xml:id XML Unique Identifier

Identifies a unique ID value of the element.

Usage/Remarks

Authoring Note
The authoring model does not permit the use of @xml:id with the elements <itemizedlist>, <orderedlist>, <listitem>, <variablelist>, <varlistentry>, and <programlisting>. Use of @xml:id with these elements is available in the production model, but only then for backwards-compatibility should prior proceedings years’ production be necessary. (Model versions, predating 2010, permitted @xreflabel’s use with these elements.)
OPTIONAL on many elements; click for list and usage
Value Meaning
An XML identifier (ID) A unique identifier for the element. An XML parser can verify that an IDREF-style attribute pointing to one of these is pointing to a valid ID.
Restriction This attribute may be specified if the element is used.
Tagged Samples
Identifier for an article (rare)
<article xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink"
  version="5.0-subset Balisage-1.5" xml:id="HR-23632987-8973">
  <title>Raleigh&#8217;s Discoveries in the New World</title>
  <subtitle>New Insight into the Roanoke Colony</subtitle>
  <info>
    ...
  </info>
  <section xml:id="mul1">
    ...
  </section>
  ...
</article>
Identifier for a footnote
...
<para>... An equally unusual fruit was <quote>metaqvesvnnaqvk</quote>; 
  notwithstanding its red fruit, that plant&#8217;s more important 
  feature lay in the cochinile insects which fed upon its prickly thick 
  leaves<footnote xml:id="mul-f2">
    <para>In the 16th century, such insects were prized in the making of a vibrant red
      dye.</para>
  </footnote>.</para>
...
Identifier for an appendix, showing a reference to the appendix (from an <xref> element)
...
<section>
  ...
  <para>The second expedition, organized by John White in 1587, fared better. It sailed with 
    seven ships filled with Devon families intent upon establishing a colony in that part of 
    Virginia called Roanoke, a word deriving from the speech of native peoples. (<emphasis 
    role="ital">See</emphasis> <xref linkend="mul-app2"/>.) ...</para>
</section>
...
<appendix xml:id="mul-app2" xreflabel="Appendix II">
  <title>The Roanoke Colony, 1587</title>
  ...
</appendix>
...
Identifier for a bibliographic entry, with a reference to the entry (from an <xref> element)
...
<section xml:id="mul3">
  <title>Native Inhabitants of the New World</title>
  <para>Upon establishing the Roanoke colony, the settlers encouraged relations with the 
    native inhabitants, of which there appear to have been a diverse group, including 
    Croatans, Mangoaks, Chaonists, and Sequotanes, as well as Roanoke from which the 
    region took its name. [<xref linkend="lane1586"/>, <xref linkend="dunbar1960"/>] 
    ...</para>
  </section>
...
<bibliography>
  <title>Bibliography</title>
  ...
  <bibliomixed xml:id="dunbar1960" xreflabel="Dunbar 1960">Dunbar, Gary S. ...</bibliomixed>
  <bibliomixed xml:id="lane1586" xreflabel="Lane">Lane, Ralph. ...</bibliomixed>
</bibliography>
...
Identifier for a figure, with a reference to the figure (from an <xref> element)
...
<section xml:id="mul4-1">
  <title>Gourds</title>
  <para>The native people grew a variety of large broad-leafed, ground-covering vines 
    which produced what they called <quote>macocqwer</quote> or gourds. (<emphasis 
    role="ital">See</emphasis> <xref linkend="mul-fig1"/>.) ...</para>
  <figure xml:id="mul-fig1">
    <title>Gourds</title>
    <mediaobject>
      <imageobject>
        <imagedata format="jpg" fileref="19450212-2.jpg" width="50%"/>
      </imageobject>
    </mediaobject>
    ...
  </figure>
  ...
</section>
...
Identifier for a section, showing a reference to the section (from an <xref> element)
...
<section xml:id="mul3">
  <title>Native Inhabitants of the New World</title>
  ...
</section>
...  
<section xml:id="mul6">
  <title>Roanoke &#8212; a Failure?</title>
  ...  
  <para>... Raleigh&#8217;s efforts &#8212; along with those of 
    countless other explorers to the New World &#8212; introduced 
    New World plants such as potatoes and tomatoes to England, as 
    described in <xref linkend="mul3"/>. ...</para>
</section>
...
Identifier for a table
...
<table xml:id="mul-table1" frame="box">
  ...
  <colgroup>
    <col align="right" valign="top"/>
    <col valign="top"/>
    <col align="center" valign="top"/>
  </colgroup> 
  <thead>
    ...
  </thead>
  <tbody>
    <tr valign="top">
      <td rowspan="8"><emphasis role="bold">Vegetables</emphasis></td>
    </tr>
    ...
  </tbody>
</table>
...