What does XUL look like?
¥<?xml version="1.0"?>
¥<?xml-stylesheet href="chrome://global/skin/"?>
¥<window id="test"
¥        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
¥        title="Hello, World!">
¥  <script type="application/x-javascript" src="test.js"/>
¥  <vbox flex="1">
¥    <listbox id="itemlist" flex="1">
¥      <listitem label="Item 1"/>
¥      <listitem label="Item 2"/>
¥    </listbox>
¥    <hbox>
¥      <textbox id="labelfield" flex="1"
¥               oninput="validateInput();"/>
¥      <button id="addButton" label="Add Item"
¥              disabled="true" oncommand="addItem();"/>
¥    </hbox>
¥  </vbox>
¥</window>