Generate a reference to each of the block-level content elements in
        this cell, in the order they appear.

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