code: def get_formset(self, request, obj=None, **kwargs):
          
          def _placeholder_initial(p):
              # p.as_dict() returns allowed_plugins too for the client-side API.
              return {
                  'slot': p.slot,
                  'title': p.title,
                  'role': p.role,
              }
  
          # Note this method is called twice, the second time in get_fieldsets() as `get_formset(request).form`
          initial = []
          if request.method == "GET":
              placeholder_admin = self._get_parent_modeladmin()
  
              # Grab the initial data from the parent PlaceholderEditorBaseMixin
              data = placeholder_admin.get_placeholder_data(request, obj)
              initial = [_placeholder_initial(d) for d in data]
  
              # Order initial properly,
  
          # Inject as default parameter to the constructor
          # This is the BaseExtendedGenericInlineFormSet constructor
          FormSetClass = super(PlaceholderEditorInline, self).get_formset(request, obj, **kwargs)
          FormSetClass.__init__ = curry(FormSetClass.__init__, initial=initial)
          return FormSetClass
docs: Pre-populate formset with the initial placeholders to display.