extending Raphael.js: draggable paths

/*
    DRAGGABLE PATHS IN RAPHAEL
    hint: convert the x and y deltas into translate values which the path object understands
*/
Raphael.el.draggablePath = function(){
    this.attr({cursor: "move"});
    this.drag(
        function(dx,dy){
          this.translate(dx - this.odx, dy - this.ody);
          this.odx = dx;
          this.ody = dy;
        },
        function(){
            this.odx = 0;
            this.ody = 0;
            this.attr({opacity: 0.4});
        }, 
        function(){
            this.attr({opacity: 1});
        });
    return this;
};