bug#47534: Subject: 28.0.50; Regexp lower case pattern matches upper case

[dalanicolai <dalanicolai@gmail.com>]

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And here is a small patch for the docs

On Thu, 1 Apr 2021 at 12:27, dalanicolai <dalanicolai@gmail.com> wrote:

> Here is a small patch for the re-builder docstring. I hope I did things
> correctly...
>
> On Thu, 1 Apr 2021 at 10:12, dalanicolai <dalanicolai@gmail.com> wrote:
>
>> Ah thanks. I thought I used case sensitive replace-regexp before, but
>> probably I am mistaking then. Section "34.3 Regular Expressions"  of the
>> Emacs manual states that "[a-z]" or "[:lower:]" should match only lower
>> case, while it is not mentioned at all that it will not work by default
>> (case-fold-search as well as reb-toggle-case and reb-change-syntax are not
>> mentioned at all in that section as far as I can find). Indeed I was
>> referring to the docstring of re-builder. Anyway, I am happy to provide a
>> patch.
>>
>>
>>
>> On Thu, 1 Apr 2021 at 00:25, Basil L. Contovounesios <contovob@tcd.ie>
>> wrote:
>>
>>> dalanicolai <dalanicolai@gmail.com> writes:
>>>
>>> > When using the regexp builder and trying to match only lower case
>>> > letters (and spaces), Emacs also includes upper case matches.
>>>
>>> I think this is the effect of the user option case-fold-search, which
>>> defaults to non-nil (this is the case across most search-related parts
>>> of Emacs, including Isearch).  You can toggle it in re-builder
>>> specifically with C-c C-c (reb-toggle-case), or across all buffers by
>>> customising case-fold-search to be nil.
>>>
>>> > Also, I am unable to find in the manual any information about the
>>> > option of setting different syntaxes in the regexp builder
>>>
>>> I think most of the documentation for re-builder.el is in its commentary
>>> at the start of the file; see M-x find-library RET re-builder RET.
>>>
>>> I haven't used re-builder much, but from M-x customize-group RET
>>> re-builder RET I see there is a user option reb-re-syntax for
>>> controlling the default syntax.  C-h m in the re-builder buffer further
>>> reveals that the command C-c C-i (reb-change-syntax) can modify
>>> reb-re-syntax on the fly.
>>>
>>> > (also the option is not mentioned in the regexp-builder docstring). So
>>> > I would additionally like to report this as a documentation bug.
>>>
>>> Are you referring to the docstring of the re-builder command, or
>>> something else?  And is it a listing of key bindings you would like to
>>> see, or something else?  Would you like to provide a patch with
>>> suggestions for improvements?
>>>
>>> Thanks,
>>>
>>> --
>>> Basil
>>>
>>

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diff --git a/doc/lispref/searching.texi b/doc/lispref/searching.texi
index 16a8e56e90..05b81f0cd1 100644
--- a/doc/lispref/searching.texi
+++ b/doc/lispref/searching.texi
@@ -239,7 +239,7 @@ This variable is used by passing it as an argument to the function
   A @dfn{regular expression}, or @dfn{regexp} for short, is a pattern that
 denotes a (possibly infinite) set of strings.  Searching for matches for
 a regexp is a very powerful operation.  This section explains how to write
-regexps; the following section says how to search for them.
+regexps; the following section says how to search for them. By default Emacs
 
 @findex re-builder
 @cindex regular expressions, developing
@@ -251,6 +251,10 @@ matches in the target buffer are highlighted.  Each parenthesized
 sub-expression of the regexp is shown in a distinct face, which makes
 it easier to verify even very complex regexps.
 
+Note that by default Emacs search ignores case (@xref{Searching and Case}).
+To enable case-sensitive regexp search and match, set @code{case-fold-search}
+to @code{nil}.
+
 @menu
 * Syntax of Regexps::       Rules for writing regular expressions.
 * Regexp Example::          Illustrates regular expression syntax.