title: NSPopUpButton placeholder value?
body: <p>Notice in Xcode's symbols list (the NSPopUpButton directly above the editor, to the right of the recently edited documents), it shows <code>&lt;No selected symbol&gt;</code> when you're out of scope of any symbols it lists, but then when you click on it that option is not there.  Is there a trick to making this "placeholder" magic happen, or is there a setter somewhere I'm not seeing?</p>
  
  <p><img src="https://i.stack.imgur.com/JWswk.png" alt="Placeholder text">
  <img src="https://i.stack.imgur.com/NOBnr.png" alt="Not actually a menu item"></p>