scrapy中编写下载器中间件类涉及的process_request(request, spider)的不同返回值的区别

Question

在阅读scrapy的文档中(http://doc.scrapy.org/en/1.1/topics/downloader-middleware.html) ,我了解到编写scrapy的下载器中间件需要实现process_request(request, spider)方法

对于返回request对象,文档中是这样描述的
If it returns a Request object, Scrapy will stop calling process_request methods and reschedule the returned request. Once the newly returned request is performed, the appropriate middleware chain will be called on the downloaded response.
我的疑惑是,在某个middleware返回了一个request,是会直接请求这个request还是会放入其他的middleware中继续处理.