if err == nil && f == u.Fragment {
			return u.RawFragment
		}
	}
	return escape(u.Fragment, encodeFragment)
}

// validOptionalPort reports whether port is either an empty string
// or matches /^:\d*$/
func validOptionalPort(port string) bool {
	if port == "" {
		return true
	}
	if port[0] != ':' {
		return false
	}
	for _, b := range port[1:] {
		if b < '0' || b > '9' {