/// functional constraints for a model of the DragAndDropConverterConcept
    void constraints() {
        // associated types:
        typedef typename dnd_converter_source_type<DragAndDropConverter>::type associated_type1;
        typedef typename dnd_converter_dest_type<DragAndDropConverter>::type associated_type2;

        using adobe::convert;
        convert(*converter, *src_value);
    }
 /// notifies the converter whether or not it should
 /// be enabled (and thus able to modify the model)
 static dest_type convert(const DragAndDropConverter& converter, const source_type& src_value)
 {
     using adobe::convert;
     return convert(converter, src_value);
 }