{from_, to, unit} argument is used, slicing cannot be specified as
                string.
            unit (str): optional, one of:
                '%': to set the slicing unit as percents of the split size.
                'abs': to set the slicing unit as absolute numbers.
        """
        # This constructor is not always called. See factory method
        # `_read_instruction_from_relative_instructions`. Common init instructions
        # MUST be placed in the _init method.
        self._init([_RelativeInstruction(split_name, from_, to, unit, rounding)])