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While the UIDocument class is the cornerstone of document storage using the iCloud service it is also of considerable use and advantage in terms of using the local file system storage of an iOS device. As an abstract class, UIDocument must be subclassed and two mandatory methods implemented within the subclass in order to operate. This chapter worked through an example of using UIDocument to save and load content using a locally stored document. The next chapter will look at using UIDocument to perform cloud based document storage and retrieval.