Earlier quoted context omitted.
Why do you decided to use XML as the basic format?
XML is a standard format for markup (e.g. HTML). When XML is used where it shouldn't (object serialization) it adds complexity. Here it signals that creating a report is as simple (or at least as standard) as creating HTML. What other format you had in mind?
XHTML is maybe the most hated incarnation of HTML, and is no longer encouraged.