title: What's the point of -primitiveValueForKey:?
body: <p><code>-setPrimitiveValue:forKey:</code> won't trigger KVO notifications. But in my brain, KVO only makes sense when something changes. But how can change something when I only access it for read?</p>
  
  <p><code>-primitiveValueForKey:</code> only gets the object for some key. But it won't modify it. So why would/could this cause KVO notifications when using <code>-valueForKey:</code>?</p>
  
  <p>(Of course there is a point, but I don't see it yet.)</p>