[HarfBuzz] Tai Tham NGA, SAKOT is not Kinzi

[Richard Wordingham]

On 7 January 2013, Behdad Esfahbod replied to Theppitak Karoonboonyaan:

>> - Final NGA (U+1A59) with virama following is not reordered after
>>   the next base consonant (at the end of line 4).

> Oh, that's new.  We need to figure out how to implement that.  That
> one will be tricky.

If it has now been implemented for Tai Tham, please reverse it.  It does
*not* represent kinzi.  The sequence occurs as normal NGA with a
subscript consonant in the 'Lanna-Thai Dictionary, Maefahluang
Volume' (MFL), e.g. in <U+1A48 TAI THAM LETTER HIGH SA, U+1A26 TAI THAM
LETTER NGA, U+1A60 TAI THAM SIGN SAKOT, U+1A25 TAI THAM LETTER LOW KHA>
'sangha'.  Indeed, <NGA, SAKOT, WA> can represent a phonetic initial
cluster in Northern Thai, and as in Burmese is written with a normal
NGA plus a subscript consonant.

A separate character exists for 'kinzi', U+1A58 TAI THAM SIGN MAI KANG
LAI.  It is regularly used for 'sangha' in the Tai Khuen articles in
'ᨡᩮᨾᩁᨭᩛᨶᨣᩬᩁᨩ᩠ᨿᨦᨲᩩᨦ / เขมรัฐนครเชียงตุง / Chieng Tung: Its Way of Life',
where the word is written <U+1A48, U+1A58, U+1A25>, with U+1A58
appearing midway between the base consonants.

Mai kang lai is written rather differently in Northern Thailand, and it
was proposed as separate character, at 1A5A, in the proposal with
Unicore reference L2/07007 and ISO reference ISO/IEC
JTC1/SC2/WG2/N3207R. Unfortunately, the ISO committee copy is no longer
on line.  I get the impression that in Thailand the symbol is in
transition from appearing above the second base consonant to appearing
above the first consonant.  I have a text book consistently showing it
on the first consonant, a text book showing between the two consonants,
and a text book consistently showing it on the second consonant except
in _tanglai_ 'all', 'many'.

The MFL explains that the symbol appears on the second consonant
and gives two examples starting <SA, MAI KANG LAI> in which the symbol
appears on the following consonant.  Neither word appears in the body
of the dictionary. The appearance in the MFL is best explained as there
being inhibiting factors which prevent it appearing on the second
consonant, such as a vowel above or SIGN RA.  However, in the body
of the dictionary, words starting <SA, MAI KANG LAI> are consistently
written with MAI KANG LAI above the SA!

A noteworthy example is Northern Thai _tanglai_ <LOW TA, MAI KANG
LAI, SIGN LA, AA, SAKOT, YA> 'all', 'many', where MAI KANG LAI
almost always starts above the initial consonant.  This may be because
SIGN LA is part of the same syllable as LOW TA.  The textbook showing
it between consonants shows it, in this case, between SIGN LA and the
vowel AA.

Is there a problem with supporting this variety in positioning?

Richard.