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 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”.
<p>... See <xref alt="figure 4">Fig&#x00A0;IV.</xref></p>
Display/Formatting Note: The content of the reference (if present) will be displayed as the link.


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 | serif | strike | underline | underline-start | underline-end | ruby | alternatives | inline-graphic | private-char | chem-struct | inline-formula | tex-math | mml:math | abbrev | index-term | index-term-range-end | milestone-end | milestone-start | named-content | styled-content | fn | target | xref | sub | sup | x | break)*


This element may be contained in:

<abbrev>, <addr-line>, <aff>, <alt-title>, <anonymous>, <article-title>, <attrib>, <award-id>, <bold>, <book-title>, <book-volume-id>, <book-volume-number>, <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>, <inline-formula>, <inline-supplementary-material>, <institution>, <issue>, <issue-part>, <issue-title>, <italic>, <kwd>, <label>, <license-p>, <meta-name>, <meta-value>, <mixed-citation>, <monospace>, <name-address-wrap>, <named-content>, <nav-pointer>, <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>, <see>, <see-also>, <see-also-entry>, <see-entry>, <self-uri>, <series>, <serif>, <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>, <version>, <volume>, <volume-id>, <volume-series>, <volume-title>, <xref>

Example 1

In the narrative text, cross-references to bibliographic references:
<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 practice</source>
<year iso-8601-date="1994">1994</year>
<ref id="B2">...</ref>

Example 2

In the narrative text, cross-references to figures:
<sec id="bid.36">
<title>Microbial Genomes</title>
<p>... A CON entry, containing instructions on how to put
the pieces back together, is also made. The CON entry
contains descriptor information, such as source organism
and references, as well as a join statement providing
explicit instructions on how to generate the complete
genome from the pieces. The Accession number assigned 
to the CON record is also added as a secondary Accession
number on each of the pieces that make up the complete
genome (see <xref ref-type="fig" rid="bid.37">Figure 2</xref>).
<fig id="bid.37">
<title>A GenBank CON entry for a complete bacterial 
<p>The information toward the <italic>bottom</italic> of the 
record describes how to generate the complete genome
from the pieces.</p>
<graphic xmlns:xlink="http://www.w3.org/1999/xlink"
xlink:href="ch1f2" mime-subtype="gif"/>
<p>Allocation of tags to individual molecules is outlined in
<xref ref-type="fig" rid="F2" alt="figure two">Fig.&#x00A0;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.&#x00A0;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>

Example 3

In 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>