title: iOS Accessibility - is there a way to tell when VoiceOver has changed focus?
body: <p>I'd like to call a method every time a different element is focused while VoiceOver is active. I was hoping there would be some <code>UIAccessibilityNotification</code> for this, but I can't seem to find any.</p>
  
  <p>Ultimately, my goal is to add an additional condition prior to reading the accessibility label. For example, as opposed to saying (by default) "If <code>UIButton</code> becomes focused: read label", I'd like to be able to say "When <code>UIButton</code> becomes focused AND <code>UIButton</code>'s background color is blue: read label".</p>
  
  <p>So my question is: how do I either add an additional condition prior to reading the label, or receive a notification when a new element becomes focused?</p>