code: private static void exportGroup(Xml nodeGroups, TileGroup group)
      {
          final Xml nodeGroup = nodeGroups.createChild(NODE_GROUP);
          nodeGroup.writeString(ATT_GROUP_NAME, group.getName());
          nodeGroup.writeString(ATT_GROUP_TYPE, group.getType().name());
  
          for (final TileRef tileRef : group.getTiles())
          {
              final Xml nodeTileRef = TileConfig.exports(tileRef);
              nodeGroup.add(nodeTileRef);
          }
      }
docs: Export the group data as a node.
  
  @param nodeGroups The root node (must not be <code>null</code>).
  @param group The group to export (must not be <code>null</code>).