubsetDecl">extSubsetDecl</nt>.</p>
</wfcnote>
<p>Like the internal subset, the external subset and any external parameter
entities <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</loc>referenced
in a <nt def="NT-DeclSep">DeclSep</nt></phrase> 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 <phrase diff="add"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</loc>these </phrase>
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.</p>
<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" diff="chg">
<lhs>extSubsetDecl</lhs><rhs>( <nt def="NT-markupdecl">markupdecl</nt> | <nt
def="NT-conditionalSect">conditionalSect</nt> | <nt diff="chg" def="NT-DeclSep">DeclSep</nt>)*</rhs>
<com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</loc></com>
</prod>
</prodgroup></scrap>
<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:</p>
<eg><![CDATA[<?xml version="1.0"?> <!DOCTYPE greeting SYSTEM "hello.dtd"> <greeting>Hello, world!</greeting> ]]></eg>
<p>The <termref def="dt-sysid">system identifier</termref> <quote><code>hello.dtd</code></quote>
gives the <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E78">[E78]</loc>address
(a URI reference)</phrase> of a DTD for the document.</p>
<p>The declarations can also be given locally, as in this example:</p>
<eg><![CDATA[<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE greeting [
  <!ELEMENT greeting (#PCDATA)>
]>
<greeting>Hello, world!</greeting>]]></eg>
<p>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><phrase diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E64">[E64]</loc>
or in parameter entities. <termdef id="dt-extmkpdecl" term="External Markup Declaration">An <term>external
markup declaration</term> is defined as a markup declaration occurring in
the external subset or in a parameter entity (external or internal, the latter
being included because non-validating processors are not required to read
them).</termdef></phrase></p>
<scrap id="fulldtd" lang="ebnf">
<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>In a standalone document declaration, the value <attval>yes</attval> indicates
that there are no <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E64">[E64]</loc><termref
def="dt-extmkpdecl">external markup declarations</termref></phrase> which
affect the information passed from the XML processor to the application. The
value <attval>no</attval> 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 <attval>no</attval> 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 <attval>no</attval> 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:</p>
<eg><?xml version="&versionOfXML;" standalone='yes'?></eg>
</div2>
<div2 id="sec-white-space">
<head>White Space Handling</head>
<p>In editing XML documents, it is often convenient to use <quote>white space</quote>
(spaces, tabs, and blank lines<phrase diff="del"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E39">[E39]</loc>,
denoted by the nonterminal <nt def="NT-S">S</nt> in this specification</phrase>)
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, <quote>significant</quote> 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 <att>xml:space</att>
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 <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E81">[E81]</loc>values
are one or both of</phrase> <attval>default</attval> and <attval>preserve</attval>.
For example:</p>
<eg diff="chg"><![CDATA[<!ATTLIST poem  xml:space (default|preserve) 'preserve'>]]>

<!-- <loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E81">[E81]</loc>-->
<!ATTLIST pre xml:space (preserve) #FIXED 'preserve'></eg>
<p>The value <attval>default</attval> signals that applications' default white-space
processing modes are acceptable for this element; the value <attval>preserve</attval>
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 <att>xml:space</att> 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 diff="del">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 <quote>#xD#xA</quote>
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>
<p diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E104">[E104]</loc>To
simplify the tasks of <termref def="dt-app">applications</termref>, the characters
passed to an application by the <termref def="dt-xml-proc">XML processor</termref>
must be as if the XML processor normalized all line breaks in external parsed
entities (including the document entity) on input, before parsing, by translating
both the two-character sequence #xD #xA and any #xD that is not followed by
#xA to a single #xA character.</p>
</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 <att>xml:lang</att> 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. <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E73">[E73]</loc>The
values of the attribute are language identifiers as defined by <bibref ref="RFC1766"/>, <titleref>Tags
for the Identification of Languages</titleref>, or its successor on the IETF
Standards Track.</phrase></p>
<note diff="add">
<p><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E73">[E73]</loc><bibref
ref="RFC1766"/> tags are constructed from two-letter language codes as defined
by <bibref ref="ISO639"/>, from two-letter country codes as defined by <bibref
ref="ISO3166"/>, or from language identifiers registered with the Internet
Assigned Numbers Authority <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E58">[E58]</loc><bibref
diff="chg" ref="IANA-LANGCODES"/></phrase>. It is expected that the successor
to <bibref ref="RFC1766"/> will introduce three-letter language codes for
languages not presently covered by <bibref ref="ISO639"/>.</p>
</note>
<p diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E73">[E73]</loc>(Productions
33 through 38 have been removed.)</p>
<scrap diff="del" 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>
<p diff="del">The <nt def="NT-Langcode">Langcode</nt> may be any of the following:</p>
<ulist diff="del">
<item><p>a two-letter language code as defined by <bibref ref="ISO639"/>, <titleref>Codes
for the representation of names of languages</titleref></p></item>
<item><p>a language identifier registered with the Internet Assigned Numbers
Authority <bibref diff="chg" ref="IANA-LANGCODES"/>; these begin with the
prefix <quote><code>i-</code></quote> (or <quote><code>I-</code></quote>)</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 <quote><code>x-</code></quote>
or <quote><code>X-</code></quote> in order to ensure that they do not conflict
with names later standardized or registered with IANA</p></item>
</ulist>
<p diff="del">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 diff="del">It is customary to give the language code in lower case, and
the country code (if any) in upper case. Note that these values, unlike other
names in XML documents, are case insensitive.</p>
<p>For example:</p>
<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 heiflem Bem¸h'n.</l>
</sp>]]></eg>
<!--<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 <att>xml:lang</att> is considered to apply to
all attributes and content of the element where it is specified, unless overridden
with an instance of <att>xml:lang</att> 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 <att>xml:lang</att> might take the form</p>
<eg>xml:lang NMTOKEN #IMPLIED</eg>
<p>but specific default values may also be given, if appropriate. In a collection
of French poems for English students, with glosses and notes in English, the <att>xml:lang</att>
attribute might be declared this way:</p>
<eg><![CDATA[<!ATTLIST poem   xml:lang NMTOKEN 'fr'>
<!ATTLIST gloss  xml:lang NMTOKEN 'en'>
<!ATTLIST note   xml:lang NMTOKEN 'en'>]]></eg>
</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 <quote>generic
identifier</quote> (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 <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E59">[E59]</loc>the
start-tag and the first child element, between child elements, or between
the last child element and the end-tag. Note that a CDATA section containing
only white space does not match the nonterminal <nt def="NT-S">S</nt>, and
hence cannot appear in these positions.</phrase></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>.</termdef></p>
<scrap lang="ebnf">
<head>Start-tag</head>
<prodgroup pcw2="6" pcw4="15" pcw5="11.5">
<prod id="NT-STag">
<lhs>STag</lhs><rhs>'<' <nt def="NT-Name">Name</nt> (<nt def="NT-S">S</nt> <nt
def="NT-Attribute">Attribute</nt>)* <nt def="NT-S">S</nt>? '>'</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>
<p>The <nt def="NT-Name">Name</nt> in the start- and end-tags gives the element's <term>type</term>. <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><phrase diff="add"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E46">[E46]</loc>Note
that the order of attribute specifications in a start-tag or empty-element
tag is not significant.</phrase></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><</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 <phrase diff="del"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E83">[E83]</loc>(other
than <quote><code>&lt;</code></quote>) </phrase>must not contain a <code><</code>.</p>
</wfcnote>
<p>An example of a start-tag:</p>
<eg><termdef id="dt-dog" term="dog"></eg>
<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:</termdef></p>
<scrap lang="ebnf">
<head>End-tag</head>
<prodgroup pcw2="6" pcw4="15" pcw5="11.5">
<prod id="NT-ETag">
<lhs>ETag</lhs><rhs>'</' <nt def="NT-Name">Name</nt> <nt def="NT-S">S</nt>?
'>'</rhs>
</prod>
</prodgroup></scrap>
<p>An example of an end-tag:</p>
<eg></termdef></eg>
<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>:</termdef></p>
<scrap lang="ebnf">
<head>Content of Elements</head>
<prodgroup pcw2="6" pcw4="15" pcw5="11.5">
<prod id="NT-content" diff="chg">
<lhs>content</lhs><rhs><nt def="NT-CharData">CharData</nt>? ((<nt def="NT-element">element</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>) <nt def="NT-CharData">CharData</nt>?)*</rhs>
<com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E71">[E71]</loc></com>
</prod>
</prodgroup></scrap>
<p><phrase diff="chg"><termdef id="dt-empty" term="Empty"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E97">[E97]</loc>An element
with no content is said to be <term>empty</term>.</termdef> The representation
of an empty element is either a start-tag immediately followed by an end-tag,
or an empty-element tag.</phrase> <termdef id="dt-eetag" term="empty-element tag">An <term>empty-element
tag</term> takes a special form:</termdef></p>
<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>'<' <nt def="NT-Name">Name</nt> (<nt def="NT-S">S</nt> <nt
def="NT-Attribute">Attribute</nt>)* <nt def="NT-S">S</nt>? '/>'</rhs><wfc
def="uniqattspec"/>
</prod>
</prodgroup></scrap>
<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 <phrase diff="chg"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E45">[E45]</loc>should
be used, and should only be used,</phrase> for elements which are declared
EMPTY.</p>
<p>Examples of empty elements:</p>
<eg><IMG align="left"
 src="http://www.w3.org/Icons/WWW/w3c_home" />
<br></br>
<br/></eg>
</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:</termdef></p>
<scrap lang="ebnf">
<head>Element Type Declaration</head>
<prodgroup pcw2="5.5" pcw4="18" pcw5="9">
<prod id="NT-elementdecl">
<lhs>elementdecl</lhs><rhs>'<!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>?
