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<para>
<indexterm id="elementsref" class='startofrange'>
  <primary>elements</primary>
  <secondary>reference</secondary>
</indexterm>This reference describes every element in the DocBook
&DTD;.</para>

<para>In DocBook V3.1, introduced in February, 1999, the following
elements were added to DocBook:
<simplelist type='inline'>
<member><sgmltag>answer</sgmltag></member>
<member><sgmltag>audiodata</sgmltag></member>
<member><sgmltag>audioobject</sgmltag></member>
<member><sgmltag>caption</sgmltag></member>
<member><sgmltag>colophon</sgmltag></member>
<member><sgmltag>constant</sgmltag></member>
<member><sgmltag>imagedata</sgmltag></member>
<member><sgmltag>imageobject</sgmltag></member>
<member><sgmltag>imageobjectco</sgmltag></member>
<member><sgmltag>informalfigure</sgmltag></member>
<member><sgmltag>inlinemediaobject</sgmltag></member>
<member><sgmltag>mediaobject</sgmltag></member>
<member><sgmltag>mediaobjectco</sgmltag></member>
<member><sgmltag>objectinfo</sgmltag></member>
<member><sgmltag>qandadiv</sgmltag></member>
<member><sgmltag>qandaentry</sgmltag></member>
<member><sgmltag>qandaset</sgmltag></member>
<member><sgmltag>question</sgmltag></member>
<member><sgmltag>section</sgmltag></member>
<member><sgmltag>sectioninfo</sgmltag></member>
<member><sgmltag>textobject</sgmltag></member>
<member><sgmltag>varname</sgmltag></member>
<member><sgmltag>videodata</sgmltag></member>
<member><sgmltag>videoobject</sgmltag></member>
</simplelist>.</para>

<para>DocBook V4.0, introduced in January, 2001, the following elements
were added:
<simplelist type='inline'>
<member><sgmltag>appendixinfo</sgmltag></member>
<member><sgmltag>articleinfo</sgmltag></member>
<member><sgmltag>bibliographyinfo</sgmltag></member>
<member><sgmltag>chapterinfo</sgmltag></member>
<member><sgmltag>classsynopsis</sgmltag></member>
<member><sgmltag>classsynopsisinfo</sgmltag></member>
<member><sgmltag>constructorsynopsis</sgmltag></member>
<member><sgmltag>destructorsynopsis</sgmltag></member>
<member><sgmltag>exceptionname</sgmltag></member>
<member><sgmltag>fieldsynopsis</sgmltag></member>
<member><sgmltag>glossaryinfo</sgmltag></member>
<member><sgmltag>indexinfo</sgmltag></member>
<member><sgmltag>initializer</sgmltag></member>
<member><sgmltag>interfacename</sgmltag></member>
<member><sgmltag>methodname</sgmltag></member>
<member><sgmltag>methodparam</sgmltag></member>
<member><sgmltag>methodsynopsis</sgmltag></member>
<member><sgmltag>modifier</sgmltag></member>
<member><sgmltag>ooclass</sgmltag></member>
<member><sgmltag>ooexception</sgmltag></member>
<member><sgmltag>oointerface</sgmltag></member>
<member><sgmltag>partinfo</sgmltag></member>
<member><sgmltag>prefaceinfo</sgmltag></member>
<member><sgmltag>refentryinfo</sgmltag></member>
<member><sgmltag>referenceinfo</sgmltag></member>
<member><sgmltag>remark</sgmltag></member>
<member><sgmltag>revdescription</sgmltag></member>
<member><sgmltag>setindexinfo</sgmltag></member>
<member><sgmltag>sidebarinfo</sgmltag></member>
<member><sgmltag>simplemsgentry</sgmltag></member>
</simplelist>.</para>

<para>The following additional changes were made in DocBook V4.0:
<sgmltag>artheader</sgmltag> was renamed <sgmltag>articleinfo</sgmltag>;
<sgmltag>comment</sgmltag> was renamed <sgmltag>remark</sgmltag>;
<sgmltag>docinfo</sgmltag> was broken into a set of other info elements;
and <sgmltag>bookbiblio</sgmltag>, <sgmltag>interfacedefinition</sgmltag>,
and <sgmltag>seriesinfo</sgmltag> were removed.</para>

