The entity name must immediately follow the '&' in the entity reference.

在flex中出现上述错误，是因为不识别&标识符，需要将：

<mx:TextInput text="{(_feed.url && !_feed.isTemporary)?_feed.url:'Save Feed to generate URL'}" 

改成

<mx:TextInput text="{(_feed.url &amp;&amp; !_feed.isTemporary)?_feed.url:'Save Feed to generate URL'}" /