title: UIViewController dismissViewControllerAnimated completion argument type syntax
body: <p>The <code>void (^)(void)</code> syntax of the 'completion' argument type implemented by the  UIViewController method:</p>
  
  <pre><code>- (void)dismissViewControllerAnimated: (BOOL)flag completion: (void (^)(void))completion
  </code></pre>
  
  <p>has piqued my curiosity and I have been unable to find any documentation for it. Please could someone help explain its purpose/meaning?</p>
  
  <p>Many thanks in advance.</p>