bug#11309: 24.1.50; Case problems with [:upper:] and Cyrillic, Greek

[Mattias Engdegård]

8 dec. 2020 kl. 17.02 skrev Eli Zaretskii <eliz@gnu.org>:

> AFAIR characters that don't have an upper-case
> form map to themselves when downcased.  E.g.
> 
>  (upcase ?1) => ?1

This is not about the Lisp (upcase x) function but the C upcase(x) function, 
which uses the upcase table directly.
They affect the uppercasep and lowercasep functions which are used in the 
regexp engine. Thus we get uppercasep(ß)=lowercasep(ß)=false which is wrong.

The logic of 'lowercasep' may need to be changed because its use of upcase and 
downcase which return their argument if the respective table has no entry for 
it. Let's see what can be done.