title: Does iOS CALayer.zPosition NOT transcend view hierarchies?
body: <p>I have a phase in my app where I need to "sync" with a device. During this interval, I want to a) prevent the user from touching things and b) show some progress of the sync operation.</p>
  
  <p>I made a custom UIView that shows my percentage feedback and placed it in the view tree at the appropriate place. That solves (b).</p>
  
  <p>For (a), I simply slap a UIView over the top of everything</p>
  
  <pre><code>myController.view.addSubview(newView)
  </code></pre>
  
  <p>and manipulate it's alpha value. By using a semi-transparent color/alpha value, I can "gray out" the app.</p>
  
  <p>BUT, I wanted my feedback control to still show "full color". I <em>thought</em> I could simply adjust the <code>layer.zPosition</code> of said view to get it to draw "above" the masking/blocking/graying view.</p>
  
  <pre><code>myFeedbackView.layer.zPosition = 100.0
  </code></pre>
  
  <p>Unfortunately, this does not seem to work. Using a 50% alpha blue for the guard view, the feedback view is not bright full color as hoped.</p>
  
  <p>I had thought that <code>zPosition</code> trumped placement in the subviews. Is that only within a given container? I assumed it was global to all views (and their associated layers) on the screen.</p>