Number of a journal (or other document) within its series.
The <volume> element is used in two contexts: as a part of the metadata describing the article itself, and as part of a description of a cited work inside a bibliographic reference (element <citation>).
Any combination of:
In article metadata
<front>
<journal-meta>...</journal-meta>
<article-meta>
<article-id pub-id-type="pmid">10092260</article-id>
<title-group>
<article-title>Systematic review of day hospital care
for elderly people</article-title>
</title-group>
<contrib-group>...</contrib-group>
<aff>...</aff>
<author-notes>...</author-notes>
<pub-date pub-type="pub">
<day>27</day>
<month>3</month>
<year>1999</year>
</pub-date>
<volume>318</volume> <issue>7187</issue>
<fpage>837</fpage><lpage>841</lpage>
<history><date
date-type="accepted">
<day>29</day><month>1</month>
<year>1999</year>
</date>
</history>
<copyright-statement>...</copyright-statement> <abstract>...</abstract>
</article-meta>
</front>
In a bibliographic reference list
<back>
... <ref-list>
...
<ref id="B8"><label>8</label>
<citation>
<name>
<surname>Weissert</surname>
<given-names>W</given-names></name>
<name>
<surname>Wan</surname>
<given-names>T</given-names></name>
<name>
<surname>Livieratos</surname>
<given-names>B</given-names></name>
<name>
<surname>Katz</surname>
<given-names>S</given-names></name>
<article-title>Effects and costs of day-care services
for the chronically ill: a randomized experiment.</article-title> <source>Medical Care</source>
<volume>18</volume>
<year>1980</year>
<fpage>567</fpage><lpage>584</lpage>.
<pub-id pub-id-type="pmid">6772889</pub-id> </citation> </ref>
...</ref-list>
...</back>
common.ent