search-spaces-regexp

search-spaces-regexp is a variable defined in `C source code'.
Its value is

nil

Documentation:
Regexp to substitute for bunches of spaces in regexp search.
Some commands use this for user-specified regexps.
Spaces that occur inside character classes or repetition operators
or other such regexp constructs are not replaced with this.
A value of nil (which is the normal value) means treat spaces literally.