Number of columns to lay out.

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