GNU bug report logs - #7267
23.1; regexp backslash-B matches word

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From: Glenn Morris <rgm <at> gnu.org>
To: "Thibault Kruse" <thibault.kruse <at> gmx.de>
Cc: 7267 <at> debbugs.gnu.org
Subject: bug#7267: 23.1; regexp backslash-B matches word
Date: Fri, 22 Oct 2010 22:49:27 -0400

"Thibault Kruse" wrote:

> According to emacs manual, \B matches the empty string, but it does not.

The elisp manual says:

Backslash Constructs in Regular Expressions
[...]

`\B'
     matches the empty string, but _not_ at the beginning or end of a
     word, nor at the beginning or end of the buffer (or string).

> start emacs with emacs -q --no-site-file
> move point over word in the splash screen.
> M-:
> (looking-at "\\B")
> minibuffer says: T, should say nil

Why do you think it should return nil?

This construct matches the empty string inside words.
It only returns nil at word boundaries. Try

(looking-at "\\B")

with point at the start, middle, and end of a word.
It returns nil, t, nil, as it should.

The empty string is _empty_, ie length zero, not whitespace or
anything like that.

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