code: func whereLabelValueMatches(containers Context, label, pattern string) (Context, error) {
  	rx, err := regexp.Compile(pattern)
  	if err != nil {
  		return nil, err
  	}
  
  	return generalizedWhereLabel("whereLabelValueMatches", containers, label, func(value string, ok bool) bool {
  		return ok && rx.MatchString(value)
  	})
  }
docs: // selects containers with a particular label whose value matches a regular expression