         }
     }
 
-    /// Synchronizes all NSUserDefaults to NSUbiquitousKeyValueStore.
+    /// Synchronizes all `UserDefaults` 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.
+    ///     - 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

        registerObserver(key: key)
    }

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

    /// The singleton for Zephyr.
    private static let shared = Zephyr()

    /// 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.
