This is not thrue. As I mentioned before, first door flag is NOT responsible for passing nonmaterial monsters through them. "Nonmaterial" monster flag has nothing to do with it. In fact, every nonmaterial can pass through every door!Door editor:
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This editor allows you to edit some basic properties of doors.
Strength: The strength of the door, dictates how much power is required to break it open.
Byte0: Includes various bits and some unknown/unused bits, which is why it is editable.
Non-materials cannot pass: Any monster that is nonmaterial cannot pass through this door. Although this bit seems to be used in the code, I swear that nonmaterial beings can pass through a porticullas door.
Projectiles can pass: Projectiles can be thrown through the door
Mirrored randomly: The door is randomly mirrored on its X and Y axis.
The flag is responsible for seeing you by a monster through closed door; if the flag is set, then monster can see you behind the closed door (perhaps to shoot a projectile). Tested.
So when you disable that flag for a porticulus door you could see a monster behind them, but a monster couldn`t see you.
If the monster see you through the closed door, it can either cast z ZO spell or bash the door by fireballing it, if destroyable. Or cast a poison cloud (succeeded when the second door flag is set).