[ttml1] Do tts:origin and tts:extent apply to the padded rectangle or the content rectangle? (c.f. XSL and CSS definitions)

palemieux has just created a new issue for 
https://github.com/w3c/ttml1:

== Do tts:origin and tts:extent apply to the padded rectangle or the 
content rectangle? (c.f. XSL and CSS definitions) ==
TTML specifies:

* _The tts:padding attribute is used to specify padding (or inset) 
space on all sides of a region area._
* _The tts:origin attribute is used to specify the x and y coordinates
 of the origin of a region area with respect to the origin of the Root
 Container Region._
* _The tts:extent attribute is used to specify the width and height of
 a region area (which may be the Root Container Region)._

The definition of `tts:padding` implies that padding is included in 
the region area ("inset"), and thus `tts:origin` is the top-left 
coordinate of the region rectangle including padding, and `tts:extent`
 is the width of the region including padding.

However, the semantics of `tts:padding` are based on XSL, which states
 that:

* "left" and other position attributes _set the position of the 
content-rectangle of the associated area_
* "width" and "height" _specify the content width/height of boxes_ 

Since the content-rectangle specifically excludes padding (Section 
4.4.1), XSL/CSS positioning and sizing do not include padding.

Do `tts:origin` and `tts:extent` apply to the padded rectangle or the 
content rectangle?

For instance, given a `<region>` with `tts:extent="100px 100px"`, does
 applying `tts:padding=20px` result in (a) a region with an effective 
`tts:extent="140px 140px"` or (b) an area available for text flow that
 is 60px by 60px?

Suggest defining "region area" explicitly in TTML and explicitly 
specifying relationship with XSL/CSS content and padding rectangles.
 

Please view or discuss this issue at 
https://github.com/w3c/ttml1/issues/221 using your GitHub account

Received on Sunday, 13 November 2016 00:35:57 UTC