\d+(?=px)                    -> "120", "48"
foo(?!bar)                   -> "foo", "foo"
(?<=\$)\d+(?:\.\d\d)?        -> "19.99", "23"
(?<![\d$.])\d+               -> "3"
policy abcdefgh   -> false
policy Abcdefg1   -> true
policy Ab1        -> false
policy ABCDEFG1x  -> true
1,234,567
compiled  (?<=a+)b
compiled  (?<=a{1,9})b
rejected  (?<=(?:ab)+)c : Look-behind group does not have an obvious maximum length