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

  while if both writingMode and direction are specified on region, then the
> value of direction will override the WM's inline direction;

Style inheritance propagates direction="ltr" (the initial value) on
all elements (unless explicitly specified as "rtl" somewhere), thereby
overriding any right-to-left direction specified using writingMode on
region.

It sounds like the style resolution process should have an exception
for 'direction', which mimics XSL (7.29.1 Second Bullet) and, whenever
writingMode is specified, also sets the value of 'direction' to the
horizontal direction implied by writingMode.

Best,

-- Pierre

On Sat, Nov 5, 2016 at 2:03 PM, Glenn Adams <glenn@skynav.com> wrote:
> yes; i.e.,
>
> if region specifies writingMode but not direction, then direction on region
> is initialized to the WM's inline direction; while if both writingMode and
> direction are specified on region, then the value of direction will override
> the WM's inline direction;
>
> we should probably note this in TTML
>
>
> On Sat, Nov 5, 2016 at 2:09 PM, Pierre-Anthony Lemieux <pal@sandflow.com>
> wrote:
>>
>> Hi Glenn,
>>
>> Ok. To determine precedence between tts:writingMode and tts:direction,
>> the following prose from XSL 7.29.1 applies, right?
>>
>> """To insure consistency with the "writing-mode" property, the
>> "direction" property is initialized to the value that sets the same
>> inline-progression-direction as is set by the "writing-mode" property
>> whenever that "writing-mode" property sets that direction. If the
>> "direction" property is explicitly specified on the same formatting
>> object the value of the "direction" property will override the
>> inline-progression-direction set by the "writing-mode"."""
>>
>> Best,
>>
>> -- Pierre
>>
>> On Sat, Nov 5, 2016 at 8:43 AM, Glenn Adams <glenn@skynav.com> wrote:
>> >
>> >
>> > On Sat, Nov 5, 2016 at 12:19 AM, Pierre-Anthony Lemieux
>> > <pal@sandflow.com>
>> > wrote:
>> >>
>> >> Hi Glenn,
>> >>
>> >> Thanks! So is writingMode="rltb" in TTML equivalent to {writing-mode:
>> >> "horizontal-tb", direction: "rtl"} in CSS? In other words,
>> >> writingMode="rltb" sets the default to default paragraph embedding
>> >> level to "RTL" just as {direction: "rtl"} does?
>> >
>> >
>> > Yes. But keep in mind that WM applies at a higher context (region) than
>> > direction (p/span). So it can be viewed as a special case of semantic
>> > inheritance.
>> >
>> >>
>> >>
>> >> Best,
>> >>
>> >> -- Pierre
>> >>
>> >> On Fri, Nov 4, 2016 at 11:00 PM, Glenn Adams <glenn@skynav.com> wrote:
>> >> >
>> >> >
>> >> > 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
>> >> >>
>> >> >
>> >
>> >
>
>

Received on Wednesday, 9 November 2016 01:30:32 UTC