I'm curious, in this example, what does MiddlewareResult::Next do?

  use feather::{App, AppContext, MiddlewareResult,Request, 
  Response};

  fn main() {
      let mut app = App::new();
      app.get("/",|_req: &mut Request, res: &mut Response, _ctx: &mut AppContext| {
              res.send_text("Hello, world!");
              MiddlewareResult::Next
      });
  
      app.listen("127.0.0.1:3000");
  }

Given my lack of experience, I'm sure it's needed, it's just unclear to me what purpose it would serve in a server app.