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 ...
>
>
> 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.
>

keep in mind that animation elements {animate, set} do not specify the
associated element to which animation applies; rather, they are associated
with an element either by context (in the case of an inline animation
element) or by the use of the @animate attribute on a content element;

so the content effectively points at the animation rather than the
animation pointing at content (or region) elements;


>
> 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 is already dealt with in step (5) [animation styling] of [1]

[1]
https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#semantics-style-resolution-processing-sss

though I see I need to update that step to handle references to out-of-line
animations;

note also that in the current specified style set algorithm, if multiple
specifications contribute to a given style, then the last one applied wins,
not the first one;


>
> 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.
>

in general, we have found it easier and more consistent to allow (at least
discrete) animation of all styles, even if one might not use them very
often (or ever); so i would not want to create an exclusion set here


>
> 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 …
>

the note under [2] indicates

"A content element
<https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#terms-content-element>
can
only be associated with a single region
<https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#terms-region>.
Consequently, if a content element
<https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#terms-content-element>
specifies
a region
<https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#layout-attribute-region>
attribute,
then any *implied inline region specification* or *explicit inline region
specification* is ignored. If the content element
<https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#terms-content-element>
does
not specify a region
<https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#layout-attribute-region>
attribute,
but it includes both an *implied inline region specification* and an *explicit
inline region specification*, then the former is ignored in favor of the
latter."

[2]
https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#semantics-inline-regions

there is an editorial note under [3] to add normative language that effects
the above informatively described semantics

[3]
https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml2/spec/ttml2.html#procedure-associate-region


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

perhaps we could introduce the ability for an inline animation to target
its region; i'll give this some thought


>
> Nigel
>
>
>
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