valid_hide - allows or disallows objects to hide and see hidden objects
int valid_hide( object ob );
Add valid_hide to master.c in order to allow objects to hide them‐ selves, or see other objects that have hidden themselves. When an object tries to use the set_hide() efun to hide itself, valid_hide will be called with the object that is wanting to hide as the sole parame‐ ter. It should return 1 to allow it, or 0 to not allow it. The same call takes place when it needs to be determined if a certain object should be able to see hidden objects.