<para>DocBook V4.2, introduced in FIXME: April, 2002, the following elements
were added:
<simplelist type='inline'>
<member><sgmltag>bibliocoverage</sgmltag></member>
<member><sgmltag>biblioid</sgmltag></member>
<member><sgmltag>bibliorelation</sgmltag></member>
<member><sgmltag>bibliosource</sgmltag></member>
<member><sgmltag>blockinfo</sgmltag></member>
<member><sgmltag>citebiblioid</sgmltag></member>
<member><sgmltag>coref</sgmltag></member>
<member><sgmltag>errortext</sgmltag></member>
<member><sgmltag>personblurb</sgmltag></member>
<member><sgmltag>personname</sgmltag></member>
<member><sgmltag>refsection</sgmltag></member>
<member><sgmltag>refsectioninfo</sgmltag></member>
<member><sgmltag>textdata</sgmltag></member>
</simplelist>.</para>

<para>Additional changes made to DocBook V4.2 are summarized in the
<ulink url="http://www.oasis-open.org/docbook/specs/docbook-4.2.html">DocBook V4.2
Specification</ulink>.</para>

<sect1>
<title>Organization of Reference Pages</title>
<para>The description of each element in this reference is divided into the
following sections:</para>
<variablelist>

<varlistentry><term>Synopsis</term>
<listitem>
<para>
<indexterm><primary>elements</primary>
  <secondary>reference</secondary>
    <tertiary>synopses</tertiary></indexterm>
<indexterm><primary>synopses</primary>
  <secondary>elements (reference pages)</secondary></indexterm>
<indexterm><primary>content models</primary>
  <secondary>elements, reference</secondary></indexterm>

Provides a quick synopsis of the element. The content of the synopsis
table varies according to the nature of the element described, but may include
any or all of the following sections:</para>
<variablelist>
<varlistentry><term>Content Model or Declared Content</term>
<listitem>
<para>Describes the content model of the element in &SGML;/&XML; &DTD; terms. See <xref linkend="s2-cmintro"/>.&rdquo;</para>
</listitem>
</varlistentry>

<varlistentry><term>Inclusions</term>
<listitem>
<para>
<indexterm><primary>inclusions</primary>
  <secondary>elements</secondary></indexterm>

Lists <quote>inclusions.</quote>  Inclusions are an &SGML; feature.
Included elements can appear anywhere inside the element
that includes them, even in places that aren't ordinarily
valid.  For example, <sgmltag>Chapter</sgmltag> includes <sgmltag>IndexTerm</sgmltag>.
This means that within a <sgmltag>Chapter</sgmltag>, <sgmltag>IndexTerm</sgmltag> can
appear inside <sgmltag>Emphasis</sgmltag>, for instance, even though the
content model of <sgmltag>Emphasis</sgmltag> does not explicitly allow
<sgmltag>IndexTerm</sgmltag>s.
</para>
</listitem>
</varlistentry>

<varlistentry><term>Exclusions</term>
<listitem>
<para>
<indexterm><primary>exclusions</primary>
  <secondary>elements</secondary></indexterm>
<indexterm><primary>nesting</primary>
  <secondary>elements</secondary></indexterm>
<indexterm><primary>elements</primary>
  <secondary>nesting</secondary></indexterm>
Lists <quote>exclusions.</quote> Exclusions are an &SGML; feature.
Excluded elements cannot appear anywhere inside the element that
excludes them, even in places that are ordinarily valid.  For
example, <sgmltag>Footnote</sgmltag> excludes <sgmltag>Footnote</sgmltag>. This
means that a <sgmltag>Footnote</sgmltag> cannot appear inside a
<sgmltag>Para</sgmltag> inside a <sgmltag>Footnote</sgmltag>, even though
<sgmltag>Footnote</sgmltag> appears in the content model of <sgmltag>Para</sgmltag>.
</para>
<indexterm><primary>lists</primary>
  <secondary>elements</secondary>
    <tertiary>exclusions</tertiary></indexterm>

<para>Lists elements that are excluded from appearing at any level below
the element described.</para>
</listitem>
</varlistentry>

<varlistentry><term>Attributes</term>
<listitem>
<para>
<indexterm><primary>attributes</primary>
  <secondary>elements, referencing</secondary></indexterm>

Provides a synopsis of the attributes on the element. For brevity, common
attributes are described only once, <link linkend="common.attributes">in this
introduction</link>.</para>
</listitem>
</varlistentry>

