Changing combobox state

There is an opportunity to change combo visibility, states of editing and availability.
Source
<script>window.dhx_globalImgPath = "../../codebase/imgs/";</script>
<link rel="STYLESHEET" type="text/css" href="../../codebase/dhtmlxcombo.css">
<script  src="../../codebase/dhtmlxcommon.js"></script>
<script  src="../../codebase/dhtmlxcombo.js"></script>
 
 
 
<div style="height:30px;">
    <div id="combo_zone2" style="width:200px; height:30px;"></div>
</div>
<table cellspacing="3" cellpadding="0" border="0">
    <tr><td align="right"> <button onclick="z.show(false)">Hide</button></td><td width="5" rowspan="3"></td><td bgcolor="black" rowspan="3" width="1"></td><td width="5" rowspan="3"></td><td><button onclick="z.show(true)">Show</button></td></tr>
    <tr><td align="right"><button onclick="z.readonly(true)">Readonly</button></td><td><button onclick="z.readonly(false)">Editable</button></td></tr>
    <tr><td align="right"><button onclick="z.disable(true)">Disable</button></td><td><button onclick="z.disable(false)">Enable</button></td></tr>
</table>
<script>var z = new dhtmlXCombo("combo_zone2", "alfa2", 200);
z.loadXML("../common/data.xml");</script>