Re: Clarification needed regarding tts:overflow

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
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<http://www.w3.org/TR/ttaf1-dfxp/#style-attribute-overflow>
>
>
>