I need to save/load data in the systems objects to/from XML files.
When I say objects, I mean C++ objects. (These generally correspond to
scene objects, but that consideration isn't important as far as
loading/saving goes.)

I think I have a reasonable grasp of XML, it's method of data
representation, and parsing XML files.
(At the moment I'm looking at using the expat XML parser for it's
callback...