var elem = Ext.get('start');

elem.on('click', function(e, t) {
alert(t.id);
});

var body = Ext.query('body')[0];
body.className = "myStyle";

<span style='display:none;' group='message_group' class='error'></span>
<span style='display:none;' group='message_group' class='error'></span>

// 這樣多個同樣屬于 group 下的元素，可以通過此種方式獲?。?
var elemMessageArray = Ext.select("span[group='message_group']");

var newCssObj = {};

if (isInfo) {
newCssObj["class"] = "info";
} else {
newCssObj["class"] = "error";
}

// 然后對每個元素重新設置css樣式就行了
elemMessageArray.each( function(el) {
el.set(newCssObj);
el.update(text);
el.show("display");
});

Uncompleted = Ext.get('uncompleted');
elemUncompleted.setDisplayed(true);

el.show("display");
el.hide("display");