<zk>
    <button onClick="tabA.setSelected(true)" label="Select Tab A"/>
    <button onClick="tabB.setSelected(true)" label="Select Tab B"/>
    <button onClick="tabC.setSelected(true)" label="Select Tab C"/>
    <tabbox id="tabbox" mold="accordion" height="400px">
        <tabs>
            <tab label="A" id="tabA"/>
            <tab label="B" id="tabB"/>
            <tab label="C" id="tabC"/>
        </tabs>
        <tabpanels>
            <tabpanel>A</tabpanel>
            <tabpanel>B</tabpanel>
            <tabpanel>C</tabpanel>
        </tabpanels>
    </tabbox>
</zk>

    zk.afterLoad('zul.tab', function() {
    	var xTabbox = {};
    	zk.override(zul.tab.Tabbox.prototype, xTabbox, {
            setSelectedTab: function (tab) {
                var selTab = this._selTab;
                if (selTab != tab) {
                    if(this._mold !== 'accordion') {
                        this._selTab = null; // it will be set in Tab._selTab
                        if (selTab)
                            selTab.setSelected(false);
                    }
                    if (tab)
                        tab.setSelected(true);
                }
            }
    	});//zk.override
    });//zk.afterLoad