On 25 Nov 2015 6:41 pm, "Eli Zaretskii" <eliz@gnu.org> wrote:
> 1. Character folding doesn't catch ligatures, such as æ (should it match
> the two characters "ae")?

I've no idea. It would be easy to add.
Those who use ligatures need to tell us whether that makes sense.

> 2. It also doesn't match ä (a single character) with ä (2 characters,
> which Emacs correctly composes into 1 grapheme cluster).  Should it?

Possibly. Since they look the same, might make things easier on users. But
I wouldn't know as I've never seen the second version used anywhere.

> 4. What is the equivalent of case-replace and the letter-case related
> behavior of replace commands to character folding?  E.g., if the
> replace command specifies to replace "foo" with "bar", and we found
> "föo", should we replace it with "bär" or something, by analogy with
> letter-case behavior?

I don't think we should do that. Case replacement makes sense because the
way you capitalize a word is frequently (though not always) independent of
the word itself. That's not the case with char folding. At least in
Portuguese, accents only go in very specific places, and I would _never_
want emacs to add an accent to the replacement text just because the word
being replaced happened to have an accent.