code: func (s *ScrollService) SearchSource(searchSource *SearchSource) *ScrollService {
  	s.ss = searchSource
  	if s.ss == nil {
  		s.ss = NewSearchSource()
  	}
  	return s
  }
docs: // SearchSource sets the search source builder to use with this iterator.
  // Notice that only a certain number of properties can be used when scrolling,
  // e.g. query and sorting.