此扩展需要 libxml PHP 扩展。这表示需要使用 --enable-libxml，尽管这将隐式完成因为 libxml 是缺省开启的。
The XMLWriter extension was initially a PECL extension for PHP 5. It was later added to the PHP source (bundled) as of PHP 5.1.2. This extension is enabled by default.
There is one resource used by the procedural version of the XMLWriter extension: returned by xmlwriter_open_memory or xmlwriter_open_uri.