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