docs: def iter_block_items(self):
          """
          Generate a reference to each of the block-level content elements in
          this cell, in the order they appear.
          """
          block_item_tags = (qn('w:p'), qn('w:tbl'), qn('w:sdt'))
          for child in self:
              if child.tag in block_item_tags:
                  yield child