code: func (f Wildcard) Regexp() string {
  	const any = `%`
  	// escape all meta-characters in pattern string
  	pattern := regexp.QuoteMeta(f.Pattern)
  	// if the pattern is anchored, add regexp analog for it
  	if !strings.HasPrefix(pattern, any) {
  		pattern = "^" + pattern
  	} else {
  		pattern = strings.TrimPrefix(pattern, any)
  	}
  	if !strings.HasSuffix(pattern, any) {
  		pattern = pattern + "$"
  	} else {
  		pattern = strings.TrimSuffix(pattern, any)
  	}
  	// replace wildcards
  	pattern = strings.NewReplacer(
  		any, `.*`,
  		`\?`, `.`,
  	).Replace(pattern)
  	return pattern
  }
docs: // Regexp returns an analog regexp pattern in format accepted by Go stdlib (RE2).