tt-profile-registry

I have just been reading the current draft of the tt-profile-registry [1].
I'm afraid I have not given this document sufficient attention, and I now
find there are a number of problems, probably the most obvious being §4.2
which purports to "describe how to identify the profile of a given TTML
Document Instance for each profile in this Registry". This information is
misleading and needs immediate attention. In fact, I envision demoting §4.2
to an informative status (in this document), since, for example, it is in
direct conflict with TTML2 §5.2.4.3 [2], at least as currently written.

I will begin posting a few PRs shortly, so that we can have something
(more) to discuss on this subject next week.

[1] https://w3c.github.io/tt-profile-registry/
[2]
https://www.w3.org/TR/2018/PR-ttml2-20181004/#semantics-procedure-construct-effective-processor-profile