docs: def btc_is_singlesig(privkey_info, **blockchain_opts):
      """
      Does the given private key info represent
      a single signature bundle? (i.e. one private key)?
  
      i.e. is this key a private key string?
      """
      try:
          jsonschema.validate(privkey_info, PRIVKEY_SINGLESIG_SCHEMA)
          return True
      except ValidationError as e:
          return False