How does hotkeys, lid close, suspend etc. work with Ubuntu on a newer Thinkpad Laptop?

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http://askubuntu.com – I am trying to setup my Thinkpad T420 with xmonad as window manager and with as little gnome as possible. If I launch gnome-settings-manager all my hotkeys (disable touchpad, volume up/down, brightness up/down mute etc) works and sleep when closing lid works. If I do not launch the gnome-settings-manager (which I am trying to avoid) only the brightness up/down works (disable touchpad, volume, sleep when closing lid etc. does not work). So I'm trying to understand how all this works. Why are the brightness keys (fn+home/end) different from disable touchpad (fn+f8)? I thought I had cracked i (HowTos)