<varlistentry><term>Tag Minimization</term>
<listitem>
<para>
<indexterm><primary>tags</primary>
  <secondary>minimization</secondary></indexterm>
<indexterm><primary>start tags</primary>
  <secondary>omitting</secondary></indexterm>
<indexterm><primary>end tags</primary>
  <secondary>omitting</secondary></indexterm>
<indexterm><primary>markup</primary>
  <secondary>minimization</secondary></indexterm>
<indexterm><primary>minimization</primary>
  <secondary>markup</secondary>
    <tertiary>start and end tags</tertiary></indexterm>

Indicates if start- or end-tags may be omitted.  Tag omission is
dependent on both the &DTD; and your &SGML; declaration.  If a tag is described
as ommissable here, it is ommissible if your declaration allows tag 
omission.  The standard DocBook declaration does not.
</para>
</listitem>
</varlistentry>

<varlistentry><term>Parameter Entities</term>
<listitem>
<para>
<indexterm><primary>parameter entities</primary>
  <secondary>elements</secondary></indexterm>

Lists the parameter entities in which the element described appears.
Parameter entities are important when you are <link linkend="app-customizing">
customizing the &DTD;</link>.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>

<varlistentry><term>Description</term>
<listitem>
<para>
<indexterm><primary>elements</primary>
  <secondary>description, semantics</secondary></indexterm>
<indexterm><primary>semantics (elements), describing</primary></indexterm>

Describes the semantics of the element in detail.</para>
<variablelist>
<varlistentry><term>Processing expectations</term>
<listitem>
<para>
<indexterm><primary>formatting</primary>
  <secondary>elements</secondary></indexterm>
<indexterm><primary>elements</primary>
  <secondary>attributes</secondary>
    <tertiary>processing expectations, affecting</tertiary></indexterm>
Summarizes specific formatting expectations of the element. Many
processing expectations are influenced by attribute values. Be sure to
consult the
description of element attributes as well.
</para>
</listitem>
</varlistentry>
<varlistentry><term>Future changes</term>
<listitem>
<para>
<indexterm><primary>DocBook DTD</primary>
  <secondary>changes, future versions</secondary></indexterm>
<indexterm><primary>compatibility, DocBook versions</primary></indexterm>
<indexterm><primary>versions</primary>
  <secondary>DocBook DTD</secondary>
    <tertiary>future changes</tertiary></indexterm>

Identifies changes that are scheduled for future versions of the
&DTD;. These changes are highlighted because they involve some 
backward-incompatability that may make currently valid DocBook documents
no longer valid under the new version.
</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>

<varlistentry><term>Attributes</term>
<listitem>
<para>
<indexterm><primary>attributes</primary>
  <secondary>semantics</secondary></indexterm>

Describes the semantics of each attribute in detail.</para>
</listitem>
</varlistentry>

<varlistentry><term>See Also</term>
<listitem>
<para>Lists similar or related elements.
<indexterm><primary>cross references</primary>
  <secondary>elements</secondary></indexterm>
</para>
</listitem>
</varlistentry>

<varlistentry><term>Examples</term>
<listitem>

<para>
<indexterm><primary>elements</primary>
  <secondary>proper usage, examples</secondary></indexterm>
Provides examples of proper usage for the
element. Generally, the smallest example required to reasonably
demonstrate the element is used. In many cases, a formatted
version of the example is also shown.
</para>
<para>
All of the examples printed in the book use the &SGML; version of
DocBook.  The <link linkend="app-cdrom"><acronym>CD-ROM</acronym></link> includes the full
text of all of the examples.
</para>
<para>Formatted examples are indicated using a vertical bar.</para>
</listitem>
</varlistentry>
</variablelist>
<sect2 id="s2-cmintro">
<title>Understanding Content Models</title>
<para>
<indexterm><primary>content models</primary>
  <secondary>overview</secondary></indexterm>

Each element synopsis begins with a concise description of the
elements it can contain.  This description is in &DTD;
&ldquo;content model&rdquo; syntax, with all parameter entities
expanded.
</para>
<para>
Content models are the way that &DTD;s describe the name, number,
and order of other elements that may be used inside an element.
The primary feature of content model syntax is that it is concise,
but this conciseness comes at the cost of legibility until you
are familiar with the syntax.
</para>
<para>
<indexterm><primary>syntax</primary>
  <secondary>content models</secondary></indexterm>
<indexterm><primary>keywords</primary>
  <secondary>content model syntax</secondary></indexterm>
<indexterm><primary>sequences</primary>
  <secondary>content model syntax</secondary></indexterm>
<indexterm><primary>alternatives (content model syntax)</primary></indexterm>
<indexterm><primary>groups</primary>
  <secondary>content model syntax</secondary></indexterm>

