private Dataset dataset;
    
    /**
     * The series key.
     * 
     * @since 1.0.6
     */
    private Comparable seriesKey;
    
    /** The dataset index. */
    private int datasetIndex;
    
    /** The series index. */
    private int series;
    
    /** The tool tip text (can be <code>null</code>). */
    private String toolTipText;