anchor.diff:    }
   }
   
  -class ShipPredicate {
  +class ShipPredicate extends Observable {
     @observable final List<ShipPredicate> or =
         new ObservableList<ShipPredicate>();
     @observable final List<ShipPredicate> and =
  
positive.code:   }
  }
  
  class ShipPropertyFilter {
    @observable String property;
    @observable dynamic value;
    @observable int operator;
  
negative.code:   }
  }
  
  class ShipSorter extends Observable {
    @observable String name;
    @observable bool reversed;
  
  