2.2.7.4 AsyncUIMessageBoxUIReply
AsyncUIMessageBoxUIReply is a string that contains a well-formed XML document ([XML1.0] section 2.1).
The root element of the document MUST be an asyncPrintUIResponse element. A messageBoxUI element MUST be nested within the asyncPrintUIResponse markup at the point where it is referenced in the XML schema.
The AsyncUIMessageBoxUIReply carries the response from a client to an AsyncUIMessageBoxUIReply notification.