@classmethod
def __replace(cls, string):
    """ replaces characters not allowed in xml string

        :param string: text
        :type string: :obj:`str`
        :returns: converted text with special characters
        :rtype: :obj:`str`
        """
    return string.replace('&', '&amp;').replace('<', '&lt;').replace('>',
        '&gt;')
