docs: 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;       
      }