[ttml1] Pull Request: Clarify semantics in absence of begin attribute

palemieux has just submitted a new pull request for https://github.com/w3c/ttml1:

== Clarify semantics in absence of begin attribute ==
Closes #224

See https://github.com/w3c/ttml1/pull/264

Received on Thursday, 23 November 2017 06:13:15 UTC