docs: def clean(self):
          """
          Check unauthenticated user's cookie as a light check to
          prevent duplicate votes.
          """
          bits = (self.data["content_type"], self.data["object_pk"])
          request = self.request
          self.current = "%s.%s" % bits
          self.previous = request.COOKIES.get("yacms-rating", "").split(",")
          already_rated = self.current in self.previous
          if already_rated and not self.request.user.is_authenticated():
              raise forms.ValidationError(ugettext("Already rated."))
          return self.cleaned_data