In case you (or anyone else) were still wondering, this is how the pitch, yaw and roll modifiers work:
The three modifiers are applied in the order they appear - that is pitch first, yaw second, and roll last.
An object starts off by pointing in the direction 0 0 0, which is along the x-axis (In the top-down view it's towards the right).
The pitch modifier is then applied, which rotates the object around its y-axis (appears green in the hammer 3D view). A good way to picture this is if a plane is your prop, with the nose pointing in the direction 0 0 0, a negative pitch will make the nose of the plane point up, while a positive pitch will make the plane point down.
The yaw modifier is applied second, and rotates it around the z-axis of the map (appears blue in the hammer 3D view at the origin, points up). In our analogy of the plane, this will determine where the plane is heading (i.e. the plane's bearing).
The roll modifier is applied last, and rotates the object around
its own x-axis after the pitch and yaw have been applied (appears red in the hammer 3D view). This is as if our plane, once tilted and heading in a particular direction, rolls its body so that its wings rotate about its body, exactly like a barrel roll.
Doors work in the way that they move in the direction that their imaginary plane moves. So pitch makes them move up and down, yaw changes the direction looking from top-down that they move, and roll has no effect, as it won't change the direction that the plane is going.
Here's a picture that outlines what I've just said:
(Note that positive numbers in hammer will make it move in the direction that these arrows point, which obeys the right-hand rule for any of the physics nerds that are out there)
