Re: Questions about isearch

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

On Fri, 27 Nov 2015 16:55:45 +0000 Artur Malabarba <bruce.connor.am@gmail.com> wrote:

> On 27 Nov 2015 2:36 pm, "Eli Zaretskii" <eliz@gnu.org> wrote:
>> > It does for me. In this very buffer, if I isearch for 'f' I can get to
>> > the ligature above.
>>
>> Right, it does. I think I tried "ff", not "f". Is that supposed to
>> work?
>
> No. We don't support having multiple characters match a single string. 

Is this why "ss" does not match the German letter "ß"?  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?  (Though I actually think that may be the
preferred behavior for the search string "s" when searching German text,
in contrast to the search string "ss", which I think should be able to
find "ß".)

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.  I would expect these three search string either all to
match or all to fail to match all three composed character strings.

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",
etc. (also, "A" and "X" fail to match "℻").

Steve Berman