Long standing problem with Vedic tone markers and post-base visarga/anusvara

[James Kass via Unicode]

On 2019-12-21 6:27 AM, Shriramana Sharma via Unicode wrote:
> However, even the simplest Vedic sequence (not involving Sama Vedic or
> multiple tone marker combinations) like दे॒वेभ्य॑ः throws up a dotted
> circle, and one is expected (see developer feedback in that bug
> report) to input the visarga before tone markers, hoping the software
> is intelligent enough to skip over the visarga (or anusvara) place the
> tone marker over the preceding syllable correctly. Why it is necessary
> to put the visarga first in input only to have to skip over it in
> shaping is beyond me.
य॔ यॆ॔
य॔ः -- visarga last
यॆ॔ः -- "
यः॔ -- visarga before accent (U+0954)
यॆः॔ -- "

य॑ यॆ॑
य॑ः -- visarga last
यॆ॑ः -- "
यः॑ ---- visarga before svarita (U+0951)
यॆः॑ ---- "

U+0951 and U+0954 have canonical combining class of 230.  Putting 
VISARGA (CCC=0) after those CCC=230 marks generates the dotted circle 
for VISARGA.  Putting VISARGA before those CCC=230 marks generates the 
dotted circle for U+0954 but drops the dotted circle for U+0951.  In 
both cases where VISARGA comes before, the mark positioning is broken.  
(Mangal font, Win 7)

As far as I can tell, the simplest solution would be for the Indic 
shaping engines to suppress the dotted circle for VISARGA (or ANUSVARA) 
where appropriate.  Entering/storing VISARGA or ANUSVARA at the end of 
the syllable makes sense since that's where it goes, visually and logically.