The polyfill currently is (was) targeting the latest WebXR API spec. The webxr-examples repo contained a shim that would patch various iterations of the implementation in Chrome (patching changes between Chrome 68, 69, 70, etc.). With the WebXR API stabilizing, it's now appropriate for the polyfill to handle these smaller 'patches' between versions. We should be explicit on what browsers/devices we attempt to support. We should:

• Define support range: e.g. last 2 major versions, plus Chrome M73 (Magic Leap, Samsung)
• Document support range in README plus any extra config/modules needed to support different browsers. <model-viewer> has great matrix+docs for its support, which require devs to include different polyfills, which aids in configuring the tradeoffs of your choosing