The Windows printer interface uses the Windows GDI printer driver (wingdiprinter) which employs BASIC @() function codes to embed character sequences into the print data stream.
The @() function codes allow you to:
create and select graphical objects (such as fonts, pens, and brushes) for use during a print job
specify the x,y coordinates on the printer page for outputting text, drawing lines or arcs, bitmaps, and drawing or filling rectangles, circles, and polygons
specify text and background attributes, such as color and extra spacing
The Windows printer driver always maintains the current x,y coordinate position on the print page. When outputting a line of text ending with a carriage return and line feed, the x,y coordinate position gets adjusted. When the outputting of a line goes beyond the end of the print page, the printer driver automatically ends the current page and advances to the next page. Note that you can force page advancement by storing a form feed character in the print data stream.
@() function codes 301 - 399 are defined in a control item of the DEVICES file to support the @() function to character sequence translations that the Windows printer driver recognizes for calling the appropriate Windows Printer API methods. Two types of Windows Printer @() function codes are provided:
@() function codes 301 - 339 perform setup tasks in preparation for a print job.
@() function codes 340 - 399 perform the actual printing.