Cursor Arrow Look up. Cursor Arrow Look down. Tab Cycle through hotspots, the destination of the highlihgted hotspot is shown in the status bar at the bottom of your browser. Space or 'h' Toggle hotspots' visibility. Press once to see all hotspots, press again to hide them.
Hotspots are always active, no matter if they are visible or invisible.
Currently 'sphere' and 'none' are yet to be implemented.