protected function checkKey(array $rule, AbstractNode $node): bool
    {
        if ($rule['noKey']) {
            if ( ! is_null($node->getAttribute($rule['key']))) {
                return false;
            }
        } else {
            if ($rule['key'] != 'plaintext' && !$node->hasAttribute($rule['key'])) {
                return false;
            }
        }

        return true;
    }