code: def make_back_acknowledgments(self):
          
          acks = self.article.root.xpath('./back/ack')
          if not acks:
              return
          ack = deepcopy(acks[0])
          #Modify the tag to div
          ack.tag = 'div'
          #Give it an id
          ack.attrib['id'] = 'acknowledgments'
          #Give it a title element--this is not an EPUB element but doing so will
          #allow it to later be depth-formatted by self.convert_div_titles()
          ack_title = etree.Element('title')
          ack_title.text = 'Acknowledgments'
          ack.insert(0, ack_title)  # Make it the first element
          return ack
docs: The <ack> is an important piece of back matter information, and will be
          including immediately after the main text.
  
          This element should only occur once, optionally, for PLoS, if a need
          becomes known, then multiple instances may be supported.