def addHostmask(self, hostmask):
        assert ircutils.isUserHostmask(hostmask), 'got %s' % hostmask
        if len(unWildcardHostmask(hostmask)) < 3:
            raise ValueError('Hostmask must contain at least 3 non-wildcard characters.')
        self.hostmasks.add(hostmask)
@return: an L{IConcept} which represents the visible aspects of this
dataset/ETHPy150Open ProgVal/Limnoria/src/ircdb.py/IrcUser.addHostmask--crossover with--dataset/ETHPy150Open twisted/imaginary/imaginary/iimaginary.py/IVisible.visualizeWithContents