code: func newKeyValueFromJSONConfig(cfg jsonconfig.Obj) (sorted.KeyValue, error) {
  	file := cfg.RequiredString("file")
  	if err := cfg.Validate(); err != nil {
  		return nil, err
  	}
  	opts := &kv.Options{}
  	db, err := kvutil.Open(file, opts)
  	if err != nil {
  		return nil, err
  	}
  	is := &kvis{
  		db:   db,
  		opts: opts,
  		path: file,
  	}
  	return is, nil
  }
docs: // newKeyValueFromJSONConfig returns a KeyValue implementation on top of a
  // github.com/cznic/kv file.