code: def _clean_page_unique_slug_required(self, slug):
          
  
          if hasattr(self, 'instance') and self.instance.id:
              if Content.objects.exclude(page=self.instance).filter(
                      body=slug, type="slug").count():
                  raise forms.ValidationError(self.err_dict['another_page_error'])
          elif Content.objects.filter(body=slug, type="slug").count():
              raise forms.ValidationError(self.err_dict['another_page_error'])
          return slug
docs: See if this slug exists already