rightYAxis (rightYAxis) {
        if (!arguments.length) {
            return this._rightYAxis;
        }
        this._rightYAxis = rightYAxis;
        return this;
    }
Set or get the right y axis used by the composite chart. This function is most useful when y
axis customization is required. The y axis in dc.js is an instance of a
[d3.axisRight](https://github.com/d3/d3-axis/blob/master/README.md#axisRight) therefore it supports any valid
d3 axis manipulation.

**Caution**: The right y axis is usually generated internally by dc; resetting it may cause
unexpected results.  Note also that when used as a getter, this function is not chainable: it
returns the axis, not the chart,
{@link https://github.com/dc-js/dc.js/wiki/FAQ#why-does-everything-break-after-a-call-to-xaxis-or-yaxis
so attempting to call chart functions after calling `.yAxis()` will fail}.
@see {@link https://github.com/d3/d3-axis/blob/master/README.md#axisRight}
@example
// customize y axis tick format
chart.rightYAxis().tickFormat(function (v) {return v + '%';});
// customize y axis tick values
chart.rightYAxis().tickValues([0, 100, 200, 300]);
@param {d3.axisRight} [rightYAxis]
@returns {d3.axisRight|CompositeChart}