Actually this is a bit off, please reference [Mutable Unordered Accessors](https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/KeyValueCoding/Articles/AccessorConventions.html#//apple_ref/doc/uid/20002174-SW16), Key-Value Coding Programming Guide (). The methods were added to facilitate faster Key-Value Coding because methods must conform to;

* `-add<Key>Object:` or `-add<Key>:`
* `-remove<Key>Object:` or `-remove<Key>:`
* `-intersect<Key>:`

I suppose the original design exposing the underlying mutable set was not the best call. Also, now we announce `subscribedViews` but privately work on `subscribedLayers` which is incongruent.