The WebXR Plane Detection API allows sites to retrieve the set of planes detected in the user's environment. This is both less work for developers and more powerful than using the depth-sensing WebXR feature as planes such as walls that are occluded by objects can still be fully represented if the system is aware of the boundaries of the wall. (Whereas a depth map would show the wall, but it would be broken up by any objects in front of the wall, potentially obscuring the full scope of the wall). Further, semantic labeling information is exposed where the device is aware of such labels and they fit into predefined categories, allowing better knowledge about the world.
Samples: https://immersive-web.github.io/webxr-samples/proposals/plane-detection.html