There are six components to content model syntax: <firstterm>element
names</firstterm>, <firstterm>keywords</firstterm>,
<firstterm>repetitions</firstterm>, <firstterm>sequences</firstterm>,
<firstterm>alternatives</firstterm>, and
<firstterm>groups</firstterm>.
</para>

<variablelist>
<varlistentry><term>Element names</term>
<listitem><para>
<indexterm><primary>elements</primary>
  <secondary >names in content models</secondary></indexterm>

An element name in a content model indicates that an element of that
type may (or must) occur at that position.
</para>
<para>
<indexterm><primary>Para element</primary></indexterm>
A content model of <literal>Para</literal> indicates
that the element must contain a single paragraph.
</para></listitem>
</varlistentry>
<varlistentry><term>Keywords</term>
<listitem><para>
<indexterm><primary>empty elements</primary></indexterm>
<indexterm><primary>elements</primary>
  <secondary>empty</secondary><see>empty elements</see></indexterm>
There are two keywords that occur in the content models of DocBook
elements: <literal>EMPTY</literal>, and <literal>#PCDATA</literal>.
</para>
<para>A content model that consists of the single keyword <literal>EMPTY</literal>
identifes an element as an empty element.  Empty elements are not allowed
to have any content.  In order for the word &ldquo;EMPTY&rdquo; to have
this special meaning, it must be the first and only word in the content
model.  The word &ldquo;EMPTY&rdquo; at any other place is treated as
an element name.
</para>
<para>
<indexterm><primary>#PCDATA keyword</primary></indexterm>
<indexterm><primary>text</primary>
  <secondary>#PCDATA keyword</secondary></indexterm>
<indexterm><primary>characters</primary>
  <secondary>character sets</secondary>
    <tertiary>SGML and XML documents</tertiary></indexterm>
The <literal>#PCDATA</literal> keyword indicates that text may
occur at that position.  The text may consist of entity references and
any characters that are legal in the document character set.  For &XML;
documents, the document character set is always Unicode. In &SGML; the
declaration can identify character sets and ranges that are allowed.
DocBook &SGML; documents use the <acronym>ISO</acronym> Latin 1 character set.
</para>
</listitem>
</varlistentry>
<varlistentry><term>Repetitions</term>
<listitem><para>
<indexterm><primary>repetitions (content model syntax)</primary></indexterm>

An unadorned element name indicates that an element must occur exactly
once at that position. A content model can also specify that an element
may occur zero or more times, one or more times, or exactly zero or one
time.  This is accomplished by following the element name with one of
the following characters: <literal>*</literal> for zero or more times,
<literal>+</literal> for one or more times, or <literal>?</literal> for exactly
zero or one times.
</para>
<para>
A content model of <literal>Para+</literal> indicates
that the element must contain at least one paragraph and may contain
many.
</para></listitem>
</varlistentry>
<varlistentry><term>Sequences</term>
<listitem><para>
<indexterm><primary>sequences</primary>
  <secondary>content model syntax</secondary></indexterm>
If element names in a content model are separated by commas,
then they must occur in sequence.
</para>
<para>
A content model of <literal>Title, Para</literal> indicates
that the element must contain a single title followed by a single paragraph.
</para>
</listitem>
</varlistentry>
<varlistentry><term>Alternatives</term>
<listitem><para>
<indexterm><primary>alternatives (content model syntax)</primary></indexterm>
If element names in a content model are separated by vertical bars (|),
then they are alternatives.  These are sometimes called &ldquo;or
groups&rdquo; because they require the selection of one or another element.
</para>
<para>
A content model of <literal>Phrase | Para</literal> indicates
that the element must contain either a single phrase or a single paragraph.
</para>
<para>

<indexterm><primary>connectors (SGML)</primary></indexterm>
<indexterm><primary>DocBook DTD</primary>
  <secondary>ampersand (&amp;) connector</secondary></indexterm>

In &SGML;, there is another connector: the ampersand (&amp;). The
ampersand is a kind of combination of alternative and sequence,
which means that all of the elements must occur, but they can occur
in any order.  DocBook does not have any content models that use
the ampersand connector.  &XML; does not allow it.
</para>
</listitem>
</varlistentry>
<varlistentry><term>Groups</term>
<listitem><para>
<indexterm><primary>groups</primary>
  <secondary>content model syntax</secondary></indexterm>

