code: func (s *NodesStatsService) IndexMetric(indexMetric ...string) *NodesStatsService {
  	s.indexMetric = append(s.indexMetric, indexMetric...)
  	return s
  }
docs: // IndexMetric limits the information returned for `indices` metric
  // to the specific index metrics. Isn't used if `indices` (or `all`)
  // metric isn't specified..