code: public Chunk<Step<T>> getOrCreateChunk()
     {
        Node node = childNode.getOrCreate("chunk");
        Chunk<Step<T>> chunk = new ChunkImpl<Step<T>>(this, "chunk", childNode, node);
        return chunk;
     }
docs: If not already created, a new <code>chunk</code> element with the given value will be created.
  Otherwise, the existing <code>chunk</code> element will be returned.
  @return  a new or existing instance of <code>Chunk<Step<T>></code>