Thanks for your help. Then IDCMP rawkey is set up in the mSetup function...

PROC mSetup(cl:PTR TO iclass,obj:PTR TO object,msg:PTR TO muip_handleinput)
IF doSuperMethodA(cl,obj,msg)=NIL THEN RETURN FALSE
Mui_RequestIDCMP(obj, IDCMP_MOUSEBUTTONS OR
IDCMP_RAWKEY OR
IDCMP_VANILLAKEY)
ENDPROC MUI_TRUE

The mHandleInput function calls the RAWKEY function...

PROC mHandleInput(cl:PTR TO iclass, obj:PTR TO object, msg:PTR TO muip_handleinput)
...
IF msg.imsg
selectdummy:=msg.imsg.class
qual := msg.imsg.qualifier
code := msg.imsg.code

SELECT selectdummy
CASE IDCMP_RAWKEY; handlerawkeyevent(qual, code)
CASE IDCMP_VANILLAKEY; handlevanillakeyevent(qual, code)
...
ENDSELECT
ENDPROC doSuperMethodA(cl,obj,msg)

And then the handlerawkeyevent() function handles what is actually pressed...

PROC handlerawkeyevent(qualifier, code)
DEF value
IF qualifier AND (IEQUAL_ALT)
SELECT code
CASE CURSOR_UP_KEY
...
ENDSELECT
...
ENDIF
ENDPROC

Am I missing something when it comes to MUI4? Thanks again!