I guess we'll need a number of iterations. Some observations:
- I read the nodeValue specification so that it raises DOMException if you try to set it, and it is "readonly", where I interpret "readonly" as "always null" (because it appears to be the only case where the value is never changing). So __setattr__ should raise that exception, IMO.
- I think that the checks for correct names should be moved out of the minidom module, into a more global place (because it might be useful independent of minidom), e.g. xml.names. See also xml.utils.characters in PyXML.
- Setting the xmlVersion to 1.1 should raise NOT_SUPPORTED_ERR IMO: we cannot guarantee that we will write out correct XML 1.1 (i.e. a document that is in Unicode normal form NFC).

More later.