Remove confusion in h1 to h6 implied mapping wording

- resolves #308

Author: carmacleod

index.html

@@ -1022,7 +1022,7 @@ <h2 id="docconformance">
             </th>
             <td>
               <code>role=<a href="#index-aria-heading">heading</a></code>,
-              with the `aria-level` = positive integer.
+              `aria-level` = the number in the element's tag name.
             </td>
             <td>
               <p>