new_contents: from django.contrib import admin
  from feincms.admin.item_editor import ItemEditor
  from feincms.extensions import ExtensionModelAdmin
  from orderable.admin import OrderableAdmin, OrderableTabularInline
  
  from . import models
  
  
  class PageAdmin(ItemEditor, ExtensionModelAdmin):
      fieldsets = [
          (None, {'fields': ['name', 'slug']}),
          # <-- extensions appear here, see fieldset_insertion_index.
      ]
      fieldset_insertion_index = 1
      filter_horizontal = []
      list_display = ['name', 'slug']
      list_filter = []
      prepopulated_fields = {'slug': ['name']}
      search_fields = ['name', 'slug']
  
  
  class GroupItemInline(OrderableTabularInline):
      model = models.GroupItem
  
  
  class GroupAdmin(admin.ModelAdmin):
      inlines = [GroupItemInline]
  
  
  class GroupItemAdmin(OrderableAdmin):
      list_display = ('page', 'group', 'sort_order_display')
  
  
  admin.site.register(models.Page, PageAdmin)
  admin.site.register(models.Group, GroupAdmin)
  admin.site.register(models.GroupItem, GroupItemAdmin)
  
subject: Add admin