     /// The singleton for Zephyr.
     private static let shared = Zephyr()
 
-    /// A shared key that stores the last synchronization date between NSUserDefaults and NSUbiquitousKeyValueStore.
+    /// A shared key that stores the last synchronization date between `UserDefaults` and `NSUbiquitousKeyValueStore`.
     private let ZephyrSyncKey = "ZephyrSyncKey"
 
     /// An array of keys that should be actively monitored for changes.

        }
    }

    /// Synchronizes all NSUserDefaults to NSUbiquitousKeyValueStore.
    ///
    /// If a key is passed, only that key will be synchronized.
    ///
    /// - Parameters:
    ///     - key: If you pass a key, only that key will be updated in NSUbiquitousKeyValueStore.
    ///     - value: The value that will be synchronized. Must be passed with a key, otherwise, nothing will happen.
    func syncToCloud(key: String? = nil, value: Any? = nil) {
        let ubiquitousStore = NSUbiquitousKeyValueStore.default

// MARK: - Synchronizers

private extension Zephyr {
    /// Synchronizes specific keys to/from `NSUbiquitousKeyValueStore` and `UserDefaults`.
    ///
    /// - Parameters:
    ///     - keys: Array of keys to synchronize.
