WPF: Editable ComboBox that drops up?

Question

Im trying to create a ComboBox thats both editable and drops up instead of down. The menu should also open when pressing the up-arrow-key (down by default).

I have tried

Answer 1

The default ControlTemplate is not for the IsEditable = true variety, but the style contains a trigger that changes it when IsEditable is set:

It changes it to another ControlTemplate where the relevant part is the popup:

...

I think you should just be able to change the Placement property to Top.