fn parse_request(mut parts: std::str::SplitWhitespace<'_>) -> RequestParserResult<'_> {

        debug_assert!(parts.next().is_none());

        Ok((Request::GetVol, ""))

    }

    fn parse_response(

        parts: ResponseAttributes<'_>,

    ) -> Result<Self::Response, ResponseParserError> {

        let parts: HashMap<_, _> = parts.into();

        assert_eq!(parts.len(), 1);

        let volume = get_and_parse_property!(parts, "volume", Text);

        Ok(volume)

    }