Position.GetWindowSize = function(w) {
	var width, height;
        w = w ? w : window;
        this.width = w.innerWidth || (w.document.documentElement.clientWidth || w.document.body.clientWidth);
        this.height = w.innerHeight || (w.document.documentElement.clientHeight || w.document.body.clientHeight);
        
        return this;
}