about some variables...

For now, here's a list:

_this

Used as target in actions and in getProperty/setProperty. References the object the current behavior is attached to.

_camera

References the camera object from actions. Can be used to get/set the camera pan/tilt/fov values, as well as panspeed/tiltspeed/fovspeed and panmin/panmax, tiltmin/tiltmax, fovmin/fovmax.

_mouse

References the mouse. Can be used to get the mouse x and y value using getproperty

_tour

References the tour node. Can be used to retreive the title, description and copyright set in the global node (read only).

_scene

References the current scene node. Can be used to retreive the title, description and copyright set of the current scene (read only).

The "_viewport" meme is a different story. A uielement by this name can be used to manipulate the rect within the viewer rect that is used to draw the panoramic scene. This way, you can draw uielements outside the pano view.