code: public static void beginContext(ControlContainerContext context)
      {
          Stack<ControlContainerContext> contextStack = _threadContexts.get();
          if (contextStack == null)
          {
              contextStack = new Stack<ControlContainerContext>();
              _threadContexts.set(contextStack);
          }
          contextStack.push(context);
      }
docs: Defines the beginning of a new control container execution context.