Avalon Edit (WPF texteditor) access

[PatrickTreutlerD]

I try to test an Avalon text-editor embedded in a WPF application.
But I actually see no way to get it's object.
When I search for AutomationIds of or inside the Avalon custom control, nothing gets found,
When I capture the parent object of the Avalon Edit it shows only items of the scrollbars.

Does someone know a possibility to access the Avalon Edit TextBox to read or modify the text inside? Or is it impossible with Teststack White?
Thanks for any help.