An exit is an object. It has the Exit (or PartExit flag), and a 'short' property (which is north, south, up, down, in, or whatever), and a 'link' property pointing at the room it is an exit to.

Usually you'd get an exit through the 'make' or 'dig' commands, and then further customise it.

'door' can be set to an object which must be state 0 to allow the exit to be traversable.

If you set Secret flag on an exit, it will deny it exists if for lack of privs a person cannot get into the room. It will also not show in 'exits' for anyone.

If quest is set on an exit you must own that object to go through the exit.

Doors

Doors are state 1 closed, 2 locked. Pairs of doors can be linked by having the 'other' property on each set to the other.

Set CanOpen to indicate a door has a handle etc.

Set CanLock to indicate a door has a lock. A key can open a door if the key property on the door is set to the key (or the treatas of the key), or if the lock property on the key is set to the door.

A door can also be CanLatch, this means you don't need a key to lock it (on this side).

If you set the Secret flag on a door, people trying to go through it when it is closed will see the message "You can't go [that way]" instead of "The [door] is closed". This is handy if the door object is sometimes not in the same room as the exit.

Objects with the Exit flag cannot be examined, picked up and so on. It won't even acknowledge the existence of the object, because it's a pseudo-object.

With some objects that also act like exits, such as ships, it is desirable to have them examinable. These should have the PartExit flag on them, not the Exit flag. All such objects should have a 'name' property, etc.