code: func (v *Oid) AppendSubIds(subs []int) (*Oid, error) {
  	buf := bytes.NewBufferString(v.String())
  	for _, i := range subs {
  		buf.WriteString(".")
  		buf.WriteString(strconv.Itoa(i))
  	}
  	return NewOid(buf.String())
  }
docs: // Returns Oid with additional sub-ids