code: func (s *Segment) addAnnotation(key string, value interface{}) {
  	s.Lock()
  	defer s.Unlock()
  
  	if s.Annotations == nil {
  		s.Annotations = make(map[string]interface{})
  	}
  	s.Annotations[key] = value
  }
docs: // addAnnotation adds a key-value pair that can be queried by AWS X-Ray.
  // AWS X-Ray only supports annotations of type string, integer or boolean.