protected function isGroupEdge($name, $row)
    {
        $result = array();
        foreach ($this->_groups[$name] as $column) {
            if ($column['start'] == $row) {
                $result['start'] = $row;
                $result['group'] = $column;
            }
            if ($column['end'] == $row) {
                $result['end'] = $row;
                $result['group'] = $column;
            }
            if (count($result)) break;
        }
        return $result;
    }