On the e85/e86 is that they dimm when a light sensor hits them.
So its the same feature on the rear view mirror, probably also triggered by the same sensor.
The 'autodip' feature is limited to the mirrorglass itself. so you can easily fit normal mirrorglasses if you dont want to pay for this feature (the autodip glasses are expensive).
Also the autodip glasses are slightly blueish and have a slight double reflection in them as the lcd screen inside it has 2 reflections when you look very closely.