code: def _check_toolplus(x):
      
      if "=" in x and len(x.split("=")) == 2:
          name, fname = x.split("=")
          fname = os.path.normpath(os.path.realpath(fname))
          if not os.path.exists(fname):
              raise argparse.ArgumentTypeError("Unexpected --toolplus argument for %s. File does not exist: %s"
                                               % (name, fname))
          return Tool(name, fname)
      else:
          raise argparse.ArgumentTypeError("Unexpected --toolplus argument. Expect toolname=filename.")
docs: Parse options for adding non-standard/commercial tools like GATK and MuTecT.