'>'</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>
<p>where the <nt def="NT-Name">Name</nt> gives the element type being declared.</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:</p>
<eg><!ELEMENT br EMPTY>
<!ELEMENT p (#PCDATA|emph)* >
<!ELEMENT %name.para; %content.para; >
<!ELEMENT container ANY></eg>
<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><termdef id="dt-content-model"
term="Content model">In this case, the constraint includes a <phrase diff="chg"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E55">[E55]</loc><term>content
model</term></phrase>, a simple grammar governing the allowed types of the
child elements and the order in which they are allowed to appear.</termdef>
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:</p>
<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" diff="chg">
<lhs>choice</lhs><rhs>'(' <nt def="NT-S">S</nt>? <nt def="NT-cp">cp</nt> ( <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><com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E50">[E50]</loc></com>
<com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E52">[E52]</loc></com>
<vc def="vc-PEinGroup"/>
</prod>
<prod id="NT-seq" diff="chg">
<lhs>seq</lhs><rhs>'(' <nt def="NT-S">S</nt>? <nt def="NT-cp">cp</nt> ( <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><com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E52">[E52]</loc></com>
<vc def="vc-PEinGroup"/>
</prod>
</prodgroup></scrap>
<p>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"/>.</p>
<!--appendix <specref ref="determinism"/>.-->
<!-- appendix on deterministic content models. -->
<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 <phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E11">[E11]</loc>parenthesized</phrase>
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 diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E19">[E19]</loc><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 contain at
least one non-blank character, and neither the first nor last non-blank character
of the replacement text should be a connector (<code>|</code> or <code>,</code>).</p>
</vcnote>
<p>Examples of element-content models:</p>
<eg><!ELEMENT spec (front, body, back?)>
<!ELEMENT div1 (head, (p | list | note)*, div2*)>
<!ELEMENT dictionary-body (%div.mix; | %dict.mix;)*></eg>
</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:</p>
<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>
<p>where the <nt def="NT-Name">Name</nt>s give the types of elements that
may appear as children. <phrase diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E10">[E10]</loc>The
keyword <kw>#PCDATA</kw> derives historically from the term <quote>parsed
character data.</quote></phrase></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:</p>
<eg><!ELEMENT p (#PCDATA|a|ul|b|i|em)*>
<!ELEMENT p (#PCDATA | %font; | %phrase; | %special; | %form;)* >
<!ELEMENT b (#PCDATA)></eg>
</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:</p>
<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><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:</termdef></p>
<scrap lang="ebnf">
<head>Attribute-list Declaration</head>
<prod id="NT-AttlistDecl">
<lhs>AttlistDecl</lhs><rhs>'<!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>? '>'</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>
<p>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.</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. <phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E9">[E9]</loc><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 in an attribute-list
declaration, and at least one attribute definition in each attribute-list
declaration.</phrase> 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<phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E8">[E8]</loc>.
The validity constraints noted in the grammar are applied after the attribute
value has been normalized as described in <specref ref="attdecls"/>.</phrase></p>
<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>
<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:</p>
<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"/>
<vc def="OneNotationPer" diff="add"/><vc def="NoNotationEmpty" diff="add"/>
</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>
<p>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="OneNotationPer" diff="add"><head><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E7">[E7]</loc>One
Notation Per Element Type</head><p>No element type may have more than one <kw>NOTATION</kw>
attribute specified.</p>
</vcnote>
<vcnote id="NoNotationEmpty" diff="add"><head><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E68">[E68]</loc>No
Notation on Empty Element</head><p><termref def="dt-compat">For compatibility</termref>,
an attribute of type <kw>NOTATION</kw> must not be declared on an element
declared <kw>EMPTY</kw>.</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.</p>
<scrap lang="ebnf">
<head>Attribute Defaults</head>
<prodgroup pcw4="14" pcw5="11.5">
<prod id="NT-DefaultDecl">
<lhs>DefaultDecl</lhs><rhs>'#REQUIRED' | '#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>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:</p>
<eg><!ATTLIST termdef
          id      ID      #REQUIRED
          name    CDATA   #IMPLIED>
<!ATTLIST list
          type    (bullets|ordered|glossary)  "ordered">
<!ATTLIST form
          method  CDATA   #FIXED "POST"></eg>
</div3>
<div3 id="AVNormalize" diff="chg">
<head><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E70">[E70]</loc>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 the attribute value by applying
the algorithm below, or by using some other method such that the value passed
to the application is the same as that produced by the algorithm.</p>
<olist>
<item><p>All line breaks must have been normalized on input to #xA as described
in <specref ref="sec-line-ends"/>, so the rest of this algorithm operates
on text normalized in this way.</p></item>
<item><p>Begin with a normalized value consisting of the empty string.</p>
</item>
<item><p>For each character, entity reference, or character reference in the
unnormalized attribute value, beginning with the first and continuing to the
last, do the following:</p>
<ulist>
<item><p>For a character reference, append the referenced character to the
normalized value.</p></item>
<item><p>For an entity reference, recursively apply step 3 of this algorithm
to the replacement text of the entity.</p></item>
<item><p>For a white space character (#x20, #xD, #xA, #x9), append a space
character (#x20) to the normalized value.</p></item>
<item><p>For another character, append the character to the normalized value.</p>
</item>
</ulist>
</item>
</olist>
<p>If the attribute type is not CDATA, then the XML processor must further
process the normalized attribute value by discarding any leading and trailing
space (#x20) characters, and by replacing sequences of space (#x20) characters
by a single space (#x20) character.</p>
<p>Note that if the unnormalized attribute value contains a character reference
to a white space character other than space (#x20), the normalized value contains
the referenced character itself (#xD, #xA or #x9). This contrasts with the
case where the unnormalized value contains a white space character (not a
reference), which is replaced with a space character (#x20) in the normalized
value and also contrasts with the case where the unnormalized value contains
an entity reference whose replacement text contains a white space character;
being recursively processed, the white space character is replaced with a
space character (#x20) in the normalized value.</p>
<p>All attributes for which no declaration has been read should be treated
by a non-validating <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E95">[E95]</loc>processor</phrase>
as if declared <kw>CDATA</kw>.</p>
<p>Following are examples of attribute normalization. Given the following
declarations:</p>
<eg><!ENTITY d "&#xD;">
<!ENTITY a "&#xA;">
<!ENTITY da "&#xD;&#xA;"></eg>
<p>the attribute specifications in the left column below would be normalized
to the character sequences of the middle column if the attribute <att>a</att>
is declared <kw>NMTOKENS</kw> and to those of the right columns if <att>a</att>
is declared <kw>CDATA</kw>.</p>
<table border="1" frame="border"><thead><tr><th>Attribute specification</th>
<th>a is NMTOKENS</th><th>a is CDATA</th></tr></thead><tbody><tr><td><eg>a="

xyz"</eg></td><td><code>x y z</code></td><td><code>#x20 #x20 x y z</code></td>
</tr><tr><td><eg>a="&d;&d;A&a;&a;B&da;"</eg></td><td><code>A
#x20 B</code></td><td><code>#x20 #x20 A #x20 #x20 B #x20 #x20</code></td>
</tr><tr><td><eg>a=
"&#xd;&#xd;A&#xa;&#xa;B&#xd;&#xa;"</eg></td><td><code>#xD
#xD A #xA #xA B #xD #xA</code></td><td><code>#xD #xD A #xA #xA B #xD #xD</code></td>
</tr></tbody></table>
<p>Note that the last example is invalid (but well-formed) if <att>a</att>
is declared to be of type <kw>NMTOKENS</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></p>
<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>'<![' S? 'INCLUDE' S? '[' <nt def="NT-extSubsetDecl">extSubsetDecl</nt>
']]>' </rhs><com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</loc></com>
<vc def="condsec-nesting" diff="add"/>
</prod>
<prod id="NT-ignoreSect">
<lhs>ignoreSect</lhs><rhs>'<![' S? 'IGNORE' S? '[' <nt def="NT-ignoreSectContents">ignoreSectContents</nt>*
']]>'</rhs><com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</loc></com>
<vc def="condsec-nesting" diff="add"/>
</prod>
<prod id="NT-ignoreSectContents">
<lhs>ignoreSectContents</lhs><rhs><nt def="NT-Ignore">Ignore</nt> ('<![' <nt
def="NT-ignoreSectContents">ignoreSectContents</nt> ']]>' <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>*
('<![' | ']]>') <nt def="NT-Char">Char</nt>*) </rhs>
</prod>
</prodgroup></scrap>
<vcnote id="condsec-nesting" diff="add"><head><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</loc>Proper
Conditional Section/PE Nesting</head><p>If any of the "<code><![</code>",
"<code>[</code>", or "<code>]]></code>" of a conditional section is contained
in the replacement text for a parameter-entity reference, all of them must
be contained in the same replacement text.</p>
</vcnote>
<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. <phrase diff="del"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</loc>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.</phrase>
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.<phrase diff="add"> <loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</loc>The contents
of an ignored conditional section are parsed by ignoring all characters after
the "<code>[</code>" following the keyword, except conditional section starts
