The native name of Tai Viet script and language(s)

[Richard Wordingham via Unicode]

On Tue, 27 Aug 2019 04:56:35 +0000
Peter Constable via Unicode <unicode at unicode.org> wrote:

> The script _is_ related to Thai script, but I’m not sure I would say
> it has “the same origin as that of Thai language/script used in
> Thailand”, as that is too simplistic a view of the historic
> connections: it suggests that Thai script and Tai Viet developed
> directly from the same precursor, which isn’t really accurate.

Can you elaborate on that?  There seems to be a chasm when we reach
back beyond the Sukhothai script, which embodies a failed reform.
(There seems to be evidence that the writing system is not a 19th
century fake - motive and opportunity had seemed available.)
Incidentally, is there a consensus view on whether the Sukhothai script
is mostly encoded, and if so, in which Unicode script(s)?

What is true is that both Thai and Tai Viet use consonants to record
the difference between two sets of three tones (though later mergers
and splits can result in 3 + 3 = 5 or 3 + 3 = 7 = 6 = 5); this seems to
be a register difference as in Cham and still in a few Khmer dialects,
going back to an ancient voicing difference.

@Eli: Ideally, you need to check that default font and language are
consistent.  There are some regional differences which make it
necessary to calibrate the writing system, and one word may not suffice.

Richard.