[imsc] Pull Request: Constrain rh/rw on tts:extent and tts:position

palemieux has just submitted a new pull request for https://github.com/w3c/imsc:

== Constrain rh/rw on tts:extent and tts:position ==
Closes #445

See https://github.com/w3c/imsc/pull/452

Received on Monday, 3 September 2018 19:12:36 UTC