title: ARC - The meaning of __unsafe_unretained?
body: <p>Just want to make sure that I got it right:</p>
  
  <ol>
  <li>Do I need to <code>__unsafe_unretain</code> objects that I don't own?</li>
  <li>If an object is <code>__unsafe_unretained</code> Do I need to use <code>assign</code> in the <code>@property</code>? Does that mean that the object is not retained, and just refers to the object I assign to?</li>
  <li>When would I want to use it except of delegates?</li>
  <li>Is that an ARC thing or was it in use before?</li>
  </ol>