Thanks, yes that's true Dave Wilson's doing great work.
One other resource I actually found very helpful, pitched just right, is Musa Al-hassy's Elisp Cheatsheet. It's short but it gets straight to the detail. If he ever wrote a book I'd prepreorder it.
https://github.com/alhassy/ElispCheatSheet/blob/master/Cheat...
[1] https://www.youtube.com/channel/UCAiiOTio8Yu69c3XnR7nQBQ