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<xref> X(cross) Reference

Reference to an object within the standards document (for example, a table, a bibliographic citation, a figure).

Usage/Remarks

This element may be used to reference anything that has an attribute of type @id.

Best Practice

The @ref-type attribute (of the <xref> element) can be used to preserve information concerning what type of element is being pointed to by the cross-reference.
Accessibility
Sometimes a <xref> needs to be pronounced in a way that is not reflected in its content or its tagging. The @alt attribute can be used to record the pronunciation for screen readers and other accessibility devices. For example, a cross-reference to a figure might be pronounced as “Figure 4”.

Custom Type of Reference (@ref-type)

The @ref-type attribute can be used to preserve information concerning the type of element that is the target of the cross-reference (for example, a figure (“fig”), a table (“table”), or a footnote (“fn”)). @ref-type has as its values a fixed list of types. If your object is not one of the listed types, you can use @custom-type to describe the actual type. Set the value of @ref-type to “custom” and also use @custom-type to hold any object type you require. For example: 
<xref ref-type="custom" custom-type="glossary".../>
... <xref ref-type="custom" custom-type="term".../>
Attributes
alt
custom-type
ref-type
rid
specific-use

Base Attributes

id
xml:base
xml:lang
Models and Context
May be contained in
<aff>, <alt-title>, <article-title>, <attrib>, <bold>, <chapter-title>, <chem-struct>, <code>, <collab>, <comment>, <compl>, <compound-kwd-part>, <contrib>, <contrib-group>, <def-head>, <element-citation>, <fixed-case>, <full>, <inline-code>, <intro>, <italic>, <label>, <license-p>, <main>, <meta-value>, <mixed-citation>, <monospace>, <named-content>, <on-behalf-of>, <overline>, <p>, <part-title>, <preformat>, <roman>, <sans-serif>, <sc>, <see>, <see-also>, <see-also-entry>, <see-entry>, <source>, <speaker>, <std>, <strike>, <styled-content>, <sub>, <subtitle>, <sup>, <tbx:crossReference>, <tbx:definition>, <tbx:entailedTerm>, <tbx:example>, <tbx:externalCrossReference>, <tbx:note>, <tbx:pronunciation>, <tbx:see>, <tbx:source>, <tbx:term>, <tbx:usageNote>, <td>, <term>, <term-display-string>, <term-head>, <th>, <title>, <trans-source>, <trans-subtitle>, <trans-title>, <underline>, <verse-line>
Description
Any combination of:
Content Model
<!ELEMENT  xref         (#PCDATA %xref-elements;)*                   >
Expanded Content Model

(#PCDATA | bold | fixed-case | italic | monospace | num | overline | roman | sans-serif | sc | strike | underline | ruby | inline-graphic | private-char | inline-code | inline-media | named-content | styled-content | sub | sup)*

