EXAMPLE

standalone:

DoMethod(obj,MUIM_CallHook,&hookstruct,13,42,"foobar","barfoo");

within a notification statement:

DoMethod(propobj,MUIM_Notify,MUIA_Prop_First,MUIV_EveryTime,
         propobj,3,MUIM_CallHook,&prophook,MUIV_TriggerValue);

prophook will be called every time the knob is moving and gets
a pointer to the knobs current level in a1.