Distinguishing COENG TA from COENG DA in Khmer script

[Richard Wordingham]

On Sun, 28 Jun 2020 22:05:35 +0200
Kent Karlsson via Unicode <unicode at unicode.org> wrote:

> And indeed, if COENG DA and COENG TA are rendered the same by many
> but not all fonts supporting the Khmer script, it is impossible to
> reliably communicate things like ”the current spelling of the word is
> <some word written with COENG TA> but the traditional spelling is
> <same word written with COENG DA>” in plain or formatted text (even
> in formatted text the font selection is not very hard, there can be
> font substitutions) without resorting to images or extraneous
> explanations of which letters were actually used. That seems like a
> pity. The different rendering need not be such that (e.g., as here,
> COENG DA) it is the old one, but needs to be distinguishable by a
> reasonable reader at reasonable font size/resolution. It could be a
> ”modernized” rendering of COENG DA, or a more traditional one, but
> sufficiently clearly distinct from  the rendering of COENG TA (and
> distinct from other Khmer subscript letters); THAT would be a font
> difference. But at the point where ”original” COENG DA is rendered
> exactly the same as COENG TA, it is a spelling change, and should be
> treated as such.

One of the fonts that comes with Windows 10, Leelawadee UI, actually
makes a distinction.  (Marc Durdin pointed that out to me in
response to this thread.)  Its COENG DA leaves a wider gap with the base
consonant, and is vertically more compressed to compensate.  This is a
modern innovation, and to me seems similar in intent to the barely
perceptible difference between an open loop U+0067 LATIN SMALL LETTER G
and U+0261 LATIN SMALL LETTER SCRIPT G that another font makes.

That font looks like part of a move to change the encoding of modern
Khmer by replacing COENG DA by COENG TA.  That promises to be another
complication in transliterating Pali and Sanskrit between Indic
scripts. 

The visible spelling change seems to have been complete in Khmer by
1930, at least as far as printed material was concerned.  Does anyone
know if COENG TA and COENG DA have been distinguished if subscripts
were encoded separately?  Still, we are where we are.

Richard.