This extension wraps the libxml xmlWriter API. Represents a writer that provides a non-cached, forward-only means of generating streams or files containing XML data.
libxml xmlWriteのラッパ。何気にバージョンがでかい。
XML書く方の問題は本気でやる場合はこれで安定か！？
ref: XML_FastCreate
ref: Proposal for RSSBuilder