code: def create_chapter_from_string(self, html_string, url=None, title=None):
          
          clean_html_string = self.clean_function(html_string)
          clean_xhtml_string = clean.html_to_xhtml(clean_html_string)
          if title:
              pass
          else:
              try:
                  root = BeautifulSoup(html_string, 'html.parser')
                  title_node = root.title
                  if title_node is not None:
                      title = unicode(title_node.string)
                  else:
                      raise ValueError
              except (IndexError, ValueError):
                  title = 'Ebook Chapter'
          return Chapter(clean_xhtml_string, title, url)
docs: Creates a Chapter object from a string. Sanitizes the
          string using the clean_function method, and saves
          it as the content of the created chapter.
  
          Args:
              html_string (string): The html or xhtml content of the created
                  Chapter
              url (Option[string]): A url to infer the title of the chapter from
              title (Option[string]): The title of the created Chapter. By
                  default, this is None, in which case the title will try to be
                  inferred from the webpage at the url.
  
          Returns:
              Chapter: A chapter object whose content is the given string
                  and whose title is that provided or inferred from the url