{"ast_node_type":"function","tokens":[{"end":65,"kind":"keyword","start":0,"text":"fn"}]}
    fn is_label_valid_from_rib(&self, rib_index: usize) -> bool {
    /// Determine whether or not a label from the `rib_index`th label rib is reachable.
        let ribs = &self.label_ribs[rib_index + 1..];