function scrollTo(target, value){
		var opts = $.data(target, 'combobox').options;
		var panel = $(target).combo('panel');
		var item = opts.finder.getEl(target, value);
		if (item.length){
			if (item.position().top <= 0){
				var h = panel.scrollTop() + item.position().top;
				panel.scrollTop(h);
			} else if (item.position().top + item.outerHeight() > panel.height()){
				var h = panel.scrollTop() + item.position().top + item.outerHeight() - panel.height();
				panel.scrollTop(h);
			}
		}
		panel.triggerHandler('scroll');	// trigger the group sticking
	}
scroll panel to display the specified item