Air Filter Box

I have a 2001 A4 1.8T, and I took the air filter box to clean the pre-filter screen.  At the bottom of the box, I noticed a spring loaded flap that opens inward.  The other side is the wheel well, as you may be aware.  Does anyone know the function of this flap? 
 
Also, on top of the filter box, there are four holes.  They appear to be threaded.  Was something attached there, or is it an option for another model?
 
Thanks.

I don't know anything about the flap but the holes on top of your air box is for older model 1.8T engines, the ICM (ignition control module) sits there, your icm's are integrated into the ignition coils.

Thanks for the info.