Re: TTML writingMode vs CSS Writing Modes Level 3 writing-mode

On Fri, Nov 4, 2016 at 11:13 PM, Pierre-Anthony Lemieux <pal@sandflow.com>
wrote:

> Hi all,
>
> TTML allows both 'lrtb' and 'rltb' as values for writingMode, and
> references Section 7.29.7 at XSL.
>
> CSS Writing Modes Level 3 [1] states that both 'lr-tb' and 'rl-tb' (as
> defined in SVG) are both replaced by 'horizontal-tb'.
>
> Why would 'lr-tb' and 'rl-tb' be redundant?
>

They aren't (in XSL-FO or TTML), since they have the added effect of
indicating the default paragraph embedding level (of LTR or RTL) for all
content targeted to a region. Keep in mind that XSL-FO defined writing mode
before CSS3 WM took it up for consideration. Apparently, CSS3 WM prefers to
use the direction property and/or character properties exclusively for this
purpose.

In TTML, a paragraph's default embedding level can be influenced by the
computed value of tts:writingMode, the computed value of tts:direction, and
the character content of the paragraph.


>
> Thanks,
>
> -- Pierre
>
>