Do incremental search forward for regular expression.
With a prefix argument, do a regular string search instead.
Like ordinary incremental search except that your input is treated
as a regexp. See the command `isearch-forward' for more information.
In incremental searches, a space or spaces normally matches any
whitespace defined by the variable `search-whitespace-regexp'.
To search for a literal space and nothing else, enter C-q SPC.
To toggle whitespace matching, use `isearch-toggle-lax-whitespace'.