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Re: Clarification needed regarding tts:overflow

From: Glenn Adams <glenn@skynav.com>
Date: Fri, 1 Nov 2013 10:56:18 -0700
Message-ID: <CACQ=j+fzQ_grnvA-gbzuxPS96MtWKdBUBiy0=d9Db-4ReSsTwA@mail.gmail.com>
To: Andreas Tai <tai@irt.de>
Cc: public-tt <public-tt@w3.org>
On Fri, Nov 1, 2013 at 10:30 AM, Andreas Tai <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

> 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<http://www.w3.org/TR/ttaf1-dfxp/#style-attribute-overflow>
Received on Friday, 1 November 2013 17:57:07 UTC

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