/// <summary>
/// Returns an observable that returns a value indicating
/// whether escape is pressed, even if one of the events involved
/// is handled or occurs in a sibling.
/// </summary>
/// <param name="that">The element to listen to.</param>
/// <returns>An observable that returns a value indicating
/// whether escape is pressed, even if one of the events involved
/// is handled or occurs in a sibling.</returns>
internal static IObservable <bool> GetEscapePressedChangedOnSelfAndSiblingsAlways(this UIElement that)
{
return
(Observable.Merge(
that
.GetKeyUpOnSelfAndSiblingsAlways()
.Where(ev => ev.EventArgs.Key == Key.Escape)
.Select(ev => false),
that
.GetKeyUpOnSelfAndSiblingsAlways()
.Where(ev => ev.EventArgs.Key == Key.Escape)
.Select(ev => true)));
}