+ * Find the next node matching an identifier.
+ *
+ * After a succesful call to ec_pnode_find() or ec_pnode_find_next(), it
+ * is possible to get the next node that has the specified id. There are
+ * 2 options:
+ * - continue the depth-first search where it was interrupted.
+ * - skip the children of the current node, and continue the depth-first
+ * search.
+ *
+ * @param pnode
+ * The root of the search, as passed to ec_pnode_find().
+ * @param prev
+ * The node returned by the previous search.
+ * @param id
+ * The node identifier string to match.
+ * @param iter_children
+ * True to iterate the children of "prev", false to skip them.
+ * @return
+ * The next node matching the identifier, or NULL if not found.