& visible()
 
  Syntax: visible(<object>,<victim>[/<attr>])
 
  Returns 1 if <object> can examine <victim>, or 0 otherwise. If 
  <object> or <victim> do not exist, 0 is returned.
 
  If an object-attribute pair is provided, 1 is returned if <object> 
  can see <attr> on <victim>. If <attr> is not present on <victim>, 1 
  is returned if <object> can examine <victim>.
 
  See Also: DARK, LIGHT