docs: function (revisionMap, callback) {
      var self = this;
      var ids = _.keys(revisionMap);
      async.each(ids, function (id, callback) {
        self.store.get(id, function (err, rev) {
          if (err) {
            return callback(err);
          }
          self.store.set(id, revisionMap[id] + 1, rev, callback);
        });
      }, callback);
    }