public static function get_notes_returns() {
        return new external_single_structure(
            array(
                'notes' => new external_multiple_structure(
                    new external_single_structure(
                        array(
                            'noteid' => new external_value(PARAM_INT, 'id of the note', VALUE_OPTIONAL),
                            'userid' => new external_value(PARAM_INT, 'id of the user the note is about', VALUE_OPTIONAL),
                            'publishstate' => new external_value(PARAM_ALPHA, '\'personal\', \'course\' or \'site\'', VALUE_OPTIONAL),
                            'courseid' => new external_value(PARAM_INT, 'course id of the note', VALUE_OPTIONAL),
                            'text' => new external_value(PARAM_RAW, 'the text of the message - text or HTML', VALUE_OPTIONAL),
                            'format' => new external_format_value('text', VALUE_OPTIONAL),
                        ), 'note'
                    )
                 ),
                 'warnings' => new external_warnings('item is always \'note\'',
                        'When errorcode is savedfailed the note could not be modified.' .
                        'When errorcode is badparam, an incorrect parameter was provided.' .
                        'When errorcode is badid, the note does not exist',
                        'errorcode can be badparam (incorrect parameter), savedfailed (could not be modified), or badid (note does not exist)')
            )
        );
    }