protected function AddCacheLifetimeField()
    {
        $name = 'CacheLifetime';
        $label = "Core.ContentForm.$name";
        $field = Input::Text($name, (string) (int) $this->Content()->GetCacheLifetime());
        $this->AddField($field, false, Trans($label));
        $this->AddValidator($name, Integer::PositiveOrNull(), $label . '.');
    }