/// <summary>
        /// ContentProperty property changed handler.
        /// </summary>
        /// <param name="d">ButtonSpinner that changed its Content.</param>
        /// <param name="e">Event arguments.</param>
        private static void OnContentPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ButtonSpinner source = d as ButtonSpinner;

            source.OnContentChanged(e.OldValue, e.NewValue);
        }
        private static void AllowSpinPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ButtonSpinner source = d as ButtonSpinner;

            source.OnAllowSpinChanged((bool)e.OldValue, (bool)e.NewValue);
        }