old_contents: from django.contrib import admin
  from world_regions.models import Region, RegionCountry
  
  
  class RegionCountriesInline(admin.TabularInline):
      model = RegionCountry
  
  
  class RegionAdmin(admin.ModelAdmin):
      inlines = [RegionCountriesInline]
  
  admin.site.register(Region, RegionAdmin)
  
new_contents: from django.contrib import admin
  from world_regions.models import Region, RegionCountry
  
  
  class RegionCountriesInline(admin.TabularInline):
      model = RegionCountry
  
  
  class RegionAdmin(admin.ModelAdmin):
      list_display = ('name', 'code')
      inlines = [RegionCountriesInline]
  
  admin.site.register(Region, RegionAdmin)
  
subject: Add Region model to admin site