code: func (s *SearchSource) SearchAfter(sortValues ...interface{}) *SearchSource {
  	s.searchAfterSortValues = append(s.searchAfterSortValues, sortValues...)
  	return s
  }
docs: // SearchAfter allows a different form of pagination by using a live cursor,
  // using the results of the previous page to help the retrieval of the next.
  //
  // See https://www.elastic.co/guide/en/elasticsearch/reference/7.0/search-request-search-after.html