TTML 1.0 (Editorial)
TTML 1.0 Test Suite
TTML IMSC 1.0
TTML IMSC 2.0
TTML Simple Delivery Profile for Closed Captions (US)
Frans de Jong
Loretta Guarino Reid
Philippe Le Hégaret
The current text specifies that for extent (which maps to width and height)
"If the value of this attribute is auto, then the initial value of the style property must be considered to be the same as the extent of the Root Container Region."
I'm not sure if this is what XSL:FO would do, but this behavior conflicts with the value auto in CSS, which works in concert with top, bottom, left and right to satisfy the constraint that, for example (ignoring margin etc for now):
'left' + 'width' + 'right' = width of containing block
If only origin is given we have the situation that both width and right would be auto, which according to CSS would give: width = shrink-to-fit and solve for 'right'
This in my mind would actually be much more useful behavior than the current specified behavior (although is a breaking change), especially in the case where origin is non zero.
shrink-to-fit width is: min(max(preferred minimum width, available width), preferred width).
If we don't do this, at minimum we have to have some rules here that explain why right, bottom should not be considered to have default = auto (but presumably zero in this case)
But my preference would be to adopt the shrink to fit concept when width/height is auto. I also believe we should consider extending extent to allow optional additional values to set right and bottom.
If we want to preserve the existing behavior for backwards compat, we might consider some kind of parameter that allows the setting of the assumed right position, this would also help with line-stacking etc too.
Add notes (no markup allowed, URIs get automatically hyperlinked):
Fixed. https://dvcs.w3.org/hg/ttml/rev/70165fde28e1 (see 9.3.3 step 5)