Add examples for customizable select

source

@@ -54822,12 +54822,50 @@ interface <dfn interface>HTMLSelectElement</dfn> : <span>HTMLElement</span> {
   &hellip;</code></pre>
   </div>
 
+  <div class="example" id="example-customizable-select">
+   <p>Here is an example which uses <code>div</code>, <code>legend</code>,
+   <code>img</code>, <code>button</code>, and <code>selectedcontent</code> elements:</p>
+
+   <pre><code class="html">&lt;select>
+  &lt;button>
+    &lt;selectedcontent>&lt;/selectedcontent>
+  &lt;/button>
+  &lt;div class="border">
+    &lt;optgroup>
+      &lt;legend>WHATWG Specifications&lt;/legend>
+      &lt;option>
+        &lt;img src="html.jpg" alt="">
+        HTML
+      &lt;/option>
+      &lt;option>
+        &lt;img src="dom.jpg" alt="">
+        DOM
+      &lt;/option>
+    &lt;/optgroup>
+  &lt;/div>
+  &lt;div class="border">
+    &lt;optgroup>
+      &lt;legend>W3C Specifications&lt;/legend>
+      &lt;option>
+        &lt;img src="forms.jpg" alt="">
+        CSS Form Control Styling
+      &lt;/option>
+      &lt;option>
+        &lt;img src="pseudo.jpg" alt="">
+        CSS Pseudo-Elements
+      &lt;/option>
+    &lt;optgroup>
+  &lt;/div>
+&lt;/select></code></pre>
+  </div>
+
   <p class="note" id="note-first-button-in-select-not-submit">The first child <code>button</code>
   element as allowed by the content model of <code>select</code> is not a submit button. It is used
   to replace the in-page rendering of the <code>select</code> element. Its form submission behavior
   is prevented because it is <span>inert</span>.</p>
 
 
+
   <h4>The <dfn element><code>datalist</code></dfn> element</h4>
 
   <dl class="element">