title: What is this Objective-C/XCode annotation // [START_EXCLUDE]
body: <p>Looking at sample code for GCM notifications on iOS found here: <a href="https://github.com/googlesamples/google-services/blob/master/ios/gcm/GcmExample/AppDelegate.m#L31" rel="nofollow">https://github.com/googlesamples/google-services/blob/master/ios/gcm/GcmExample/AppDelegate.m#L31</a></p>
  
  <pre><code>....
  // [START register_for_remote_notifications]
  - (BOOL)application:(UIApplication *)application
        didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
        // [START_EXCLUDE]
        ....
        // [END_EXCLUDE]
  </code></pre>
  
  <p>What purpose do the   // [START_EXCLUDE] // [END_EXCLUDE] serve. Is it part of a convention, part of Objective C or something for xCode?</p>