TTML2 anonymous inline region creation


Right now in TTML2 if a style attribute is specified on a p element that
only has an effect on regions then an anonymous inline region is created.
The style attribute inheritance chain is:

>initial values -> anonymous region -> body -> div ... -> p -> span ...

In considering how to fix tts:disparity it occurred to me that this isn't
always what document authors might want or indeed expect.

Another idea that I'm considering is: change from creating an anonymous
inline region to creating an anonymous inline <set> element whose target
is the region that applies to the element on which it applies and whose
timing is coincident with the timing of the same element.

In case of temporally overlapping elements that set the same style
attributes to different values I would resolve the conflict using a
begin-time-then-document-order rule, where last one wins.

This would apply to the following style attributes that only have an
effect on regions: tts:disparity, tts:extent, tts:origin, tts:position and
tts:zIndex. I would probably exclude tts:displayAlign, tts:overflow,
tts:showBackground and tts:writingMode because changing those on the fly
would be weird.

I'm just thinking this through right now, not definitively proposing it.
The main thing I'm worried about is how the current solution interacts
with issue-341 and issue-368. Even if we do go down the route of creating
anonymous inline regions I imagine that authors will want a semantic like
"just like a template region but with the specified style attributes
differing", where the template region is the one that would have applied
in the absence of the region-based style attributes on the p. That would
also require a change to the inheritance chain, which would then be:

Initial values -> specified region (if any) ... -> anonymous region ->
body -> div … -> p -> span …

Any thoughts on this appreciated, even if they're "Aargh don't change it



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Received on Tuesday, 20 October 2015 14:49:14 UTC