Re: TTML2 anonymous inline region creation

On Tue, Oct 20, 2015 at 8:48 AM, Nigel Megitt <nigel.megitt@bbc.co.uk>
wrote:

> All,
>
> 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 ...
>

a minor correction since we introduced root style inheritance in ttml2:

initial values -> tt -> 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
> now"!
>
> Nigel
>
>
>
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