Playing Frames Backwards

I have a movie clip that has a button within it. Basically all I want to do is, if the user clicks on the button, the movie will play the frames backwards until it gets to a 'stop' action.
Does anyone know how this could be done?

here's the basic approach
but you'll need to figure out the right syntax
for yourself

you need to combine an onenterframe event with a gotoandstop.prevframe

onenterframe performs the function each frame
prevframe takes the playhead back on frame each time