code: public static IterationBuilderOver over(Class<? extends WindupVertexFrame> sourceType, String source)
      {
          Iteration iterationImpl = new Iteration(new TypedNamedFramesSelector(sourceType, source));
          iterationImpl.setPayloadManager(new TypedNamedIterationPayloadManager(sourceType,
                      singleVariableIterationName(source)));
          return iterationImpl;
      }
docs: Begin an {@link Iteration} over the named selection of the given type. Also sets the name and type of the variable for this iteration's
  "current element". The type serves for automatic type check.