[ttml2] Pull Request: Clarify support for R217 (#141).

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

== Clarify support for R217 (#141). ==
Closes #141.

See https://github.com/w3c/ttml2/pull/318

Received on Wednesday, 17 May 2017 19:10:59 UTC