code: def spline_backwards_hankel(ht, htarg, opt):
      r
      ht = ht.lower()
      if ht in ['fht', 'qwe', 'hqwe']:
          if ht == 'fht':
              htarg = _check_targ(htarg, ['fhtfilt', 'pts_per_dec'])
          elif ht in ['qwe', 'hqwe']:
              htarg = _check_targ(htarg, ['rtol', 'atol', 'nquad', 'maxint',
                                  'pts_per_dec', 'diff_quad', 'a', 'b', 'limit'])
          if opt == 'spline':
              mesg = ("\n    The use of `opt='spline'` is deprecated and will " +
                      "be removed\n    in v2.0.0; use the corresponding " +
                      "setting in `htarg`.")
              warnings.warn(mesg, DeprecationWarning)
              opt = None
              if 'pts_per_dec' not in htarg:
                  if ht == 'fht':
                      htarg['pts_per_dec'] = -1
                  elif ht in ['qwe', 'hqwe']:
                      htarg['pts_per_dec'] = 80
      return htarg, opt