public function remove_row_group(Frame $group)
    {
        $key = $group->get_id();
        if (!isset($this->_frames[$key])) {
            return; // Presumably this row has alredy been removed
        }

        $iter = $group->get_first_child();
        while ($iter) {
            $this->remove_row($iter);
            $iter = $iter->get_next_sibling();
        }

        $this->_frames[$key] = null;
        unset($this->_frames[$key]);
    }