[ttml2] Define new feature designator for extent modifications, including measure

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

== Define new feature designator for extent modifications, including measure ==
TTML1 defines extent based on `<length>`
TTML2 defines extent based on `<extent>`. 
This requires a new feature designator.

I suggest (based on Glenn's input) to define the following:
- `#extent-measure`
- `#extent-image` (extent applies to `image`)
- `#extent-block` (special extent semantics for `div`/`p`)
- `#extent-version-2` as
   - `#extent`
   - `#extent-block`
   - `#extent-image`
   - `#extent-measure`

Please view or discuss this issue at https://github.com/w3c/ttml2/issues/582 using your GitHub account

Received on Friday, 19 January 2018 01:48:48 UTC