"<code><![</code>" and ends "<code>]]></code>", until the matching conditional
section end is found. Parameter entity references are not recognized in this
process.</phrase></p>
<p>If the keyword of the conditional section is a parameter-entity reference,
the parameter entity must be replaced by its content before the processor
decides whether to include or ignore the conditional section.</p>
<p>An example:</p>
<eg><!ENTITY % draft 'INCLUDE' >
<!ENTITY % final 'IGNORE' >

<![%draft;[
<!ELEMENT book (comments*, title, body, supplements?)>
]]>
<![%final;[
<!ELEMENT book (title, body, supplements?)>
]]></eg>
</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. <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E6">[E6]</loc>These
are called <term>entities</term>; they all have <term>content</term> and are
all (except for the <termref def="dt-docent">document entity</termref> and
the <termref def="dt-doctype">external DTD subset</termref>) identified by
entity <term>name</term></phrase>.</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, <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E25">[E25]</loc>may
be other than</phrase> 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"><phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E53">[E53]</loc><term>Parameter
entities</term></phrase> 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.</termdef></p>
<scrap lang="ebnf">
<head>Character Reference</head>
<prod id="NT-CharRef">
<lhs>CharRef</lhs><rhs>'&#' [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>
<p>If the character reference begins with <quote><code>&#x</code></quote>,
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 <quote><code>&#</code></quote>, the digits up to the terminating <code>;</code>
provide a decimal representation of the character's code point.</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>&</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>'&' <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 <quote><code>standalone='yes'</code></quote>, <phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E34">[E34]</loc>for
an entity reference that does not occur within the external subset or a parameter
entity, 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> that does not occur within the external subset or a
parameter entity</phrase>, except that well-formed documents need not declare
any of the following entities: &magicents;. <phrase diff="del"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E29">[E29]</loc>The declaration
of a parameter entity must precede any reference to it. Similarly, </phrase>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 <quote><code>standalone='no'</code></quote>,
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 <phrase diff="chg"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E92">[E92]</loc>attribute-list
declaration containing a default value with a direct or indirect reference
to that general entity.</phrase></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:</p>
<eg>Type <key>less-than</key> (&hcro;3C;) to save options.
This document was prepared on &docdate; and
is classified &security-level;.</eg>
<p>Example of a parameter-entity reference:</p>
<eg><![CDATA[<!-- declare the parameter entity "ISOLat2"... -->
<!ENTITY % ISOLat2
         SYSTEM "http://www.xml.com/iso/isolat2-xml.entities" >
<!-- ... now reference it. -->
%ISOLat2;]]></eg>
</div2>
<div2 id="sec-entity-decl">
<head>Entity Declarations</head>
<p><termdef id="dt-entdecl" term="entity declaration"> Entities are declared
thus:</termdef></p>
<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>'<!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>?
'>'</rhs>
</prod>
<prod id="NT-PEDecl">
<lhs>PEDecl</lhs><rhs>'<!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>? '>'</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>
<p>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.</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:</p>
<eg><!ENTITY Pub-Status "This is a pre-release of the
 specification."></eg>
</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:</termdef></p>
<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>
<p>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.</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><phrase diff="chg"><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 <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E88">[E88]</loc>URI
reference</phrase><phrase diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E66">[E66]</loc>
(as defined in <bibref ref="rfc2396"/>, updated by <bibref ref="rfc2732"/>)</phrase>, <loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E76">[E76]</loc>meant
to be dereferenced to obtain input for the XML processor to construct the
entity's replacement text.</termdef> It is an error for a fragment identifier
(beginning with a <code>#</code> character) to be part of a system identifier.</phrase>
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 diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E78">[E78]</loc>URI
references require encoding and escaping of certain characters. The disallowed
characters include all non-ASCII characters, plus the excluded characters
listed in Section 2.4 of <bibref ref="rfc2396"/>, except for the number sign
(<code>#</code>) and percent sign (<code>%</code>) characters and the square
bracket characters re-allowed in <bibref ref="rfc2732"/>. Disallowed characters
must be escaped as follows:</p>
<olist diff="add">
<item><p>Each disallowed character is converted to UTF-8 <bibref ref="rfc2279"/>
as one or more bytes.</p></item>
<item><p>Any octets corresponding to a disallowed character are escaped with
the URI escaping mechanism (that is, converted to <code>%</code><var>HH</var>,
where HH is the hexadecimal notation of the byte value).</p></item>
<item><p>The original character is replaced by the resulting character sequence.</p>
</item>
</olist>
<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 <phrase diff="chg"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E88">[E88]</loc>URI reference</phrase>.
If the processor is unable to do so, it must use the <phrase diff="chg"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E88">[E88]</loc>URI
reference</phrase> specified in the system literal. Before a match is attempted,
all strings of white space in the public identifier must be normalized to
single space characters (#x20), and leading and trailing white space must
be removed.</p>
<p>Examples of external entity declarations:</p>
<eg><!ENTITY open-hatch
         SYSTEM "http://www.textuality.com/boilerplate/OpenHatch.xml">
<!ENTITY open-hatch
         PUBLIC "-//Textuality//TEXT Standard open-hatch boilerplate//EN"
         "http://www.textuality.com/boilerplate/OpenHatch.xml">
<!ENTITY hatch-pic
         SYSTEM "../grafix/OpenHatch.gif"
         NDATA gif ></eg>
</div3>
</div2>
<div2 id="TextEntities">
<head>Parsed Entities</head>
<div3 id="sec-TextDecl">
<head>The Text Declaration</head>
<p>External parsed entities <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E107">[E107]</loc>should</phrase
> each begin with a <term>text declaration</term>.</p>
<scrap lang="ebnf">
<head>Text Declaration</head>
<prodgroup pcw4="12.5" pcw5="13">
<prod id="NT-TextDecl">
<lhs>TextDecl</lhs><rhs>&pio; <nt def="NT-VersionInfo">VersionInfo</nt>? <nt
def="NT-EncodingDecl">EncodingDecl</nt> <nt def="NT-S">S</nt>? &pic;</rhs>
</prod>
</prodgroup></scrap>
<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. <phrase diff="add"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E94">[E94]</loc>The text declaration
in an external parsed entity is not considered part of its <termref def="dt-repltext">replacement
text</termref>.</phrase></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>. <phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</loc>All
external parameter entities are well-formed by definition.</phrase></p>
<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" diff="del">
<lhs>extPE</lhs><rhs><nt def="NT-TextDecl">TextDecl</nt>? <nt def="NT-extSubsetDecl">extSubsetDecl</nt></rhs>
<com><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E109">[E109]</loc></com>
</prod>
</scrap>
<p>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 <phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E56">[E56]</loc>both
the UTF-8 and UTF-16 encodings.</phrase> <phrase diff="add"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E77">[E77]</loc>The terms <quote>UTF-8</quote>
and <quote>UTF-16</quote> in this specification do not apply to character
encodings with any other labels, even if the encodings or labels are very
similar to UTF-8 or UTF-16.</phrase></p>
<p>Entities encoded in UTF-16 must begin with the Byte Order Mark described
by <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</loc>Annex
F of <bibref ref="ISO10646"/>, Annex H of <bibref ref="ISO10646-2000"/>, section
2.4 of <bibref ref="Unicode"/>, and section 2.7 of <bibref ref="Unicode3"/></phrase>
(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. <phrase diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E47">[E47]</loc>In
the absence of external character encoding information (such as MIME headers),</phrase>
parsed entities which are stored in an encoding other than UTF-8 or UTF-16
must begin with a text declaration <phrase diff="add">(see <specref ref="sec-TextDecl"/>) </phrase>containing
an encoding declaration:</p>
<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>
<p>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 <quote><code>UTF-8</code></quote>, <quote><code>UTF-16</code></quote>, <quote><code>ISO-10646-UCS-2</code
></quote>, and <quote><code>ISO-10646-UCS-4</code></quote> should be used
for the various encodings and transformations of Unicode / ISO/IEC 10646,
the values <quote><code>ISO-8859-1</code></quote>, <quote><code>ISO-8859-2</code></quote>,
... <loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E106">[E106]</loc><phrase
diff="chg"><quote><code>ISO-8859-</code><var>n</var></quote> (where <var>n</var>
is the part number)</phrase> should be used for the parts of ISO 8859, and
the values <quote><code>ISO-2022-JP</code></quote>, <quote><code>Shift_JIS</code></quote>,
and <quote><code>EUC-JP</code></quote> should be used for the various encoded
forms of JIS X-0208-1997. <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E57">[E57]</loc>It
is recommended that character encodings registered (as <emph>charset</emph>s)
with the Internet Assigned Numbers Authority <phrase diff="chg"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E58">[E58]</loc><bibref ref="IANA"/></phrase>,
other than those just listed, be referred to using their registered names;
other encodings should use names starting with an <quote>x-</quote> prefix.
