title: How to add a docked item into another docked item?
body: <p>I have a panel which has a toolbar as docked item. I want to add a button inside this docked toolbar. But when i add it, it doesn't show up at all.
  So how do I do that? Or is there a more convenient way to achieve this?</p>
  
  <p>And, if I want to add it to the right side of the toolbar?</p>
  
  <p>Thanks.</p>