Gnome 3.21: how to define compose key?

[Joost Kraaijeveld <J.Kraaijeveld@Askesis.nl>]

Hi,

I want to use my right super key (right win) as my compose key to be
able to type accented letters. 

I have read the online manual regarding the compose key but that does
not work: there is no (disabled) "Compose Key" in "Activities-
>Keyboard->Typing". (The manual actually say "Activities->Keyboard-
>Shortcut tab->Typing" but I assume that that is for a previous version
of Gnome)

How do I enable a Compose  Key in Gnome 3.21?

TIA

-- 
Groeten,

Joost Kraaijeveld