{"ast_node_type":"variable","tokens":[{"end":37,"kind":"keyword","start":0,"text":"let"}]}
        let idx = self.subtree.len();
    fn enqueue(&mut self, subtree: &'a tt::Subtree<S>, contents: tt::iter::TtIter<'a, S>) -> u32 {
        let open = self.token_id_of(subtree.delimiter.open);