you misunderstood the post 'qr' is a perl operated (standing for quoted regex), the regex is the part after the delimiter following qr ('/' in this case) up to the next non-escaped instance of the delimiter: [A-Za-z][A-Za-z0-9\.\-_]+. so basically a token identifier has to start with a letter, followed by letters, numbers, or the characters '.', '-' or '_'. hope that helps!