code: func (s *SearchService) SearchType(searchType string) *SearchService {
  	s.searchType = searchType
  	return s
  }
docs: // SearchType sets the search operation type. Valid values are:
  // "dfs_query_then_fetch" and "query_then_fetch".
  // See https://www.elastic.co/guide/en/elasticsearch/reference/7.0/search-request-search-type.html
  // for details.