Offtopic but I'm curious - how do you parse "he jumped off of the dock"? To me that would say he was on the dock and jumped off it (into water or whatever), so

Offtopic but I'm curious - how do you parse "he jumped off of the dock"? To me that would say he was on the dock and jumped off it (into water or whatever), so equivalent to "he jumped off the dock". I would parse it as "on" in a sentence like "he based his site off of facebook".