One of CUPS's capabilities is the facility to group printers together into a
"class". When printing to the class, the CUPS server will pass the job on to
whichever of the printers happens to be available at the time.
Debian bug #263540 reports that Xprint does not recognise these CUPS classes.
Closing WONTFIX because nobody cares about Xprint. Reopen if you plan to address this bug.