The optional objects are: language, copyright, managingEditor, webMaster, pubDate, lastBuildDate, category, generator, docs, cloud, ttl, image, rating, textInput, skipHours, and skipDays.
可选对象是：language, copyright、managingEditor, webMaster、pubDate, lastBuildDate、category, generator、docs、cloud、ttl、image、rating、textInput、skipHours 和 skipDays。