DST rules change all the time, all over the world. Any software that gets DST right today must be using a library. Even if you only look at the US, ten years ag

DST rules change all the time, all over the world. Any software that gets DST right today must be using a library. Even if you only look at the US, ten years ago Congress changed the dates that DST starts and ends and it wasn't a big deal. There's also many places in the US today that use permanent DST or permanent non-DST, so that's not even new, really.