Add more accessibility-related advice for <details>

This adds two pieces of advice discussed in w3c/html-aam#509 and #9899.

Co-authored-by: Scott O'Hara <[email protected]>

source

@@ -60166,6 +60166,11 @@ interface <dfn interface>HTMLDetailsElement</dfn> : <span>HTMLElement</span> {
   <p>The <code>details</code> element <span>represents</span> a disclosure widget from which the
   user can obtain additional information or controls.</p>
 
+  <p class="note">As with all HTML elements, it is not conforming to use the <code>details</code>
+  element when attempting to represent another type of control. For example, tab widgets and
+  menu widgets are not disclosure widgets, so abusing the <code>details</code> element to
+  implement these patterns is incorrect.</p>
+
   <p class="note">The <code>details</code> element is not appropriate for footnotes. Please see <a
   href="#footnotes">the section on footnotes</a> for details on how to mark up footnotes.</p>
 
@@ -60201,9 +60206,14 @@ interface <dfn interface>HTMLDetailsElement</dfn> : <span>HTMLElement</span> {
 
   <p>Documents that use the <code data-x="attr-details-name">name</code> attribute to group multiple
   related <code>details</code> elements should keep those related elements together in a containing
-  element (such as a <code>section</code> element).</p>
-
-  <p class="note">Keeping related elements together can be important for accessibility.</p>
+  element (such as a <code>section</code> element or <code>article</code> element). When it makes
+  sense for the group to be introduced with a heading, authors should put that heading in a <span
+  data-x="concept-heading">heading</span> element at the start of the containing element.</p>
+
+  <p class="note">Visually and programmatically grouping related elements together can be important
+  for accessible user experiences. This can help users understand the relationship between such
+  elements. When related elements are in disparate sections of a web page rather than being grouped,
+  the elements' relationships to each other can be less discoverable or understandable.</p>
 
   <p>The <dfn element-attr for="details"><code data-x="attr-details-open">open</code></dfn> content
   attribute is a <span>boolean attribute</span>. If present, it indicates that both the summary and