<Canvas x:Name="page0" xmlns="http://schemas.microsoft.com/client/2007"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Background="blue" Loaded="OnLoaded"
  Width="500" Height="500">
<!-- We can't nest a Canvas.Clip inside a RenderTransform, make sure we deal -->
<!-- with that safely --> 
  <Canvas.RenderTransform>
  <Canvas.Clip>
    <PathGeometry>
      <PathFigure>
        <LineSegment x:Name="clipPoint0" Point="0,570"/>
        <LineSegment x:Name="clipPoint1" Point="0,570"/>
        <LineSegment x:Name="clipPoint2" Point="0,570"/>
        <LineSegment x:Name="clipPoint3" Point="0,570"/>
        <LineSegment x:Name="clipPoint4" Point="0,570"/>
      </PathFigure>
    </PathGeometry>
  </Canvas.Clip>
  </Canvas.RenderTransform>
  <Rectangle Height="1000" Width="20" Opacity="0.6" Fill="Red">
  </Rectangle>
  <Canvas Width="25" Height="25" Fill="Yellow"/>
</Canvas>
