WPT details: No tests as of yet.
The Viewport Segments API allows developers to adapt their website/webapp layout to target foldable devices. The viewport segments defines the position and dimensions of a logically separate region of the viewport. Viewport segments are created when the viewport is split by one or more hardware features (such as a fold or a hinge between separate displays) that act as a divider; segments are the regions of the viewport that can be treated as logically distinct by the author.
Add a new CSS/JavaScript API to enable web developers to target a new class of foldable devices. JS API spec: https://drafts.csswg.org/css-viewport/#segments
Docs: https://github.com/WICG/visual-viewport/blob/gh-pages/segments-explainer/SEGMENTS-EXPLAINER.md
Samples: https://github.com/foldable-devices/demos
Explainers: https://github.com/WICG/visual-viewport/blob/gh-pages/segments-explainer/SEGMENTS-EXPLAINER.md