if we take a look at the signature (Func<Object, DependencyObject>) of the above convention we notice that the “in” parameter is an Object and is not constrained to be an AbstractViewModel, this is in line with the fact that for the Radical toolkit a ViewModel is not required to be an AbstractViewModel, but if you need to use the above convention or the UI Composition system be aware that if the ViewModel is not an AbstractViewModel you end up with 2 options: