Setter for **self.__content** attribute.

        :param value: Attribute value.
        :type value: list

def content(self, value):
        """
        Setter for **self.__content** attribute.

        :param value: Attribute value.
        :type value: list
        """

        if value is not None:
            assert type(value) is list, "'{0}' attribute: '{1}' type is not 'list'!".format("content", value)
        self.__content = value