Finally, parentheses may be used around part of a content model.  A group
formed this way can have repetition indicators and may occur as part of
a sequence.
</para>
<para>
A content model of <literal>(Literal | Replaceable)+</literal>
indicates that either <sgmltag>Literal</sgmltag> or <sgmltag>Replaceable</sgmltag>
must occur and they can be repeated (and mixed) any number of times.
</para></listitem>
</varlistentry>
</variablelist>
<sect3><title>Content models and validity</title>
<para>
<indexterm><primary>parsers</primary>
  <secondary>content models, matching to elements</secondary></indexterm>
<indexterm><primary>elements</primary>
  <secondary>parsing</secondary></indexterm>

A parser uses the content models to determine if a given document is valid.
In order for a document to be valid, the content of every element in the
document must <quote>match</quote> the content model for that element.
</para>
<para>
In practical terms, match means that it must be possible to expand the
content model until it exactly matches the sequence of elements in the
document.
</para>
<para>
For example, consider the content model of the <sgmltag>Epigraph</sgmltag> element:
<literal>Attribution?, (FormalPara | Para | SimPara)+</literal>.
This indicates that the following document fragment is valid:
<indexterm><primary>content models</primary>
  <secondary>examples</secondary></indexterm>

<screen>
<![CDATA[
<epigraph>
<para>Some text</para>
</epigraph>
]]>
</screen>
</para>
<para>
It is valid because the following expansion of the content model exactly
matches the actual content: choose zero occurances of
<sgmltag>Attribution</sgmltag>, choose the alternative <sgmltag>Para</sgmltag> from
the group, and choose to let the &ldquo;+&rdquo; match once.
</para>
<para>
By the same token, this example is not valid because there is no 
expansion of the content model that can match it:
<screen>
<![CDATA[
<epigraph>
<para>Some text</para>
<attribution>John Doe</attribution>
</epigraph>
]]>
</screen>
</para>
<para>
<indexterm><primary>ambiguity, content models</primary></indexterm>

There is one additional restriction on the matching ability of the
parser: it is not allowed to <quote>look ahead.</quote>  This means that
there are many useful content models that are ambiguous.
</para>
</sect3>
<sect3><title>Ambiguity</title>
<para>
Ambiguity is not allowed. The parser must always be able to choose 
exactly what to match based upon the next input token. 
Consider the
following content model:
<literal>Meta*, Title?, Meta*</literal>.
</para>
<para>
The intent is clear: to allow some meta-information and a single,
optional <sgmltag>Title</sgmltag>.  But this content model is ambiguous
for the following reason: if the document content begins with a
<sgmltag>Meta</sgmltag> element, it is impossible to tell if it matches
the <sgmltag>Meta</sgmltag> before the <sgmltag>Title</sgmltag> or after
without looking ahead.
</para>
<para>
Ambiguous content models are detected by the parser when it reads the
&DTD;. It is not sufficient that your document simply be unambiguous;
it must not be possible to construct any ambiguous document.
</para>
</sect3>
<sect3><title>#PCDATA and repetition</title>
<para>
<indexterm><primary>#PCDATA keyword</primary>
  <secondary>repetition and</secondary></indexterm>
<indexterm><primary>empty elements</primary>
  <secondary>PCDATA keyword and</secondary></indexterm>

The &PCDATA; keyword can always match the empty string.  This
makes it impossible to force an element that may contain
characters not to be empty. In other words, the following content
model <emphasis>does not</emphasis> guarantee that the element is not
empty: <literal>(#PCDATA)+</literal>.
</para>
<para>
<indexterm><primary>groups</primary>
  <secondary>PCDATA keyword</secondary></indexterm>

In &XML;, the &PCDATA; keyword is only allowed in optional, repeatable
<quote>or groups</quote>, and it must be the first member of the
group.
</para>
</sect3>
</sect2>
</sect1>
<sect1 id="common.attributes">
<title>Common Attributes</title>
<para>
<indexterm><primary>attributes</primary>
  <secondary>common</secondary></indexterm>
<indexterm><primary>common attributes</primary></indexterm>

The following attributes occur on all elements. They are summarized
here once for brevity and to make the additional attributes that occur on
many elements stand out.</para>

