code: def plot_prior_dates(self, dwidth=30, ax=None):
          
          if ax is None:
              ax = plt.gca()
          depth, probs = self.prior_dates()
          pat = []
          for i, d in enumerate(depth):
              p = probs[i]
              z = np.array([p[:, 0], dwidth * p[:, 1] / np.sum(p[:, 1])])  # Normalize
              z = z[:, z[0].argsort(kind='mergesort')]  # np.interp requires `xp` arg to be sorted
              zy = np.linspace(np.min(z[0]), np.max(z[0]), num=200)
              zp = np.interp(x=zy, xp=z[0], fp=z[1])
              pol = np.vstack([np.concatenate([d + zp, d - zp[::-1]]),
                               np.concatenate([zy, zy[::-1]])])
              pat.append(Polygon(pol.T))
          p = PatchCollection(pat)
          p.set_label('Prior dates')
          ax.add_collection(p)
          ax.autoscale_view()
          ax.set_ylabel('Age (cal yr BP)')
          ax.set_xlabel('Depth (cm)')
          ax.grid(True)
          return ax
docs: Plot prior chronology dates in age-depth plot