India TAN Validator
Validate India Tax Deduction and Collection Account Numbers (TAN). QA.
How TAN validation works
The validator checks if the input is exactly 10 characters and matches the standard regex layout `AAAA11111A` (4 letters, 5 digits, 1 letter).
It evaluates the weighted Modulo 26 sum of the first 9 positions and confirms if the output maps to the 10th checksum letter.