有时，使用简单的基于时间的对象过期更为容易和简洁。
Sometimes, it's easier and cleaner to use simple timed-based expiration of objects.
执行 HTTP 缓存时，最重要的部分就是确定哪些对象可以存储在缓存之中，以及这些对象将在何时过期等。
The most important part of performing HTTP caching is determining which objects can be stored in the cache, when they are to expire, etc.
这个技术允许缓存Cells视图，直到一个加载的版本更新方法决定其已经过期，而不会使得一个Cell实例失去其面向对象的特性。
It allows Cell views to be cached until an attached versioning method decides to expire it, without loosing the object-oriented features of a Cell instance.
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