code: def post(self, request, *args, **kwargs):
          
          url = request.POST.get('url')
  
          if not url:
              return self.get(request, *args, **kwargs)
  
          entry = self.get_object()
          site = Site.objects.get_current()
  
          if not entry.trackbacks_are_open:
              return self.render_to_response(
                  {'error': 'Trackback is not enabled for %s' % entry.title})
  
          title = request.POST.get('title') or url
          excerpt = request.POST.get('excerpt') or title
          blog_name = request.POST.get('blog_name') or title
          ip_address = request.META.get('REMOTE_ADDR', None)
  
          trackback_klass = comments.get_model()
          trackback_datas = {
              'content_type': ContentType.objects.get_for_model(Entry),
              'object_pk': entry.pk,
              'site': site,
              'user_url': url,
              'user_name': blog_name,
              'ip_address': ip_address,
              'comment': excerpt
          }
  
          trackback = trackback_klass(**trackback_datas)
          if check_is_spam(trackback, entry, request):
              return self.render_to_response(
                  {'error': 'Trackback considered like spam'})
  
          trackback_defaults = {'comment': trackback_datas.pop('comment')}
          trackback, created = trackback_klass.objects.get_or_create(
              defaults=trackback_defaults,
              **trackback_datas)
          if created:
              trackback.flags.create(user=get_user_flagger(), flag=TRACKBACK)
              trackback_was_posted.send(trackback.__class__,
                                        trackback=trackback,
                                        entry=entry)
          else:
              return self.render_to_response(
                  {'error': 'Trackback is already registered'})
          return self.render_to_response({})
docs: Check if an URL is provided and if trackbacks
          are enabled on the Entry.
          If so the URL is registered one time as a trackback.