code: func (o *Offset) MarshalText() ([]byte, error) {
  	switch *o {
  	case OffsetNewest:
  		return []byte("newest"), nil
  	case OffsetOldest:
  		return []byte("oldest"), nil
  	}
  	return []byte(fmt.Sprintf("%v", *o)), nil
  }
docs: // MarshalText marshals offset. It's used to handle two special cases "newest" and "oldest".