protected function addBasicPurgeFilters() {
        if ($this->purgeFiltersInitialized) {
            return;
        }

        $this->purgeFilters[] = function ($attributeKey) {
            // disallow password confirmation fields
            if (Str::endsWith($attributeKey, '_confirmation')) {
                return false;
            }

            // "_method" is used by Fly\Routing\Router to simulate custom HTTP verbs
            if (strcmp($attributeKey, '_method') === 0) {
                return false;
            }

            // "_token" is used by Fly\Html\FormBuilder to add CSRF protection
            if (strcmp($attributeKey, '_token') === 0) {
                return false;
            }

            return true;
        };

        $this->purgeFiltersInitialized = true;
    }