toXML method
Implementation
@override
String toXML() {
return '''
<?xml version="1.0" encoding="utf-8"?>
<cupps xmlns="$xmlns" messageID="$messageID" xmlns:xsi="$xsi" messageName="$messageName">
<notify>
<dStgExitedEvent device="$device"/>
</notify>
</cupps>
''';
}