code: func Tags(tags map[string]string) SpanOption {
  	return func(t *Tracer, s *spanImpl) {
  		for k, v := range tags {
  			s.Tags[k] = v
  		}
  	}
  }
docs: // Tags sets initial tags for the span being created. If default tracer tags
  // are present they will be overwritten on key collisions.