title: Why aren't all CATransition animation types listed in the documentation?
body: <p>I was poking around stackoverflow trying to figure out how to do a curl up animation on a layer when I ran into this post: <a href="https://stackoverflow.com/questions/3652724/catransition-page-curl-from-top">CATransition page curl from top</a></p>
  
  <p>The author of the post used a constant string 'pageCurl' to define the animation type:
  <code>animation.type = @"pageCurl";</code></p>
  
  <p>When looking in the apple documentation for transition animation types only the following types are listed:</p>
  
  <pre><code>NSString * const kCATransitionFade;
  NSString * const kCATransitionMoveIn;
  NSString * const kCATransitionPush;
  NSString * const kCATransitionReveal;
  </code></pre>
  
  <p>Did I miss something? Why isn't the curl up transition listed? I tested using "pageCurl" as a transition type in my program and confirmed that it works!</p>