docs: def plot_factor_rank_auto_correlation(factor_autocorrelation,
                                        period=1,
                                        ax=None):
      """
      Plots factor rank autocorrelation over time.
      See factor_rank_autocorrelation for more details.
  
      Parameters
      ----------
      factor_autocorrelation : pd.Series
          Rolling 1 period (defined by time_rule) autocorrelation
          of factor values.
      period: int, optional
          Period over which the autocorrelation is calculated
      ax : matplotlib.Axes, optional
          Axes upon which to plot.
  
      Returns
      -------
      ax : matplotlib.Axes
          The axes that were plotted on.
      """
      if ax is None:
          f, ax = plt.subplots(1, 1, figsize=(18, 6))
  
      factor_autocorrelation.plot(title='{} Period Factor Rank Autocorrelation'
                                  .format(period), ax=ax)
      ax.set(ylabel='Autocorrelation Coefficient', xlabel='')
      ax.axhline(0.0, linestyle='-', color='black', lw=1)
      ax.text(.05, .95, "Mean %.3f" % factor_autocorrelation.mean(),
              fontsize=16,
              bbox={'facecolor': 'white', 'alpha': 1, 'pad': 5},
              transform=ax.transAxes,
              verticalalignment='top')
  
      return ax