code: def findEndpoint(html):
      
      poss_rels = ['webmention', 'http://webmention.org', 'http://webmention.org/', 'https://webmention.org', 'https://webmention.org/']
  
      # find elements with correct rels and a href value
      all_links = BeautifulSoup(html, _html_parser).find_all(rel=poss_rels, href=True)
      for link in all_links:
          s = link.get('href', None)
          if s is not None:
              return s
  
      return None
docs: Search the given html content for all <link /> elements
      and return any discovered WebMention URL.
  
      :param html: html content
      :rtype: WebMention URL