
No no, totally unrelated to docking at all; I just used AdvancedTabControl with Left aligned tabs and overflow scrolling, which the original TabControl is not capable at all.
I applied the strike-through style to the text due to the lack of a "delete thread" button (or I just missed it, if it exists).
As said, original TabControl and AdvancedTabControl behave the same:
<Page
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<TabControl>
<TabItem Header="Inheritable properties inherit into header AND content" FontSize="20" FontWeight="ExtraBold">
<StackPanel>
<TextBlock>some content also in bold and size 20</TextBlock>
</StackPanel>
</TabItem>
<TabItem Header="Inheritable properties inherit ONLY into header" FontSize="20" FontWeight="ExtraBold" Content="some content in default size and weight">
<TabItem.ContentTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding}" />
</StackPanel>
</DataTemplate>
</TabItem.ContentTemplate>
</TabItem>
</TabControl>
</Page>
This happens to all sort of inheritable properties, attachable or not. In my case it was my own "HelpProvider.Topic" attachable property.