Add AT support tables to example pages for alert, link, and radio using activedescendant

[mcking65]

Updates three example pages to include a section for AT support:

• Alert
• Link
• Radio Using aria-activedescendant

---

WAI Preview Link (Last built on Thu, 30 Mar 2023 19:05:07 GMT).

[mcking65]

@alflennik , please fix the code so the tables display.

In #2569, I had aked why we had a class specific to each ifram, e.g., class="support-levels-toggle-button". and where these classes are defined. Is this necessary? Can't we have a single "at-support-table" class?

I guessed at the parameter values and got it right for alert but wrong for link and radio. We need a way to get rid of the guessing.

[alflennik]

Hi @mcking65, the slug-style names originate here in the aria-at repo, so for link, the link-span-text name is the one to use, and for radio the name in question is radiogroup-aria-activedescendant. The reason there are unique class names for each iframe is that message-passing script which fixes the iframe heights when the iframe height changes (like on page resize or when the details box opens and closes) needs a way to uniquely refer to the iframes when there are multiple instances on the page at once. I think in the near-to-medium-term future, both of these irritations will be resolved by having a "copy embed code" button directly in the aria-at-app. Hopefully that helps. I'll update the code in this PR to use the accurate names.

[alflennik]

Great to see more ARIA-AT data in the APG! I tested and they work well.

[mcking65]

Thank you @alflennik for the helpful info, speedy fix, and review! I understand a little better how it works now, and it's easy enough for me to add the iframes to additional pages as needed.