Default value
null
For player mobs (PCs) this is the value of the player’s key. For non-player mobs (NPCs), this is the value of the “desired” key. This means that if a player with that key logs into the world, he will be connected to that mob (as opposed to a new one of type world.mob).
Setting the mob’s key will cause a client with the same key to connect to the mob. Any other mob with the same key will lose it.
Key values are always compared in canonical form (ie the form returned by ckey()) so setting a mob’s key to “Dan”, “dan” are equivalent as far as controlling player linkage.