Update documentation for route layer usage

axum/src/docs/method_routing/route_layer.md

@@ -2,9 +2,12 @@ Apply a [`tower::Layer`] to the router that will only run if the request matches
 a route.
 
 Note that the middleware is only applied to existing routes. So you have to
-first add your routes (and / or fallback) and then call `route_layer`
-afterwards. Additional routes added after `route_layer` is called will not have
-the middleware added.
+first add your routes and then call `route_layer` afterwards. Additional routes
+added after `route_layer` is called will not have the middleware added.
+
+**Important**: The middleware is NOT applied to fallback handlers. Fallback handlers
+will run without the middleware applied. This is because `route_layer` only applies
+to matched requests, while fallbacks handle unmatched requests.
 
 This works similarly to [`MethodRouter::layer`] except the middleware will only run if
 the request matches a route. This is useful for middleware that return early
@@ -28,6 +31,6 @@ let app = Router::new().route(
 
 // `GET /foo` with a valid token will receive `200 OK`
 // `GET /foo` with a invalid token will receive `401 Unauthorized`
-// `POST /FOO` with a invalid token will receive `405 Method Not Allowed`
+// `POST /foo` with a invalid token will receive `405 Method Not Allowed`
 # let _: Router = app;
 ```

axum/src/docs/routing/route_layer.md

@@ -2,9 +2,12 @@ Apply a [`tower::Layer`] to the router that will only run if the request matches
 a route.
 
 Note that the middleware is only applied to existing routes. So you have to
-first add your routes (and / or fallback) and then call `route_layer`
-afterwards. Additional routes added after `route_layer` is called will not have
-the middleware added.
+first add your routes and then call `route_layer` afterwards. Additional routes
+added after `route_layer` is called will not have the middleware added.
+
+**Important**: The middleware is NOT applied to fallback handlers. Fallback handlers
+will run without the middleware applied. This is because `route_layer` only applies
+to matched requests, while fallbacks handle unmatched requests.
 
 This works similarly to [`Router::layer`] except the middleware will only run if
 the request matches a route. This is useful for middleware that return early
@@ -26,10 +29,11 @@ use tower_http::validate_request::ValidateRequestHeaderLayer;
 
 let app = Router::new()
     .route("/foo", get(|| async {}))
+    .fallback(|| async { "fallback" })
     .route_layer(ValidateRequestHeaderLayer::bearer("password"));
 
 // `GET /foo` with a valid token will receive `200 OK`
 // `GET /foo` with a invalid token will receive `401 Unauthorized`
-// `GET /not-found` with a invalid token will receive `404 Not Found`
+// `GET /not-found` with a invalid token will receive `200 OK` (fallback)
 # let _: Router = app;
 ```