code: func RuneLen(r rune) int {
  	switch {
  	case r < 0:
  		return -1
  	case r <= rune1Max:
  		return 1
  	case r <= rune2Max:
  		return 2
  	case r <= rune3Max:
  		return 3
  	case r <= utf8.MaxRune:
  		return CESUMax
  	}
  	return -1
  }
docs: // RuneLen returns the number of bytes required to encode the rune.