docs: public Versioned<V> addChild(String name, V newValue, long newVersion) {
      DefaultDocumentTreeNode<V> child = (DefaultDocumentTreeNode<V>) children.get(name);
      if (child != null) {
        return child.value();
      }
      children.put(name, new DefaultDocumentTreeNode<>(
          new DocumentPath(name, path()), newValue, newVersion, ordering, this));
      return null;
    }