Hi Michel,
 
i have work on my problem.
 
I implement the #displayString but it d'ont solve my question.
    ( #displayString isn't call when rendering )
 
I have  solved my problem with #optionsAndLabels:
 
^MASingleOptionDescription new
        
        reference: .....
        optionsAndLabels: ..............
 
For you, this it's a valid solution ?
 
Thanks,
 
Dario