ringSizes (ringSizes) {
        if (!arguments.length) {
            if (!this._ringSizes) {
                this._ringSizes = this.defaultRingSizes();
            }
            return this._ringSizes;
        }
        this._ringSizes = ringSizes;
        return this;
    }
Get or set the strategy to use for sizing the charts rings.

There are three strategies available
* {@link SunburstChart#defaultRingSizes `defaultRingSizes`}: the rings get narrower farther away from the center
* {@link SunburstChart#relativeRingSizes `relativeRingSizes`}: set the ring sizes as portions of 1
* {@link SunburstChart#equalRingSizes `equalRingSizes`}: the rings are equally wide

You can modify the returned strategy, or create your own, for custom ring sizing.

RingSizes is a duck-typed interface that must support the following methods:
* `partitionDy()`: used for
  {@link https://github.com/d3/d3-hierarchy/blob/v1.1.9/README.md#partition_size `d3.partition.size`}
* `scaleInnerRadius(d)`: takes datum and returns radius for
   {@link https://github.com/d3/d3-shape/blob/v1.3.7/README.md#arc_innerRadius `d3.arc.innerRadius`}
* `scaleOuterRadius(d)`: takes datum and returns radius for
   {@link https://github.com/d3/d3-shape/blob/v1.3.7/README.md#arc_outerRadius `d3.arc.outerRadius`}
* `relativeRingSizesFunction(ringCount)`: takes ring count and returns an array of portions that
  must add up to 1

@example
// make rings equally wide
chart.ringSizes(chart.equalRingSizes())
// reset to default behavior
chart.ringSizes(chart.defaultRingSizes()))
@param {RingSizes} ringSizes
@returns {Object|SunburstChart}