Had a very heartening day today: these are the things I learned how to do:

• Create directories, copy files, etc. using platform-independent calls.
• Read an XML file using the QXmlStreamReader object (which is rather like a sophisticated SAX parser, or perhaps a nodeIterator).
• Create a DOM document and save it to disk.

XML handling looks to be really easy and practical, and my little app is now able to load and save files correctly. All that's left for the trial app phase now is to figure out how to save and restore window geometry and state, and handle enabling/disabling actions.