Clarification needed regarding tts:overflow

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)

2) Does tts:overflow "hidden" create a "dynamic sized region" where 
width and height adopts to the size of the content?

 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. 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.

Furthermore I believe that if the constrain is meant in that way it is 
not compatible with CSS.

- Andreas

[1] http://www.w3.org/TR/ttaf1-dfxp/#style-attribute-overflow

Received on Friday, 1 November 2013 17:32:35 UTC