From the parent's depth and the last labelled node, we obtain the node id and depth of a child.
get_next_depth_id(parent_node_id, env_ni)A list containing the id and depth of the next node.
The id of the parent node we are considering.
An environment object, possibly containing a data frame with columns id, name, call_status, arg_type and depth.
This is for internal use. It may be removed from user-view soon!