Tips for Documenting an XML DTD  

XML-based development projects often require the development of a Document Type Definition (DTD), which defines the XML code used in an XML document or application. Even if you are customizing an existing DTD like the DocBook DTD, documenting the DTD is a best practice for a number of reasons, including:Providing documentation

Kelly, William T. TechRepublic (2003). Articles>Documentation>Programming>XML