Convenience property to retrieve the value tuple as a tuple of
        date objects.

        Added in version 1.1

def value_as_date(self):
        ''' Convenience property to retrieve the value tuple as a tuple of
        date objects.

        Added in version 1.1
        '''
        if self.value is None:
            return None
        v1, v2 = self.value
        if isinstance(v1, numbers.Number):
            dt = datetime.utcfromtimestamp(v1 / 1000)
            d1 = date(*dt.timetuple()[:3])
        else:
            d1 = v1
        if isinstance(v2, numbers.Number):
            dt = datetime.utcfromtimestamp(v2 / 1000)
            d2 = date(*dt.timetuple()[:3])
        else:
            d2 = v2
        return d1, d2