:param str prefix:
        :param str hidden:
        :param kwargs: passed to :func:`fold_text`
        :rtype: str

def fold_text_string(self, prefix, hidden, **kwargs):
        """
        :param str prefix:
        :param str hidden:
        :param kwargs: passed to :func:`fold_text`
        :rtype: str
        """
        import io
        output_buf = io.StringIO()
        self.fold_text(prefix=prefix, hidden=hidden, file=output_buf, **kwargs)
        return output_buf.getvalue()