{"ast_node_type":"other","tokens":[{"end":60,"kind":"keyword","start":0,"text":"for"}]}
        for &[a, b] in path_buf.array_windows::<2>().rev() {
        // reverse it to become `a <- b`, while preserving `claiming_node`.
            let SpantreeEdge { is_reversed, claiming_node, span_parent } = self.span_edges[a]