code: def get_fieldsets(self, request, obj=None):
          
  
          # some ugly business to remove freeze_date
          # from the field list
          general_module = {
              'fields': list(self.general_fields),
              'classes': ('module-general',),
          }
  
          default_fieldsets = list(self.fieldsets)
          if not request.user.has_perm('pages.can_freeze'):
              general_module['fields'].remove('freeze_date')
          if not request.user.has_perm('pages.can_publish'):
              general_module['fields'].remove('status')
  
          default_fieldsets[0][1] = general_module
  
          placeholder_fieldsets = []
          template = get_template_from_request(request, obj)
          for placeholder in get_placeholders(template):
              if placeholder.name not in self.mandatory_placeholders:
                  placeholder_fieldsets.append(placeholder.name)
  
          additional_fieldsets = []
  
          # meta fields
          metadata_fieldsets = [f['name'] for f in self.metadata_fields]
          additional_fieldsets.append((_('Metadata'), {
              'fields': metadata_fieldsets,
              'classes': ('module-content', 'grp-collapse grp-closed'),
          }))
          additional_fieldsets.append((_('Content'), {
              'fields': placeholder_fieldsets,
              'classes': ('module-content',),
          }))
  
          return default_fieldsets + additional_fieldsets
docs: Add fieldsets of placeholders to the list of already
          existing fieldsets.