docs: def _highest_perm_from_iter(self, perm_iter):
          """Return the highest perm present in ``perm_iter`` or None if ``perm_iter`` is
          empty."""
          perm_set = set(perm_iter)
          for perm_str in reversed(ORDERED_PERM_LIST):
              if perm_str in perm_set:
                  return perm_str