Analysis of TTML2 2nd Ed and test suite

Hi all,

I had a look at the list of changes in TTML2 2nd Ed (
https://www.w3.org/TR/2020/CR-ttml2-20200128/ttml2-changes.html). We have
13 syntax changes and 14 semantic only changes, for a total of 27. Thanks
to Glenn's work it's fairly easy to track the associated tests. Out of
these, 14 already have tests (corresponding to 50 new files, thanks to
Glenn again). 4 are marked as 'untestable'. We are left with 9 changes that
need review. Here they are:

Syntax Changes
* Add #presentation-audio feature designation (w3c/ttml2#1097).
* Add IMSC profile designators (w3c/ttml2#1123).
* Permit audio|image in body content model (w3c/ttml2#1125).

Semantic (Only) Changes
* Ignore text children of ruby container spans (w3c/ttml2#1077).
* Define shear value to degree mapping (w3c/ttml2#1094).
* Clarify media type parameters (w3c/ttml2#1099).
* Define font selection strategy used by line height algorithm
(w3c/ttml2#1106).
* Remove error condition from scaling procedure (w3c/ttml2#1109).
* Correct #extent-root-version-2 designation (w3c/ttml2#1110).

Glenn, does this match your analysis?

We could start populating the Implementation report with the 50 rows for
the 50 test files currently available, to determine the gap in terms of
implementation support.

Glenn, is there a script to generate these rows from the JSON "since:
"2e"" attribute?

Nigel, I noticed that we have 4 open PR on the test repo that we should
probably review and possibly merge or discuss at the next meeting.

HTH,
Cyril