XML processors should match character encoding names in a case-insensitive
way and should either interpret an IANA-registered name as the encoding registered
at IANA for that name or treat it as unknown (processors are, of course, not
required to support all IANA-registered encodings).</phrase></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, <phrase diff="del"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E5">[E5]</loc>for
an encoding declaration to occur other than at the beginning of an external
entity, </phrase>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 diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E5">[E5]</loc>It
is <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E36">[E36]</loc>a
fatal</phrase> error for a <nt def="NT-TextDecl">TextDecl</nt> to occur other
than at the beginning of an external entity.</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. <phrase
diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E79">[E79]</loc>It
is a fatal error if an XML entity is determined (via default, encoding declaration,
or higher-level protocol) to be in a certain encoding but contains octet sequences
that are not legal in that encoding. It is also a fatal error if an XML entity
contains no encoding declaration and its content is not legal UTF-8 or UTF-16.</phrase></p>
<p>Examples of <phrase diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E23">[E23]</loc>text
declarations containing </phrase>encoding declarations:</p>
<eg><?xml encoding='UTF-8'?>
<?xml encoding='EUC-JP'?></eg>
</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 diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E90">[E90]</loc>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>, <nt
def="NT-AttValue">AttValue</nt>, <nt def="NT-PI">PI</nt>, <nt def="NT-Comment">Comment</nt>, <nt
def="NT-SystemLiteral">SystemLiteral</nt>, <nt def="NT-PubidLiteral">PubidLiteral</nt>,
or the contents of an ignored conditional section (see <specref ref="sec-condition-sect"/>).</p>
<p>.</p>
</def></gitem>
</glist></p>
<table border="1" frame="border" cellpadding="7"><tbody align="center"><tr>
<td rowspan="2" colspan="1"></td><td colspan="4" align="center" valign="bottom">Entity
Type</td><td rowspan="2" align="center">Character</td></tr><tr align="center"
valign="bottom"><td>Parameter</td><td>Internal General</td><td>External Parsed
General</td><td>Unparsed</td></tr><tr align="center" valign="middle"><td align="right">Reference
in Content</td><td><titleref href="#not-recognized">Not recognized</titleref></td>
<td><titleref href="#included">Included</titleref></td><td><titleref href="#include-if-valid">Included
if validating</titleref></td><td><titleref href="#forbidden">Forbidden</titleref></td>
<td><titleref href="#included">Included</titleref></td></tr><tr align="center"
valign="middle"><td align="right">Reference in Attribute Value</td><td><titleref
href="#not-recognized">Not recognized</titleref></td><td><titleref href="#inliteral">Included
in literal</titleref></td><td><titleref href="#forbidden">Forbidden</titleref></td>
<td><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E51">[E51]</loc><titleref
diff="chg" href="#forbidden">Forbidden</titleref></td><td><titleref href="#included">Included</titleref></td>
</tr><tr align="center" valign="middle"><td align="right">Occurs as Attribute
Value</td><td><titleref href="#not-recognized">Not recognized</titleref></td>
<td><titleref href="#forbidden">Forbidden</titleref></td><td><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E51">[E51]</loc><titleref
diff="chg" href="#forbidden">Forbidden</titleref></td><td><titleref href="#notify">Notify</titleref></td>
<td><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E51">[E51]</loc><titleref
diff="chg" href="#not-recognized">Not recognized</titleref></td></tr><tr align="center"
valign="middle"><td align="right">Reference in EntityValue</td><td><titleref
href="#inliteral">Included in literal</titleref></td><td><titleref href="#bypass">Bypassed</titleref></td>
<td><titleref href="#bypass">Bypassed</titleref></td><td><titleref href="#forbidden">Forbidden</titleref></td>
<td><titleref href="#included">Included</titleref></td></tr><tr align="center"
valign="middle"><td align="right">Reference in DTD</td><td><titleref href="#as-PE">Included
as PE</titleref></td><td><titleref href="#forbidden">Forbidden</titleref></td>
<td><titleref href="#forbidden">Forbidden</titleref></td><td><titleref href="#forbidden">Forbidden</titleref></td>
<td><titleref href="#forbidden">Forbidden</titleref></td></tr></tbody></table>
<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.</termdef> 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<phrase diff="del"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E65">[E65]</loc>, except that
the replacement text of entities used to escape markup delimiters (the entities &magicents;)
is always treated as data</phrase>. (The string <quote><code>AT&amp;T;</code></quote>
expands to <quote><code>AT&T;</code></quote> 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. </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 <phrase diff="chg"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E95">[E95]</loc>processor</phrase>
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:</p>
<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>
</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:</p>
<eg diff="chg"><!-- <loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E4">[E4]</loc> -->
<![CDATA[<!ENTITY % YN '"Yes"' >
<!ENTITY WhatHeSaid "He said %YN;" >]]></eg>
<p>while this is not:</p>
<eg><!ENTITY EndAttr "27'" >
<element attribute='a-&EndAttr;></eg>
</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. <phrase diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E96">[E96]</loc>This
behavior does not apply to parameter entity references within entity values;
these are described in <specref ref="inliteral"/>.</phrase></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:</p>
<eg><![CDATA[<!ENTITY % pub    "Éditions Gallimard" >
<!ENTITY   rights "All rights reserved" >
<!ENTITY   book   "La Peste: Albert Camus,
© 1947 %pub;. &rights;" >]]></eg>
<p>then the replacement text for the entity <quote><code>book</code></quote>
is:</p>
<eg>La Peste: Albert Camus,
© 1947 …ditions Gallimard. &rights;</eg>
<p>The general-entity reference <quote><code>&rights;</code></quote> would
be expanded should the reference <quote><code>&book;</code></quote> 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 <quote><code>&#60;</code></quote> and <quote><code>&#38;</code></quote>
may be used to escape <code><</code> and <code>&</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. <phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E80">[E80]</loc>If
the entities <code>lt</code> or <code>amp</code> are declared, they must be
declared as internal entities whose replacement text is a character reference
to the <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E103">[E103]</loc>respective
character (less-than sign or ampersand)</phrase> being escaped; the double
escaping is required for these entities so that references to them produce
a well-formed result. If the entities <code>gt</code>, <code>apos</code>,
or <code>quot</code> are declared, they must be declared as internal entities
whose replacement text is the single character being escaped (or a character
reference to that character; the double escaping here is unnecessary but harmless).
For example:</phrase></p>
<eg><![CDATA[<!ENTITY lt     "&#60;">
<!ENTITY gt     ">">
<!ENTITY amp    "&#38;">
<!ENTITY apos   "'">
<!ENTITY quot   """>]]></eg>
<p diff="del">Note that the <code><</code> and <code>&</code> characters
in the declarations of <quote><code>lt</code></quote> and <quote><code>amp</code></quote>
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.</termdef></p>
<scrap lang="ebnf">
<head>Notation Declarations</head>
<prod id="NT-NotationDecl">
<lhs>NotationDecl</lhs><rhs>'<!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>? '>'</rhs><vc def="UniqueNotationName" diff="add"/>
</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>
<vcnote id="UniqueNotationName" diff="add"><head><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E22">[E22]</loc>Unique
Notation Name</head><p>Only one notation declaration can declare a given <nt
def="NT-Name">Name</nt>.</p>
</vcnote>
<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<phrase diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E21">[E21]</loc>,
at user option,</phrase> 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> <phrase diff="add"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E33">[E33]</loc>Except when <code>standalone="yes"</code>, </phrase>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:</p>
<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="#textent">Parsed Entity</titleref>, and <titleref href="#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>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</p>
<eg>symbol ::= expression</eg>
<p>Symbols are written with an initial capital letter if they are <phrase
diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E42">[E42]</loc>the
start symbol of a regular language,</phrase> otherwise with an initial lower
case letter. Literal strings are quoted.</p>
<p>Within the expression on the right-hand side of a rule, the following expressions
are used to match strings of one or more characters: <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 <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E93">[E93]</loc><nt
def="NT-Char">Char</nt></phrase> with a value in the range(s) indicated (inclusive).</p>
</def></gitem>
<gitem diff="add"><label><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E3">[E3]</loc><code>[abc]</code>, <code>[#xN#xN#xN]</code
></label>
<def>
<p>matches any <nt def="NT-Char">Char</nt> with a value among the characters
enumerated. Enumerations and ranges can be mixed in one set of brackets.</p>
</def></gitem>
<gitem><label><code>[^a-z]</code>, <code>[^#xN-#xN]</code></label>
<def>
<p>matches any <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E93">[E93]</loc><nt
def="NT-Char">Char</nt></phrase> 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 <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E93">[E93]</loc><nt
def="NT-Char">Char</nt></phrase> with a value not among the characters given. <phrase
diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E3">[E3]</loc>Enumerations
and ranges of forbidden values can be mixed in one set of brackets.</phrase></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>. <phrase diff="add"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E20">[E20]</loc>This
operator has higher precedence than alternation; thus <code>A B | C D</code>
is identical to <code>(A B) | (C D)</code>.</phrase></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>.<phrase diff="add"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E20">[E20]</loc>Concatenation
has higher precedence than alternation; thus <code>A+ | B+</code> is identical
to <code>(A+) | (B+)</code>.</phrase></p>
</def></gitem>
<gitem><label><code>A*</code></label>
<def>
<p>matches zero or more occurrences of <code>A</code>. <phrase diff="add"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E20">[E20]</loc>Concatenation
has higher precedence than alternation; thus <code>A* | B*</code> is identical
to <code>(A*) | (B*)</code>.</phrase></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" diff="chg" key="IANA-CHARSETS"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E58">[E58]</loc>(Internet
Assigned Numbers Authority) <titleref>Official Names for Character Sets</titleref>,
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" href="http://www.ietf.org/rfc/rfc1766.txt" key="IETF RFC 1766">IETF
(Internet Engineering Task Force). <titleref>RFC 1766: Tags for the Identification
of Languages</titleref>, ed. H. Alvestrand. 1995.</bibl>
<bibl id="ISO639-old" diff="del" key="ISO 639"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E38">[E38]</loc>
(International Organization for Standardization). <titleref>ISO 639:1988 (E).
