private IBorder GetDefaultBorder()
{
// Setup initial conditions.
if (defaultBorder != null) return defaultBorder;
// Create and wire up events.
defaultBorder = new BorderModel { Color = transparent };
defaultBorderObserver = new PropertyObserver<IBorder>(defaultBorder)
.RegisterHandler(m => m.CornerRadius, m => OnBorderCornerRadiusChanged());
// Finish up.
return defaultBorder;
}