Breadcrumbs appear at the top of the screen when navigating between different apps in iOS. For example, on the iPhone running iOS 9 or later tapping a banner notification will jump to the associated app.
If there was already another app running, a shortcut to return to the previous app will be present at the top of the screen. This is a breadcrumb to help navigate directly to the previous app, without having to exit to the iOS home screen first.
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