{"ast_node_type":"function","tokens":[{"end":83,"kind":"keyword","start":0,"text":"pub(crate)"}]}
    pub(crate) fn add_element(&mut self, r: N, elem: impl ToElementIndex) -> bool {
    /// the element is newly added (i.e., was not already present).
        debug!("add(r={:?}, elem={:?})", r, elem);