title: How to popup ANY content in Cocoa?
body: <p>Is there a right way to do this? I could not find any direct how-to for this; only gather some ideas from another kind of problems... </p>
  
  <p>So my closest to this is to create a new <code>NSWindow</code> or <code>NSPanel</code>, and make it the current window's child with order Above. </p>
  
  <p>But how to make it close when the user clicks off?<br>
  (This question is especially important in case this popup window does not contain any focusable controls, eg only a message or a drawing)</p>
  
  <p>Is this approach a good idea anyway?<br>
  Is there a better way to do this?</p>