When researching how to handle invisibility, I came across the Rules of the Hidden Club which state: "The First Premise: Everyone knows where everyone else is, at all times, period.". But I can't find that rule in the official rulebooks. How do I handle encounters where the monsters aren't initially visible?
Basically I am wondering whether I handled the following situation correctly: The players are moving into a room in which they had previously (days before) encountered monsters, but ran away. What I did was let the players move their characters in the first round as if in combat, but not show the positions of the monsters, which were out of sight (some inside sarcophagi, others behind walls). I only put the monsters on the battlemap once they started moving or coming out of their sarcophagi.
Where in the rulebooks does it say that the players always know the positions of all monsters on the battlemap? Should I have put all the monster miniatures/tokens on the map as soon as the players step on to the map? Or would it be okay to let players enter a room "out of combat" (using what movement rules), and only show the monster positions once the monsters reveal themselves?
Reading the question and answer BESW linked to, I found what is probably the relevant rulebook section on page 223 of the PHB2: "Invisible Creatures and Stealth: If an invisible creature is hidden from you (“Stealth,” page 188), you can neither hear nor see it, and you have to guess what space it occupies. If an invisible creature is not hidden from you, you can hear it or sense some other sign of its presence and therefore know what space it occupies, although you still can’t see it."
However it feels strange to apply this rule out of combat. The players enter a tavern and immediately know the location of everybody in the tavern, even those upstairs in a room with closed doors? I don't think so! Shouldn't it be possible for the players to be on a battlemap of a room they explore "out of combat", with the encounter starting as soon as the first monster jumps out of hiding?