title: Why isn't UIPopoverController KVO compliant?
body: <p>I'm using a <code>UIPopoverController</code> to display some content, and I wanted to use KVO to observe the <code>popoverVisible</code> property. Unfortunately it seems that <code>UIPopoverController</code> isn't KVO compliant.</p>
  
  <p>Could anyone shed some light into why this is the case? Is there some way to subclass <code>UIPopoverController</code> and <em>make</em> its <code>popoverVisible</code> property KVO? I feel like this won't necessarily work if Apple's code is changing the instance variable directly rather than via a property.</p>