isValid method
function to check if the PAN has valid format or not.
returns true if the PAN has valid format.
Implementation
bool isValid(String? pan) {
if (pan == null || pan.length != 10) {
// PAN length is not 10
return false;
}
RegExp panRegEx = RegExp(r'[A-Za-z]{5}[0-9]{4}[A-Za-z]{1}');
return panRegEx.hasMatch(pan);
}