Code for the representation of names of languages.</titleref> [Geneva]: International
Organization for Standardization, 1988.</bibl>
<bibl id="ISO3166-old" diff="del" key="ISO 3166"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E38">[E38]</loc>
(International Organization for Standardization). <titleref>ISO 3166-1:1997
(E). Codes for the representation of names of countries and their subdivisions —
Part 1: Country codes</titleref> [Geneva]: International Organization for
Standardization, 1997.</bibl>
<bibl id="ISO10646" key="ISO/IEC 10646">ISO (International Organization for
Standardization). <titleref>ISO/IEC 10646-1993 (E). Information technology —
Universal Multiple-Octet Coded Character Set (UCS) — Part 1: Architecture
and Basic Multilingual Plane.</titleref> [Geneva]: International Organization
for Standardization, 1993 (plus amendments AM 1 through AM 7).</bibl>
<bibl id="ISO10646-2000" diff="add" key="ISO/IEC 10646-2000"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</loc> ISO (International
Organization for Standardization). <titleref>ISO/IEC 10646-1:2000. Information
technology — Universal Multiple-Octet Coded Character Set (UCS) —
Part 1: Architecture and Basic Multilingual Plane.</titleref> [Geneva]: International
Organization for Standardization, 2000.</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>
<bibl id="Unicode3" diff="add" key="Unicode3"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</loc>
The Unicode Consortium. <emph>The Unicode Standard, Version 3.0.</emph> Reading,
Mass.: Addison-Wesley Developers Press, 2000. ISBN 0-201-61633-5.</bibl>
</blist></div2>
<div2 id="null">
<!--
ID made "null" to match its previous value in the First
Edition; it's odd, but if there's no set value, the stylesheet
currently generates an odd string that would be backwards
incompatible with any references anyone might have made before.
-->
<head>Other References</head>
<blist>
<bibl id="Aho" key="Aho/Ullman">Aho, Alfred V., Ravi Sethi, and Jeffrey D.
Ullman. <titleref>Compilers: Principles, Techniques, and Tools</titleref>.
Reading: Addison-Wesley, 1986, rpt. corr. 1988.</bibl>
<bibl id="Berners-Lee" key="Berners-Lee et al."> Berners-Lee, T., R. Fielding,
and L. Masinter. <titleref>Uniform Resource Identifiers (URI): Generic Syntax
and Semantics</titleref>. 1997. (Work in progress; see updates to RFC1738.)</bibl>
<bibl id="ABK" diff="chg" key="Br¸ggemann-Klein"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E2">[E2]</loc>Br¸ggemann-Klein,
Anne. Formal Models in Document Processing. Habilitationsschrift. Faculty
of Mathematics at the University of Freiburg, 1993. (See <loc href="ftp://ftp.informatik.uni-freiburg.de/documents/papers/brueggem/habil.ps">ftp://ftp.informatik.uni-freiburg.de/documents/papers/brueggem/habil.ps</loc
>.)</bibl>
<bibl id="ABKDW" diff="chg" key="Br¸ggemann-Klein and Wood"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E2">[E2]</loc>Br¸ggemann-Klein,
Anne, and Derick Wood. <titleref>Deterministic Regular Languages</titleref>.
Universit‰t Freiburg, Institut f¸r Informatik, Bericht 38, Oktober 1991. Extended
abstract in A. Finkel, M. Jantzen, Hrsg., STACS 1992, S. 173-184. Springer-Verlag,
Berlin 1992. Lecture Notes in Computer Science 577. Full version titled <titleref>One-Unambiguous
Regular Languages</titleref> in Information and Computation 140 (2): 229-253,
February 1998.</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="IANA-LANGCODES" diff="add" href="http://www.isi.edu/in-notes/iana/assignments/languages/"
key="IANA-LANGCODES"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E58">[E58]</loc>(Internet
Assigned Numbers Authority) <titleref>Registry of Language Tags</titleref>,
ed. Keld Simonsen et al.</bibl>
<bibl id="RFC1738" diff="del" href="http://www.ietf.org/rfc/rfc1738.txt" key="IETF RFC1738">IETF
(Internet Engineering Task Force). <titleref>RFC 1738: Uniform Resource Locators
(URL)</titleref>, ed. T. Berners-Lee, L. Masinter, M. McCahill. 1994. </bibl>
<bibl id="RFC1808" diff="del" href="http://www.ietf.org/rfc/rfc1808.txt" key="IETF RFC1808">IETF
(Internet Engineering Task Force). <titleref>RFC 1808: Relative Uniform Resource
Locators</titleref>, ed. R. Fielding. 1995. </bibl>
<bibl id="RFC2141" href="http://www.ietf.org/rfc/rfc2141.txt" key="IETF RFC2141">IETF
(Internet Engineering Task Force). <emph>RFC 2141: URN Syntax</emph>, ed.
R. Moats. 1997. </bibl>
<bibl id="rfc2279" diff="add" href="http://www.ietf.org/rfc/rfc2279.txt" key="IETF RFC 2279"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E78">[E78]</loc>IETF
(Internet Engineering Task Force). <titleref>RFC 2279: UTF-8, a transformation
format of ISO 10646</titleref>, <phrase diff="add">ed. F. Yergeau, </phrase>1998.</bibl>
<bibl id="rfc2376" diff="add" href="http://www.ietf.org/rfc/rfc2376.txt" key="IETF RFC 2376"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E48">[E48]</loc>IETF
(Internet Engineering Task Force). <titleref>RFC 2376: XML Media Types</titleref>.
ed. E. Whitehead, M. Murata. 1998.</bibl>
<bibl id="rfc2396" diff="add" href="http://www.ietf.org/rfc/rfc2396.txt" key="IETF RFC 2396"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E66">[E66]</loc>IETF
(Internet Engineering Task Force). <titleref>RFC 2396: Uniform Resource Identifiers
(URI): Generic Syntax</titleref>. T. Berners-Lee, R. Fielding, L. Masinter.
1998.</bibl>
<bibl id="rfc2732" diff="add" href="http://www.ietf.org/rfc/rfc2732.txt" key="IETF RFC 2732"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E66">[E66]</loc>IETF
(Internet Engineering Task Force). <titleref>RFC 2732: Format for Literal
IPv6 Addresses in URL's</titleref>. R. Hinden, B. Carpenter, L. Masinter.
1999.</bibl>
<bibl id="rfc2781" diff="add" href="http://www.ietf.org/rfc/rfc2781.txt" key="IETF RFC 2781"><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E77">[E77]</loc>
IETF (Internet Engineering Task Force). <emph>RFC 2781: UTF-16, an encoding
of ISO 10646</emph>, ed. P. Hoffman, F. Yergeau. 2000.</bibl>
<bibl id="ISO639" diff="add" key="ISO 639"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E38">[E38]</loc>
(International Organization for Standardization). <titleref>ISO 639:1988 (E).
