[Ogg a11y] Milestones 1&2 for video accessibility project

Silvia Pfeiffer silviapfeiffer1 at gmail.com
Thu Nov 27 03:16:31 PST 2008

On Wed, Nov 26, 2008 at 11:34 PM, Henri Sivonen <hsivonen at iki.fi> wrote:
> On Nov 26, 2008, at 13:48, ogg.k.ogg.k at googlemail.com wrote:
>> Unicode defines directionality for *some* ranges, in two "strengths".
>> This is what I use (through Pango). The directionality that can be set
>> in a Kate stream is used as a weak default only.
>> Now, a script may imply a default directionality too. Languages map in
>> a fuzzy way to scripts, so you could get a default directionality from the
>> language, I think.
>> So, directionality could be Unicode based if known from the text we're
>> parsing, then default to either script or stream declared directionality
>> if
>> not known.
> Markup-like formats should provide functionality corresponding to the dir
> attribute in HTML. Non-markup-like text formats should use LEFT-TO-RIGHT
> MARK and RIGHT-TO-LEFT mark to give the dominant direction of a block of
> text.
> I think text track formats in Ogg shouldn't specify their own directionality
> handling any further that HTML does and should defer to
> http://unicode.org/reports/tr9/ for the rest. Whether it's necessary to have
> exactly as much format-level directionality control as HTML, I'm not so sure
> about. (HTML has markup for declaring the dominant direction of a block
> (dir='...' on anything but <bdo>) and markup for overriding the intrinsic
> directionality of characters (<bdo dir='...'>).)

I quote from http://www.w3.org/TR/REC-html40/struct/dirlang.html#h-8.2.2 :

"The Unicode bidirectional algorithm requires a base text direction
for text blocks. To specify the base direction of a block-level
element, set the element's dir attribute. The default value of the dir
attribute is "ltr" (left-to-right text)."

So, HTML assumes a default "ltr" directionality. If we assume this,
too, we will not require a directionality field.

>> Could there be cases where one might want to override the directionality
>> (eg, render English r2l or Arabic l2r ?)
> I take it that you mean overriding the intrinsic directionality of
> characters. HTML, CSS and W3C TimedText provide this, but *I* can't think of
> legitimate captioning use cases off the top of my head.

So, Unicode characters have an intrinsic (or default) directionality?
I think this confirms it:
But I guess not every charset defines intrinsic directionalities for
its characters.

So, we could add a directionality attribute to provide a default
directionality for a charset, if that charset is not unicode.
Or we could just assume the default to be "ltr".

Is that logic correct?


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