Sets the metrics in the given printer.
set-printer-metrics sets the left margin and top margin, and the printable width and printable height, of the given printer. Values outside the bounds of the printer will be corrected.
To set the margins as large as possible:
(let ((metrics (capi:get-printer-metrics printer)))
Actually this sets the margins to the whole paper size, but the printer driver will move these in to take account of the minimum margins of the device.
CAPI User Guide and Reference Manual (Macintosh version) - 3 Aug 2017