Apple's new iPhone Duo has a special option in its display settings that adds a narrow black border to the left side of the front screen. Blogger Nicolas Lellouche discovered the setting in the Display & Brightness menu during his hands-on time with the device shortly after Apple's iPhone event stream last week. The idea behind the 'Shift Left Edge' setting – which roughly doubles the width of the black border – is to accommodate cases that slightly cover that edge of the iPhone Duo's display while making the iOS back swipe gesture work as expected.

Apple offers two official cases for its new foldable: an iPhone Duo Case and a Folio with Kickstand. It's unclear if either of these cases covers the left edge of the display, but it seems unlikely that Apple would design them to do so. What's more likely is that Apple is trying to accommodate bulky protective third-party cases that tend to cover the left edge.

We'll know for sure when the first reviews of the iPhone Duo hit the web. Pre-orders for the iPhone Duo go live October 16, with availability starting October 23.