The easiest way to describe prototypes, in the movieclip sense, is that all of the current functions in a movieclip (stop() lineTo() etc.) are all prototypes, each movieclip has access to these functions.. lets say we define a function


movieclip.prototype.moveto = function(x,y){
this._x = x;
this._y = y;
}

then EVERY single movieclip in that timeline can call:

moveto(150,145);