private static function addMessage($rule, $params) {

		if(false === is_string($rule)) {
			return trigger_error(sprintf('Argument 1 passed to %s() must be of the type string, "%s" given', __METHOD__, gettype($rule)), E_USER_ERROR);
		}

		if(false === is_array($params)) {
			return trigger_error(sprintf('Argument 2 passed to %s() must be of the type array, "%s" given', __METHOD__, gettype($params)), E_USER_ERROR);
		}

		if(false === isset($params[0])) {
			return trigger_error(sprintf('Params passed to %s() are not well formed', __METHOD__), E_USER_ERROR);
		}

		foreach(static :: $fieldnames as $fieldname) {

			if(false === isset(static :: $messages[$fieldname][$rule])) {
				static :: $messages[$fieldname][$rule] = [];
			}

			static :: $messages[$fieldname][$rule] = $params[0];
		}
	}