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 Document Internal Identifier
ref-type Type of Cross-Reference
rid Reference to an Identifier
specific-use Specific Use
xml:base Base
xml:lang Language

Content Model

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

Expanded Content Model

(#PCDATA | email | ext-link | uri | inline-supplementary-material | related-article | related-object | hr | bold | fixed-case | italic | monospace | overline | overline-start | overline-end | roman | sans-serif | sc | strike | underline | underline-start | underline-end | ruby | alternatives | inline-graphic | private-char | chem-struct | inline-formula | tex-math | mml:math | abbrev | milestone-end | milestone-start | named-content | styled-content | fn | target | xref | sub | sup | x | break)*


Any combination of:

This element may be contained in:

<abbrev>, <abbrev-journal-title>, <addr-line>, <aff>, <alt-title>, <anonymous>, <article-title>, <attrib>, <award-id>, <bold>, <chapter-title>, <chem-struct>, <code>, <collab>, <comment>, <compound-kwd-part>, <conf-acronym>, <conf-loc>, <conf-name>, <conf-num>, <conf-sponsor>, <conf-theme>, <contrib>, <contrib-group>, <copyright-statement>, <corresp>, <def-head>, <degrees>, <disp-formula>, <edition>, <element-citation>, <email>, <etal>, <ext-link>, <fax>, <fixed-case>, <funding-source>, <funding-statement>, <given-names>, <gov>, <history>, <inline-formula>, <inline-supplementary-material>, <institution>, <issue>, <issue-part>, <issue-sponsor>, <issue-title>, <italic>, <journal-subtitle>, <journal-title>, <kwd>, <label>, <license-p>, <meta-name>, <meta-value>, <mixed-citation>, <monospace>, <named-content>, <on-behalf-of>, <overline>, <p>, <part-title>, <patent>, <phone>, <prefix>, <preformat>, <product>, <publisher-loc>, <publisher-name>, <rb>, <related-article>, <related-object>, <role>, <roman>, <sans-serif>, <sc>, <self-uri>, <series>, <series-text>, <series-title>, <sig>, <sig-block>, <source>, <speaker>, <std-organization>, <strike>, <string-conf>, <string-date>, <string-name>, <styled-content>, <sub>, <subject>, <subtitle>, <suffix>, <sup>, <supplement>, <surname>, <target>, <td>, <term>, <term-head>, <th>, <title>, <trans-source>, <trans-subtitle>, <trans-title>, <underline>, <unstructured-kwd-group>, <uri>, <verse-line>, <volume>, <volume-id>, <volume-series>, <xref>

Example 1

In the narrative text, cross-references to bibliographic citations:

<article dtd-version="1.1d1">
<p>... 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"><label>1</label>
<element-citation publication-type="book">
<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">...</ref>

Example 2

In the narrative text, cross-references to figures:

<sec id="sec3">
<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 strand.</p>
<fig id="F2">...</fig>
<fig id="F3">...</fig>
<fig id="F4">...</fig>

Example 3

In article metadata, cross-references linking authors to both affiliations and author notes:

<contrib contrib-type="author"> 
<name name-style="western"><surname>Zhang</surname>
<given-names>Y. P.</given-names></name>
<string-name name-style="eastern" xml:lang="zh">张轶泼</string-name>
<xref ref-type="aff" rid="a1">1</xref>
<xref ref-type="author-notes" rid="n1">a)</xref>
<contrib contrib-type="author">
<name name-style="western"><surname>Isobe</surname>
<string-name name-style="eastern" xml:lang="zh">磯部光孝</string-name>
<xref ref-type="aff" rid="a2">2</xref>
<contrib contrib-type="author">
<name name-style="western"><surname>Liu</surname>
<string-name name-style="eastern" xml:lang="zh">刘仪</string-name>
<xref ref-type="aff" rid="a1">1</xref>
<aff id="a1">...</aff>
<aff id="a2">...</aff>
<author-notes id="n1">...</author-notes>