>On the other hand someone definitely needs to worry about the context and will have to tell the Developer "Please do use this class" (by this implicitly defining the context). If so, they also could
>get Context-Key's for specific objects.
>
>To me this sounds highly performance problematic and somehow complicated.
>
>But certain tasks sometimes demand certain actions that are not easy to see from the outside.

Yes. Performance might be a reason to abandon this design.
But the class won't implicitly define the context.
David's idea of creating the context key on design time using a builder might be the better solution.
I'll study it.