Suppose we have the following TTML document:
<tt xml:lang="en" xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling">
<head>
<layout>
<region xml:id="a"/>
<region xml:id="b"/>
</layout>
</head>
<body>
<div region="a">
<p region="b">abc</p>
</div>
</body>
</tt>
According to 9.3.2 Intermediate Synchronic Document Construction, what visual marks will be produced by regions a and b?
At first I was expecting a to produce nothing and b to produce abc, but the specification seems to contradict this implying that the anonymous span abc will be pruned (directly or indirectly) both when evaluating region a and b, which seems a bit counter-intuitive.
The algorithm prunes the content and nothing is displayed. This is captured on the W3C TTWG Issue tracker in Issue-341.
Why would you author a document with this behaviour though - I mean, what would you intend to happen? Under which conditions would you not achieve the same thing simply by removing the region reference from the div? I ask for interest - if there's a use case here then we can use it to help drive the spec development in TTML.