title: Window vs Offscreen window
body: <p>In the 3xx versions of <a href="https://glade.gnome.org/" rel="nofollow noreferrer">GLADE Interface Designer</a> there is a toplevel widget called "Offscreen window", which icon has the looking of that: <a href="https://i.stack.imgur.com/BxKGi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BxKGi.png" alt="enter image description here"></a></p>
  
  <p>How it differs from the common window toplevel widget <a href="https://i.stack.imgur.com/AHsQL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AHsQL.png" alt="enter image description here"></a> and what is it used for?</p>