disallow aria-hidden on body element (#447)

* disallow aria-hidden on body element

related to w3c/aria#1254

closes #221 - there were comments to do more with aria-hidden rules beyond just disallowing it on body, but i'm going to make a new issue for potentially covering those topics.

as `aria-hidden=false` doesn't seem to cause any problems, even per the note in ARIA to use with caution:
>At the time of this writing, aria-hidden="false" is known to work inconsistently in browsers. As future implementations improve, use caution and test thoroughly before relying on this approach.

call out that not all global attributes are allowed on generic

index.html

@@ -63,13 +63,17 @@
         the following substantive additions and/or corrections have been proposed:
       </p>
       <ul>
+        <li>
+          <a href="https://github.com/w3c/html-aria/pull/447">6 March 2023 - Addition:</a>
+          Disallow `aria-hidden=true` on the `body` element.
+        </li>
         <li>
           <a href="https://github.com/w3c/html-aria/pull/415">13 February 2023 - Addition:</a>
-           update figure role allowances to include `doc-example`.
+           Update `figure` element role allowances to include `doc-example`.
         </li>
         <li>
           <a href="https://github.com/w3c/html-aria/pull/437">07 November 2022 - Correction:</a>
-           Revisions to 'any role' term description.
+          Revisions to 'any role' term description.
         </li>
         <li>
           <a href="https://github.com/w3c/html-aria/pull/383">14 July 2022 - Correction:</a>
@@ -802,7 +806,10 @@ <h2 id="docconformance">
               </p>
               <p class="addition"><a>Naming Prohibited</a></p>
               <p>
-                Otherwise, <a data-cite="wai-aria-1.2#global_states">global `aria-*` attributes</a>.
+                Otherwise, <a data-cite="wai-aria-1.2#global_states">global `aria-*` attributes</a> 
+                <span class="addition proposal">
+                  allowed for the `generic` role, with the exception that authors MUST NOT specify `aria-hidden=true` on the `body` element.
+                </span>
               </p>
             </td>
           </tr>