var $validation = array( 'field1' => array( 'get_rules' => array('max_tacos' => 75), ), 'field2' => array( 'get_rules' => array('max_tacos'), ), ... function _max_tacos($field, $param=5){ //field1 $param type is int, value is 75 //field2 $param type is string, value is '' }