In a DocBook reference page, the manvolnum holds the number of the volume in which the refentry belongs.

The notion of a volume number is historical. UNIX manual pages (“man pages”), for which refentry was devised, were typically stored in three-ring binders. Each bound manual was a volume in a set and contained information about a particular class of things. For example, volume 1 was for user commands, and volume 8 was for administrator commands.

Volume numbers need not be strictly numerical; volume “l” frequently held manual pages for local additions to the system, and the X Window System manual pages had an “x” in the volume number: for example, 1x.

<article xmlns='http://docbook.org/ns/docbook'>
<title>Example manvolnum</title>

<para>For a further description of print formats, consult the
<citerefentry><refentrytitle>printf</refentrytitle>
<manvolnum>3S</manvolnum></citerefentry> manual page.
</para>

</article>