added a label to the combobox listbox example (#1728)

index.html

@@ -2342,12 +2342,12 @@ <h2>Definition of Roles</h2>
 					<li>Otherwise, the value of the <code>combobox</code> is represented by its descendant elements and can be determined using the same method used to compute the name of a <rref>button</rref> from its descendant content.</li>
 				</ul>
 				<pre class="example highlight">
-          &lt;label for="tag_combo">Tag&lt;/label>
+          &lt;label id="tag_label" for="tag_combo">Tag&lt;/label>
 		      &lt;input type="text" id="tag_combo"
             role="combobox" aria-autocomplete="list"
             aria-haspopup="listbox" aria-expanded="true"
             aria-controls="popup_listbox" aria-activedescendant="selected_option"&gt;
-				  &lt;ul role="listbox" id="popup_listbox"&gt;
+				  &lt;ul role="listbox" id="popup_listbox" aria-labelledby="tag_label"&gt;
 			      &lt;li role="option"&gt;Zebra&lt;/li&gt;
 			      &lt;li role="option" id="selected_option"&gt;Zoom&lt;/li&gt;
 				  &lt;/ul&gt;