The idea of the changeTrack module was to allow change tracking on any valid XLIFF element and its attributes. That being said, the changeTrack module is only defined at the <unit> level and so can only specify change tracking for elements and attributes at the <unit> level. Does it need to be defined at any other higher level? Opinions?
If not, then the checksum attribute should be defined as being used in "any XLIFF element within the scope of a <unit> that accepts attributes from any namespace" instead of just "any XLIFF element that accepts attributes from any namespace." Also, the example in this module for simple change tracking (which I believe will be the more commonly used version) uses the author and datetime attributes on , <target>, and <note> directly. So those two attributes should probably also be defined as used in "any XLIFF element within the scope of a <unit> that accepts attributes from any namespace" as well.
Thanks,
Ryan