docs: def plot(self, x, y, xerr=[], yerr=[], mark='o',
               linestyle='solid', use_steps=False, markstyle=None, legend=None):
          """Add a data series to the plot.
  
          :param x: array containing x-values.
          :param y: array containing y-values.
          :param xerr: (optional) array containing errors on the x-values.
          :param yerr: (optional) array containing errors on the y-values.
          :param mark: the symbol used to mark the data point.  May be None,
              or any plot mark accepted by TikZ (e.g. ``*, x, +, o, square,
              triangle``).
          :param linestyle: the line style used to connect the data points.
              May be None, or any line style accepted by TikZ (e.g. solid,
              dashed, dotted, thick, or even combinations like
              "red,thick,dashed").
          :param use_steps: if True, draw a stepped plot.
          :param markstyle: the style of the plot marks (e.g. 'mark
              size=.75pt')
  
          The dimensions of x, y, xerr and yerr should be equal.  However,
          xerr and yerr may be empty lists.  Each element in xerr and yerr
          may be a single value for symmetric error bars, or a tuple of
          two values for assymetric errors.
  
          """
          if len(x) != len(y):
              raise RuntimeError(
                  'The length of the x and y coordinates should be equal')
          if (len(xerr) and len(xerr) != len(x) or
                  len(yerr) and len(yerr) != len(y)):
              raise RuntimeError(
                  'The length of the errors and coordinates should be equal')
  
          # clear the background of the marks
          self._clear_plot_mark_background(x, y, mark, markstyle)
          # draw the plot series over the background
          options = self._parse_plot_options(mark, linestyle, use_steps,
                                             markstyle)
          plot_series = self._create_plot_series_object(x, y, xerr, yerr,
                                                        options, legend)
          self.plot_series_list.append(plot_series)