Merge pull request #434 from w3c/summary-role-editorial

Editorial: clarify summary element role mapping

Author: stevefaulkner

index.html

@@ -2775,7 +2775,13 @@ <h2 id="docconformance">
               [^summary^]
             </th>
             <td>
-              <code>role=<a href="#index-aria-button">button</a></code>
+              <p>
+                <a>No corresponding role</a>
+              </p>
+              <div class="note">
+                Many, but not all, user agents expose the `summary` element with an implicit ARIA <code>role=<a href="#index-aria-button">button</a></code>
+                role.
+              </div>
             </td>
             <td>
               <p>