{ AssignPrn - Assigns a Text variable to the currently selected printer. Any
Write or Writeln's going to that file variable will be written on the
printer using the Canvas property's font. A new page is automatically
started if a CR is encountered on (or a Writeln is written to) the last
line on the page. Closing the text file will imply a call to the
Printer.EndDoc method. Note: only one Text variable can be open on the
printer at a time. Opening a second will cause an exception.}