A file is considered to be a DocBook 5 document when the namespace is http://docbook.org/ns/docbook.
The default Relax NG and Schematron schema, docbookxi.rng, for these documents is stored in [OXYGEN_DIR]/frameworks/docbook/5.0/rng/.
The default CSS files used for rendering DocBook content in Author mode is stored in [OXYGEN_DIR]/frameworks/docbook/css/.
The default XML catalog,catalog.xml, is stored in [OXYGEN_DIR]/frameworks/docbook/5.0/.
To watch our video demonstration about editing DocBook documents, go to http://oxygenxml.com/demo/DocBook_Editing_in_Author.html.