code: function endChoice(stack) {
      if (stack._parentChoice) {
        var choice=stack._parentChoice;
        delete stack._parentChoice;
        delete stack._parentGroup;
        delete stack.groupCounter;
        var parentStack=choice._parentStack;
        delete choice._parentStack;
        
        return parentStack;
      }
      return stack;
    }
docs: if current stack is a choice's branch,return the original parent stack