What keysym is for scroll-wheel-up and scroll-wheel-down in bindings?

[Christopher Roy Bratusek <zanghar freenet de>]

Hi all,

I just wanted to try to bind cycle-windows to "scroll-wheel-up" and
cycle-windows-backwards to "scroll-wheel-down", but I can't find the
correct binding for that (Tried Button4-Off/Click, same for Button5). 

Any ideas?

Chris