Regex Editor & Tester

Validates PHP DateInterval specification strings (ISO 8601 durations) such as P1Y2M3D, PT2H30M, or P1W, enforcing correct component ordering (Y→M→D/W, then T with H→M→S). Also accepts the alternate date-time form like 2020-12-31T23:59:59 with basic range checks on month, day, hour, minute, and second. Useful for validating input before passing it to PHP's DateInterval constructor.