Re: space in multiline interactive search / differences between Emacs 23 and 24

[Eli Zaretskii <eliz@gnu.org>]

> From: David Madore <david+news@madore.org>
> Date: Wed, 25 Jun 2014 15:13:57 +0200
> 
> Under Emacs 23 (at least as provided by my Ubuntu 14.04 LTS under the
> name emacs23 23.4+1-4.1ubuntu1), the interactive regexp search succeeds
> (i.e., the space character matches the ^J line separator) and the simple
> (non-regexp) interactive search fails (i.e., the space character does
> not match the ^J line separator).  Under Emacs 24 (24.3+1-2ubuntu1),
> it's exactly the other way around: the simple search succeeds (=space
> matches ^J) and the regexp search does not.
> 
> What is the reason for this difference, and why is it exactly opposite
> in Emacs 23 and Emacs 24?  (I couldn't find anything in the NEWS file.)
>  How can I configure whether space matches ^J in simple versus regexp
> interactive search?

From NEWS, under "Editing Changes in Emacs 24.3":

   ** Search and Replace

   *** Non-regexp Isearch now performs "lax" space matching.
   Each sequence of spaces in the supplied search string may match any
   sequence of one or more whitespace characters, as specified by the
   variable `search-whitespace-regexp'.  (This variable is also used by a
   similar existing feature for regexp Isearch.)

   *** New Isearch command `M-s SPC' toggles lax space matching.
   This applies to both ordinary and regexp Isearch.

   *** New option `replace-lax-whitespace'.
   If non-nil, `query-replace' uses flexible whitespace matching too.
   The default is nil.