title: React Router - path with regular expression and parameter not equal to a string
body: <p>I'm trying to figure out what the path could be if there are condition:</p>
  <p>should match:</p>
  <pre><code>/app/project/37gfhdjf87
  </code></pre>
  <p>should not match:</p>
  <pre><code>/app/project/item
  </code></pre>
  <p>So, the idea is to create a path that would match a route only if its id not equal 'item'. I tried this one but it's not working:</p>
  <pre><code>/app/project/:id(^(?!item$))
  </code></pre>
  <p>I have the exception &quot;Invalid regular expression: /^/app/project/((?:[^/]+?))(^((?:?!item$)))(?:/(?=$))?(?=/|$)/: Nothing to repeat&quot;</p>
  <p>Upd. I can't control the order of routes that is why I need to distinguish them.</p>