title: NSOutlineView with badge of unread messages like Mail.app
body: <p>I'm trying to create a user interface similar to the iTunes source list or the Mail.app mailbox list where a badge with a number (e.g. unread emails, new podcasts) is shown at the right hand side of an element.</p>
  
  <p>Based on Apple's SourceList example, I have an <code>NSOutlineView</code> set up to display a couple of groups and a few items in each group. </p>
  
  <p>Is there a standard UI element to represent the "badge" with a number for each entry? I could not find anything in the docs. I suspect I will have to extend <code>NSTextFieldCell</code> and do the drawing myself.</p>
  
  <p>Are there any examples out there of how to do this?</p>