/// <summary>
        /// The DirectionProperty property changed handler.
        /// </summary>
        /// <param name="d">GridExpander that changed IsCollapsed.</param>
        /// <param name="e">An instance of DependencyPropertyChangedEventArgs.</param>
        private static void OnDirectionPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            GridExpander s = d as GridExpander;

            GridExpanderDirection value = (GridExpanderDirection)e.NewValue;

            s.OnDirectionChanged(value);
        }
        /// <summary>
        /// The IsCollapsed property porperty changed handler.
        /// </summary>
        /// <param name="d">GridExpander that changed IsCollapsed.</param>
        /// <param name="e">An instance of DependencyPropertyChangedEventArgs.</param>
        private static void OnIsCollapsedPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            GridExpander s = d as GridExpander;

            bool value = (bool)e.NewValue;

            s.OnIsCollapsedChanged(value);
        }