How to: Build a dock UI using the MVVM pattern

<UserControl x:Class="DockingMVVM.SL.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:dxb="http://schemas.devexpress.com/winfx/2008/xaml/bars"
    xmlns:dxd="http://schemas.devexpress.com/winfx/2008/xaml/docking"
    xmlns:local="clr-namespace:DockingMVVM.SL"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">
    <UserControl.Resources>
        <DataTemplate DataType="local:DocumentViewModel">
            <Border Background="#FFBEC8D9">
                <ContentPresenter Content="{Binding Content}" />
            </Border>
        </DataTemplate>
        <DataTemplate DataType="local:PanelViewModel">
            <Border Background="#FFDADFE4">
                <ContentPresenter Content="{Binding Content}" />
            </Border>
        </DataTemplate>
        <Style TargetType="dxd:LayoutPanel">
            <Setter Property="Caption" Value="{Binding DisplayName}" />
        </Style>
        <Style TargetType="dxd:DocumentPanel">
            <Setter Property="Caption" Value="{Binding DisplayName}" />
        </Style>
    </UserControl.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition />
        </Grid.RowDefinitions>
        <StackPanel Orientation="Horizontal">
            <Button Name="AddPanel" Click="AddPanel_Click" Content="Add Panel" />
            <Button Name="AddDocument" Click="AddDocument_Click" Content="Add Document" />
        </StackPanel>
        <dxb:BarManager Grid.Row="1">
            <dxd:DockLayoutManager ItemsSource="{Binding Workspaces}">
                <dxd:LayoutGroup>
                    <dxd:LayoutGroup Name="PanelHost" DestroyOnClosingChildren="False"/>
                    <dxd:DocumentGroup Name="DocumentHost" DestroyOnClosingChildren="False" />
                </dxd:LayoutGroup>
            </dxd:DockLayoutManager>
        </dxb:BarManager>
    </Grid>
</UserControl>