Browsers do not parse xml documents and create dom models instantly , and this can reduce the feeling of " snappiness " needed by some ajax components , especially when parsing large documents on slower machines 浏览器不能立即解析xml文档并生成dom模型，所以这会降低某些ajax组件需要的“迅捷”感，特别是在较慢的机器上解析大型文档的时候更是如此。
