[Harfbuzz-indic] Unicode vs OpenType: nukta after halant

[Bernard Massot]

Hello,

Another point on which Microsoft's OpenType specification disagrees
with Unicode specification: OT says nukta can follow a halant (or a
vedic sign) in Devanagari, whereas Unicode says nukta must appear before
a halant.

OT states "Reorder marks to canonical order: Adjacent nukta and halant
or nukta and vedic sign are always repositioned if necessary, so that
the nukta is first.". By the way OT's specification is
self-contradicting since syllable regular expressions don't allow that.

On the other hand, in chapter 9.1 of Unicode standard, Devanagari
rendering rule R9 states "The nukta sign is placed immediately after the
consonant in the memory representation. If the consonant represents a
dead consonant, then NUKTA should precede VIRAMA in the memory
representation.".

I seems clear to me that when a consonant both has a nukta and a halant,
nukta must come first. If a nukta follows a halant, a dotted circle
glyph should be inserted before it. Moreover encouraging people not to
be cautious with character order (by visually correcting their mistake
instead of displaying an ugly dotted circle) could make indexing,
searching, sorting, etc., of Indic text fail.
As far as vedic signs are concerned, OT's saying doesn't even make much
sense since vedic signs are used only with ancient Sanskrit, whereas
nukta was invented afterwards to represent sounds alien to Sanskrit.
They should never occur together.
-- 
Bernard Massot