public function setOperator($pOperator = self::AUTOFILTER_COLUMN_RULE_EQUAL) {
		if (empty($pOperator))
			$pOperator = self::AUTOFILTER_COLUMN_RULE_EQUAL;
		if ((!in_array($pOperator,self::$_operators)) &&
			(!in_array($pOperator,self::$_topTenValue))) {
			throw new PHPExcel_Exception('Invalid operator for column AutoFilter Rule.');
		}
		$this->_operator = $pOperator;

		return $this;
	}