Code for the representation of names of languages.</titleref> [Geneva]: International
Organization for Standardization, 1988.</bibl>
<bibl id="ISO3166" diff="add" key="ISO 3166"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E38">[E38]</loc>
(International Organization for Standardization). <titleref>ISO 3166-1:1997
(E). Codes for the representation of names of countries and their subdivisions —
Part 1: Country codes</titleref> [Geneva]: International Organization for
Standardization, 1997.</bibl>
<bibl id="ISO8879" key="ISO 8879">ISO (International Organization for Standardization). <titleref>ISO
8879:1986(E). Information processing — Text and Office Systems —
Standard Generalized Markup Language (SGML).</titleref> First edition —
1986-10-15. [Geneva]: International Organization for Standardization, 1986. </bibl>
<bibl id="ISO10744" key="ISO/IEC 10744">ISO (International Organization for
Standardization). <titleref>ISO/IEC 10744-1992 (E). Information technology —
Hypermedia/Time-based Structuring Language (HyTime). </titleref> [Geneva]:
International Organization for Standardization, 1992. <emph>Extended Facilities
Annexe.</emph> [Geneva]: International Organization for Standardization, 1996. </bibl>
<bibl id="websgml" diff="add" href="http://www.sgmlsource.com/8879rev/n0029.htm"
key="WEBSGML"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E43">[E43]</loc>ISO
(International Organization for Standardization). <titleref>ISO 8879:1986
TC2. Information technology — Document Description and Processing Languages. </titleref>
[Geneva]: International Organization for Standardization, 1998.</bibl>
<bibl id="xml-names" diff="add" xmlns:xlink="http://www.w3.org/TR/WD-xlink"
href="http://www.w3.org/TR/REC-xml-names/" key="XML Names"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E98">[E98]</loc>Tim Bray,
Dave Hollander, and Andrew Layman, editors. <titleref>Namespaces in XML</titleref>.
Textuality, Hewlett-Packard, and Microsoft. World Wide Web Consortium, 1999.</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<phrase diff="del"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E84">[E84]</loc>, without
diacritics</phrase>), ideographic characters, and combining characters (among
others, this class contains most diacritics)<phrase diff="del"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E30">[E30]</loc>; these classes
combine to form the class of letters.</phrase> Digits and extenders are also
distinguished.</p>
<scrap id="CHARACTERS" lang="ebnf">
<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] | [#x0061-#x007A] | [#x00C0-#x00D6]
| [#x00D8-#x00F6] | [#x00F8-#x00FF] | [#x0100-#x0131] | [#x0134-#x013E]
| [#x0141-#x0148] | [#x014A-#x017E] | [#x0180-#x01C3] | [#x01CD-#x01F0]
| [#x01F4-#x01F5] | [#x01FA-#x0217] | [#x0250-#x02A8] | [#x02BB-#x02C1]
| #x0386 | [#x0388-#x038A] | #x038C | [#x038E-#x03A1]
| [#x03A3-#x03CE] | [#x03D0-#x03D6] | #x03DA | #x03DC
| #x03DE | #x03E0 | [#x03E2-#x03F3] | [#x0401-#x040C]
| [#x040E-#x044F] | [#x0451-#x045C] | [#x045E-#x0481] | [#x0490-#x04C4]
| [#x04C7-#x04C8] | [#x04CB-#x04CC] | [#x04D0-#x04EB] | [#x04EE-#x04F5]
| [#x04F8-#x04F9] | [#x0531-#x0556] | #x0559 | [#x0561-#x0586]
| [#x05D0-#x05EA] | [#x05F0-#x05F2] | [#x0621-#x063A] | [#x0641-#x064A]
| [#x0671-#x06B7] | [#x06BA-#x06BE] | [#x06C0-#x06CE] | [#x06D0-#x06D3]
| #x06D5 | [#x06E5-#x06E6] | [#x0905-#x0939] | #x093D
| [#x0958-#x0961] | [#x0985-#x098C] | [#x098F-#x0990] | [#x0993-#x09A8]
| [#x09AA-#x09B0] | #x09B2 | [#x09B6-#x09B9] | [#x09DC-#x09DD]
| [#x09DF-#x09E1] | [#x09F0-#x09F1] | [#x0A05-#x0A0A] | [#x0A0F-#x0A10]
| [#x0A13-#x0A28] | [#x0A2A-#x0A30] | [#x0A32-#x0A33] | [#x0A35-#x0A36]
| [#x0A38-#x0A39] | [#x0A59-#x0A5C] | #x0A5E | [#x0A72-#x0A74]
| [#x0A85-#x0A8B] | #x0A8D | [#x0A8F-#x0A91] | [#x0A93-#x0AA8]
| [#x0AAA-#x0AB0] | [#x0AB2-#x0AB3] | [#x0AB5-#x0AB9] | #x0ABD
| #x0AE0 | [#x0B05-#x0B0C] | [#x0B0F-#x0B10] | [#x0B13-#x0B28]
| [#x0B2A-#x0B30] | [#x0B32-#x0B33] | [#x0B36-#x0B39] | #x0B3D
| [#x0B5C-#x0B5D] | [#x0B5F-#x0B61] | [#x0B85-#x0B8A] | [#x0B8E-#x0B90]
| [#x0B92-#x0B95] | [#x0B99-#x0B9A] | #x0B9C | [#x0B9E-#x0B9F]
| [#x0BA3-#x0BA4] | [#x0BA8-#x0BAA] | [#x0BAE-#x0BB5] | [#x0BB7-#x0BB9]
| [#x0C05-#x0C0C] | [#x0C0E-#x0C10] | [#x0C12-#x0C28] | [#x0C2A-#x0C33]
| [#x0C35-#x0C39] | [#x0C60-#x0C61] | [#x0C85-#x0C8C] | [#x0C8E-#x0C90]
| [#x0C92-#x0CA8] | [#x0CAA-#x0CB3] | [#x0CB5-#x0CB9] | #x0CDE
| [#x0CE0-#x0CE1] | [#x0D05-#x0D0C] | [#x0D0E-#x0D10] | [#x0D12-#x0D28]
| [#x0D2A-#x0D39] | [#x0D60-#x0D61] | [#x0E01-#x0E2E] | #x0E30
| [#x0E32-#x0E33] | [#x0E40-#x0E45] | [#x0E81-#x0E82] | #x0E84
| [#x0E87-#x0E88] | #x0E8A | #x0E8D | [#x0E94-#x0E97]
| [#x0E99-#x0E9F] | [#x0EA1-#x0EA3] | #x0EA5 | #x0EA7
| [#x0EAA-#x0EAB] | [#x0EAD-#x0EAE] | #x0EB0 | [#x0EB2-#x0EB3]
| #x0EBD | [#x0EC0-#x0EC4] | [#x0F40-#x0F47] | [#x0F49-#x0F69]
| [#x10A0-#x10C5] | [#x10D0-#x10F6] | #x1100 | [#x1102-#x1103]
| [#x1105-#x1107] | #x1109 | [#x110B-#x110C] | [#x110E-#x1112]
| #x113C | #x113E | #x1140 | #x114C | #x114E | #x1150
| [#x1154-#x1155] | #x1159 | [#x115F-#x1161] | #x1163
| #x1165 | #x1167 | #x1169 | [#x116D-#x116E] | [#x1172-#x1173]
| #x1175 | #x119E | #x11A8 | #x11AB | [#x11AE-#x11AF]
| [#x11B7-#x11B8] | #x11BA | [#x11BC-#x11C2] | #x11EB
| #x11F0 | #x11F9 | [#x1E00-#x1E9B] | [#x1EA0-#x1EF9]
| [#x1F00-#x1F15] | [#x1F18-#x1F1D] | [#x1F20-#x1F45] | [#x1F48-#x1F4D]
| [#x1F50-#x1F57] | #x1F59 | #x1F5B | #x1F5D | [#x1F5F-#x1F7D]
| [#x1F80-#x1FB4] | [#x1FB6-#x1FBC] | #x1FBE | [#x1FC2-#x1FC4]
| [#x1FC6-#x1FCC] | [#x1FD0-#x1FD3] | [#x1FD6-#x1FDB] | [#x1FE0-#x1FEC]
| [#x1FF2-#x1FF4] | [#x1FF6-#x1FFC] | #x2126 | [#x212A-#x212B]
| #x212E | [#x2180-#x2182] | [#x3041-#x3094] | [#x30A1-#x30FA]
| [#x3105-#x312C] | [#xAC00-#xD7A3] </rhs>
</prod>
<prod id="NT-Ideographic">
<lhs>Ideographic</lhs><rhs>[#x4E00-#x9FA5] | #x3007 | [#x3021-#x3029] </rhs>
</prod>
<prod id="NT-CombiningChar">
<lhs>CombiningChar</lhs><rhs>[#x0300-#x0345] | [#x0360-#x0361] | [#x0483-#x0486]
| [#x0591-#x05A1] | [#x05A3-#x05B9] | [#x05BB-#x05BD] | #x05BF
| [#x05C1-#x05C2] | #x05C4 | [#x064B-#x0652] | #x0670
| [#x06D6-#x06DC] | [#x06DD-#x06DF] | [#x06E0-#x06E4] | [#x06E7-#x06E8]
| [#x06EA-#x06ED] | [#x0901-#x0903] | #x093C | [#x093E-#x094C]
| #x094D | [#x0951-#x0954] | [#x0962-#x0963] | [#x0981-#x0983]
| #x09BC | #x09BE | #x09BF | [#x09C0-#x09C4] | [#x09C7-#x09C8]
| [#x09CB-#x09CD] | #x09D7 | [#x09E2-#x09E3] | #x0A02
| #x0A3C | #x0A3E | #x0A3F | [#x0A40-#x0A42] | [#x0A47-#x0A48]
| [#x0A4B-#x0A4D] | [#x0A70-#x0A71] | [#x0A81-#x0A83] | #x0ABC
| [#x0ABE-#x0AC5] | [#x0AC7-#x0AC9] | [#x0ACB-#x0ACD] | [#x0B01-#x0B03]
| #x0B3C | [#x0B3E-#x0B43] | [#x0B47-#x0B48] | [#x0B4B-#x0B4D]
| [#x0B56-#x0B57] | [#x0B82-#x0B83] | [#x0BBE-#x0BC2] | [#x0BC6-#x0BC8]
| [#x0BCA-#x0BCD] | #x0BD7 | [#x0C01-#x0C03] | [#x0C3E-#x0C44]
| [#x0C46-#x0C48] | [#x0C4A-#x0C4D] | [#x0C55-#x0C56] | [#x0C82-#x0C83]
| [#x0CBE-#x0CC4] | [#x0CC6-#x0CC8] | [#x0CCA-#x0CCD] | [#x0CD5-#x0CD6]
| [#x0D02-#x0D03] | [#x0D3E-#x0D43] | [#x0D46-#x0D48] | [#x0D4A-#x0D4D]
| #x0D57 | #x0E31 | [#x0E34-#x0E3A] | [#x0E47-#x0E4E]
| #x0EB1 | [#x0EB4-#x0EB9] | [#x0EBB-#x0EBC] | [#x0EC8-#x0ECD]
| [#x0F18-#x0F19] | #x0F35 | #x0F37 | #x0F39 | #x0F3E
| #x0F3F | [#x0F71-#x0F84] | [#x0F86-#x0F8B] | [#x0F90-#x0F95]
| #x0F97 | [#x0F99-#x0FAD] | [#x0FB1-#x0FB7] | #x0FB9
| [#x20D0-#x20DC] | #x20E1 | [#x302A-#x302F] | #x3099
| #x309A </rhs>
</prod>
<prod id="NT-Digit">
<lhs>Digit</lhs><rhs>[#x0030-#x0039] | [#x0660-#x0669] | [#x06F0-#x06F9]
| [#x0966-#x096F] | [#x09E6-#x09EF] | [#x0A66-#x0A6F] | [#x0AE6-#x0AEF]
| [#x0B66-#x0B6F] | [#x0BE7-#x0BEF] | [#x0C66-#x0C6F] | [#x0CE6-#x0CEF]
| [#x0D66-#x0D6F] | [#x0E50-#x0E59] | [#x0ED0-#x0ED9] | [#x0F20-#x0F29] </rhs>
</prod>
<prod id="NT-Extender">
<lhs>Extender</lhs><rhs>#x00B7 | #x02D0 | #x02D1 | #x0387 | #x0640
| #x0E46 | #x0EC6 | #x3005 | [#x3031-#x3035] | [#x309D-#x309E]
| [#x30FC-#x30FE] </rhs>
</prod>
</prodgroup></scrap>
