.isValidRF()

.isValidRF() method checks if the given text is a valid RF creditor reference code. Method checks that the value is in alphanumeric format and contains a maximum of 25 characters. RF Creditor Reference is based on ISO 11649. The method also checks the following:

• The first two characters contains the identifier 'RF'
• The next two characters contains the check digit
• The rest of the characters contain alphanumeric characters forming the actual reference. 

In the reference section of RF, letters are converted into numbers and mod-97 operation is done to the reference in a numeric format. Result of this calculation will have to match the check digits indicated in position 3-4.