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

[Bernard Massot]

Hello,

Here is a point on which Microsoft's OpenType specification disagrees
with Unicode specification: OT says nukta can follow a vowel in
Devanagari, whereas Unicode says nukta can only follow a consonant.

OT's definition of nukta states "alters the way a preceding consonant
(or matra) is pronounced". Then the regular expression that defines a
"consonant syllable" confirms it, and "vowel-based syllable" even
includes the possibility of having a nukta after an independent vowel.
A bit later we have "A nukta can be placed on a consonant, matra or
independent vowel". The Mangal Font (MS's Devanagari demonstration font)
has such glyphs.
On the other hand, in chapter 9.1 of Unicode standard, Devanagari
rendering rule R9 states "nukta sign, which modifies a consonant form".
Then "Combining Marks" paragraph says "[Nukta] is used to extend the
basic set of consonant letters".

I personally agree with Unicode. I've never seen a nukta following a
vowel, and linguistics books I've read on Indian scripts don't speak of
that. Can you think of any real world use of such a thing?
I think nukta can't follow a vowel in Devanagari, nor in Gujarati. It
probably stands for Gurmukhi as well.
-- 
Bernard Massot