Scrolling two listboxes together

<zk xmlns:w="http://www.zkoss.org/2005/zk/client">
	<window title="Livedata Demo" border="normal">
		<zscript><![CDATA[	
			String[] data = new String[30];
			for (int j = 0; j < data.length; ++j) {
				data = "option " + j;
			}
			ListModel strset = new SimpleListModel(data);
		]]></zscript>
		<hbox>
			<listbox width="200px" rows="10" model="${strset}">
				<attribute w:name="_doScroll"><![CDATA[
					function () { 
						this.$_doScroll();
						this.nextSibling.ebody.scrollTop = this._currentTop;
					}
				]]></attribute>
				<listhead>
					<listheader label="Load on demend" />
				</listhead>
			</listbox>
			<listbox width="200px" rows="10" model="${strset}">
				<attribute w:name="_doScroll"><![CDATA[
					function () { 
						this.$_doScroll();
						this.previousSibling.ebody.scrollTop = this._currentTop;
					}
				]]></attribute>
				<listhead>
					<listheader label="Load on demend 2" />
				</listhead>
			</listbox>
		</hbox>
	</window>
</zk>