A preview event adds a Cancel property to an existing event. Preview events are fired before event processing (OnMouseDown, OnPaint, etc.) gets invoked. They are first fired for the top-most interactor in the visual tree (a document interactor), then for the childs that the event applies to, etc. At any point, the preview event may be cancelled. This means that the event will not be processed by the corresponding interactor, nor by its children. Eventually, the event will be processed by the bottom-most (= most specific) interactor for which the event was not cancelled.

public class PreviewEvent<EventType> : EventArgs

Public Class PreviewEvent(Of EventType) _
	Inherits EventArgs