From: Richard Wordingham (richard.wordingham@ntlworld.com)
Date: Thu Feb 15 2007 - 17:31:33 CST
Philippe Verdy wrote on Thursday, February 15, 2007 10:28 PM
> Regarding the question of the validity of Thai sequences, the following
> specification of the Thai support in OpenType (here the HTML version
> available on Microsoft Typography website) is worth noting:
> http://www.microsoft.com/typography/otfntdev/thaiot/shaping.aspx
I don't know if those rules have been re-instated, but a tighter set was in
use for Windows XP. They were so tight that you couldn't type Pali and
Sanskrit, which was a nuisance for etymologies in on-line Thai dictionaries.
(The Thai Royal Institute's dictionary on-line resorted to using U+0E36 THAI
CHARACTER SARA UE for <U+0E34 THAI CHARACTER SARA I U+0E4D THAI CHARACTER
NIKHAHIT>, which actually isn't quite as bad as it seems. Outside
computing, it is legitimate to regard the former as being composed of the
latter pair.)
I'm pretty sure the corresponding Lao set at
http://www.microsoft.com/typography/OpenType%20Dev/lao/shaping.mspx has been
relaxed. They prohibit having multiple tonemarks on the same consonant, but
Tai Dam uses the tone mark U+00ECB MAI CATAWA on mid consonants to shift
from one set of tones to another. There's a list of problem sequences at
http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&item_id=ThaiLaoSeq
. Peter Constable of Microsoft is well aware of these problems and was
endeavouring to ensure there would be no such problems in Windows Vista.
I don't know whether Microsoft have dealt with the problem the old rules
imposed for Pali and Sanskrit in Lao. Of course, Pali and Sanskrit need the
missing consonants to be restored for Lao. I don't know how standard the
improper use of the unassigned code points in the Lao block is - I have had
some surprises looking at the Lao fonts that provide the unencoded
consonants. I had expected the encoding to be basically Thai + 0x80, though
that can't work for Indic NYA and YA.
Richard.
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