fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

        self.display(f, 0)

    }

    fn display(&self, f: &mut fmt::Formatter, depth: usize) -> fmt::Result {

        let span = self.0.clone().as_span();

        let rule = self.0.as_rule();

        let inner = self.0.clone().into_inner();

        let indent = "  ".repeat(depth);

        let children_possible = if let Some(len) = inner.size_hint().1 {

            len > 0

            true

        write!(

            f,

            span.start_pos().pos(),

            span.end_pos().pos(),

            span.as_str()

        )?;

        if children_possible {

            writeln!(f, ", [")?;

            for pair in self.0.clone().into_inner() {

                DisplayPair(pair).display(f, depth + 1)?;

            write!(f, "{indent}]),")?;

            write!(f, ")")?;

        if depth > 0 {

            writeln!(f)?;

        }

        Ok(())

    }