refentry should be wrapped in article in DocBook output for man page

refentry is not a root-level tag. Therefore the current DocBook output for a man page does not validate against the DocBook 5 RELAX NG schema. The refentry should be wrapped in an article tag. There are several examples of this in the DocBook documentation. See https://tdg.docbook.org/tdg/5.0/refentry.html This differs from DocBook 4.5, which allows refentry as a root element.