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

        let version = parts.next().ok_or(RequestParserError::UnexpectedEOF)?;

        let version = version

            .parse()

            .map_err(|_| RequestParserError::SyntaxError(0, version.to_string()))?;

        let window = parts

            .next()

            .map(|w| {

                w.parse()

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

            })

            .transpose()?;

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

        Ok((Request::PlChanges(version, window), ""))

    }

    fn parse_response(

        parts: ResponseAttributes<'_>,

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

        unimplemented!()