bug#22038: 25.1.50; Character folding issues with isearch

[Stephen Berman <stephen.berman@gmx.net>]

On Sat, 28 Nov 2015 18:39:36 +0200 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Date: Sat, 28 Nov 2015 17:07:22 +0100
>> 
>> Issue 1: Please support having multiple characters match a single
>> string in searches, so that e.g. "ss" can match the German letter "ß".
>
> You mean, allow equivalent strings be of different length, I believe.

Yes.

> (That's the only way I could parse "multiple characters matching a
> single string".)  We will have that, but it won't allow "ss" to match
> "ß", unless you customize character-fold-table to include that.  The
> reason is that "ß" doesn't have any decompositions in the Unicode
> database, so the default character-fold-table doesn't include any
> expansions for it.

This suggests to me that basing character folding solely on character
decomposition is insufficient.  From a user's point of view I see no
reason why the search string "a" under character-folding matches "ä" but
not e.g. "æ".  Requiring a customization to get the latter strikes me as
a user-unfriendly crutch to work around a deficient implementation.  (I
don't know if it's easy to improve, I'm just giving my impression as a
user.)

Steve Berman