code: def locateChild(self, ctx, segments):
          
          result = self._getAppStoreResource(ctx, segments[0])
          if result is not None:
              child, segments = result, segments[1:]
              return child, segments
  
          if segments[0] == '':
              result = self.child_(ctx)
              if result is not None:
                  child, segments = result, segments[1:]
                  return child, segments
  
          # If the user is trying to access /private/*, then his session has
          # expired or he is otherwise not logged in. Redirect him to /login,
          # preserving the URL segments, rather than giving him an obscure 404.
          if segments[0] == 'private':
              u = URL.fromContext(ctx).click('/').child('login')
              for seg in segments:
                  u = u.child(seg)
              return u, ()
  
          return rend.NotFound
docs: Look up children in the normal manner, but then customize them for the
          authenticated user if they support the L{ICustomizable} interface.  If
          the user is attempting to access a private URL, redirect them.