<informaltable pgwide="1">
<tgroup cols="3" colsep="1" rowsep="1">
<colspec colnum="1" colname="C1"/>
<colspec colnum="2" colname="C2"/>
<colspec colnum="3" colname="C3"/>
<spanspec namest="C1" nameend="C3" spanname="C1C3"/>
<thead>
<row><entry><para>Name</para></entry><entry>Type</entry><entry>Default</entry>
</row>
</thead>
<tbody>
<row>
<entry><sgmltag class="attribute">Arch</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry revision="4.0"><sgmltag class="attribute">Condition</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry><sgmltag class="attribute">Conformance</sgmltag></entry>
<entry>&AT.NMTOKENS;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry><sgmltag class="attribute">ID</sgmltag></entry>
<entry>&AT.ID;</entry>
<entry><para><emphasis>None/Required</emphasis><footnote><para>On a
few elements, the <sgmltag class="attribute">ID</sgmltag> is required,
but on most it is not.</para></footnote></para></entry>
</row>
<row>
<entry><sgmltag class="attribute">Lang</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry><sgmltag class="attribute">OS</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry><sgmltag class="attribute">Remap</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry><sgmltag class="attribute">Role</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry><sgmltag class="attribute">Revision</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry valign="top"><sgmltag class="attribute">RevisionFlag</sgmltag></entry>
<entry><simplelist>
<member><emphasis>Enumeration:</emphasis></member>
<member>Changed</member>
<member>Added</member>
<member>Deleted</member>
<member>Off</member>
</simplelist></entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry revision="4.0"><sgmltag class="attribute">Security</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry><sgmltag class="attribute">UserLevel</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry><sgmltag class="attribute">Vendor</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
<row>
<entry><sgmltag class="attribute">XrefLabel</sgmltag></entry>
<entry>&AT.CDATA;</entry>
<entry><emphasis>None</emphasis></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<variablelist>
<varlistentry><term><sgmltag class="attribute">Arch</sgmltag></term>
<listitem>
<para>
<indexterm><primary>Arch attribute</primary></indexterm>
<indexterm><primary>architecture</primary>
  <secondary>computer or chip</secondary></indexterm>
<indexterm><primary>computer architecture (elements)</primary></indexterm>
<indexterm><primary>chip architecture (elements)</primary></indexterm>

<sgmltag class="attribute">Arch</sgmltag> designates the
computer or chip architecture to which the element applies.</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">Condition</sgmltag></term>
<listitem>
<para revision="4.0">
<indexterm><primary>Condition attribute</primary></indexterm>

<sgmltag class="attribute">Condition</sgmltag> is a general-purpose
effectivity attribute with no specified semantics. Many DocBook users
observed that in order to add an effectivity condition that was unique
to their environment required <quote>abusing</quote> the semantics of
one of the existing attributes, or adding their own, making their
customization <link linkend="s-notdocbook">an extension rather than a
subset</link>.</para>

<para>The <sgmltag class="attribute">Condition</sgmltag> attribute
provides a standard place for application-specific effectivity.</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">Conformance</sgmltag></term>
<listitem>
<para>
<indexterm><primary>Conformance attribute</primary></indexterm>

<sgmltag class="attribute">Conformance</sgmltag> indicates
standards conformance characteristics of the item contained in the
element. These characteristics are application-specific.  DocBook
provides no defaults.</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">ID</sgmltag></term>
<listitem>
<para>
<indexterm><primary>ID attribute</primary></indexterm>

<sgmltag class="attribute">ID</sgmltag> is an identifying string
for the element.  It must be unique at least within the document and
must begin with a letter.</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">Lang</sgmltag></term>
<listitem>
<para>
<indexterm><primary>Lang attribute</primary></indexterm>
<indexterm><primary>country codes</primary></indexterm>
<indexterm><primary>languages</primary>
  <secondary>codes</secondary></indexterm>
<indexterm><primary>ISO standards</primary>
  <secondary>language codes</secondary></indexterm>
<indexterm><primary>ISO standards</primary>
  <secondary>country codes</secondary></indexterm>

<sgmltag class="attribute">Lang</sgmltag> should be a language
code drawn from <acronym>ISO</acronym> 639 (perhaps extended with a
country code drawn from <acronym>ISO</acronym> 3166, as
<literal>en-US</literal>).  Use it when you need to signal your
application to change hyphenation and other display
characteristics.</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">OS</sgmltag></term>
<listitem>
<para>
<indexterm><primary>OS attribute</primary></indexterm>
<indexterm><primary>operating systems</primary>
  <secondary>elements</secondary></indexterm>

