def want_dnssec(self, wanted=True):
        """Enable or disable 'DNSSEC desired' flag in requests.
        @param wanted: Is DNSSEC desired?  If True, EDNS is enabled if
        required, and then the DO bit is set.  If False, the DO bit is
        cleared if EDNS is enabled.
        @type wanted: bool
        """
        if wanted:
            if self.edns < 0:
                self.use_edns()
            self.ednsflags |= dns.flags.DO
        elif self.edns >= 0:
            self.ednsflags &= ~dns.flags.DO