code: func (s *SearchSource) FetchSourceIncludeExclude(include, exclude []string) *SearchSource {
  	s.fetchSourceContext = NewFetchSourceContext(true).
  		Include(include...).
  		Exclude(exclude...)
  	return s
  }
docs: // FetchSourceIncludeExclude specifies that _source should be returned
  // with each hit, where "include" and "exclude" serve as a simple wildcard
  // matcher that gets applied to its fields
  // (e.g. include := []string{"obj1.*","obj2.*"}, exclude := []string{"description.*"}).