bug#17130: 24.4.50; Deficient Unicode case folding

[Nathan Trapuzzano <nbtrap@nbtrap.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> I know.  But if Emacs doesn't do Unicode folding, what is there other
>> than lower/upper variants?
>
> You can make it have whatever you like, because you can set up
> buffer-specific tables.

Makes me wonder if whoever implemented the CANONICALIZE slot had Unicode
folding in mind.

>> Finding the non-canonical variants is not something that happens (at
>> least in principle) during case-insensitive matching.
>
> The case database is not only for searching.
>
>> There is no reverse mapping when it comes to folding.  There can't be,
>> since multiple characters can fold into the same character.
>
> You can use the case of the string being replaced as guidelines.
> E.g., if the replaced string was capitalized, you can capitalize the
> replacement.

I think you're still conflating case conversion and case folding.  As I
said, there is no case called "fold".  There's just upper, lower, and
title.  And the fact that these three overlap is already a problem for
case-preserving replace.  I spent most of my last email trying to
explain this.