How to enable whitespace insensitive mode of regular expression in PHP?

Question

I've tried "m" modifier,but not working:

$reg = '/...
        /m';

preg_match($reg,...,$match);

EDIT

Or maybe I need a modifier that can ignore white space like ENTER,TAB and so on. Because when I remove the white space in my regex it works.

EDIT AGAIN:

I need a modifier so that regular expression

"/aaaa b/",
"/aaaa
 b/"

are the same thing,say,it just ignores the white space in regex itself.

Answer 1

The modifier you need is x

print_r(preg_match('/aaa
        bbb/x', 'aaabbb'));