public function setBlackTagList(array $tags)
    {
        if (!$this->special_characters_allowed) {
            throw new RuntimeException('All special chars will be escaped. Set AllowHtml to use black list');
        }

        if ($this->white_tag_list) {
            throw new RuntimeException('White list already added.');
        }

        $this->black_tag_list = $tags;
    }