@classmethod
def _is_claim(cls, instance_var: str) ->bool:
    """
            Determine if a given instance variable is part of the token's claim set.

            An instance variable will be considered to be a claim if:

            * it is listed in :attr:`_private_claims`, or
            * it does not start with an underscore, but
                * is not listed in :attr:`_public_non_claims'.

            :param instance_var: The name of the instance variable to check.
            :return: `True` if the instance variable is part of the claim set, `False` otherwise.
        """
    if instance_var in cls._private_claims:
        return True
    if instance_var.startswith('_'):
        return False
    if instance_var in cls._public_non_claims:
        return False
    return True
