The 'hide' command allows you to become hidden from others in a room. Each
room has a 'cover' factor built into it, i.e. there are some places you simply
cannot hide (oh, the floor of the arena for example). Searching for a hiding
place takes action time. Your chance of finding a suitable hiding place is 
based strictly on the amount of cover available. Once hidden, monsters 
entering a room will not be aware of your presence ('look' at a monster to 
see if he knows you are there or not). You have a better chance of scoring 
an excellent hit on a monster that does not know you're there. Further, 
monsters who are not aware of you will not attack you, stop you from leaving, 
or stop you from picking something up off the ground.

Once hidden in a room, you remain in your hiding place until you exit the
room (an 'H' next to your prompt indicates that you are hiding). However,
most commands where you perform an action will cause monsters to spot you in
your hiding place. Once spotted, they can then decide to attack you.

If you suspect that another player is hidden in your room, you may 'search'
for them.
