enc := expfmt.NewEncoder(w, FmtText)
	if err != nil {
		return err
	}
	for _, mf := range mfs {
		if err := enc.Encode(mf); err != nil {
			return err
		}
	}
	return nil
}

func applyHeaders(into http.Header, from http.Header, keys ...string) {
	for _, key := range keys {
		val := from.Get(key)
		if val != "" {
			into.Set(key, val)
		}
	}
}