code: func NewRegexpMatcher(name, pattern string) (Matcher, error) {
  	re, err := regexp.Compile(pattern)
  	if err != nil {
  		return nil, err
  	}
  	return &regexpMatcher{name: name, re: re}, nil
  }
docs: // NewRegexpMatcher returns a new matcher verifying that a value matches
  // the regular expression pattern.