WPF: How to create custom preview routed event?

Question

I mean the following: I have a custom control which has StateChangedEvent:

public class WindowControl : ContentControl
{
public static readonly RoutedEvent StateChangedEvent;

static WindowControl()
{
WindowControl.StateChangedEvent = EventManager.RegisterRoutedEvent("StateChanged", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(WindowControl));
}

        public event RoutedEventHandler StateChanged
        {
            add { base.AddHandler(WindowControl.StateChangedEvent, value); }
            remove { base.RemoveHandler(WindowControl.StateChangedEvent, value); }
        }

}

so Now I need PreviewStateChangedEvent - how do I need to declare it (to link it to the bubble event) in order it being generated before StateChangedEvent?