code: public OrderingList<S> concat(OrderingList<S> other) {
          if (size() == 0) {
              return other;
          }
          OrderingList<S> newList = this;
          if (other.size() > 0) {
              for (OrderedProperty<S> property : other) {
                  newList = newList.concat(property);
              }
          }
          return newList;
      }
docs: Returns a list which concatenates this one with the other one.