client.go
func OptQueryShards(shards ...uint64) QueryOption {
	return func(options *QueryOptions) error {
		options.Shards = append(options.Shards, shards...)
		return nil
	}
}
func OptQueryShards(shards ...uint64) QueryOption {
	return func(options *QueryOptions) error {
		options.Shards = append(options.Shards, shards...)
		return nil
	}
}
// OptQueryShards restricts the set of shards on which a query operates.