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Re: ISSUE-202: restoring metadata support to style element [TTML 1.0]

From: Andreas Tai <tai@irt.de>
Date: Thu, 04 Apr 2013 15:20:42 +0200
Message-ID: <515D7E2A.2030307@irt.de>
To: public-tt <public-tt@w3.org>, Glenn Adams <glenn@skynav.com>
I support the revert of this change. EBU-TT allows every TTML element to 
have one tt:metadata child (incl. tt:style). This change would makes 
EBU-TT/TTML documents that use this content structure not 
standard-compliant with TTML 1.0SE.

Best  regards,


Am 01.04.2013 03:36, schrieb Timed Text Working Group Issue Tracker:
> ISSUE-202: restoring metadata support to style element [TTML 1.0]
> http://www.w3.org/AudioVideo/TT/tracker/issues/202
> Raised by: Glenn Adams
> On product: TTML 1.0
> In a revision to TTML 1.0 between the last published CR [1] (on Feb 23, 2010) and the published PR [2] (on Sep 14, 2010), a technical change was made to make the content model for the <style/> element to be EMPTY instead of permitting metadata child elements (Metadata.class*). This change was described in the public TT reflector at [3], and the actual change can be seen in [4].
> Although that email [3] describes the change as non-substantive, I wonder now if that was actually the case. In particular, it changed the language to prevent the inclusion of metadata items as children of <style/> elements, while they had been permitted before this change.
> I'm raising the issue now because that change introduced an asymmetry regarding the ability to express metadata on non-metadata TTML vocabulary. Before this change, every non-metadata vocabulary item, even <br/>, permitted the use of metadata children. [N.B. This did not and does not hold for ttm:* vocabulary, since we did not want to have recursive metadata under ttm:* elements.]
> Our original intent was that an author should be able to add metadata as children to any non-metadata element. As such, I think the change to exclude metadata from <style/> should be reconsidered, and that ability restored. The original suggestion in [3] that the reason for making it EMPTY was to potentially permit #PCDATA children in the future does not seem well motivated, since there is nothing preventing that even if metadata children are permitted.
> The only question in my mind is whether to revert this earlier change in TTML 1.0SE or in TTML 1.1. It probably should not have been made between a CR and PR back in 2010, so we would be undoing that. However, one might argue undoing it would be a technical change, and that two wrongs don't make a right. I don't have a strong preference where we fix it, but I think we should fix it.
> [1] http://www.w3.org/TR/2010/CR-ttaf1-dfxp-20100223/
> [2] http://www.w3.org/TR/2010/PR-ttaf1-dfxp-20100914/
> [3] http://lists.w3.org/Archives/Public/public-tt/2010May/0000.html
> [4] http://dev.w3.org/cvsweb/2008/tt/spec/Attic/ttaf1-dfxp.xml.diff?r1=1.32;r2=1.33;hideattic=0;f=h

Andreas Tai
Production Systems Television IRT - Institut fuer Rundfunktechnik GmbH
R&D Institute of ARD, ZDF, DRadio, ORF and SRG/SSR
Floriansmuehlstrasse 60, D-80939 Munich, Germany

Phone: +49 89 32399-389 | Fax: +49 89 32399-200
http: www.irt.de | Email: tai@irt.de

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Received on Thursday, 4 April 2013 14:00:30 UTC

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