Mine

<?phpclass Register extends Guest_Controller {	function Register() {		parent::Guest_Controller();		$this->load->helper('form');		$this->load->library('validation');	}		function index() {		// Setup some rules.....		$rules['verify'] = "trim|xss_clean|callback_verify_checkbox";			$this->validation->set_rules($rules);.....	}		function verify_checkbox($str) {		if(!isset($str)) {			$this->validation->set_message('verify_checkbox', 'zomg error!');			return false;		} else {			return true;		}	}	}?>