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Re: Clarification needed regarding tts:overflow

From: Andreas Tai <tai@irt.de>
Date: Sat, 02 Nov 2013 17:00:13 +0100
Message-ID: <5275218D.5060509@irt.de>
To: Glenn Adams <glenn@skynav.com>
CC: public-tt <public-tt@w3.org>
Thanks Glenn for the clarification!

>
>
>     >From the TTML Spec:
>
>     "If the value of this attribute is visible [...] region
>     composition and layout must be performed as if the region's width
>     and height were unconstrained" [1]
>
>     >From my reading content that overflows the region extents the
>     "box" of the region.
>
>
> No. It merely goes outside of that box (and is not clipped by it).
>
>     That is different what is shown in the first example of
>     tts:overflow where the background color is only applied to the
>     contrained region extent. Only the text content is rendered
>     outside of the regions box.
>
>
> The size of the box should not be changed for the purpose of drawing 
> its background.

OK. Seems that I misunderstood it. But from the conversation I had with 
others I am not the only one. From my view the text marked in red (and 
'*') leads to this misreading. From my view it would be better to omit 
it (but possibly it is to late for a change).

"If the value of this attribute is|visible|, then content should not be 
clipped outside of the affected region*, and region composition and 
layout must be performed as if the region's width and height were 
unconstrained, but with a well-defined origin*. "


- Andreas


Am 01.11.2013 18:56, schrieb Glenn Adams:
>
> On Fri, Nov 1, 2013 at 10:30 AM, Andreas Tai <tai@irt.de 
> <mailto:tai@irt.de>> wrote:
>
>     I need some clarification regarding the tts:overflow [1] attribute
>     in TTML 1.0 (2nd edition).
>
>     1) Is this attribute only an indicator how presentation processors
>     should handle content that overflows a region?
>
>     In the description of the desired presentation behaviour for
>     "visible" and "hidden" the key word "should" and not "must" is used.
>     (This seems to reflect the usage of overflow in XSL 1.1 and CSS)
>
>
> Yes. I suspect we used "should not be clipped" because other semantics 
> outside the scope of interpreting this property may cause clipping.
>
>
>     2) Does tts:overflow "hidden" create a "dynamic sized region"
>     where width and height adopts to the size of the content?
>
>
> No. It simply behaves as if the region into which this content is 
> selected is unconstrained in width (or height) in the inline 
> progression dimension.
>
>
>     >From the TTML Spec:
>
>     "If the value of this attribute is visible [...] region
>     composition and layout must be performed as if the region's width
>     and height were unconstrained" [1]
>
>     >From my reading content that overflows the region extents the
>     "box" of the region.
>
>
> No. It merely goes outside of that box (and is not clipped by it).
>
>     That is different what is shown in the first example of
>     tts:overflow where the background color is only applied to the
>     contrained region extent. Only the text content is rendered
>     outside of the regions box.
>
>
> The size of the box should not be changed for the purpose of drawing 
> its background.
>
>
>     Furthermore I believe that if the constrain is meant in that way
>     it is not compatible with CSS.
>
>
> I'm not sure what you mean here. Could you be more precise, and 
> provide an example (in both TTML and HTML/CSS)?
>
>
>     - Andreas
>
>     [1] http://www.w3.org/TR/ttaf1-dfxp/#style-attribute-overflow
>
>
>


-- 
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Andreas Tai
Production Systems Television IRT - Institut fuer Rundfunktechnik GmbH
R&D Institute of ARD, ZDF, DRadio, ORF and SRG/SSR
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Phone: +49 89 32399-389 | Fax: +49 89 32399-200
http: www.irt.de | Email: tai@irt.de
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Received on Saturday, 2 November 2013 16:01:10 UTC

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