// ObservePropertyChanged ================================
/// <example><code>
/// model
/// .ObservePropertyChanged()
/// .Subscribe(e => Console.WriteLine($"SomePropertyChangedEvent occurred."));
/// </code></example>
public static IObservable <EventPattern <PropertyChangedEventArgs> > ObservePropertyChanged(this INotifyPropertyChanged source)
{
return(source.ObserveEvent <PropertyChangedEventArgs>(nameof(source.PropertyChanged)));
}