code: function(node) {
      cnt++;
      if (!node || cnt >= step) {
        if (ydn.db.core.req.SimpleCursor.DEBUG) {
          goog.global.console.log('advance to ' + (node ? node.value : 'null'));
        }
        return me.defaultOnSuccess_(node);
      }
    }
docs: Node traversal function.
  @param {goog.structs.AvlTree.Node} node
  @return {boolean|undefined} continuation.