在Visual Studio 2010中，如何在设计视图中使用母版页编辑aspx页面的内容？

I've noticed that whenever I add a new asp.net with a master page to a project, I am unable to edit it in the design view. I am able to see the master page content and an element that says ; however, I am unable to edit the content. I'd like to drop things in there and adjust their properties but I am unable to access them in the design view. How can I accomplish this?I've noticed that whenever I add a new asp.net