Investigate making use of ARIA annotations

The ARIA specifications are gaining [explicit support for annotations](https://github.com/aleventhal/aria-annotations/blob/master/README.md#simplified-aria-annotations-proposal--explainer) and browser vendors are beginning to implement this [1][2]. The stated initial customers are web apps like Google Docs. Once the implementation is available in one or more browsers, we should investigate this to see if we can make use of it to provide a better experience for assistive technology users.

[1] [Chrome "Intent to Implement" announcement](https://groups.google.com/a/chromium.org/d/msg/blink-dev/2uume_z0n8M/dUFRWmVNBgAJ)
[2] [Firefox "Intent to Implement" announcement](https://groups.google.com/d/msg/mozilla.dev.platform/eh_O7G4H26Q/mFy5IambGQAJ)

Update: There is new [MDN documentation](https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Annotations) which has a clearer explanation of the new attributes and how/when to use them.