Added IBAN verification for Pakistani bank account using preg_match which intially checks for the pattern that is 'PK(2 check digits)(bank abbreviation--4 characters)(16 digits account number)' After that followed the steps:

1. Move the two alphabetic character country code and check digit pair from the front of the IBAN to back
2. Convert all alphabetic characters to numeric digits according to the standard character Conversion Table – ‘Annexure A’
3. Take modulus 97 of the number obtained in the above step, if this remainder is 1, then the IBAN is valid