Hi, I am developing a regular expression that will test whether a string ends with test1234 or man2345. E.g.  coolguy/most/test1234 is invalid where as coolguy/most/testtest is valid. The pattern I have developed is coolguy/most/.*(?<!(test[0-9]{4}|man[0-9]{4})). But I am getting error "Look-behind group does not have an obvious ...