2.2.7.7 AsyncUICustomData
AsyncUICustomData is a null-terminated string containing a well-formed XML document ([XML1.0] section 2.1) followed by binary data.
The root element of the document MUST be the asyncPrintUIRequest element (section 2.2.7.1.1). A customData element MUST be nested within the asyncPrintUIRequest markup at the point where it is referenced in the XML schema.
The entry point specified in the customData element MUST be called, passing the binary data as an argument.
AsyncUICustomData can be used in any case where a printer driver on a server might choose to use AsyncUICustomUI. However, because AsyncUICustomData encodes the data passed to the specified entry point in binary form, the AsyncUICustomData notification can transport argument values that cannot be expressed in legal XML within an AsyncUICustomUI notification.