docs: def plot_shade_mask(ax, ind, mask, facecolor='gray', alpha=0.5):
      '''Shade across x values where boolean mask is `True`
  
      Args
      ----
      ax: pyplot.ax
          Axes object to plot with a shaded region
      ind: ndarray
          The indices to use for the x-axis values of the data
      mask: ndarray
          Boolean mask array to determine which regions should be shaded
      facecolor: matplotlib color
          Color of the shaded area
  
      Returns
      -------
      ax: pyplot.ax
          Axes object with the shaded region added
      '''
      ymin, ymax = ax.get_ylim()
      ax.fill_between(ind, ymin, ymax, where=mask,
                      facecolor=facecolor, alpha=alpha)
      return ax