[ttml2] Question for region visibility

pkajdas has just created a new issue for https://github.com/w3c/ttml2:

== Question for region visibility ==
Hi!
I'm sorry if that is a lame question, I've started fiddling with TTML not that long ago.

And to the crux of the matter, let's consider such example:

```
<tt
    <head>
        <styling>
            <style xml:id="regionStyle" tts:backgroundColor="#000000"/>
        </styling>
        <layout>
            <region xml:id="myregion" style="regionStyle" tts:showBackground="whenActive"/>
        </layout>
    </head>
    <body>
        <div>
            <p  xml:id="p1" region="myregion">
                <span xml:id="s1" begin="00:00:00.120" end="00:00:01.880">
                    1
                </span>
            </p>
        </div>
    </body>
</tt>
```

The question is, what is the intended behaviour here regarding visibility (or, being active) of the instance of `myregion` bound to `p1` p element?
Spec (I'm using the one from https://www.w3.org/TR/ttml2/ ) says

> A region satisfies the whenActive case if (1) it is a temporally active region and (2) content is selected into the region, where that content is also temporally active.

The spec also says

> if the value is whenActive, then the background color of a region is rendered only when some content is flowed into the region.

Now, because there are no `begin` nor `end` attributes for `p1`, then does it say that instance of region bound to `p1` always satisfies (1)? And is it true that it satisfies also (2) (which is equivalent to "content flowing into region") if and only if `s1` is between its `begin` and `end` attributes' values? So that, as a result, region from `p1` should be visible if and only if the "1" from `s1` element?
I'm uncertain about satisfying point (2) above, because there is no region bound to `s1` (or if there is an implicit one, then how does it relate to `p1`'s ?).

Please view or discuss this issue at https://github.com/w3c/ttml2/issues/475 using your GitHub account

Received on Wednesday, 25 October 2017 10:14:59 UTC