答案:因为在这种情况下，我们只是重新路由了对servlet的请求.如果还有其他内容，将会造成混乱.基本上，我们正在将一个子分支变为根的一个子分支，但是还有其他子分支.

Answer: Because in this case we are just rerouting the requests for the servlet. If there's any other content there will be confusion. We are basically moving a sub-branch to be a sub-branch of the root, but there are other sub-branches.