[Updated: see below] Norman Walsh has just posted an unusual essay. The gist of it seems to be that the W3C (at some level) has decided to modify the xml:id specification (released only days ago as a Candidate Recommendation, as I mentioned here) — there is some other specification (not named) that has a bug, most likely an incorrect closed enumeration of all the possible attributes in the XML namespace. At some level, the W3C has decided that the attribute will be renamed to the unqualified xmlid to avoid upsetting the people who messed up the other spec.
Norm sounds mad, and I don’t blame him. I remember when I was on the original XML working group and we were ordered from above to rewrite the XML Namespaces spec substantially for extremely questionable reasons (mainly the ability to embed XML inside non-XML HTML documents for v3 browsers — seriously).
[Update: Norm has revised the essay, adding enough extra information to the essay to let us figure out the problem — it has to do with the interaction between the XML Canonicalization (C14N) and xml: attributes, where C14N mistakenly assumes that all xml: attributes should be automatically inherited. Here’s the official request to deal with the issue.
I had already mentioned the incompatibility with C14N in my first posting on xml:id, then forgot it completely when reading Norm’s essay. So far, this is just a dispute, not a done decision.]