def _fromstring(value):
    '''_fromstring

    Convert XML string value to None, boolean, int or float.
    '''

    if not value:
        return [None]
    std_value = value.strip().lower()
    if std_value == 'true':
        return True
    elif std_value == 'false':
        return False
    try:
        return int(std_value)
    except ValueError:
        pass
    try:
        return float(std_value)
    except ValueError:
        pass
    return value