     
     /// Notification sent when the sync has finished.
     @objc public static let SyncDidFinishNotification = "AlgoliaSearch.MirroredIndex.SyncDidFinishNotification"
+    
+    /// Notification user info key used to pass the error, when an error occurred during the sync.
+    @objc public static let SyncErrorKey = "AlgoliaSearch.MirroredIndex.SyncErrorKey"
 
     // ----------------------------------------------------------------------
     // MARK: Properties

    // ----------------------------------------------------------------------
    // MARK: Browse
    // ----------------------------------------------------------------------

    /// Browse the local mirror (initial call).
    /// Same semantics as `Index.browse()`.

        
        // Notify observers.
        dispatch_async(dispatch_get_main_queue()) {
            var userInfo: [String: AnyObject]? = nil
            if self.syncError != nil {
                userInfo = [MirroredIndex.SyncErrorKey: self.syncError!]
            }
            NSNotificationCenter.defaultCenter().postNotificationName(MirroredIndex.SyncDidFinishNotification, object: self, userInfo: userInfo)
        }
    }
    
