private function save()
 {
     $this->config->set_categories_number_per_page($this->form->get_value('categories_number_per_page'));
     $this->config->set_columns_number_per_line($this->form->get_value('columns_number_per_line'));
     $this->config->set_display_type($this->form->get_value('display_type')->get_raw_value());
     $this->config->set_root_category_description($this->form->get_value('root_category_description'));
     $this->config->set_authorizations($this->form->get_value('authorizations')->build_auth_array());
     FaqConfig::save();
     FaqService::get_categories_manager()->regenerate_cache();
     FaqCache::invalidate();
 }