@EFFect (exit) [= (Add|Remove|Toggle) ((group)) [:(target)]], ...
@EFFect (exit) = Delete (Effect Number)
Causes an (exit) to Add, Remove or Toggle a group on the player
using the exit by default, or on a specified (target).
Several effects can be associated with an exit.
@EFFECT (exit) by itself will display an exit's existing effects.
The ":" operator can be used in locks to verify that (target) is
a member of (group).