X (cross) Reference

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


This element may be used to reference anything that has an attribute of type @id. This single element takes the place of the many named types of references (such as figure references, table references, and footnote references) that are common in many journal tag sets.

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, the element cross-reference to a figure that follows might be pronounced as “Figure 4”.

See <xref alt="figure 4">Fig&amp;#x00A0;IV.</xref>

Display/Formatting Note: The content of the reference (if present) will be displayed as the link.


alt Alternative Text
id Identifier
ref-type Type of Cross-Reference
rid Reference to an Identifier
specific-use Specific Use
xml:lang Language

Content Model

<!ELEMENT  xref         (#PCDATA %xref-elements;)*                   >

Expanded Content Model

(#PCDATA | bold | italic | monospace | overline | roman | sans-serif | sc | strike | underline | named-content | styled-content | sub | sup)*


Any combination of:

This element may be contained in:

<aff>, <alt-title>, <article-title>, <attrib>, <bold>, <chem-struct>, <collab>, <comment>, <compound-kwd-part>, <contrib>, <contrib-group>, <def-head>, <italic>, <license-p>, <meta-value>, <monospace>, <named-content>, <overline>, <p>, <product>, <roman>, <sans-serif>, <sc>, <speaker>, <strike>, <styled-content>, <sub>, <subtitle>, <sup>, <td>, <term>, <term-head>, <th>, <title>, <trans-subtitle>, <trans-title>, <underline>, <verse-line>

Example 1

<p>Geriatric day hospitals developed rapidly in the United Kingdom in
the 1960s as an important component of care provision. ... Although
there is considerable descriptive literature on day hospital
care,<xref ref-type="bibr" rid="B1">1</xref> concern has been expressed
that evidence for effectiveness is equivocal and that day hospital care
is expensive.<xref ref-type="bibr" rid="B2">2</xref> ...</p>
<ref id="B1">
<collab>Research Unit of the Royal College of Physicians and British
Geriatric Society</collab>
<source>Geriatric day hospitals: their role and guidelines for good
<year iso-8601-date="1994">1994</year>
<ref id="B2">
<collab>National Audit Office</collab>
<source>National health service day hospitals for elderly people
in England</source>
<year iso-8601-date="1994">1994</year>

Example 2

<p>Allocation of tags to individual molecules is outlined in
<xref ref-type="fig" rid="F2" alt="figure two">Fig.&amp;#x00A012;2</xref>.
First, the complete repertoire of tags in a plasmid library is ligated
to the entire population of cDNAs ...
After separating loaded microbeads from unloaded microbeads
by FACS, as shown in <xref ref-type="fig" rid="F4"
alt="figure four">Fig.&amp;#x00A012;4</xref>,
the hybridized DNA is ligated to the anti-tag, covalently
attaching one strand of the DNA to the microbead's surface.
This permits easy removal of the noncovalently attached