Oh yeah, well spotted mate. There are also some gaps in the codes, like l=1, r=2 , middle=4 and then it jumps to 8 so maybe 5,6 and 7 are more buttons? I'll have to check this out later. Thanks. ;)
this is a binary set values, and makes it easier to combine values, and also read input.. ie. if the mousebuttons return "3", then you know that the left and right buttons are both pressed.. (1 + 2)