Fix #144: add note about upgrading after cloning

spec/custom/index.html

@@ -139,7 +139,7 @@ <h2>Concepts</h2>
     <li><code>font-face-src</code></li>
     <li><code>font-face-uri</code></li>
     <li><code>font-face-format</code></li>
-    <li><codE>font-face-name</code></li>
+    <li><code>font-face-name</code></li>
     <li><code>missing-glyph</code></li>
 </ul>
 
@@ -676,6 +676,14 @@ <h3>Upgrading</h3>
 
 </section>
 
+<section>
+<h3>Changes to Cloning</h3>
+
+The following informational note should be added to the <a href="https://dom.spec.whatwg.org/#concept-node-clone">clone</a> algorithm's section on cloning elements:
+
+<p class="note">Custom elements will be <a data-lt="upgrade a custom element">upgraded</a> when the calling operation finishes and <a data-lt="invoke custom element callbacks">invokes custom element callbacks</a>.</p>
+
+</section>
 </section>
 
 <section id="semantics">