// 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.