private ObjectList rangeAxes;

    /** The range axis location. */
    private ObjectList rangeAxisLocations;

    /** Storage for the datasets. */
    private ObjectList datasets;

    /** Storage for the renderers. */
    private ObjectList renderers;

    /**
     * Storage for keys that map datasets/renderers to domain axes.  If the
     * map contains no entry for a dataset, it is assumed to map to the
     * primary domain axis (index = 0).
     */
    private Map datasetToDomainAxisMap;