docs: def spec_fn(spec_dir='.'):
      """
      Return the filename for a .spec file in this directory.
      """
      specs = [f for f in os.listdir(spec_dir)
               if os.path.isfile(f) and f.endswith('.spec')]
      if not specs:
          raise exception.SpecFileNotFound()
      if len(specs) != 1:
          raise exception.MultipleSpecFilesFound()
      return specs[0]