title: Is middleware reserved subdir for Nodejs/express app?
body: <p>I have a few dumb question about middleware. I understand that middleware function in nodejs takes <code>req, res</code> and pass to <code>next</code> at the end for next function to be executed. The middleware runs at app, router, error handling and 3rd party. </p>
  
  <ol>
  <li>is the <code>middleware</code> for <code>exprss</code> ONLY?  Or it is common for any <code>nodejs</code> app.</li>
  <li>is the <code>middleware</code> subdir reserved for every nodejs or express app? </li>
  <li>Also is every file under <code>middleware</code> subdir automatically picked up and executed by the app? </li>
  </ol>