public function getPromotion($couponCode = null) {
		if ($this->getResponseType() != 'promotions') {
			throw new CheddarGetter_Response_Exception("Can't get a promotion from a response doc that isn't of type 'promotions'", CheddarGetter_Response_Exception::USAGE_INVALID);
		}
		if (!$couponCode && $this->getElementsByTagName('promotion')->length > 1) {
			throw new CheddarGetter_Response_Exception("This response contains more than one promotion so you need to provide the coupon code for the promotion you wish to get", CheddarGetter_Response_Exception::USAGE_INVALID);
		}
		if (!$couponCode) {
			return current($this->toArray());
		}
		$array = $this->toArray();
		return $array[$couponCode];
	}