[ttml2] Refine #extent-version-2 feature designator

palemieux has just created a new issue for https://github.com/w3c/ttml2:

== Refine #extent-version-2 feature designator ==
`#extent-version-2` feature is unusual as it both permits subordinate features and permit new attribute vocabulary.

This makes it difficult for profiles such as IMSC 1.1 to prohibit the new attribute vocabulary, without also prohibiting subordinate features.

Suggest factoring out the new attribute vocabulary into a `#extent-attribute-values-version-2` feature designator.

Please view or discuss this issue at https://github.com/w3c/ttml2/issues/693 using your GitHub account

Received on Friday, 9 March 2018 16:42:40 UTC