code: def generate_pingback_content(soup, target, max_length, trunc_char='...'):
      
      link = soup.find('a', href=target)
  
      content = strip_tags(six.text_type(link.findParent()))
      index = content.index(link.string)
  
      if len(content) > max_length:
          middle = max_length // 2
          start = index - middle
          end = index + middle
  
          if start <= 0:
              end -= start
              extract = content[0:end]
          else:
              extract = '%s%s' % (trunc_char, content[start:end])
  
          if end < len(content):
              extract += trunc_char
          return extract
  
      return content
docs: Generate a description text for the pingback.