         // Must have a public init for client code to initialize this class.
     }
 
-    // MARK: Observer API
+    // MARK: - Observer API
 
     /// Register an observer.
     open func observe<T>(owner: T, _ handler: @escaping () -> Void) where T: AnyObject, T: Equatable {

    }
}

// MARK: Observer: Equatable

extension Observer: Equatable {
    static func ==(lhs: Observer, rhs: Observer) -> Bool {

        return observers.isEmpty
    }

    // MARK: - Notify API

    /// A boolean value to determine whether the notifications should be sent.
    /// This flag is checked before firing any notification calls to the registered
