code: public static IterationBuilderOver over(String source)
      {
          Iteration iterationImpl = new Iteration(new NamedFramesSelector(source));
          iterationImpl.setPayloadManager(new NamedIterationPayloadManager(singleVariableIterationName(source)));
          return iterationImpl;
      }
docs: Begin an {@link Iteration} over the named selection. Also sets the name of the variable for this iteration's "current element".