Tabbing focus not working with control template that wraps control - wpf

Question

I've tried all kinds of template binding and such to get this to work, but if I use this style on a control, the internal textbox control doesn't show focus.
I'm doing this because I want to set an error template that wraps around the textbox and the spot reserved for displaying units.
Now, typing in the box correct updates the text inside. And clicking on it will show the highlighted border and input caret, but tabbing into it won't.
<Style x:Key="Special" TargetType="{x:Type TextBox}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<DockPanel
LastChildFill="True"
Visibility="Visible">
<Border
Name="PART_UnitContainer"
DockPanel.Dock="Right"
Visibility="Collapsed">
<Label
Content="ft"
Style="{DynamicResource UnitLabel}"
/>
</Border>
<TextBox Name="PART_Control" Text="{Binding Text, RelativeSource={RelativeSource TemplatedParent}}"/>
</DockPanel>
<ControlTemplate.Triggers>
<Trigger Property="IsFocused" Value="True">
<Setter TargetName="PART_UnitContainer" Property="Visibility" Value="Visible"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 1

Initially I set the whole control as no tab stop, and internal one with tabstop, but apparently you also have to set the tab navigation to continue. I didn't when I tried playing with navigation, so I overlooked this setting.
<Style x:Key="Special" TargetType="{x:Type TextBox}">
<Setter Property="KeyboardNavigation.TabNavigation" Value="Continue"/>
<Setter Property="IsTabStop" Value="False"/>
<Setter Property="Template">
<ControlTemplate>
...
<Text IsTabStop="True" Name="PART_Control" ...
...
</ControlTemplate>
</Setter>
</Style>
However, this little trick doesn't work for shift-tab out of an editable combobox. I'll update the answer if I figure it out.
For comboboxes you have to do it differently. You don't set TabNavigation to Continue, and you don't set IsTabStop on internal combobox to true.
See
<Style x:Key="Special" TargetType="{x:Type ComboBox}">
<Setter Property="IsTabStop" Value="False"/>
<Setter Property="Template">
<ControlTemplate>
...
<ComboBox Name="PART_Control" ...
...
</ControlTemplate>
</Setter>
</Style>