[ttml2] Pull Request: Clarify constraint on presence of xml:id (#989).

skynavga has just submitted a new pull request for https://github.com/w3c/ttml2:

== Clarify constraint on presence of xml:id (#989). ==
Closes #989.

See https://github.com/w3c/ttml2/pull/1162

Received on Sunday, 22 September 2019 03:59:18 UTC