[ttml2] Pull Request: Improve prose semantics for tts:showBackground (#498).

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

== Improve prose semantics for tts:showBackground (#498). ==
Closes #498.

See https://github.com/w3c/ttml2/pull/514

Received on Monday, 25 December 2017 22:31:50 UTC