docs: def _is_empty(self):
          """
          True if this cell contains only a single empty ``<w:p>`` element.
          """
          block_items = list(self.iter_block_items())
          if len(block_items) > 1:
              return False
          p = block_items[0]  # cell must include at least one <w:p> element
          if len(p.r_lst) == 0:
              return True
          return False