if c := s[n]; c < utf8.RuneSelf {
			if isIdentASCII(c) && (n > 0 || c < '0' || c > '9') {
				n++
				continue
			}
			break
		}
		r, nr := utf8.DecodeRuneInString(s[n:])
		if unicode.IsLetter(r) {
			n += nr
			continue
		}
		break
	}
	return s[:n], n > 0
}

// isIdentASCII reports whether c is an ASCII identifier byte.
func isIdentASCII(c byte) bool {

	var p textPrinter
	p.oneLongLine(&out, h.Text)
	s := strings.TrimSpace(out.String())
	if s == "" {
		return ""
	}
	out.Reset()
	out.WriteString("hdr-")
	for _, r := range s {
		if r < 0x80 && isIdentASCII(byte(r)) {
			out.WriteByte(byte(r))
		} else {
			out.WriteByte('_')
		}
	}
	return out.String()
}

type commentPrinter struct {
	*Printer
}

	for n < len(s) {
		if c := s[n]; c < utf8.RuneSelf {
			if isIdentASCII(c) && (n > 0 || c < '0' || c > '9') {
				n++
				continue
			}
			break
		}
		r, nr := utf8.DecodeRuneInString(s[n:])
		if unicode.IsLetter(r) {
			n += nr
			continue
		}
		break
	}
	return s[:n], n > 0
}

// isIdentASCII reports whether c is an ASCII identifier byte.