Secret Doors by Andrew Owen begins here.

"Doors and switches that cannot be acted upon until they are
discovered."

A secret door is a kind of door.
A secret door can be revealed or unrevealed.
A secret door is unrevealed.
A secret door is scenery.
A secret door is closed.

A secret switch is a kind of thing.
A secret switch can be revealed or unrevealed.
A secret switch is unrevealed.
A secret switch is scenery.

To print the you can't go message:
    (- L__M(##Go, 2, 0); -).

To print the you can't see message:
    (- L__M(##Miscellany, 30, 0); -).

Before going through a secret door which is unrevealed:
    print the you can't go message instead.

Before doing something to a secret door which is unrevealed:
    print the you can't see message instead.

Before doing something when when a secret door is the second noun and
the
second noun is unrevealed:
    print the you can't see message instead.

Before doing something to a secret switch which is unrevealed:
    print the you can't see message instead.

Before doing something when when a secret switch is the second noun and
the
second noun is unrevealed:
    print the you can't see message instead.

Secret Doors ends here.