static object CoerceSelectedCallback(DependencyObject sender, object val)
        {
            TabHeader tabHeader = sender as TabHeader;

            return((bool)val);
        }
        static object CoerceHighlightedCallback(DependencyObject sender, object val)
        {
            TabHeader tabHeader = sender as TabHeader;

            return(tabHeader.IsMouseOver && !tabHeader.IsSelected);
        }