Clarify li element role mapping

The intent of this text change is to clarify that a list item that is still a child of a list, but has intervening generic elements should still be exposed as a listitem.

e.g.,

```
<li>with no list ancestor = generic</li>

<ul>
  <div> <!-- invalid html, but SHOULD be ignored since generic  -->
    <li> since this has 'accessibility parent' of list, it should remain exposed as a list item </li>
  </div>
</ul>
```

index.html

@@ -5104,7 +5104,7 @@ <h4 id=el-li>`li`</h4>
     <tr>
       <th>Comments</th>
       <td>
-        If `li` element is not a child of <a data-cite="html">`ol`</a> , <a data-cite="html">`menu`</a> or <a data-cite="html">`ul`</a>, or if the containing
+        If `li` element is not an accessibility child of an <a data-cite="html">`ol`</a> , <a data-cite="html">`menu`</a> or <a data-cite="html">`ul`</a>, or if the containing
         list element is no longer exposed with a `list` role, then expose the `li` element with a `generic` role.
       </td>
     </tr>