Partitioned-off duke

Ok, imagine a big castle with lots of rooms inside. One of the rooms is where the duke lives. Now, for some reason, the castle people want to make sure that the duke doesn't come out of his room and bother other people in the castle. So, what they do is they build a wall and a door in front of his room so that he can only stay inside his room. This is what we call a partitioned-off duke. It's like putting an invisible fence around a dog's house so that the dog can only stay inside and not run outside and cause trouble. The partitioned-off Duke is now kind of like a king in his own little castle.