Fix warnings

index.html

@@ -1565,7 +1565,7 @@ <h2>Capabilities</h2>
  </tr>
 
  <tr>
- <td><dfn>Unhandled prompt behavior</dfn>
+ <td>Unhandled prompt behavior
  <td>"<code>unhandledPromptBehavior</code>"
  <td>string
  <td>Describes the <a>session</a>&apos;s <a>user prompt handler</a>.
@@ -11705,7 +11705,6 @@ <h2>Index</h2>
 
  <dd><p>The following events are also defined in the HTML specification:
  <ul>
- <!-- beforeunload --> <li><dfn><a href=https://html.spec.whatwg.org/#event-beforeunload><code>beforeunload</code></a></dfn>
  <!-- change --> <li><dfn><a href="https://html.spec.whatwg.org/multipage/indices.html#event-change"><code>change</code></a></dfn>
  <!-- DOMContentLoaded --> <li><dfn><a href=https://html.spec.whatwg.org/#event-domcontentloaded><code>DOMContentLoaded</code></a></dfn>
  <!-- input --> <li><dfn><a href=https://html.spec.whatwg.org/#event-input><code>input</code></a></dfn>