Tagged Samples
For footnote 
...
<p>A standard shall indicate ... the document is not measurement 
 sensitive by placing one of the designations below in a rectangular 
 box above the standard identifier.<xref ref-type="fn"><sup>1</sup></xref>
 <fn>
  <label><sup>1</sup></label>
  <p>At one time, the letters &ldquo;DOD&rdquo; were used in the 
   document identifier to designate standards that could be used 
   in metric design; for example, DOD-STD-12345. ...</p>
 </fn>
</p>
...
...
<p>... Stakeholders should include older persons and 
 persons with disabilities from organizations representing 
 these populations and those persons with a knowledge of 
 the accessibility needs of children and gender-related 
 groups<sup><xref ref-type="fn" rid="fn1">1</xref>)</sup>.
 <fn id="fn1">
  <p>Further information relating to the involvement of users and 
   potential users can be found in ...</p>
 </fn>
</p>
...
For figure 
...
<sec id="s5_1">
 <label>5.1</label>
 <title>Two approaches to addressing accessibility in 
  standards</title>
 ...
 <p><xref ref-type="fig" rid="f1">Figure 1</xref> provides 
  a graphical summary of how this Guide can be used.</p>
 <fig id="f1" orientation="portrait" position="anchor">
  <label>Figure 1</label>
  <caption>
   <title>Two approaches to address accessibility in 
    standards</title>
  </caption>
  <graphic xlink:href="g3658.jpg"/>
 </fig>
 ...
</sec>
...
For bibliographic reference 
...
<back>
 <app-group>
  <app content-type="inform-annex" id="annA">
   <label>Annex A</label>
   <annex-type>(informative)</annex-type>
   <title>Global trends supporting accessibility</title>
   ...
   <sec id="A1">
    <label>A.1</label>
    <title>Trends in global demographics and market diversity</title>
    <p>According to the <italic>World Report on Disability</italic> 
     (published by the World Health Organization and the World Bank 
     in June 2011,<sup><xref ref-type="bibr" rid="bibr40">[40]</xref></sup> 
     approximately 15 % of the world population (over one billion 
     people) has ...</p>
   </sec>
   ...
  </app>
 </app-group>
 <ref-list>
  <title>Bibliography</title>
  ...
  <ref id="bibr40">
   <label>[40]</label>
   <mixed-citation
    ><person-group><collab>World Health Organization</collab>, 
     <collab>World Bank</collab></person-group>. 
    <year iso-8601-date="2011">2011</year>), 
    <source>World Report on Disability</source>, 
    <publisher-loc>Geneva</publisher-loc>, available at: 
    <ext-link 
      xlink:href="http://www.who.int/disabilities/world_report/2011/en/index.html"
     >http://www.who.int/disabilities/world_report/2011/en/index.html</ext-link
   ></mixed-citation>
  </ref>
 </ref-list>
</back>
...
For section 
...
<body>
 ...
 <sec id="s4">
  <label>4</label>
  <title>Accessibility in the standards development 
   process</title>
  <sec id="s4_1">
   <label>4.1</label>
   <title>General</title>
   <p>This clause outlines how accessibility can be 
    addressed in the standards development process:
    <list list-type="bullet">
     <list-item><p><xref ref-type="sec" rid="s4_2">4.2</xref> 
      contains general considerations for standards bodies 
      related to ...</p></list-item>
     <list-item><p><xref ref-type="sec" rid="s4_3">4.3</xref> 
      provides guidance for each of the respective stages of 
      the standards development process to ensure ...</p></list-item>
    </list>
   </p>
  </sec>
  <sec id="s4_2">
   <label>4.2</label>
   <title>Considerations by standards bodies</title>
   <p>Standards bodies should develop a process for ...</p>
  </sec>
  ...
 </sec>
 ...
</body>
...
For table 
...
<sec id="s6.7.1.5">
 <label>6.7.1.5</label>
 <title>Ambient illumination</title>
 <p>This test is used to determine the ambient light 
  levels under which the scanner will operate.</p>
 <p>... Specific applications may not require the 
  extended range noted in <xref ref-type="table" 
  rid="t11">Table 11</xref>.</p>
 <table-wrap id="t11">
  <label>Table 11</label>
  <caption><title>Ambient illumination levels</title></caption>
  <table>
   <thead>
    <tr>
     <th>Lighting Conditions</th>
     <th>Illumination Level Lux</th>
    </tr>
   </thead>
   <tbody>
    <tr>
     <td>Dark room</td>
     <td>0</td>
    </tr>
    <tr>
     <td>Desk top</td>
     <td>100</td>
    </tr>
    <tr>
     <td>Overcast daylight</td>
     <td>1,000</td>
    </tr>
    <tr>
     <td>Bright sunlight</td>
     <td>100,000</td>
    </tr>
   </tbody>
  </table>
 </table-wrap>
 ...
</sec>
...
For equation 
...
<p>In the case of dollies of diameter 20 mm, the 
 breaking strength, in megapascals, is given by
 <xref ref-type="disp-formula" rid="formula_2">Formula
 (2)</xref>
 <disp-formula id="formula_2"
  ><mml:math display="block" 
     id="mml_m2"
     xmlns:mml="http://www.w3.org/1998/Math/MathML" >
   <mml:mrow>
    <mml:mi>s</mml:mi><mml:mo>=</mml:mo>
    <mml:mfrac>
     <mml:mrow>
      <mml:mn>4</mml:mn><mml:mi>F</mml:mi></mml:mrow>
     <mml:mrow>
      <mml:mn>400</mml:mn><mml:mi>p</mml:mi></mml:mrow>
    </mml:mfrac>
    <mml:mo>=</mml:mo>
    <mml:mfrac>
     <mml:mi>F</mml:mi>
     <mml:mrow>
      <mml:mn>314</mml:mn></mml:mrow>
    </mml:mfrac>
   </mml:mrow>
  </mml:math>
  <label>(2)</label>
 </disp-formula>
</p>
...