Validation on document before to save in Arbortext Editor.

I'm adding a callback on the Save option in the Arbortext Editor menu.

The callback works perfectly but I don't know how to prevent the save from being made in a particular case.

Here is my addition of the callback :

doc_add_callback(current_doc(), 'save', 'triggerSaveDocument');

Here is my implementation of that callback :

function triggerSaveDocument(doc, op){
 local isValidDocument = callComparaison();
 if(!$isValidDocument){
 #I need here to prevent the save process of being made.
 return 0;
 }
}

 I tried return 0;  but that didn't work.

Do you know how to bypass the saving ?

Thanks for your time.