The test checks how well a browser supports accessibility technology such as screen readers and includes if they are keyboard accessible, mapped to the platform accessibility APIs, and if any accessibility-related features are supported. An accessibly supported feature means it is usable by people who rely on assistive technology, without developers having to supplement with ARIA or other additional workarounds.
In celebrating the score, the official Edge twitter account noted that the Edge team worked hard at improving accessibility support, with features like UI Automation and more accessible controls.
Eagle-eyed readers may note that while Edge 80 was tested Chrome 62 is far from a recent browser, making it a rather unfair comparison. Microsoft says the HTML5Accessibility team are responsible for updating the browser versions they check, and their main focus was on showing the improvement in Edge, which had fallen behind on accessibility after transitioning to Chromium.
The test page can be seen here.