def _validate_inputs_outputs_var_format(value: str) -> str:
    """Validate inputs/outputs variables

    Arguments:
        value {str} -- A '.' seperated string to be checked for inputs/outputs variable
            formatting

    Returns:
        str -- A string with validation error messages
    """
    add_info = ''
    parts = value.split('.')
    if len(parts) > 0 and parts[0] != 'inputs':
        add_info = f'Inputs and outputs variables can only refer to an input value' \
                   f' not: {parts[0]}'
    elif len(parts) > 1 and parts[1] != 'parameters':
        add_info = f'Inputs and outputs variables can only refer to an input parameter' \
                   f' not: {parts[1]}'
    elif len(parts) != 3:
        add_info = 'Inputs and outputs variables must have 3 segments.'
    return add_info