<sgmltag class="attribute">OS</sgmltag> indicates the operating
system to which the element is applicable.
</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">Remap</sgmltag></term>
<listitem>
<para>
<indexterm><primary>Remap attribute</primary></indexterm>
<indexterm><primary>markup</primary>
  <secondary>previous schemes, identifying</secondary></indexterm>

<sgmltag class="attribute">Remap</sgmltag> contains an element
name or similar semantic identifier assigned to the content in a
previous markup scheme.</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">Role</sgmltag></term>
<listitem>
<para>
<indexterm><primary>Role attribute</primary></indexterm>
<indexterm><primary>elements</primary>
  <secondary>classifying or subclassifying</secondary></indexterm>
<indexterm><primary>parameter entities</primary>
  <secondary>Role attribute</secondary></indexterm>

<sgmltag class="attribute">Role</sgmltag> contains a string used
to classify or subclassify an element.</para>
<para>While Role is a common attribute in the sense that it occurs on
almost all elements, it is not part of either of the common attributes
parameter entities (<sgmltag class="paramentity">common.attrib</sgmltag> or <sgmltag class="paramentity">idreq.common.attrib</sgmltag>).  It is
parameterized differently because it is useful to be able to subclass
<sgmltag class="attribute">Role</sgmltag> independently on different
elements.</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">Revision</sgmltag></term>
<listitem>
<para>
<indexterm><primary>Revision attribute</primary></indexterm>

<sgmltag class="attribute">Revision</sgmltag> indicates the
editorial revision to which the element belongs.
</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">RevisionFlag</sgmltag></term>
<listitem>
<para>
<indexterm><primary>RevisionFlag attribute</primary></indexterm>
<indexterm><primary>versions</primary>
  <secondary>revision control, documents</secondary></indexterm>

<sgmltag class="attribute">RevisionFlag</sgmltag> indicates the
revision status of element; the default is that the element hasn't
been revised.  <sgmltag class="attribute">RevisionFlag</sgmltag> is
intended only for simple revision management: to track the entire
history of a document use a proper revision control system.  Use
<sgmltag class="attribute">RevisionFlag</sgmltag> for indicating
changes from one version to the next, no more.</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">Security</sgmltag></term>
<listitem>
<para revision="4.0">
<indexterm><primary>Security attribute</primary></indexterm>

<sgmltag class="attribute">Security</sgmltag> identifies something about
the security level associated with the element to which it applies.
</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">UserLevel</sgmltag></term>
<listitem>
<para>
<indexterm><primary>UserLevel attribute</primary></indexterm>
<indexterm><primary>experience levels (users)</primary></indexterm>

<sgmltag class="attribute">UserLevel</sgmltag> indicates the
level of user experience to which element applies.
</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">Vendor</sgmltag></term>
<listitem>
<para>
<indexterm><primary>Vendor attribute</primary></indexterm>
<indexterm><primary>computer vendors</primary></indexterm>

<sgmltag class="attribute">Vendor</sgmltag> indicates the
computer vendor to which the element applies.</para>
</listitem>
</varlistentry>
<varlistentry><term><sgmltag class="attribute">XrefLabel</sgmltag></term>
<listitem>
<para>
<indexterm><primary>XrefLabel attribute</primary></indexterm>
<indexterm><primary>cross references</primary>
  <secondary>XrefLabel attribute</secondary></indexterm>
<sgmltag class="attribute">XrefLabel</sgmltag> holds text to be
used when a cross reference (<sgmltag>XRef</sgmltag>) is made to the
element.</para>
</listitem>
</varlistentry>
</variablelist>
</sect1>
<sect1>
<title>Attribute Types</title>
<para>
<indexterm><primary>types (attributes)</primary></indexterm>
<indexterm><primary>attributes</primary>
  <secondary>types</secondary></indexterm>

&SGML; offers a small selection of attribute types. (&XML;
offers a subset of these.) For convenience, a brief description of
each of these types is provided here:</para>
<variablelist>
<varlistentry id="AT.CDATA"><term><sgmltag class="attribute">&AT.CDATA;</sgmltag></term>
<listitem>
<para>
<indexterm><primary>characters</primary>
  <secondary>strings (CDATA attribute)</secondary></indexterm>
<indexterm><primary>strings (characters)</primary></indexterm>
<indexterm><primary>CDATA</primary></indexterm>

