@SET (object) = DARK
Dark rooms conceal their contents. Concealed objects only appear to
players who can control them, or to the players who can control the
room. "Has arrived" and "has left" messages are suppressed.
Dark players and things do not appear to the casual observer, but
if looked at directly (by name) then they will yield their description.
Dark objects can't be dropped in rooms the player doesn't control.
Dark players do not appear on either the WHO or WHERE lists.
Trying to page an unpageable dark player yields a "That person is
not connected." message.
Dark groups do not appear on players, nor will they display their
memberlist to anyone but the players who can control them.
Dark exits never appear in the [ Commands: ] or [ Exits: ] lists.
Auto-osuccess messages are suppressed when dark exits are used.