def METHOD_NAME(self, conference, fieldname, s):
    maxlens = "Max lengths are: {}".format(', '.join(['{}: {}'.format(mess.provider.internalname, get_messaging(mess.provider).max_post_length) for mess in conference.conferencemessaging_set.select_related('provider').filter(broadcast=True, provider__active=True)]))
    if fieldname == 'content_template':
        # Generate a preview of 3 (an arbitrary number) sessions
        posts = [self.form.generate_tweet(conference, session, s) for session in ConferenceSession.objects.filter(conference=conference, status=1, cross_schedule=False)[:3]]
        sesslist = list(ConferenceSession.objects.filter(conference=conference, status=1, cross_schedule=False))
        if sesslist:
            longest = max((get_shortened_post_length(self.form.generate_tweet(conference, session, s)) for session in sesslist))
        else:
            longest = 0
        previews = "\n\n".join([
            "{}\n\n------------------------------- (length {})".format(
                p,
                get_shortened_post_length(p),
            )
            for p in posts
        ])
        return HttpResponse("{}\n\nLongest to generate: {} ({})\n".format(previews, longest, maxlens), content_type='text/plain')