func AppendRune(p []byte, r rune) []byte {
	// This function is inlineable for fast handling of ASCII.
	if uint32(r) <= rune1Max {
		return append(p, byte(r))
	}
	return appendRuneNonASCII(p, r)
}

func appendRuneNonASCII(p []byte, r rune) []byte {
	// Negative values are erroneous. Making it unsigned addresses the problem.
	switch i := uint32(r); {
	case i <= rune2Max: