The Nissan Path

I have a 98 pathy with a factory tape radio and cd player and have been scratching my head trying to figure out what in the world does this button do?? To the left of the clock button is a changer button and above a up and down arrows I can only use 1 cd at a time so this leaves me wondering what in the world is this button for??
is this for an aftermarket cd changer and if so how come I can find it in my pathy??
or does this changer button have no purpose at all HELP PLEASE[/list][/list]

is it possible that your model had an option of a cd changer that went in the rear cargo area and this is how you would control it ?