Over in immersive-web/webxr-test-api#37 there is a discussion about whether WebXR tests can assert anything about viewport sizes. The motivation for this is to make sure that the dimensions being reported are based on the device, not based on the canvas providing the WebGL rendering context. (This was a bug that Servo had, so we'd like to make sure we don't regress.) In immersive-web/webxr-test-api#37 (comment), @alcooper91 said "I’m unable to find anything in the WebXR spec calling out any requirements for sizing the canvas/viewport, so the output size is largely up to the UAs."

This is true, there is text at https://immersive-web.github.io/webxr/#native-webgl-framebuffer-resolution about the native viewport resolution, but there is no text about a native viewport size. https://immersive-web.github.io/webxr/#list-of-viewports requires that the XRSession keep a list of viewports, but nothing about the size of the viewports.

Can we add matching requirements for viewport size?