A string of characters.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.NUMBER"><term><sgmltag class="attribute">&AT.NUMBER;</sgmltag></term>
<listitem>
<para>
<indexterm><primary>numbers (attributes)</primary></indexterm>
<indexterm><primary>hyphens (-), numbers</primary></indexterm>
<indexterm><primary>decimal points (.), numbers</primary></indexterm>

A number.  Numbers must begin with a hyphen or digit and can include
the decimal point.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.NMTOKEN"><term><sgmltag class="attribute">&AT.NMTOKEN;</sgmltag></term>
<listitem>
<para>
<indexterm><primary>NMTOKEN(S) attribute</primary></indexterm>
<indexterm><primary>names</primary>
  <secondary>NMTOKEN attribute</secondary></indexterm>
<indexterm><primary>attributes</primary>
  <secondary>names</secondary></indexterm>
<indexterm><primary>characters</primary>
  <secondary>names</secondary></indexterm>


A sequence of name characters (letters, digits, hyphens, and
periods).  This differs from a <sgmltag class="attribute">&AT.CDATA;</sgmltag> attribute because it cannot
contain spaces, punctuation, or other non-name characters.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.NMTOKENS"><term><sgmltag class="attribute">&AT.NMTOKENS;</sgmltag></term>
<listitem>
<para>A sequence of one or more space-delimited <sgmltag class="attribute">&AT.NMTOKEN;</sgmltag> values.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.NUTOKEN"><term><sgmltag class="attribute">&AT.NUTOKEN;</sgmltag></term>
<listitem>
<para>
<indexterm><primary>NUTOKEN attribute</primary></indexterm>
<indexterm><primary>digits</primary>
  <secondary>numbers</secondary></indexterm>
<indexterm><primary>decimal points (.), numbers</primary></indexterm>

A sequence of number characters (digits, hyphens, and periods).
This differs from a <sgmltag class="attribute">&AT.NUMBER;</sgmltag>
field because it is not required to begin with a digit or a
hyphen.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.ENTITY"><term><sgmltag class="attribute">&AT.ENTITY;</sgmltag></term>
<listitem>
<para>
<indexterm><primary>ENTITY attribute</primary></indexterm>

An entity name.  The value of an <sgmltag class="attribute">&AT.ENTITY;</sgmltag> attribute must be the name of
a declared entity.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.NAME"><term><sgmltag class="attribute">&AT.NAME;</sgmltag></term>
<listitem>
<para>
<indexterm><primary>NAME attribute</primary></indexterm>
<indexterm><primary>digits</primary>
  <secondary>names</secondary></indexterm>
<indexterm><primary>periods (.), names</primary></indexterm>
<indexterm><primary>NAMES attribute</primary></indexterm>

A name.  A name must begin with a letter and can consist of
letters, digits, hyphens, and periods.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.NAMES"><term><sgmltag class="attribute">&AT.NAMES;</sgmltag></term>
<listitem>
<para>A sequence of one or more space-delimited <sgmltag class="attribute">&AT.NAME;</sgmltag> values.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.ID"><term><sgmltag class="attribute">&AT.ID;</sgmltag></term>
<listitem>
<para>
<indexterm><primary>ID attribute</primary></indexterm>
<indexterm><primary>uniqueness</primary>
  <secondary>ID attributes</secondary></indexterm>

An <acronym>ID</acronym>.  <acronym>ID</acronym>s are names that
must be globally unique within the document.  The <sgmltag class="attribute">&AT.ID;</sgmltag> attribute declares the
<acronym>ID</acronym>.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.IDREF"><term><sgmltag class="attribute">&AT.IDREF;</sgmltag></term>
<listitem>
<para>
<indexterm><primary>IDREF attribute</primary></indexterm>

An single <acronym>ID</acronym>.  <acronym>ID</acronym>s are
names that must be globally unique within the document. The value of
an <sgmltag class="attribute">&AT.IDREF;</sgmltag> attribute must be
the name of an <sgmltag class="attribute">&AT.ID;</sgmltag> attribute
defined in the document.</para>
</listitem>
</varlistentry>
<varlistentry id="AT.IDREFS"><term><sgmltag class="attribute">&AT.IDREFS;</sgmltag></term>
<listitem>
<para>
<indexterm><primary>IDREFS attribute</primary></indexterm>

A sequence of one or more space-delimited <sgmltag class="attribute">&AT.ID;</sgmltag> values.
<indexterm startref="elementsref" class='endofrange'/>
</para>
</listitem>
</varlistentry>
</variablelist>
</sect1><?Pub Caret1?>
</partintro>

