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[ttml2] base padding on CSS padding property

From: Nigel Megitt via GitHub <sysbot+gh@w3.org>
Date: Tue, 12 Sep 2017 14:45:59 +0000
To: public-tt@w3.org
Message-ID: <issues.opened-257070082-1505227549-sysbot+gh@w3.org>
nigelmegitt has just created a new issue for https://github.com/w3c/ttml2:

== base padding on CSS padding property ==
Part of umbrella #406 

Current semantic based on: XSL 1.1 §7.31.15 https://www.w3.org/TR/2006/REC-xsl11-20061205/#padding with writing mode relative padding values

Current CSS snapshot version of this semantic: CSS 2.1 §8.4 https://www.w3.org/TR/2011/REC-CSS2-20110607/box.html#padding-properties

The XSL spec references an earlier CSS spec to define the semantic. CSS does not use writing mode and direction dependent edge specifications, so we need to state that the following equivalents exist as defined at https://www.w3.org/TR/css-writing-modes-3/#logical-directions:

|TTML/XSL edge descriptor|CSS flow-relative edge descriptor|
|---------------------------|-----------------------------|
|before| block-start |
|end| inline-end|
|after| block-end|
|start| inline-start|

Actions to take: 

* replace XSL spec reference with CSS snapshot spec reference.
* describe that the edges in the TTML padding property are abstract edge equivalents as in the table above.
* include text to state that the abstract to physical mappings in https://www.w3.org/TR/css-writing-modes-3/#logical-to-physical apply, so that calculating the equivalent to, say, `padding-top` depends on the writing mode and the direction that apply locally.

Please view or discuss this issue at https://github.com/w3c/ttml2/issues/422 using your GitHub account
Received on Tuesday, 12 September 2017 14:45:53 UTC

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