What is annotation:(id)annotation in openURL method?

Question

In the app delegate, there is this method

- (BOOL)application:(UIApplication *)application openURL:(NSURL *)url sourceApplication:(NSString *)sourceApplication annotation:(id)annotation {

I am wondering what the "annotation" is? Also, how would I use it/view it to see what it contains?

Thanks

Answer 1

annotation: A property-list object supplied by the source application to communicate information to the receiving application.

It is what the application that triggered the url opening wants to share with you.

UIApplicationDelegate apple documentation

Answer 2

It is a dictionary. I have only found it useful for determining the referrer when opening deeplinks from mobile Safari: