title: CALayer compositingFilter, iOS 5 and CoreImage
body: <p>The API Docs for CALayer state:  (I'm not sure if the docs are up to date??)</p>
  
  <blockquote>
    <p>compositingFilter A CoreImage filter used to composite the receiver’s
    contents with the background. Animatable.</p>
    
    <p>@property(retain) id compositingFilter</p>
    
    <p>...</p>
    
    <p>Special Considerations While the CALayer class exposes this property,
    Core Image is not available in iOS. Currently the filters available
    for this property are undefined.</p>
  </blockquote>
  
  <p>But CoreImage IS available on iOS5, so could I add a CoreImage filter to a CALayer and add that layer to another layer and expect it to work?</p>
  
  <p>I want to add a sublayer to a layer and have it use a specific blend mode (multiply).  I can't figure out how to do this otherwise.</p>