ToolBar ToggleButton/Panel for Overflow Items

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:TestToolBarTemplateProject.resources"
>
    <!-- DONE: ToolBar Grip (ToolBarThumb) Template -->
    <ControlTemplate x:Key="UniformGridToolBarThumb"
        TargetType="{x:Type Thumb}"
    >
        <Border
            SnapsToDevicePixels="True"
        >
            <Rectangle
                Margin="3,2"
                MinHeight="4"
                MinWidth="4"
            >
                <Rectangle.Fill>
                    <DrawingBrush
                        TileMode="Tile"
                        Viewbox="0,0,8,8"
                        ViewboxUnits="Absolute"
                        Viewport="0,0,4,4"
                        ViewportUnits="Absolute"
                    >
                        <DrawingBrush.Drawing>
                            <DrawingGroup>
                                <GeometryDrawing
                                    Brush="{StaticResource
                                        {x:Static SystemColors.ControlDarkDarkBrushKey}
                                    }"
                                    Geometry="M 4 4 L 4 8 L 8 8 L 8 4 z"
                                />
                            </DrawingGroup>
                        </DrawingBrush.Drawing>
                    </DrawingBrush>
                </Rectangle.Fill>
            </Rectangle>
        </Border>
    </ControlTemplate>
    <!-- FIXME: OverflowPanel not working -->
    <ControlTemplate x:Key="UniformGridToolBarOverflowButtonTemplate"
        TargetType="{x:Type ToggleButton}"
    >
        <Border x:Name="Border"
            Background="{Binding
                Path=Background,
                RelativeSource={
                    RelativeSource FindAncestor,
                    AncestorType=ToolBar
                }
            }"
            HorizontalAlignment="Right"
            SnapsToDevicePixels="true"
        >
            <Grid>
                <Path x:Name="Arrow"
                    Data="M -0.5 3 L 5.5 3 L 2.5 6 Z"
                    Fill="{StaticResource {x:Static
                        SystemColors.ControlTextBrushKey
                    }}"
                    Margin="2,3"
                    VerticalAlignment="Bottom"
                />
                <ContentPresenter />
            </Grid>
        </Border>
        <ControlTemplate.Triggers>
            <DataTrigger
                Binding="{Binding
                    Path=Orientation,
                    RelativeSource={RelativeSource TemplatedParent}
                }"
                Value="Vertical"
            >
                <Setter TargetName="Arrow"
                    Property="Data"
                    Value="M 3 -0.5 L 3 5.5 L 6 2.5 Z"
                />
            </DataTrigger>
        </ControlTemplate.Triggers>
    </ControlTemplate>
    <!-- FIXME: OverflowPanel not working, UniformGrid.Columns|Rows not working -->
    <ControlTemplate x:Key="UniformGridToolBar"
        TargetType="ToolBar"
    >
        <Border x:Name="Border"
            Background="{Binding
                Path=Background,
                RelativeSource={RelativeSource TemplatedParent}
            }"
            BorderBrush="{Binding
                Path=Border,
                RelativeSource={RelativeSource TemplatedParent}
            }"
            BorderThickness="1"
            CornerRadius="2"
        >
            <DockPanel>
                <Thumb x:Name="ToolBarThumb"
                    DockPanel.Dock="Left"
                    Cursor="SizeAll"
                    Template="{StaticResource UniformGridToolBarThumb}"
                />
                <ToggleButton x:Name="OverflowButton"
                    DockPanel.Dock="Right"
                    ClickMode="Press"
                    IsChecked="{Binding
                        IsOverflowOpen,
                        Mode=TwoWay,
                        RelativeSource={RelativeSource TemplatedParent}
                    }"
                    IsEnabled="{TemplateBinding HasOverflowItems}"
                    Template="{StaticResource
                        UniformGridToolBarOverflowButtonTemplate
                    }"
                >
                    <Popup x:Name="OverflowPopup"
                        AllowsTransparency="true"
                        Focusable="false"
                        IsOpen="{Binding
                            IsOverflowOpen,
                            RelativeSource={RelativeSource TemplatedParent}
                        }"
                        Placement="Bottom"
                        PopupAnimation="Slide"
                        StaysOpen="false"
                    >
                        <Border x:Name="DropDownBorder"
                            Background="{Binding
                                Path=Background,
                                RelativeSource={RelativeSource TemplatedParent}
                            }"
                            BorderBrush="{Binding
                                Path=Border,
                                RelativeSource={RelativeSource TemplatedParent}
                            }"
                            BorderThickness="1"
                        >
                            <!--<StackPanel x:Name="PART_ToolBarOverflowPanel"
                                Focusable="true"
                                FocusVisualStyle="{x:Null}"
                                KeyboardNavigation.TabNavigation="Cycle"
                                KeyboardNavigation.DirectionalNavigation="Cycle"
                                Margin="2"
                            />-->
                            <ToolBarOverflowPanel
                                x:Name="PART_ToolBarOverflowPanel"
                                Focusable="true"
                                FocusVisualStyle="{x:Null}"
                                KeyboardNavigation.TabNavigation="Cycle"
                                KeyboardNavigation.DirectionalNavigation="Cycle"
                                Margin="2"
                                WrapWidth="200"
                            />
                        </Border>
                    </Popup>
                </ToggleButton>
                <!--<ToolBarPanel x:Name="PART_ToolBarPanel"
                    IsItemsHost="True"
                    Visibility="Collapsed"
                />
                <ItemsControl
                    ItemsSource="{Binding StaticResource PART_ToolBarPanel.Panel}"
                >
                    <ItemsControl.ItemsPanel>
                        <ItemsPanelTemplate>-->
                            <UniformGrid
                                ClipToBounds="True"
                                Columns="{Binding
                                    Path=local:UniformGridToolBarAttachedProperties.ItemColumns,
                                    RelativeSource={RelativeSource TemplatedParent}
                                }"
                                Rows="{Binding
                                    Path=local:UniformGridToolBarAttachedProperties.ItemRows,
                                    RelativeSource={RelativeSource TemplatedParent}
                                }"

                                IsItemsHost="True"
                                Margin="0,1,2,2"
                            />
                        <!--</ItemsPanelTemplate>
                    </ItemsControl.ItemsPanel>
                </ItemsControl>-->
            </DockPanel>
        </Border>
        <ControlTemplate.Triggers>
            <Trigger Property="IsOverflowOpen" Value="true">
                <Setter TargetName="ToolBarThumb"
                    Property="IsEnabled"
                    Value="false"
                />
            </Trigger>
            <Trigger Property="ToolBarTray.IsLocked" Value="true">
                <Setter TargetName="ToolBarThumb"
                    Property="Visibility"
                    Value="Collapsed"
                />
            </Trigger>

            <Trigger Property="Orientation" Value="Vertical">
                <Setter TargetName="ToolBarThumb"
                    Property="DockPanel.Dock"
                    Value="Top"
                />
            </Trigger>
            <Trigger Property="Orientation" Value="Vertical">
                <Setter TargetName="OverflowButton"
                    Property="DockPanel.Dock"
                    Value="Bottom"
                />
            </Trigger>
        </ControlTemplate.Triggers>
    </ControlTemplate>
</ResourceDictionary>