> First, the default behavior seems changed, and I'm not really aware
> (yet) of what exactly "char folding" is.  I did not found any definition
> for this, even if I have some ideas.

There's another thread here about hiding that string from the prompt. I
agree it's a little confusing, and char folding can be used without
flashing it on the user. Somebody offered to do something about it, though
I forget who.

> Second, I don't think the new default is right.  I prefer to search for
> text, not for regexps by default.  Otherwise, we could also invert `C-s'
> and `C-M-s', right?

Char fold search is a text search, not a regexp search. It does use a
regexp underneath, but that should be invisible to the user. You type some
text and it matches that text or similar texts.

> Finally, it *seems* buggy to me when using `C-w' to complete the search
> pattern (or shouldn't we use that anymore?).

I can't see your link on my phone, but if it's like you describe then it's
certainly a bug.
I'll try out your examples when I get home.