Number of groups to lay out.

<CollectionPanel Color="Black" GroupCount="10">
    <!-- Lay out lots of yellow circles and red rectangles in groups -->
    <Each Count="70">
        <Circle Margin="5" Width="10" Height="10" Color="Yellow" />
        <Rectangle Margin="5" Width="10" Height="40" Color="Red" />
    </Each>
</CollectionPanel>