def METHOD_NAME(self, var_name: str, var_value: Any) -> None:
    """Register a variable.
    Args:
        var_name: Name of the config field that can contain a variable
            lookup.
        var_value: Literal value supplied in the config to be resolved
            as a variable if it contains a lookup.
    """
    self._vars[var_name] = Variable(
        name=f"{self.name}.{var_name}", value=var_value, variable_type="runway"
    )