code: function(indexer, newNode, nextNode) {
          var returnVal = OpenLayers.ElementsIndexer.IndexingMethods.Z_ORDER(
              indexer, 
              newNode, 
              nextNode
          );
          
          if (nextNode && returnVal === 0) {            
              var result = nextNode._boundsBottom - newNode._boundsBottom;
              returnVal = (result === 0) ? 1 : result;
          }
          
          return returnVal;       
      }
docs: APIMethod: Z_ORDER_Y_ORDER
  This one should really be called Z_ORDER_Y_ORDER_DRAWING_ORDER, as it
  best describes which ordering methods have precedence (though, the
  name would be too long). 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 nodes with the lower y position will be "closer" than
  those with a higher y position. If two nodes have the exact same y
  position, however, then this method will revert to using drawing
  order to decide placement.
  
  Parameters:
  indexer - {<OpenLayers.ElementsIndexer>}
  newNode - {DOMElement}
  nextNode - {DOMElement}
  
  Returns:
  {Integer}