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Re: [css-text] I18N-ISSUE-334: 'letter-spacing' and Indic

From: Koji Ishii <kojiishi@gluesoft.co.jp>
Date: Thu, 8 May 2014 18:08:51 +0000
To: Richard Ishida <ishida@w3.org>
CC: W3C Style <www-style@w3.org>, www International <www-international@w3.org>
Message-ID: <8BA83302-862D-4357-A4FF-949AB8B7C9FA@gluesoft.co.jp>
>>>> I would thus be careful about specifying that this bar should always
>>>> have visible gaps when letter-spacing is non-zero.
>>> 
>>> More practically in terms of how to word the spec when addressing this
>>> issue (if indeed we don't wish to specify that this bar should always have
>>> visible gaps): the spec might merely say where letter-spacing is applied
>>> (namely at syllable boundaries), without necessarily even mentioning the bar.  If
>>> gaps in the bar are mentioned, then the requirement might be on where gaps
>>> should/must not appear.
>> 
>> Hm, I agree to leave things that weíre not certain undefined.
>> 
>> Is the ďsyllable boundariesĒ different from the current grapheme cluster
>> definitions? If no, I suppose thereís no need to update the spec.
>> 
>> If different, is it possible to change Unicode grapheme cluster, or is
>> it something that letter-spacing point needs to be different from
>> grapheme cluster boundaries?
> 
> I have sent a note to the Indic Layout Task Force list asking for clarification, and will report back what they say.
> 
> My current understanding is that the units around which letter-spacing applies are different depending on which font is used. If the font indicates consonant clusters without showing the virama, then the unit is the whole consonant cluster plus vowel-signs, diacritics etc. This is very often likely to NOT coincide with extended grapheme clusters.
> 
> If the font does show the virama explicitly, then the stretching appears just after the virama.  I think that this DOES map to grapheme clusters as defined by Unicode.
> 
> As i said, I'll let you know if the indic experts get back to me to confirm this one way or another.

CSS Text already has this text:

> In some scripts such as Thai or Lao, the UA may apply the additional spacing within a character sometimes along with decompositions. In other scripts such as Myanmar, the UA may disallow applying the additional spacing between a specific pair of characters such as within a syllable.

and I donít think itís right to talk about the bar in CSS. On the other hand, I had informal conversation with Unicode folks but itís unlikely that Unicode defines letter-spacing point.

If we want to make this information available, I think itís best for the Indic Layout Task Force and I18N WG to publish a note, so that CSS can point to when itís available. Itís great if we could get something like JLREQ/KLREQ, but a note specifically for Indic letter spacing could also work, and I guess itís much easier to work on.

Is this reasonable?

/koji
Received on Thursday, 8 May 2014 18:09:45 UTC

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