def is_docbook?(doc)
     dbns = doc.root.namespaces.default
     (!dbns.nil? && (dbns.href.casecmp(DOCBOOK_NS) == 0))
   end
def is_docbook?(doc)
     dbns = doc.root.namespaces.default
     (!dbns.nil? && (dbns.href.casecmp(DOCBOOK_NS) == 0))
   end
Check whether the document has a DocBook default namespace