public function required($required = null) {

		if(false === is_bool($required) && null !== $required) {
			return trigger_error(sprintf('Argument 1 passed to %s() must be of the type boolean, "%s" given', __METHOD__, gettype($required)), E_USER_ERROR);
		}

		if(null === $required) {
			$required = true;
		}

		foreach($this -> getFieldnames() as $field) {
			$this -> required[$field] = $required;
		}

		return $this;
	}