bug#36923: Combining Diacritical Marks are not Latin only

[Juri Linkov <juri@linkov.net>]

>>   (aref char-script-table ?\N{COMBINING ACUTE ACCENT})
>>
>> could return
>>
>>   (latin greek cyrillic)
>>
>> instead of the current
>>
>>   latin
>
> char-script-table is documented to yield a single symbol, so returning
> a list would be an incompatible change, which we should avoid.

The docstring of char-script-table says:

  Char table of script symbols.
  It has one extra slot whose value is a list of script symbols.

So it seems char-script-table should yield a list of script symbols?

I searched more for char-script-table in the documentation, and one
place where it's used is forward-word.  But I don't understand why
forward-word doesn't stop between “COMBINING ACUTE ACCENT” (that is
the Latin script) and non-Latin letters.

This is good that it doesn't stop here, and I'm just trying to
understand why - so the same logic could be used in markchars-mode.
Maybe it doesn't stop because of special script handling in
‘find-word-boundary-function-table’?  Or because it ignores all
combining characters?

BTW, while looking at forward-word and right-word I noticed inconsistency:
there are left-word and right-word commands, but no left-sexp and right-sexp
to accompany forward-sexp.

> More generally, I think what you describe is a clear conceptual bug in
> markchars-mode: it should only pay attention to the script of the base
> characters, not to the script of combining accents.  The latter is
> mostly irrelevant, certainly so for the purpose of detecting
> confusables.

Could you suggest a proper function to strip all combining characters
from the string?