def __post_init__(self):
        if self.unit is not None and self.unit not in ["%", "abs"]:
            raise ValueError("unit must be either % or abs")
        if self.rounding is not None and self.rounding not in ["closest", "pct1_dropremainder"]:
            raise ValueError("rounding must be either closest or pct1_dropremainder")
        if self.unit != "%" and self.rounding is not None:
            raise ValueError("It is forbidden to specify rounding if not using percent slicing.")
        if self.unit == "%" and self.from_ is not None and abs(self.from_) > 100:
            raise ValueError("Percent slice boundaries must be > -100 and < 100.")
        if self.unit == "%" and self.to is not None and abs(self.to) > 100:
            raise ValueError("Percent slice boundaries must be > -100 and < 100.")
        # Update via __dict__ due to instance being "frozen"
        self.__dict__["rounding"] = "closest" if self.rounding is None and self.unit == "%" else self.rounding