code: def prt_outfiles_flat(self, goea_results, outfiles):
          
          kws = {'indent':self.args.indent, 'itemid2name':self.itemid2name}
          for outfile in outfiles:
              if outfile.endswith(".xlsx"):
                  self.objgoea.wr_xlsx(outfile, goea_results, **kws)
              #elif outfile.endswith(".txt"):  # TBD
              #    pass
              else:
                  self.objgoea.wr_tsv(outfile, goea_results, **kws)
docs: Write to outfiles.