I'm playing with coffee-mode for editing coffee-script, but I'm a total emacs newb.
In coffee-mode there are key bindings like "A-r" for compiling a buffer and "A-M-r" (I assume the "M" is meta) to open a coffeescript repl. However I can't find which key "A" refers to (it's really hard to google for A-).
I figured out the problem. "A-r" apparently is the command key and r on a mac!