docs: function(options) {
      options = options ? _.clone(options) : {};
      options.indexKeys = this.indexKeys || options.indexKeys;
      options.unionKey = this.unionKey || options.unionKey;
      if (this.indexKey) options.indexKeys.push(this.indexKey);
      var args = [this, options];
      return nodefn.apply(_.bind(this.indexDb.readFromIndexes, this.indexDb), args);
    }