Gets or sets a value indicating whether the operation which raised an event should be canceled.
true if the operation raising the event should be canceled; otherwise, false.
The NavPaneExpandedChangingEventArgs object is passed to events that fire before specific initiated actions are completed. The Cancel property of this object enables you to cancel the action which is about to be performed.
For example, this property is useful when you handle the NavigationPaneView.NavPaneExpandedChanging event. Set this property to true to cancel the expanding or collapsing of the Navigation Pane. This can be used if you want to prohibit Navigation Pane expanding/collapsing with respect to specific conditions.