XAML - How do I access a parent control's DataTemplate property from a child in a ControlTemplate?

Question

CustomUserControl.xaml.cs

public partial class CustomUserControl : UserControl
{
    public CustomUserControl ()
    {
        InitializeComponent();
        var style = (Style)FindResource("Styling");
        Style = style;
    }

    public static readonly DependencyProperty ItemHeaderTemplateProperty = DependencyProperty.Register(nameof(ItemHeaderTemplate), typeof(DataTemplate), typeof(CustomUserControl), new PropertyMetadata(default(DataTemplate)));

    public DataTemplate ItemHeaderTemplate
    {
        get => (DataTemplate)GetValue(ItemHeaderTemplateProperty);
        set => SetValue(ItemHeaderTemplateProperty, value);
    }
}

CustomUserControl.xaml

 <Style x:Key="Styling" TargetType="{x:Type local:CustomUserControl}">
    <Setter Property="Template">
        <Setter.Value>          
            <ControlTemplate TargetType="{x:Type local:CustomUserControl}">
                
                <!-- This works -->
                <ContentControl ContentTemplate="{TemplateBinding ItemHeaderTemplate}"/>
                
                <TabControl Name="TestName" ItemsSource="{Binding Items}">
                    <TabControl.ContentTemplate>
                        <DataTemplate>

                            <DockPanel>
                                <!-- These don't work -->
                                <ContentControl ContentTemplate="{TemplateBinding ItemHeaderTemplate}"/>
                                <ContentControl ContentTemplate="{Binding ElementName=TestName, Path=DataContext.ItemHeaderTemplate}"/>
                                <ContentControl ContentTemplate="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=ItemHeaderTemplate}"/>
                            </DockPanel>
                        
                        </DataTemplate>
                    </TabControl.ContentTemplate>
                </TabControl>   
            
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

The reference to ItemHeaderTemplate outside the TabControl works properly, but none of the references to ItemHeaderTemplate inside the TabControl work.

What is the proper way to access a parent control's property from within a child control in a ControlTemplate?

Answer 1

I realized the answer to my own question was pretty simple.

I just needed to directly set the ContentTemplate.

<Style x:Key="Styling" TargetType="{x:Type local:CustomUserControl}">
    <Setter Property="Template">
        <Setter.Value>          
            <ControlTemplate TargetType="{x:Type local:CustomUserControl}">
                
                <!-- This works -->
                <ContentControl ContentTemplate="{TemplateBinding ItemHeaderTemplate}"/>
                
                <!-- This now works too -->
                <TabControl ItemsSource="{Binding Items}"
                            ContentTemplate="{TemplateBinding ItemHeaderTemplate}"/>                    
            
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>