docs: def add_series(self, values, **kwargs):
          """
          Adds a series to the chart.
          
          :param values: A :py:class:`xltable.Expression` object that evaluates to the data series.
          :param categories: A :py:class:`xltable.Expression` object that evaluates to the data series.
          :param name: Name to show in the legend for the series
          :param line: Line style, eg {'color': 'blue', 'width': 3.25} or {'none': True}
          :param marker: dict specifying how the markers should look, eg {type: square}.
          :param trendline: dict specifying how the trendline should be drawn, eg {type: linear}.
          """
          series = {"values": values}
          series.update(kwargs)
          self.__series.append(series)