code: public boolean enterFrame() {
          if (level++ > 0) {
              if (stack == null) stack = new LinkedList<T>();
              stack.add(get());
          }
          return set(initialValueFactory.create());
      }
docs: Provides a new frame for the variable.
  Potentially existing previous frames are saved.
  Normally you do not have to call this method manually as parboiled provides for automatic Var frame management.
  
  @return true