此处的规范
http://www.rssboard.org/rss-specification#requiredChannelElements具有为channel元素指定的这些可选参数：
这些告诉客户什么时候不需要更新..
skipHours – A hint for aggregators telling them which hours they can skip. This element contains up to 24 < hour > sub-elements whose value is a number between 0 and 23,representing a time in GMT,when aggregators,if they support the feature,may not read the channel on hours listed in the < skipHours > element. The hour beginning at midnight is hour zero.
skipDays – A hint for aggregators telling them which days they can skip. This element contains up to seven < day > sub-elements whose value is Monday,Tuesday,Wednesday,Thursday,Friday,Saturday or Sunday. Aggregators may not read the channel during days listed in the < skipDays > element.
和/或这告诉客户他们需要更新的频率.
