I think this is useful in this case:
I want to have DNI calling .net framework installer by parameter /passive. If the invoker hasn't enough privilege, .net framework installer will terminate and return an error code.
I just want tell user what has happened. I can't do it in WIX as the installer I created by WIX isn't running at that time.
Maybe the better way is adding an "error code - message" table to DNI. Then we can show different message to user for each of the error code.