<p>The character classes defined here can be derived from the Unicode <phrase
diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</loc>2.0</phrase>
character database as follows:</p>
<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 <quote>compatibility formatting tag</quote> in field 5 of the
database -- marked by field 5 beginning with a <quote><</quote>) 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 <phrase
diff="add"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E67">[E67]</loc>2.0</phrase>,
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>
</div1>
<inform-div1 id="sec-xml-and-sgml">
<head>XML and SGML</head>
<p><phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E43">[E43]</loc>XML
is designed to be a subset of SGML, in that every XML document should also
be a conforming SGML document.</phrase> 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</p>
<eg><![CDATA[<!ENTITY example "<p>An ampersand (&#38;) may be escaped
numerically (&#38;#38;) or with a general entity
(&amp;).</p>" >]]></eg>
<p>then the XML processor will recognize the character references when it
parses the entity declaration, and resolve them before storing the following
string as the value of the entity <quote><code>example</code></quote>:</p>
<eg><![CDATA[<p>An ampersand (&) may be escaped
numerically (&#38;) or with a general entity
(&amp;).</p>]]></eg>
<p>A reference in the document to <quote><code>&example;</code></quote>
will cause the text to be reparsed, at which time the start- and end-tags
of the <el>p</el> element will be recognized and the three references will
be recognized and expanded, resulting in a <el>p</el> element with the following
content (all data, no delimiters or markup):</p>
<eg><![CDATA[An ampersand (&) may be escaped
numerically (&) or with a general entity
(&).]]></eg>
<p>A more complex example will illustrate the rules and their effects fully.
In the following example, the line numbers are solely for reference.</p>
<eg><![CDATA[1 <?xml version='1.0'?>
2 <!DOCTYPE test [
3 <!ELEMENT test (#PCDATA) >
4 <!ENTITY % xx '%zz;'>
5 <!ENTITY % zz '<!ENTITY tricky "error-prone" >' >
6 %xx;
7 ]>
8 <test>This sample shows a &tricky; method.</test>]]></eg>
<p>This produces the following:</p>
<ulist spacing="compact">
<item><p>in line 4, the reference to character 37 is expanded immediately,
and the parameter entity <quote><code>xx</code></quote> is stored in the symbol
table with the value <quote><code>%zz;</code></quote>. Since the replacement
text is not rescanned, the reference to parameter entity <quote><code>zz</code></quote>
is not recognized. (And it would be an error if it were, since <quote><code>zz</code></quote>
is not yet declared.)</p></item>
<item><p>in line 5, the character reference <quote><code>&#60;</code></quote>
is expanded immediately and the parameter entity <quote><code>zz</code></quote>
is stored with the replacement text <quote><code><!ENTITY tricky "error-prone"
></code></quote>, which is a well-formed entity declaration.</p></item>
<item><p>in line 6, the reference to <quote><code>xx</code></quote> is recognized,
and the replacement text of <quote><code>xx</code></quote> (namely <quote><code>%zz;</code></quote>)
is parsed. The reference to <quote><code>zz</code></quote> is recognized in
its turn, and its replacement text (<quote><code><!ENTITY tricky "error-prone"
></code></quote>) is parsed. The general entity <quote><code>tricky</code></quote>
has now been declared, with the replacement text <quote><code>error-prone</code></quote>.</p>
</item>
<item><p>in line 8, the reference to the general entity <quote><code>tricky</code></quote>
is recognized, and it is expanded, so the full content of the <el>test</el>
element is the self-describing (and ungrammatical) string <emph>This sample
shows a error-prone method.</emph></p></item>
</ulist>
</inform-div1>
<inform-div1 id="determinism">
<head>Deterministic Content Models</head>
<p><phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E102">[E102]</loc>As
noted in <specref ref="sec-element-content"/>, it is required that content
models in element type declarations be deterministic. This requirement is <termref
def="dt-compat">for compatibility</termref> with SGML (which calls deterministic
content models <quote>unambiguous</quote>);</phrase> 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 <el>b</el> the <phrase diff="chg"><loc role="erratumref"
href="http://www.w3.org/XML/xml-19980210-errata#E95">[E95]</loc>XML processor</phrase>
cannot know which <el>b</el> in the model is being matched without looking
ahead to see which element follows the <el>b</el>. In this case, the two references
to <el>b</el> can be collapsed into a single reference, making the model read <code>(b,
(c | d))</code>. An initial <el>b</el> now clearly matches only a single name
in the content model. The <phrase diff="chg"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E95">[E95]</loc>processor</phrase
> doesn't need to look ahead to see what follows; either <el>c</el> or <el>d</el>
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
Br¸ggemann-Klein 1991 <bibref ref="ABK"/>.</p>
</inform-div1>
<inform-div1 id="sec-guessing">
<head><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E105">[E105]</loc><loc
role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E48">[E48]</loc>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—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>
<div2 id="sec-guessing-no-ext-info">
<head diff="add">Detection Without External Encoding Information</head>
<p>Because each XML entity <phrase diff="add">not accompanied by external
encoding information and </phrase>not in UTF-8 or UTF-16 <phrase diff="chg">encoding</phrase> <emph>must</emph>
begin with an XML encoding declaration, in which the first characters must
be '<code><?xml</code>', any conforming processor can detect, after two
to four octets of input, which of the following cases apply. In reading this
list, it may help to know that in UCS-4, '<' is <quote><code>#x0000003C</code></quote>
and '?' is <quote><code>#x0000003F</code></quote>, and the Byte Order Mark
required of UTF-16 data streams is <quote><code>#xFEFF</code></quote>. <phrase
diff="add">The notation <var>##</var> is used to denote any byte value except <phrase
diff="chg">that two consecutive <var>##</var>s cannot be both 00</phrase>.</phrase></p>
<p diff="add">With a Byte Order Mark:</p>
<table diff="add" border="1" frame="border"><tbody><tr><td><code>00 00 FE
FF</code></td><td>UCS-4, big-endian machine (1234 order)</td></tr><tr><td><code>FF
FE 00 00</code></td><td>UCS-4, little-endian machine (4321 order)</td></tr>
<tr><td><code>00 00 FF FE</code></td><td>UCS-4, unusual octet order (2143)</td>
</tr><tr><td><code>FE FF 00 00</code></td><td>UCS-4, unusual octet order (3412)</td>
</tr><tr><td><code>FE FF ## ##</code></td><td>UTF-16, big-endian</td></tr>
<tr><td><code>FF FE ## ##</code></td><td>UTF-16, little-endian</td></tr><tr>
<td><code>EF BB BF</code></td><td>UTF-8</td></tr></tbody></table>
<p diff="add">Without a Byte Order Mark:</p>
<table diff="add" border="1" frame="border"><tbody><tr><td><code>00 00 00 3C</code></td>
<td rowspan="4">UCS-4 or other encoding with a 32-bit code unit and ASCII
characters encoded as ASCII values, in respectively big-endian (1234), little-endian
(4321) and two unusual byte orders (2143 and 3412). The encoding declaration
must be read to determine which of UCS-4 or other supported 32-bit encodings
applies.</td></tr><tr><td><code>3C 00 00 00</code></td>
<!--<td>UCS-4, little-endian machine (4321 order)</td>-->
</tr><tr><td><code>00 00 3C 00</code></td>
<!--<td>UCS-4, unusual octet order (2143)</td>-->
</tr><tr><td><code>00 3C 00 00</code></td>
<!--<td>UCS-4, unusual octet order (3412)</td>-->
</tr><tr><td><code>00 3C 00 3F</code></td><td>UTF-16BE or big-endian ISO-10646-UCS-2
