Subject: Re: bug#26580: 25.1; inappropriate case folding while isearch-forward-regexp

From: Tino Calancha <[email-masked]>
Date: Fri, 21 Apr 2017 12:40:50 +0900

[email-masked] writes:

> 'M-C-s \A' matches both lower letter a and upper letter A.
> 'M-C-s [\A]' matches \ and lower letter a and upper letter A.
> 'M-C-s \cCa' matches 一a, but does not match 一A.

Thanks for the report.  I guess this is a feature.
A capital letter triggers a case sensitive search.  In your last example,
upper letter C turned on the case sensitive search.  It might be argue
if that should happen in this case.  I think the current way is handy.
Maybe we should mention about this in the `isearch-forward' docstring.

In the former examples the slash somehow prevents this to happen.  For instance,
if you don't escape 'A' in the first example, then the search will match just 'A'.

Try the following:
'M-C-s A' matches upper letter A.
'M-C-s [a\]' matches \ and lower letter a and upper letter A.
'M-C-s [A\]' matches \ and upper letter A.

'M-C-s \cca' matches 一a, and 一A.
'M-C-s \ccA' just matches 一A.
'M-C-s \cCA' just matches 一A.
'M-C-s \cCa' just matches 一a.

Of couse, you always can toggle the case sensitivity during
those searches with M-c:
'M-C-s A M-c' matches both lower letter a and upper letter A.
'M-C-s \cCa M-c' matches 一a, and 一A.

Regards,
Tino