真正的事件dispatch者是event.target,监听事件（addEventListner）的对象是event.currentTarget，Flex skd中有言曰：
"Event objects also have target properties that reference the actual object which dispatched the event. In some cases, the target may not be the object for which you have registered a listener. This can occur when the object for which you have registered a listener contains a child component that also dispatches the same event (and
the event bubbles). If you want to ensure that you are getting a reference to the object for which the listener is registered to listen for the event, use the currentTarget property"
例：如为容器mc1创建了一个同类型（或者说拥有相同事件）的子容器mc2，再为mc1注册click事件监听器，当单击子容器mc2时，则event.target指事件dispatch者mc2，而event.currentTarget指当前的事件处理者mc1，因此在使用时如果是要获取被注册事件监听器的对象（一般都是如此）则用event.currentTarget，currentTarget属性应具备两条件，一是它注册了侦听器，二是正在处理事件。
