spec on "multimedia buttons"

[st at stereolyzer.net]

Hello, 

i'd like to ask for your opinion on a common spec for handling
"multimedia keys" like volume +/- which are commonly used on laptops
and (recent) usb keyboards.

Let me briefly describe a showcase using the above example setting
volume (for GNOME volume-applet):
When the user modifies the volume via keys the volume-applet on the
panel is activated and moves the slider up and down following the
user input.
So we wouldn't have to ways of displaying and setting the actual
volume level with gtkpbbuttons / applet for keyboard / mouse.

I think apple does something like that on OSX.

The same would apply to screen brightness.

Sorry if that's already an old topic, I might have missed the search
function on the list archives.

Thanks for your time, 
Robert