title: Why does a declared property use both retain and readonly?
body: <p>I've noticed that some of Apple's examples include both a <code>retain</code> and <code>readonly</code> modifier on properties. What's the point of including <code>retain</code> if no setter gets generated when we're using the <code>readonly</code> modifier?</p>
  
  <p>Example: <code>@property (retain, readonly) NSString *title;</code> from the AnimatedTableView sample.</p>