title: What is the graphical layout editor's "fragment providing context" pulldown used for?
body: <p>There is a pulldown menu next to the theme pulldown; its hover text reads "associated activity or fragment providing context".  </p>
  
  <p>This (new) widget is not described (or shown) in the graphical layout editor <a href="http://developer.android.com/tools/help/adt.html#graphical-editor" rel="nofollow noreferrer">documentation</a>.  </p>
  
  <p>I assume that this is an activity or fragment that typically displays this view.  But what does the layout editor do with this information?   Can it somehow be used to preview action bar customizations?</p>
  
  <p><img src="https://i.stack.imgur.com/KdRh9.png" alt="enter image description here"></p>