func isQtext(r rune) bool {
	// Printable US-ASCII, excluding backslash or quote.
	if r == '\\' || r == '"' {
		return false
	}
	return isVchar(r)
}

// quoteString renders a string as an RFC 5322 quoted-string.
func quoteString(s string) string {
	var b strings.Builder
	b.WriteByte('"')
	for _, r := range s {
		if isQtext(r) || isWSP(r) {
			b.WriteRune(r)
		} else if isVchar(r) {

	}

	return result, remainder, nil
}

func parseQuotedString(quotedString string) (string, string, error) {
	if len(quotedString) == 0 {
		return "", "", errors.New("invalid quoted string: 0-length")
	}

	if quotedString[0] != '"' {
		return "", "", errors.New("invalid quoted string: missing initial quote")
	}

	quotedString = quotedString[1:]
	var remainder string
	escaping := false
	closedQuote := false

	s.SkipSpace()
	s.notEOF()
	switch verb {
	case 'q':
		str = s.quotedString()
	case 'x', 'X':
		str = s.hexString()
	default:
		str = string(s.token(true, notSpace)) // %s and %v just return the next word
	}
	return
}

// quotedString returns the double- or back-quoted string represented by the next input characters.
func (s *ss) quotedString() string {
	s.notEOF()
	quote := s.getRune()
	switch quote {

		// Section 4. Since it has been 16 years, we no longer accept that.)
		in = in[1:]
	QuotedString:
		for {
			if len(in) == 0 {
				return mailbox, false
			}
			c := in[0]
			in = in[1:]

			switch {
			case c == '"':
				break QuotedString

			case c == '\\':
				// quoted-pair
				if len(in) == 0 {
					return mailbox, false
				}