old_contents: 
  from django.db.models import TextField
  
  
  class HtmlField(TextField):
      """
      TextField that stores HTML.
      """
  
      def formfield(self, **kwargs):
          """
          Apply the class to the widget that will render the field as a
          TincyMCE Editor.
          """
          formfield = super(HtmlField, self).formfield(**kwargs)
          formfield.widget.attrs["class"] = "mceEditor"
          return formfield
  
new_contents: 
  from django.db.models import TextField
  
  from mezzanine.conf import settings
  
  
  class HtmlField(TextField):
      """
      TextField that stores HTML.
      """
  
      def formfield(self, **kwargs):
          """
          Apply the class to the widget that will render the field as a
          TincyMCE Editor.
          """
          formfield = super(HtmlField, self).formfield(**kwargs)
          formfield.widget.attrs["class"] = "mceEditor"
          return formfield
  
  
  # South requires custom fields to be given "rules".
  # See http://south.aeracode.org/docs/customfields.html
  if "south" in settings.INSTALLED_APPS:
      try:
          from south.modelsinspector import add_introspection_rules
          add_introspection_rules(rules=[((HtmlField,), [], {})], 
                                        patterns=["mezzanine\.core\.fields\."])
      except ImportError:
          pass
  
subject: Add south introspection rules for mezzanine.core.fields.HtmlField.