Remember the dual-screen Surface Neo and Surface Duo that Microsoft previewed last year, finally giving us a glimpse of how to control apps across multiple screens on Windows 10X and Android devices? Now. [Microsoft released the Surface Duo SDK (Software Development Kit) on January 22. This way, app makers can be the first to know how their apps will be designed for these upcoming devices.

For a visual taste of how Surface Duo will work, check out these two animations: Windows Central's Zac Bowden plays with an animation for Android Surface Duo and designer Jonas Daehnert rendered the clip on the device.

The introduction to the Surface Pro SDK provides a lot of detail for the curious and (even better) is written in language that can be understood without a degree in coding.

One of the major warnings Microsoft proclaims in this post is that developers should avoid putting important objects in the gap between both screens (Microsoft calls this a "seam").

Apps default to a maximized view on one screen, and other options include straddling the app across both panes. Both view modes will offer a full-screen option that hides the system interface, including the taskbar and system tray.

Microsoft advises app developers to consider five main view modes for how their apps will work on these paired screens. Extended Canvas, the most obvious view, is essentially a full-screen mode that spreads the app across both display panes.

Microsoft primarily suggests using this mode for drawing apps and "free canvases that users can scroll freely to avoid seams (dots between two screens)," such as map apps like Tile.

Next, Master-detail is like a split-view interface with a list view on one side (the "master" side) and a view focused on what was selected on the former display (the "detail" side). This would be for apps that can be split in half and keep each part on its own side. Microsoft suggests that e-mail, calendar, photo, and music apps would work well in this format. This content would be adjusted to landscape orientation when rotated.

The two pages are very simple and targeted at books, with similar content on each screen, following in turn. There is a small amount of border space, but the majority of each screen is for each "page," and this content will likely remain intact even if the user rotates the screen.

The dual view is targeted at creative professional apps and displays similar content on both sides. According to the documentation, one side could be used to preview edits made on the other, or for apps that have two separate screens.

Finally, the companion pane is designed to allow a second screen that turns one display into a set of controls for the other. One proposal suggests slider controls for image editing (contrast, brightness, and other options), another shows multi-track editing of video, and a third looks like a giant GameBoy, with a directional pad and two circular buttons on the second screen, while the first screen showing the game being played.

The development kit release includes an Android Emulator that previews the app on the Surface Duo image. The Surface Duo SDK Preview, which can be downloaded here, runs in Android Studio and Microsoft Visual Studio. Surface Duo is an Android device and Surface Neo is a Windows 10X device.