Examples:

There are currently four data files, the second of which has a current background file ÇURRB.PHA and the last of which has no background being subtracted, equivalent to a background file none.

XSPEC> fakeit backa,,none 4    ! Four fake data PHA files are created. The
                                    first and second use BACKA.PHA and
                                    CURB.PHA for background, and their
                                    associated response files for the
                                    response.  The third and fourth files
                                    will have no background files;
                                    the user will be prompted for the
                                    response file to be used.  The 4
                                    indicates that four data files will
                                    be created.