outerPadding (padding) {
        if (!arguments.length) {
            return this._outerRangeBandPadding();
        }
        return this._outerRangeBandPadding(padding);
    }
Get or set the outer padding on an ordinal bar chart. This setting has no effect on non-ordinal charts.
Will pad the width by `padding * barWidth` on each side of the chart.
@param {Number} [padding=0.5]
@returns {Number|BarChart}