public function setGrouping($pGrouping = NULL) {
		if (($pGrouping !== NULL) &&
			(!in_array($pGrouping,self::$_dateTimeGroups)) &&
			(!in_array($pGrouping,self::$_dynamicTypes)) &&
			(!in_array($pGrouping,self::$_topTenType))) {
			throw new PHPExcel_Exception('Invalid rule type for column AutoFilter Rule.');
		}

		$this->_grouping = $pGrouping;

		return $this;
	}