code: function(indexer, newNode, nextNode) {
          var returnVal = OpenLayers.ElementsIndexer.IndexingMethods.Z_ORDER(
              indexer, 
              newNode, 
              nextNode
          );
          
          // Make Z_ORDER subscribe to drawing order by pushing it above
          // all of the other nodes with the same z-index.
          if (nextNode && returnVal == 0) {
              returnVal = 1;
          }
          
          return returnVal;
      }
docs: APIMethod: Z_ORDER_DRAWING_ORDER
  This method orders nodes by their z-index, but does so in a way
  that, if there are other nodes with the same z-index, the newest
  drawn will be the front most within that z-index. This is the
  default indexing method.
  
  Parameters:
  indexer - {<OpenLayers.ElementsIndexer>}
  newNode - {DOMElement}
  nextNode - {DOMElement}
  
  Returns:
  {Integer}