gistfile1.xml

<UserControl x:Class="Company.ProjectionBufferTutorial.MyControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             Background="{DynamicResource VsBrush.Window}"
             Foreground="{DynamicResource VsBrush.WindowText}"
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300"
             Name="MyToolWindow">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <ContentControl Name="fullFile" Grid.Column="0" />
        <ContentControl Name="partialFile" Grid.Column="1" />
    </Grid>
</UserControl>