<ul>
                            <li>a - Represents an alpha character (A-Z,a-z) - Only allows letters to be entered. </li>
                            <li>9 - Represents a numeric character (0-9) - Only allows numbers to be entered.</li>
                            <li>* - Represents an alphanumeric character (A-Z,a-z,0-9) - This allows both numbers and
                            letters to be entered.</li>
                        </ul>