XML Copy Editor

I'm juts trying out XML Copy Editor, v. 1.2.0.6, on Ubuntu 11.10. I thought it might be useful in editing docbook 5 documents. From File==>New, I select "DocBook 5.0b book (*.xml)", and I get a new document window with the framework of a book. So I run XML==>Validate==>DTD/XML Schema, and I get an error: Validation stopped at line 2, column 123: element 'html:form' is referenced in a content model but was never declared So I run XML==>Validate==>docbook, and I get an error: Error at line 3: Did not expect element book there I'd have expected the boilerplate document, unmodified, to validate. Any ideas as to what is going wrong?