Overridden by subclasses to print the current document’s (the receiver’s) data.
Overridden by subclasses to print the current document’s (the receiver’s) data; if flag is YES, the implementation should first display the Print panel. This method is typically invoked by printDocument: with an argument of YES. The default implementation does nothing. If there is any printing information other than that encoded in the receiver’s NSPrintInfo object, subclasses should get it here.