bug#10869: 24.0.93; Index (elisp) `Regexp Special' for backslash syntax

["Drew Adams" <drew.adams@oracle.com>]

emacs -Q
 
C-h i ; choose Elisp
 
i backslash
 
Shows only these index entries:
 
backslash in character constant
backslash in strings
backslash in symbols
 
But it is vital for Emacs Lisp users to know about escaping backslashes
in Lisp strings intended to represent regexps: escape \ once for the
regexp syntax, and escape that again for the Lisp string syntax.
 
What's needed is an index entry for `(elisp) `Regexp Special', which
node explains:
 
 Note that `\' also has special meaning in the read syntax of Lisp
 strings (*note String Type::), and must be quoted with `\'.  For
 example, the regular expression that matches the `\' character is
 `\\'.  To write a Lisp string that contains the characters `\\',
 Lisp syntax requires you to quote each `\' with another `\'.
     Therefore, the read syntax for a regular expression matching `\'
 is `"\\\\"'.
 

In GNU Emacs 24.0.93.1 (i386-mingw-nt5.1.2600)
 of 2012-02-15 on MARVIN
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.6) --no-opt --enable-checking --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include'