What View is at the top of the Navigator panel in Xcode?

Can someone tell me how Xcode provides the row of images (see above) at the top of the Navigator panel to switch among the various options? It does the same thing with the Inspector panel.

Thanks, Mark

It looks like a toolbar. But it could as well be a very custom view in which they add butoons for instance.

What is the point ?

What View is at the top of the Navigator panel in Xcode?
 
 
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