1Regexp: (a{1,2}|ab){2} 2abab: Ok 3Regexp: ((1?[0-9]{1,2}|2[0-4][0-9]|25[0-5])\.){3}(1?[0-9]{1,2}|2[0-4][0-9]|25[0-5]) 4192.168.254.0: Ok 5