hover column graphael

I'm using the graphael bookstore to draw a line graph. I wanted the mouse to show the two values, x and y. In this case I can only display the value of y. How can I show both? Example: link

.hoverColumn(function () {
    this.tags = r.set();

    for (var i = 0, ii = this.y.length; i < ii; i++) {
        this.tags.push(r.tag(this.x, this.y[i], this.values).insertBefore(this).attr([{ fill: "#fff" }, { fill: this.symbols[i].attr("fill") }]));

    }, function () {
        this.tags && this.tags.remove();
        });