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

        let one_or_range = parts

            .next()

            .map(|s| {

                s.parse()

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

            })

            .transpose()?;

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

        Ok((Request::PlaylistInfo(one_or_range), ""))

    }

    fn parse_response(

        _parts: ResponseAttributes<'_>,

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

        unimplemented!()