title: Regex to match 1 or 2 alphabets followed by 1 or 2 digits
body: <p>I need help forming a regular expression to check if the input string is ONLY of the pattern 1 or 2 alphabets (can be lower or uppercase) followed by 1 or 2 digits. Valid strings would be d1,d15,ha1,ha20 so on. </p>