bug#22038: 25.1.50; Character folding issues with isearch

[Eli Zaretskii <eliz@gnu.org>]

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: 22038@debbugs.gnu.org
> Date: Sat, 28 Nov 2015 19:26:20 +0100
> 
> > Easiness is not the most important issue here: there's a more basic
> > problem involved.  Both "ß" vs "ss" and "æ" vs "a" (or "ae") are
> > language-specific: they are only valid matches in the context of
> > specific languages.  AFAIU, that is why they are not in the Unicode
> > database.  And we don't yet have language-specific text processing
> > capabilities and infrastructure (well, string-collate-lessp and
> > string-collate-equalp are a beginning, but only that).  So allowing
> > those by default risk running afoul of what users want.
> 
> I'm not sure what you mean by "only valid matches in the context of
> specific languages", but it sounds like what Per Starbäck said about "ä"
> being considered a completely separate character from "a" in Swedish,
> unlike in German.  Yet if this is a language-specific difference, Emacs
> doesn't respect it by default, since "a" does match "ä" under
> character-folding.  (Or does it fail to do so when
> current-language-environment is Swedish?  I suspect it doesn't.)

We simply go by the decompositions that the (language-agnostic)
Unicode database specified, and do not augment that by anything that
is only valid or relevant in the context of specific languages.

> But I know nothing about the Unicode specifications; maybe you are
> referring to a more subtle issue, which may be unrelated to my point,
> which is simply that I think it should be just as convenient for a user
> whose keyboard may lack "ß" or "æ" to match these characters by
> searching with "s" or "a" (or "e" or "ae") as it is to match "ff" by
> searching with "f".  This is not a language-specific issue AFAICS.

The character folding feature is primarily a feature of search, not a
convenience feature for typing characters, although it might double as
that.