/// <summary>
        /// Callback called when the Content property's value has changed.
        /// </summary>
        /// <param name="d">Sender object</param>
        /// <param name="e">Callback arguments</param>
        private static void ContentPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ContentControl3D c = (ContentControl3D)d;

            if (e.OldValue != null)
            {
                c.RemoveVisual3DChild((UIElement3D)e.OldValue);
            }
            c.AddVisual3DChild((UIElement3D)e.NewValue);
        }
        private static object ContentCoerceValue(DependencyObject d, object value)
        {
            ContentControl3D c = (ContentControl3D)d;

            if (c._contentJustLoadedFromSkin || c.OverridesDefaultSkin)
            {
                c._contentJustLoadedFromSkin = false;
                return(value);
            }
            else
            {
                return(c.Content);
            }
        }