We've been diddling around with the extra buttons on the AccuPoint
and the iPaq/Bitsy.  It's early to tell, but it looks like there are some
interesting possibilities.  Please play and see if you come up with
ideas.

Go to /sys/src/libdraw/mouse.c and delete the the line that masks
the buttons with 7.  Then rio will get the buttons delivered to it. You
can then figure out how to get the buttons from the mouse to the
driver, and rio will get them. I'm pretty sure the system went out
with a mouse driver that supports the AccuPoint, which is a variant
of the Intellimouse, and has its lunatic versions of buttons 4 and 5.
The important point is that those buttons do move through the
system.  (Rio didn't care beforehand because aux/accupoint remaps
these two buttons to button two; the iPaq uses six buttons and rio
now does a few things with these.)

Happy hacking.

-rob