Single-field validation is where regex starts. The pain begins when one pattern has to recognise a structure with several parts, some optional, some with alternatives, and hand back each part as a separate value. That is the job behind parsing access logs, pulling settings out of free-form config strings, or turning a vendor's "almost CSV" export into rows. Our gateway log parser had grown into one 230-character line where nobody could tell which group was the latency field. After rewr...