boxWidth (boxWidth) {
        if (!arguments.length) {
            return this._boxWidth;
        }
        this._boxWidth = typeof boxWidth === 'function' ? boxWidth : utils.constant(boxWidth);
        return this;
    }
Get or set the numerical width of the boxplot box. The width may also be a function taking as
parameters the chart width excluding the right and left margins, as well as the number of x
units.
@example
// Using numerical parameter
chart.boxWidth(10);
// Using function
chart.boxWidth((innerChartWidth, xUnits) { ... });
@param {Number|Function} [boxWidth=0.5]
@returns {Number|Function|BoxPlot}