<category> element represents
any category by which a topic might be classified for retrieval
or navigation. For example, the categories could be used to group
topics in a generated navigation bar. Topics can belong to multiple
Such classifications are likely to come from an enumerated or hierarchical set.
This element is equivalent to both
<Coverage> element and the
<Subject> element in Dublin Core.
See appendix for information about this element in OASIS document type shells.
The following attributes are available on this element: Universal attribute group .