Requirement to support TTML styling of a presentation processor

[andreastai]

At the moment a presentation processor must support some TTML styling. Discussing if other presentation mechanisms would also be allowed may be worthwhile. For example, a processor may translate a DAPT document to WebVTT so that a web browser can render it. In this case, the disposition of the styling features (#styling, styling-chained etc.) should be optional.

If the current semantics are kept, the following statement in the note of section 7.2 should be re-considered for clarification:

A presentation processor can also support additional rendering features from TTML2, such as styles for DAPT documents that use that.

In fact (at the moment) a presentation processor MUST support some sort of TTML2 styling.

[nigelmegitt]

In fact (at the moment) a presentation processor MUST support some sort of TTML2 styling.

What's the basis for this? I can't see it in TTML2, so I'm not sure where this comes from. Regardless, there are audio styling features for which processor support is required, so I think the requirement is actually met.

I think it's arguable whether a translation of DAPT into WebVTT is a presentation process or a transformation one, since WebVTT is not in itself a presentation.

[nigelmegitt]

My thinking on this right now is to close with no spec change, but I'm not sure I've fully understood your point @andreastai .

[andreastai]

In fact (at the moment) a presentation processor MUST support some sort of TTML2 styling.

What's the basis for this? I can't see it in TTML2, so I'm not sure where this comes from.

The following feature are all marked as permitted and are therefore required for a transformation and a presentation processor.

• #styling-chained
• #styling-inheritance-content
• #styling-inline  
• #styling-referential