A form with a CheckBox control
<?xml version="1.0"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"> <mx:Form> <mx:FormItem label="Subscribe"> <mx:CheckBox label="Subscribe?" click="emAddr.required=true" /> </mx:FormItem> <mx:FormItem id="emAddr" label="e-mail address"> <mx:TextInput id="emailAddr" /> </mx:FormItem> </mx:Form> </mx:Application>