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

        let change = match parts.next() {

            Some(s) => VolumeValue::from_str(s)

                .map_err(|_| RequestParserError::SyntaxError(0, s.to_owned()))?,

            None => return Err(RequestParserError::UnexpectedEOF),

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

        Ok((Request::Volume(change), ""))

    }

    fn parse_response(

        parts: ResponseAttributes<'_>,

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

        debug_assert!(parts.is_empty());

        Ok(())

    }