public function setI5Error($errNum, $errCat = I5_CAT_PHP, $errMsg = '', $errDesc = '')
    {
        // the array (eventually returned by i5_error()
        // likes to have both numeric and alphanumeric keys.
        $i5ErrorArray = array(0=>$errNum,     1=>$errCat,      2=>$errMsg,    3=>$errDesc,
            'num'=>$errNum, 'cat'=>$errCat, 'msg'=>$errMsg, 'desc'=>$errDesc);

        self::$_i5Error = $i5ErrorArray;
    }