Thanks but I already wrote the code and after catching a couple gotchas with the validation tool it's fully compliant now.

My point was not that GPX is hard (it's not) but that when something is open source most of the time you have to put some elbow grease in it because no one is paid to make it polished.

FWIW, it took me less time to write the GPX export code than to look for a binary of the validation tool, fail, then launch WSL and compile the goddam tool.