g (gElement) {
        if (!arguments.length) {
            return this._g;
        }
        this._g = gElement;
        return this;
    }
Get or set the root g element. This method is usually used to retrieve the g element in order to
overlay custom svg drawing programatically. **Caution**: The root g element is usually generated
by dc.js internals, and resetting it might produce unpredictable result.
@param {SVGElement} [gElement]
@returns {SVGElement|CoordinateGridMixin}