or other encoding with a 16-bit code unit in big-endian order and ASCII characters
encoded as ASCII values (the encoding declaration must be read to determine
which)</td></tr><tr><td><code>3C 00 3F 00</code></td><td>UTF-16LE or little-endian
ISO-10646-UCS-2 or other encoding with a 16-bit code unit in little-endian
order and ASCII characters encoded as ASCII values (the encoding declaration
must be read to determine which)</td></tr><tr><td><code>3C 3F 78 6D</code></td>
<td>UTF-8, ISO 646, ASCII, some part of ISO 8859, Shift-JIS, EUC, or any other
7-bit, 8-bit, or mixed-width encoding which ensures that the characters of
ASCII have their normal positions, width, and values; the actual encoding
declaration must be read to detect which of these applies, but since all of
these encodings use the same bit patterns for the relevant ASCII characters,
the encoding declaration itself may be read reliably</td></tr><tr><td><code>4C
6F A7 94</code></td><td>EBCDIC (in some flavor; the full encoding declaration
must be read to tell which code page is in use)</td></tr><tr><td>Other</td>
<td>UTF-8 without an encoding declaration, or else the data stream is mislabeled
(lacking a required encoding declaration), corrupt, fragmentary, or enclosed
in a wrapper of some kind</td></tr></tbody></table>
<note diff="add">
<p>In cases above which do not require reading the encoding declaration to
determine the encoding, section 4.3.3 still requires that the encoding declaration,
if present, be read and that the encoding name be checked to match the actual
encoding of the entity. Also, it is possible that new character encodings
will be invented that will make it necessary to use the encoding declaration
to determine the encoding, in cases where this is not required at present.</p>
</note>
<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 <phrase
diff="chg">characters from the ASCII repertoire (however encoded)</phrase>,
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. <phrase diff="del">Note that since external parsed entities
in UTF-16 may begin with any character, this autodetection does not always
work. Also, </phrase><phrase diff="add">Character encodings such as UTF-7
that make overloaded usage of ASCII-valued bytes may fail to be reliably detected.</phrase></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>
</div2>
<div2 id="sec-guessing-with-ext-info">
<head diff="add">Priorities in the Presence of External Encoding Information</head>
<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. <phrase diff="chg">In particular, please refer
to <bibref ref="rfc2376"/> or its successor, which defines the <code>text/xml</code>
and <code>application/xml</code> MIME types and provides some useful guidance.
In the interests of interoperability, however, the following rule is recommended.</phrase></p>
<ulist>
<item><p>If an XML entity is in a file, the Byte-Order Mark and encoding declaration <phrase
diff="del">PI </phrase>are used (if present) to determine the character encoding.<phrase
diff="del"><loc role="erratumref" href="http://www.w3.org/XML/xml-19980210-errata#E74">[E74]</loc>
All other heuristics and sources of information are solely for error recovery.</phrase></p>
</item>
</ulist>
<ulist diff="del">
<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>
<p diff="del">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>
</div2>
</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</name><affiliation>Sun</affiliation><role>Chair</role>
</member>
<member><name>James Clark</name><role>Technical Lead</role></member>
<member><name>Tim Bray</name><affiliation>Textuality and Netscape</affiliation>
<role>XML Co-editor</role></member>
<member><name>Jean Paoli</name><affiliation>Microsoft</affiliation><role>XML
Co-editor</role></member>
<member><name>C. M. Sperberg-McQueen</name><affiliation>U. of Ill.</affiliation>
<role>XML Co-editor</role></member>
<member><name>Dan Connolly</name><affiliation>W3C</affiliation><role>W3C Liaison</role>
</member>
<member><name>Paula Angerstein</name><affiliation>Texcel</affiliation></member>
<member><name>Steve DeRose</name><affiliation>INSO</affiliation></member>
<member><name>Dave Hollander</name><affiliation>HP</affiliation></member>
<member><name>Eliot Kimber</name><affiliation>ISOGEN</affiliation></member>
<member><name>Eve Maler</name><affiliation>ArborText</affiliation></member>
<member><name>Tom Magliery</name><affiliation>NCSA</affiliation></member>
<member><name>Murray Maloney</name><affiliation diff="chg">SoftQuad, Grif
SA, Muzmo and Veo Systems</affiliation></member>
<member><name diff="chg">MURATA Makoto (FAMILY Given)</name><affiliation>Fuji
Xerox Information Systems</affiliation></member>
<member><name>Joel Nava</name><affiliation>Adobe</affiliation></member>
<member><name>Conleth O'Connell</name><affiliation>Vignette</affiliation>
</member>
<member><name>Peter Sharpe</name><affiliation>SoftQuad</affiliation></member>
<member><name>John Tigue</name><affiliation>DataChannel</affiliation></member>
</orglist>
</inform-div1>
<inform-div1 id="sec-core-wg" diff="add">
<head>W3C XML Core Group</head>
<p>The second edition of this specification was prepared by the W3C XML Core
Working Group (WG). The members of the WG at the time of publication of this
edition were:</p>
<orglist>
<member><name>Paula Angerstein</name><affiliation>Vignette</affiliation></member>
<member><name>Daniel Austin</name><affiliation>Ask Jeeves</affiliation></member>
<member><name>Tim Boland</name></member>
<member><name>Allen Brown</name><affiliation>Microsoft</affiliation></member>
<member><name>Dan Connolly</name><affiliation>W3C</affiliation><role>Staff
Contact</role></member>
<member><name>John Cowan</name><affiliation>Reuters Limited</affiliation>
</member>
<member><name>John Evdemon</name><affiliation>XMLSolutions Corporation</affiliation>
</member>
<member><name>Paul Grosso</name><affiliation>Arbortext</affiliation><role>Co-Chair</role>
</member>
<member><name>Arnaud Le Hors</name><affiliation>IBM</affiliation><role>Co-Chair</role>
</member>
<member><name>Eve Maler</name><affiliation>Sun Microsystems</affiliation>
<role>Second Edition Editor</role></member>
<member><name>Jonathan Marsh</name><affiliation>Microsoft</affiliation></member>
<member><name>MURATA Makoto (FAMILY Given)</name><affiliation>IBM</affiliation>
</member>
<member><name>Mark Needleman</name><affiliation>Data Research Associates</affiliation>
</member>
<member><name>David Orchard</name><affiliation>Jamcracker</affiliation></member>
<member><name>Lew Shannon</name><affiliation>NCR</affiliation></member>
<member><name>Richard Tobin</name><affiliation>University of Edinburgh</affiliation>
</member>
<member><name>Daniel Veillard</name><affiliation>W3C</affiliation></member>
<member><name>Dan Vint</name><affiliation>Lexica</affiliation></member>
<member><name>Norman Walsh</name><affiliation>Sun Microsystems</affiliation>
</member>
<member><name>FranÁois Yergeau</name><affiliation>Alis Technologies</affiliation>
<role>Errata List Editor</role></member>
<member><name>Kongyi Zhou</name><affiliation>Oracle</affiliation></member>
</orglist>
</inform-div1>
<inform-div1 diff="add">
<head>Production Notes</head>
<p>This Second Edition was encoded in the <loc href="http://www.w3.org/XML/1998/06/xmlspec-v21.dtd">XMLspec
DTD</loc> (which has <loc href="http://www.w3.org/XML/1998/06/xmlspec-report-v21.htm">documentation</loc>
available). The HTML versions were produced with a combination of the <loc
href="http://www.w3.org/XML/1998/06/xmlspec.xsl">xmlspec.xsl</loc>, <loc href="http://www.w3.org/XML/1998/06/diffspec.xsl">diffspec.xsl</loc>,
and <loc href="http://www.w3.org/XML/1998/06/REC-xml-2e.xsl">REC-xml-2e.xsl</loc>
XSLT stylesheets.  The PDF version was produced with the <loc href="http://www.tdb.uu.se/~jan/html2ps.html">html2ps</loc>
facility and a distiller program.</p>
</inform-div1>
</back></spec>