title: What is the '^' in Objective-C
body: <h1>What does the '^' mean in the code below?</h1>
  
  <pre><code>@implementation AppController
  
  - (IBAction) loadComposition:(id)sender
  {
      void (^handler)(NSInteger);
  
      NSOpenPanel *panel = [NSOpenPanel openPanel];
  
      [panel setAllowedFileTypes:[NSArray arrayWithObjects: @"qtz", nil]];
  
      handler = ^(NSInteger result) {
          if (result == NSFileHandlingPanelOKButton) {
              NSString *filePath = [[[panel URLs] objectAtIndex:0] path];
              if (![qcView loadCompositionFromFile:filePath]) {
                  NSLog(@"Could not load composition");
              }
          }
      };
  
      [panel beginSheetModalForWindow:qcWindow completionHandler:handler];
  }
  @end
  </code></pre>
  
  <p>===
  I've searched and searched - is it some sort of particular reference to memory?</p>