code: def handle_starttag(self, tag, attrs):
      '''
      PDF link handler; never gets explicitly called by user
      '''
      if tag == 'a' and ( ('class', 'download-pdf') in attrs or ('id', 'download-pdf') in attrs ):
          for attr in attrs:
            if attr[0] == 'href':
              self.download_link = 'http://www.nature.com' + attr[1f handle_starttag(self, tag, attrs):
      '''
      PDF link handler; never gets explicitly called by user
      '''
      if tag == 'a' and ( ('class', 'download-pdf') in attrs or ('id', 'download-pdf') in attrs ):
          for attr in attrs:
            if attr[0] == 'href':
              self.download_link = 'http://www.nature.com' + attr[1]
docs: PDF link handler; never gets explicitly called by user