...that is the question :)
One of the (many) unique capabilities of the Harrier is it's ability to vector it's thrust nozzles during forward flight ( hence VIFF = VectorInForwardFlight ). In a close-in dogfight the Harrier being able to vector more than 23000 lbs of thrust through 98.5 degrees from aft gives an opposing pilot a serious problem most probably resulting in an overshoot and a switch to a defensive posture.
Naturally CAP2 implements this capability. If you fly with a split throttle HOTAS controller or flight stick with two extra analogue inputs you have full control over nozzle position and thrust. Additionally you can map nozzle position increments or absolute positions to other buttons or keys.