volumenum — The volume number of a document in a set (as of books in a set or articles in a journal)
volumenum ::=
altanchorannotationbibliorefindexterm (db.indexterm.endofrange)indexterm (db.indexterm.singular)indexterm (db.indexterm.startofrange)inlinemediaobjectlinkolinkphrase (db._phrase)remarkreplaceablesubscriptsuperscriptxrefVolumeNum identifies the volume number of a
Book in a Set, or a periodical. 
It is a wrapper for bibliographic information.
These elements contain volumenum: biblioentry, bibliomixed, bibliomset, biblioset, info (db.info), info (db.titleforbidden.info), info (db.titleonly.info), info (db.titleonlyreq.info), info (db.titlereq.info).
The following elements occur in volumenum: text, alt, anchor, annotation, biblioref, indexterm (db.indexterm.endofrange), indexterm (db.indexterm.singular), indexterm (db.indexterm.startofrange), inlinemediaobject, link, olink, phrase (db._phrase), remark, replaceable, subscript, superscript, xref.