bug#17130: 24.4.50; Deficient Unicode case folding

[Nathan Trapuzzano]

Eli Zaretskii <eliz@gnu.org> writes:

>> > What is "full Unicode case folding"?
>> 
>> Somthing that implements this:
>> http://www.unicode.org/Public/UNIDATA/CaseFolding.txt
>> 
>> And perhaps more.  I don't know, but someone on this list probably does.
>> 
>> If you look about a third of the way down, there's a line saying that
>> U+03C2 (ς) should fold into U+03C3 (σ).
>
> Patches are welcome to import those tables into Emacs, and make case
> folding support them.

Reading through the manual section on case tables, it seems that this
could be supported via the extra "canonicalize" slot:

    CANONICALIZE
      The canonicalize table maps all of a set of case-related
      characters into a particular member of that set.

If this isn't already used for Unicode case folding, what _is_ it used
for?