Regex regex extension

^ $ Meaning representation corresponding start from here to the end of $ portion;

(:? Pattern) represents the combined pattern as part of a combination of items can be unified operations;

? 0 is repeated once or twice a

IP： (0-255).(0-255).(0-255).(0-255)

@"^(?:(?:(25[0-5])|(2[0-4]\d)|((1\d{2})|([1-9]?\d))).){3}(?:(25[0-5])|(2[0-4]\d)|((1\d{2})|([1-9]?\d)))$";