Re: Questions about isearch

[Eli Zaretskii <eliz@gnu.org>]

> From: Rasmus <rasmus@gmx.us>
> Date: Wed, 25 Nov 2015 20:20:20 +0100
> 
> > 1. Character folding doesn't catch ligatures, such as æ (should it match
> > the two characters "ae")?
> 
> In Danish I would not consider this a ligature, but a separate letter.  It
> can be written as ae, however.  Thus, it would probably be nice to match
> it via ’ae’.  But where to stop?  How about ’å’ (matched by ’a’)?  Should
> it be captured by "aa"?  Ø by ’oe’?  There’s also ’œ’...
> 
> Probably there’s lots of these weird cases.

Please read the node "Lax Search" in the Emacs manual.  That ship
sailed several months ago, and Emacs already supports "character
folding", and thus yes, 'a' matches 'å' (and also 'ä' and 'á' and 'ǎ'
and many others).  We don't make these matches language dependent,
because Emacs is a multi-lingual environment, and most text is not
tagged with a particular language.  So we use language-independent
folding, and AFAIU "ae" should have matched 'æ' under the rules we
use.  But it doesn't.  (Similarly "ff" and 'ff' and others.)

> > 2. It also doesn't match ä (a single character) with ä (2 characters,
> > which Emacs correctly composes into 1 grapheme cluster).  Should it?
> 
> This reminds me: UTF-8 "stroked through a" (a̶) is also displayed as ä
> rather than the stroke through a Emacs on my system.  But this is probably
> a different issue.

Display is a different issue, indeed.