old_contents: from django.contrib.contenttypes.models import ContentType
  from django.forms import ModelChoiceField, ModelForm
  
  from .models import FieldSanitizer
  
  
  class ContentTypeChoiceFieldWithAppLabel(ModelChoiceField):
      """A ModelChoiceField for ContentTypes that displays the app_label in
      addition to the name.
      """
      def label_from_instance(self, obj):
          return u"{0}/{1}".format(obj.app_label, obj.name)
  
  
  class FieldSanitizerAdminForm(ModelForm):
      content_type = ContentTypeChoiceFieldWithAppLabel(
          ContentType.objects.all().order_by('app_label', 'model')
      )
  
      class Meta:
          model = FieldSanitizer
  
new_contents: from django.contrib.contenttypes.models import ContentType
  from django.forms import ModelChoiceField, ModelForm
  
  from .models import FieldSanitizer
  
  
  class ContentTypeChoiceFieldWithAppLabel(ModelChoiceField):
      """A ModelChoiceField for ContentTypes that displays the app_label in
      addition to the name.
      """
      def label_from_instance(self, obj):
          return u"{0}/{1}".format(obj.app_label, obj.name)
  
  
  class FieldSanitizerAdminForm(ModelForm):
      content_type = ContentTypeChoiceFieldWithAppLabel(
          ContentType.objects.all().order_by('app_label', 'model')
      )
  
      class Meta:
          model = FieldSanitizer
          fields = [
              'content_type',
              'field_name',
              'tags',
              'attributes',
              'styles',
              'strip',
              'strip_comments',
          ]
  
subject: add a list of fields to the modelform