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ISSUE-310 (progressivelyDecodable needs hierarchical definition): Forward reference rule doesn't take into account child elements [TTML IMSC 1.0]

From: Timed Text Working Group Issue Tracker <sysbot+tracker@w3.org>
Date: Wed, 21 May 2014 11:10:53 +0000
Message-Id: <E1Wn4Q9-0001zM-Li@stuart.w3.org>
To: public-tt@w3.org
ISSUE-310 (progressivelyDecodable needs hierarchical definition): Forward reference rule doesn't take into account child elements [TTML IMSC 1.0]

http://www.w3.org/AudioVideo/TT/tracker/issues/310

Raised by: Nigel Megitt
On product: TTML IMSC 1.0

The definition of ttp:progressivelyDecodable [1] could be interpreted as describing an impossible scenario as it requires that no element references another element occurring later in the document. It does not define "later" to mean 'after the close tag'. 

Since the computed time for a content element may depend on the computed times of its children, and those children are defined later (bytewise) in the document than the opening tag this possibly unintended interpretation would result in all documents being invalid if progressivelyDecodable is "true".

However, if the "after the close tag" clarification is added then the concept becomes meaningless because validation would require waiting until </body> which would negate the utility of the attribute. Something needs to be added that references the hierarchical structure of the document when interpreting this attribute.

Incidentally there is also a typo somewhere because the attribute is described alternately as being in ttp: namespace and imsc: namespace, and both shouldn't be true.

[1] http://www.w3.org/TR/ttml-imsc1/#ttp-progressivelyDecodable
Received on Wednesday, 21 May 2014 11:10:59 UTC

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