In the [OS X v10.11 beta release notes](https://developer.apple.com/library/prerelease/mac/releasenotes/MacOSX/WhatsNewInOSX/Articles/MacOSX10_11.html#//apple_ref/doc/uid/TP40016227-SW1), I find the following:

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> NSNotificationCenter and NSDistributedNotificationCenter no longer send notifications to registered observers that may be deallocated. If the observer is able to be stored as a zeroing-weak reference the underlying storage stores the observer as a zeroing weak reference. Alternatively, if the object cannot be stored weakly (because it has a custom retain/release mechanism that would prevent the runtime from being able to store the object weakly) **the object is stored as a non-weak zeroing reference**. This means that observers are not required to un-register in their deallocation method. [emphasis mine]
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This doesn't make sense to me. If it is a non-weak reference, wouldn't it be a strong reference, then? So the NSNotificationCenter would still be an owner, so the object wouldn't deallocate (until manually unregistered), so it's nonsensical in this context to say it's "zeroing".

If this is referring to a sort of `__unsafe_unretained` reference, then the question is…how then would NSNotificationCenter avoid messaging a zombie?