<Canvas xmlns="http://schemas.microsoft.com/client/2007">
        <!-- the edges of the rectangles should be pixel aligned shouldn't they? -->
	<Rectangle Opacity="0.5" Fill="Red" Width="100" Height="100" Canvas.Top="200" Canvas.Left="20" />
	<Rectangle Opacity="0.5" Canvas.Top="250" Canvas.Left="50" Fill="Blue" Width="100" Height="100" />
</Canvas>

