code: private static void join(StringBuilder buf, Node<PluralType> parent, String delimiter) {
      List<Node<PluralType>> nodes = parent.asStruct().nodes();
      int size = nodes.size();
      for (int i = 0; i < size; i++) {
        if (i > 0) {
          buf.append(delimiter);
        }
        print(buf, nodes.get(i));
      }
    }
docs: Print each child node of a struct, joining them together with a
  delimiter string.