&directoronly will show the audio and video of the director but not of the guests. It is basically the same as &broadcast but the guests can't hear each other. It is just the same as doing &view=DirectorStreamID, but without having to know the stream ID for the director.
It will actually connect to any director, including co-directors, not just the main one.
&view, &include, &exclude have a lower priority to &directoronly. So if there are two directors, you can do &directoronly&exclude=coDirector123, so that the codirector doesn't connect.
I changed the toggle in the director's room for "Guests hear others" from &view= to &directoronly. The point of this change is that the director can now still talk to those in the room.
Purpose of change: I had a user who wanted &broadcast, but also not have the guests hear each other. It's a bit of a hassle to do &view=DirectorStreamID, and the toggle is labelled to be misleading by saying "guests", not "everyone".
You can use &directoronly to replace &broadcast if you don't want the guests hearing each other.