Re: Questions about isearch

[Eli Zaretskii]

> Date: Sat, 28 Nov 2015 00:04:33 +0000
> From: Artur Malabarba <address@hidden>
> Cc: emacs-devel <address@hidden>, Eli Zaretskii <address@hidden>
> 
> On 27 Nov 2015 9:18 pm, "Stephen Berman" <address@hidden> wrote:
> > > No. We don't support having multiple characters match a single string.
> >
> > Is this why "ss" does not match the German letter "ß"? 
> 
> Indeed. 

In fact, ß doesn't have a decomposition at all in the Unicode
database:

  (get-char-code-property ?ß 'decomposition) => 223

IOW, it "decomposes" into itself, an indication of no decomposition.

> > I assume the
> > reason "s" does not match "ß" is that the latter does not have a
> > decomposition including "s", whereas the decomposition of e.g. "ff" does
> > include "f", correct? 
> 
> Yes. 
> 
> > In fact, looking at the value of character-fold-table, it seems to me
> > that the current implementation of folding based on character
> > decomposition often yields surprising results: e.g. "f" matches not only
> > "ff" but also "㎙" and "ffl", but "m" and "l" fail to match the latter two,
> > respectively. 
> 
> This was by choice, and it would be trivial to change. Do others find it
> surprising? 

I do.  I think these should match.

> > Another shortcoming is that the decompositions do not respect
> > case-folding, e.g. "f" fails to match "ℱ" and "℻" (with case-folding
> > enabled), whereas "F" does match them, but fails to match "ff". 
> 
> True. This can be fixed, I think. Could you file a bug report so we don't
> forget? 

This should be fixed for v25.1 as well, I think.

Thanks.