dimension (dimension) {
        if (!arguments.length) {
            return this._dimension;
        }
        this._dimension = dimension;
        this.expireCache();
        return this;
    }
**mandatory**

Set or get the dimension attribute of a chart. In `dc`, a dimension can be any valid
{@link https://github.com/crossfilter/crossfilter/wiki/API-Reference#dimension crossfilter dimension}

If a value is given, then it will be used as the new dimension. If no value is specified then
the current dimension will be returned.
@see {@link https://github.com/crossfilter/crossfilter/wiki/API-Reference#dimension crossfilter.dimension}
@example
var index = crossfilter([]);
var dimension = index.dimension(pluck('key'));
chart.dimension(dimension);
@param {crossfilter.dimension} [dimension]
@returns {crossfilter.dimension|BaseMixin}