Good guide on VIM Scripting?

I've used VIM for 10+ years, but never really into VIM scripting (always subjectively beliving that this was one area where VIM was weaker than Emacs).

Recently, the realization "in a VIM script, I can execute normal mode commands" made my mind go "a-ha" and suddenly start realizing why parts of VIM script is the way it is.

normal ma10jd'a20kp

is much more elegant than

Marker m = currentLocation();
advanceLines(10);
Buffer b = delete(currentLocation(), m);
advanceLines(-20);
insertBuffer(b);

Now question is -- what's a good resource to learn vim scripting from?

Thanks!