code: func (s *TranslateFile) TranslateRowToString(index, field string, id uint64) (string, error) {
  	s.mu.RLock()
  	if idx := s.rows[fieldKey{index, field}]; idx != nil {
  		if ret, ok := idx.keyByID(id); ok {
  			s.mu.RUnlock()
  			return string(ret), nil
  		}
  	}
  	s.mu.RUnlock()
  	return "", nil
  }
docs: // TranslateRowToString translates a row ID to a string key.