// Use &re.Rune instead of &class to avoid allocation.
	re.Rune = class
	class = cleanClass(&re.Rune)
	if sign < 0 {
		class = negateClass(class)
	}
	re.Rune = class
	p.push(re)
	return t, nil
}

// cleanClass sorts the ranges (pairs of elements of r),
// merges them, and eliminates duplicates.
func cleanClass(rp *[]rune) []rune {

	// Sort by lo increasing, hi decreasing to break ties.

	// AppendRange should collapse each of the new ranges
	// into the earlier ones (it looks back two ranges), so that
	// the slice never grows very large.
	// Note that we are not calling cleanClass.
	var r []rune
	for i := rune('A'); i <= 'Z'; i++ {
		r = appendRange(r, i, i)
		r = appendRange(r, i+'a'-'A', i+'a'-'A')
	}
	if string(r) != "AZaz" {