static CommandButton()
 {
     CommandProperty.AddOwner(typeof(CommandButton),
                              new FrameworkPropertyMetadata(OnCommandChanged));
     //ContentProperty.AddOwner(typeof(CommandButton),
     //	new FrameworkPropertyMetadata(null, CoerceContent));
     IconSourceProperty.AddOwner(typeof(CommandButton),
                                 new FrameworkPropertyMetadata(null, CoerceSource));
     ToolTipProperty.AddOwner(typeof(CommandButton),
                              new FrameworkPropertyMetadata(null, CoerceToolTip));
 }
 set => SetValue(IconSourceProperty, value);