title: Express app.get documentation
body: <p>I am looking for some documentation on the <code>app.get</code> function of express.js.</p>
  
  <pre><code>app.get(
      '/path', 
      middleware(),
      function(req, res) {
          res.redirect('/');
      }
  );
  </code></pre>
  
  <p>The example above takes three parameters. The normal docs only show two. I'm interested in what this middle param does and how to use it.</p>