title: Notifications for any window events
body: <p>Currently I am using the following code to get notifications when applications are started or ended in OSX.</p>
  
  <pre><code>[[NSWorkspace sharedWorkspace] addObserver: self
                                 forKeyPath: @"runningApplications"
                                 options: NSKeyValueObservingOptionNew
                                 context: NULL];
  </code></pre>
  
  <p>This has worked really well so that my app is aware of the general state of the running applications in the system.  However now I'm wondering if I can go a level lower. What I would like is to be notified when any window in the system experiences a state change. If any window in the system is closed, minimized, resized, etc I would like my app to be notified.</p>
  
  <p>Is this possible? I am under the impression that my application really can only know these things about the windows that I own. But I figured it couldn't hurt to ask here.</p>
  
  <p>Thanks!</p>