codeigniter validation text length

$this->form_validation->set_rules('email', 'Email', 'trim|required|valid_email');

 $this->form_validation->set_rules('ratingMessage', 'Review message', 'trim|max_length[255]|max_length[10]');

 $this->form_validation->set_message('max_length', 'Message you have entered for %s is too long please try again!');