How does the RPL tail-cap work?

The one I have is seemingly a switch that selects from a variety of resistors, all less than 2Ω. As far as I can tell, this would only serve to drop extra voltage from the supply for the driver, but if it is a constant current driver, why is it affected by supply voltage? Does a battery at lower charge have the same effect as a fully charged battery with an Ω or two in series?

How does the driver "see" the value in the tail cap?

Ask http://laserpointerforums.com/members/bootleg2go/. He owns the company.