private ObjectList rangeAxes;

    /** Storage for the range axis locations. */
    private ObjectList rangeAxisLocations;

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

    /** Storage for keys that map datasets to domain axes. */
    private ObjectList datasetToDomainAxisMap;

    /** Storage for keys that map datasets to range axes. */
    private ObjectList datasetToRangeAxisMap;