public function scroll($lines, $enter_from, $exit_to)
    {
        $keyframes   = $this->enterFrom($lines, $enter_from);
        $keyframes   = array_merge($keyframes, $this->exitTo($lines, $exit_to));
        $keyframes   = array_unique($keyframes, SORT_REGULAR);
        $keyframes[] = reset($keyframes);

        return $keyframes;
    }