title: Is it true that for iPad and iPhone, using CADisplayLink must be for 60fps?
body: <p>In other words, can we choose to invoke the handler at 20 times per second, or at 45 times per second, or must it be 60 times per second?</p>
  
  <p>I guess one way to simulate it will be to use the timestamp given to the handler to determine if it is "time for action yet" -- if not, simply return without doing anything?</p>