Use of the Wii Classic Controller's backside?

Question

There's these two rectangular slots, one bigger than the other, on the back of the Wii Classic Controller. Anyone have an idea of what this is used for?

Answer 1

Absolutely nothing.

Answer 2

No, you're not supposed to use the Wii Classic Controller in your backside.  Voids your warranty.

Answer 3

This is used for attaching certain grips like hand grips and Wiimote grips.