code: public static XElement storeList(String container, String item, Iterable<? extends XSerializable> source) {
          XElement result = new XElement(container);
          for (XSerializable e : source) {
              e.save(result.add(item));
          }
          return result;
      }
docs: Create an XElement with the given name and items stored from the source sequence.
  @param container the container name
  @param item the item name
  @param source the source of items
  @return the list in XElement