code: function getNextRank(callback) {
  
        return self.getNextRank(parent, function(err, rank) {
          if (err) {
            return callback(err);
          }
          nextRank = rank;
          return callback(null);
        });
      }
docs: TODO: there's a potential race condition here. It's not a huge deal, having two pages with the same rank just leads to them sorting randomly, the page tree is not destroyed. But we should have a cleanup task or a lock mechanism