Normalise Tai Tham or not?

[Eli Zaretskii via Unicode]

> Date: Tue, 10 Oct 2017 21:51:55 +0100
> From: Richard Wordingham via Unicode <unicode at unicode.org>
> 
> > Emacs lately introduced character-folding in searches, but it's turned
> > off by default, as many users objected.
> 
> I don't see how that helps with this problem.  If I search for the
> Northern Thai word /kin/ with the low tone, which means 'smell', I want
> to find it whichever way round SAKOT and TONE-1 are, and I don't want to
> find /kin/ with the rising tone, which is implied by having no tone
> mark and means 'to eat'.

That's what this feature is supposed to allow, see char-fold.el in the
Emacs sources.