code: @Override
      public IterationBuilderVar as(Class<? extends WindupVertexFrame> varType, String var)
      {
          setPayloadManager(new TypedNamedIterationPayloadManager(varType, var));
          return this;
      }
docs: Change the name of the single variable of the given type. If this method is not called, the name is calculated using the
  {@link Iteration#singleVariableIterationName(String)} method.