What happened to the Compose Key?

[Jan Willem Stumpel <jstumpel@planet.nl>]

I noticed that I don't have a Compose Key under X (= Multi_key) anymore.
I don't know which of my rather frequent Sid upgrades made it disappear.
Does anyone know where Debian used to set this?

I know I can get it back by calling

  xmodmap -e xmodmap -e "keycode 116 = Multi_key"

(this makes the right Windows key the Compose key). But I would like to 
make it a system-wide default.

From Google, it appears this can be set in modern versions of
/etc/X11/XF86Config-4, as an "Option" in the "InputDevice" section. But 
which Option? I could not find a list of such "Options" anywhere.

Regards, Jan