Version XML schema (don't discourage usage of XML namespaces)

[marcusmueller]

The docs prominently discourage the use of the xmlns specifier.

Which, as someone who's had to maintain a file format over multiple versions of my own software, under my own control have found to be a bad idea: Should you ever need to somehow non-compatibly modify what your XML entities actually mean and what is legal and what not, you have no way of telling whether a file is of the old or of the new format.

An xmlns hurts nobody, but allows for revision, and also for the really crucial disambiguation between different versions, especially on multiple platforms, with parsers you might not control; metainfo is undubitably a metadata format that should have archival qualities, and not versioning one's metadata schema is a big no-no of file format design.