docs: def format_output(self, rendered_widgets):
          """
          Wraps the output HTML with a list of all available ``Keyword``
          instances that can be clicked on to toggle a keyword.
          """
          rendered = super(KeywordsWidget, self).format_output(rendered_widgets)
          links = ""
          for keyword in Keyword.objects.all().order_by("title"):
              prefix = "+" if str(keyword.id) not in self._ids else "-"
              links += ("<a href='#'>%s%s</a>" % (prefix, str(keyword)))
          rendered += mark_safe("<p class='keywords-field'>%s</p>" % links)
          return rendered