Timed Text / CSS styling requirements

Dear CSS WG,

Following up from the request for horizontal review of TTML2 and also on an observation that mapping even some TTML1 styling permitted in the IMSC1 text profile is not straightforward, TTWG has created a wiki page<https://www.w3.org/wiki/TTML/CSSRequirements> [1] listing all the styling features in TTML2 and IMSC with their mapping to CSS where available, for review, with each classified as unsupported/partial mapping/direct mapping as appropriate.

Disclaimer: there may be some errors in understanding in which case the mappings might be inappropriately classified. Review comments/fixes welcome.

It's probably worth noting that the most important high level objective is for the styling requirements for subtitles and captions are supported in CSS.

In terms of specific issues TTWG is probably less concerned about syntactic differences than semantic ones, since any CSS based TTML implementation would need to map syntax in any case.

Thanks also to @dbaron<https://github.com/dbaron> for his email that began this assessment for us back in November.


This alignment requirement is also being looked at by TAG at https://github.com/w3ctag/design-reviews/issues/138<https://github.com/w3ctag/design-reviews/issues/138#issuecomment-317093817>


[1] wiki page: https://www.w3.org/wiki/TTML/CSSRequirements



Kind regards,


Nigel