code: func (c designateClient) ForEachRecordSet(zoneID string, handler func(recordSet *recordsets.RecordSet) error) error {
  	pager := recordsets.ListByZone(c.serviceClient, zoneID, recordsets.ListOpts{})
  	return pager.EachPage(
  		func(page pagination.Page) (bool, error) {
  			list, err := recordsets.ExtractRecordSets(page)
  			if err != nil {
  				return false, err
  			}
  			for _, recordSet := range list {
  				err := handler(&recordSet)
  				if err != nil {
  					return false, err
  				}
  			}
  			return true, nil
  		},
  	)
  }
docs: // ForEachRecordSet calls handler for each recordset in the given DNS zone