public function rating($value, $rating) {
		if (strpos($value, $this->baseUrl) === false && strpos($value, $this->httpsUrl) === false) {
			throw new InvalidArgumentException("You can only add a rating to an existing Gravatar URL");
		}
		else if (!in_array(strtolower($rating), $this->ratings)) {
			throw new InvalidArgumentException("Rating must be g,pg,r or x");
		}
		else {
			return $this->query($value, array("rating" => $rating));
		}
	}