The Early Adopters Guide is updated when spec changes land in Chrome. Feel free to open issues or submit pull requests.
I'll be expanding the latter as the origin trial progresses. You can find more information in both the original explainer and our Immersive Web Early Adopters Guide. I want to give you enough to start making sense of the WebXR samples. There's more to this new API than I can go to in an article like this.
Read about it in Augmented reality for the web. When this article was originally published during the Chrome 67 beta period, only VR capabilities were enabled. It's available in the previously mentioned origin trial as well as through a polyfill. The 'X in XR is intended as a sort of algebraic variable that stands for anything in the spectrum of immersive experiences. Like the WebVR spec before it, the WebXR Device API is a product of the Immersive Web Community Group which has contributors from Google, Microsoft, Mozilla, and others. Implementors of WebVR have committed to migrating to the WebXR Device API.
The WebXR Device API was designed and named with these expanded use cases in mind and provides a better path forward. At the same time, AR and other use cases were emerging and it became important that the API be extensible to support those in the future. The new design facilitates simpler implementations and large performance improvements. (Magic window is a technique for viewing immersive content without a headset wherein the app renders a single view based on the device's orientation sensor.)
The full list of lessons learned is too long to go into here, but includes issues like the API being explicitly tied to the main JavaScript thread, too many opportunities for developers to set up obviously wrong configurations, and common uses like magic window being a side effect rather than an intentional feature. We learned a lot from WebVR 1.1, but over time, it became clear that some major changes were needed to support the types of applications developers want to build.
If you're participating in the WebVR origin trial, you need a separate registration for the WebXR Origin Trial ( explainer, sign-up form).
The origin trial ended on July 24, 2018, and the spec has been superseded by the WebXR Device API and a new origin trial. That API is also supported by Firefox and Edge as well as a polyfill for Safari. This was done through the WebVR 1.1 API, which has been available in an origin trial since Chrome 62. The immersive web has been available for nearly a year now in embryonic form.
The immersive web means virtual world experiences hosted through the browser.