The release of a new build of Windows 10 is always an opportunity to also see what new APIs Microsoft has added to the OS, which can give us a glimpse into what features the company is developing software and hardware wise.
A diff of Windows 10 Build 17704 compared to an earlier version of the OS shows Microsoft is currently actively developing ways the OS can respond to the hinge state of a 2-panel dual-screen device.
The 5 states listed are closed (presumably with the 2 screens facing inwards), concave (i.e. less than 180 degrees open), flat (ie 180 degrees open), convex, or what Lenovo has christened as Tent mode, and full, which I can only assume means nearly 360 degrees open.
The API would mean applications will be able to respond to changes in the orientation of the device, with Microsoft in patents suggesting that in tent mode the device could display an alarm clock and in convex mode one side could present an on-screen keyboard like a laptop to users.
Microsoft is of course not the only one developing dual-screen Windows 10 devices, with companies like Lenovo an Asus doing it much more publicly. The so-called Surface Phone is however still rumoured to not just be in development but also heading to the market this year, in what we can only assume is a launch linked to Windows 10 RS5.
The full API diff, by Vitorgrs, can be seen here.