Clean up a slug by removing slug separator characters that occur at
        the beginning or end of a slug.

        If an alternate separator is used, it will also replace any instances
        of the default '-' separator with the new separator.

def _slug_strip(self, value):
        """
        Clean up a slug by removing slug separator characters that occur at
        the beginning or end of a slug.

        If an alternate separator is used, it will also replace any instances
        of the default '-' separator with the new separator.
        """
        re_sep = '(?:-|%s)' % re.escape(self.separator)
        value = re.sub('%s+' % re_sep, self.separator, value)
        return re.sub(r'^%s+|%s+$' % (re_sep, re_sep), '', value)