订阅将在一段时间后失效，比方说，24小时，或将其作为一个参数传入。
The subscription would lapse after, say, 24 hours, or that could be passed in as a parameter.
大英图书馆第一阶段专注于数字化19世纪的作品，因为它们没有涉及到版权保护，可以免费提供给读者阅读，（版权保护在原作者死后70年后失效）。
The library concentrated the first stage of digitisation on the 19th century because the books are out of copyright and so can be offered free. Copyright runs out 70 years after an author’s death.
除此以外，它还具有绝对有效期，即在定义的时间段之后将会失效。
On top of this, it has an absolute validity period which invalidates its usage after a defined period of time.
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