Documenting req.route in relation to route handlers vs middleware

[womcauliff]

This request for docs comes from expressjs/express#4193, where the person is trying to understanding why req.route is undefined.

The answer in response wrote:

That is a distinguishing feature between middlewares and routes; routes (like app.all) have a route (visible in req.route) and middlewares do not have a route.

I encountered a similar error to the person who raised the issue, and although I understand the high-level differences between middleware and a route handler, it hadn't occurred to me that the shape of the req object is different within a route handler vs within a middleware.

I believe the docs would benefit by explaining this as explicitly as the responder did in that issue thread.

[arnaudoff]

Same here. Please update the docs, I also wasted a lot of time trying to figure out what's wrong..