gistfile1.cs

//If you copy and paste this, you'll need to change the x:Class value
<UserControl x:Class="Waterloo.ProjectKiwi.CustomEditorControl" 
             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"
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="1*"/>
            <ColumnDefinition Width="1*"/>
        </Grid.ColumnDefinitions>
        <ContentControl x:Name="leftEditorContainer" Grid.Row="0" Grid.Column="0" />
        <ContentControl x:Name="rightEditorContainer" Grid.Row="0" Grid.Column="1"/>
    </Grid>
</UserControl>