Build, test, and debug regular expressions
Matches a 15-character Indian GSTIN (GST Identification Number). It validates the 2-digit state code, a PAN segment where the entity-type letter must be one of P, C, H, A, B, G, J, L, F, or T, followed by entity digit, the mandatory 'Z' suffix, and a check digit. Note: the character class includes commas as a likely oversight.