old_contents: from lxml.html.clean import Cleaner
  
  TAGS = ['br', 'p', 'hr', 'b', 'strong', 'em', 'i', 'a', 'blockquote']
  ATTRS = ['href', 'target']
  
  cleaner = Cleaner(style=False, links=True, add_nofollow=False,
                    page_structure=False, safe_attrs_only=True,
                    remove_unknown_tags=False, comments=False,
                    safe_attrs=ATTRS, allow_tags=TAGS)
  
  
  def clean_html(html):
      if html is None or not len(html):
          return '<p></p>'
      return cleaner.clean_html(html)
  
new_contents: from lxml.html.clean import Cleaner
  
  TAGS = ['br', 'p', 'hr', 'b', 'strong', 'em', 'i', 'a',
          'blockquote', 'ul', 'li']
  ATTRS = ['href', 'target']
  
  cleaner = Cleaner(style=False, links=True, add_nofollow=False,
                    page_structure=False, safe_attrs_only=True,
                    remove_unknown_tags=False, comments=False,
                    safe_attrs=ATTRS, allow_tags=TAGS)
  
  
  def clean_html(html):
      if html is None or not len(html):
          return '<p></p>'
      return cleaner.clean_html(html)
  
subject: Allow lists.