prevFrame to move back more than just 1

programming flash
1 

btn.onRelease = function() {
	movie = "content";
	load();
};
function load() {
	if (this.mask._currentframe == 20) {
		//code to make this.mask run in reverse to frame 1
	}
	if (this.mask._currentframe == 1) {
		this.attachMovie(movie, movie, 0);
	}
}

I tried it this way


 btn.onRelease = function() {
 	movie = "content";
 	load();
 };
 function load() {
 	if (this.mask._currentframe == 20) {
 		this.mask.onEnterFrame = function() {
 			this.mask.prevFrame();
 }
 	}
 	if (this.mask._currentframe == 1) {
 		this.attachMovie(movie, movie, 0);
 	}
 }

but it didn’t seem to do the trick, any help is great appreciated!

D