How do you use townlong yak and similar resources?

[oddnecessity]

Hello, I've been lurking the addon development forums and I always see people mentioning these websites:

https://www.townlong-yak.com/globe/
and Github links to FrameXML like this one
https://github.com/Gethe/wow-ui-source/tree/classic

but I can't figure out how to use this stuff. Let's tackle this with an example:

I've been playing with frame:RegisterAllEvents() lately and I've noticed the event
PLAYER_STARTED_MOVING
How can I see if this event existed in the Classic Beta? What parameters go with it? Copy-pasting the event name into townlong-yak does not find anything. I've found websites like gamepedia and fandom to be outdated and unreliable.

give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime