Hi oXygen 8.2 supports both DocBook 4.4 and 5.0. According to Norm Welsh DockBook5 Definitive Guide [quote/unquote]: "The normative schema for DocBook V5.0 is the RELAX NG Grammar with its Schematron annotations. The only reason to use a DTD with DocBook V5.0 is if your editing environment (or other tool) requires one, for example, for syntax directed editing." The sample provided with oXygen 8.2 has this declaration: <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V5.0//EN" "http://www.oasis-open.org/docbook/xml/5.0/docbook.dtd"> Anyone knows what should be the proper DOCTYPE declaration if the document is to be based on the RNG. And is there any specific impact on transformation functions in that case? Thanks for help. ka