public Comparable getSeriesKey() {
        return this.seriesKey;
    }

    /**
     * Sets the series key.
     *
     * @param key  the series key.
     *
     * @since 1.0.6
     */
    public void setSeriesKey(Comparable key) {
        this.seriesKey = key;
    }

    /**
     * Returns the series index for this legend item.
     *
     * @return The series index.
     *
     * @since 1.0.2
     */
    public int getSeriesIndex() {
        return this.series;
    }

    /**
     * Sets the series index for this legend item.
     *
     * @param index  the index.
     *
     * @since 1.0.2
     */
    public void setSeriesIndex(int index) {
        this.series = index;