This is used to set yourself as the owner of a player-castle door
or clear the owner of a player-castle door key.  The syntax is:

keyowner 
keyowner clear 

Where key is the name of the key you wish to set or clear.

Once you are set as the owner of a key, you cannot drop it, toss it or 
otherwise remove it from your inventory.  When you quit, it disappears.
When you log on it is put in your inventory automatically.

See also: help spell locksmithing, help castles