Middleware runs just before a user request hits the destination server endpoint. In effect it intercepts the request. In Deno Fresh, you just create a `_middleware.ts` file in the `routes` directory. Add a handler there and Deno Fresh will apply it to all routes on your site. Let's day you have a /newsfeed route on your site that is always changing. If you wanted to add middleware there to set more appropriate caching headers, this is also easy. Just create a routes/newsfeed directory and place a `_middleware.ts` file in there. This middleware file will only apply to the newsfeed route and any child routes you might define.