title: Which properties should be used with CSSearchableItemAttributeSet on NSUserActivity?
body: <p>I added Web Markup to my website so items will appear in Spotlight Search results when users search in iOS 9. Users can browse the same items in the app, therefore I want to create <code>NSUserActivity</code> objects that link to the web content as users browse the items.</p>
  
  <p>Now, <code>NSUserActivity</code> has a <code>contentAttributeSet</code> property which I will use to to attach a thumbnail photo to the activity. <code>CSSearchableItemAttributeSet</code> has some properties that <code>NSUserActivity</code> also has, so I am not sure which one I should implement or if I should specify the same data for both. Do I set the <code>title</code> for the <code>NSUserActivity</code> as well as the <code>title</code> on the <code>CSSearchableItemAttributeSet</code>, or only one or the other? Same with <code>keywords</code> which is a property on both as well.</p>
  
  <pre><code>NSUserActivity *activity = [[NSUserActivity alloc] initWithActivityType:@“com.domain.appname-something"];
  activity.title = @“My Title";
  activity.keywords = [NSSet setWithArray:@[@“one", @“two", @“three"]];
  activity.userInfo = @{@“id": @“12345"};
  activity.requiredUserInfoKeys = [NSSet setWithArray:@[@“id"]];
  activity.eligibleForSearch = YES;
  activity.eligibleForPublicIndexing = YES;
  activity.webpageURL = [NSURL URLWithString:@"https://someurl.com"];
  
  //QUESTION: Do I need to duplicate title and keywords here:
  CSSearchableItemAttributeSet *contentAttributeSet = [[CSSearchableItemAttributeSet alloc] initWithItemContentType:(NSString *)kUTTypeImage];
  contentAttributeSet.title = activity.title;
  contentAttributeSet.displayName = activity.title;
  contentAttributeSet.keywords = [activity.keywords allObjects];
  contentAttributeSet.contentDescription = @“My Description Here";
  contentAttributeSet.thumbnailData = [self generateImage];
  
  activity.contentAttributeSet = contentAttributeSet;
  </code></pre>