code: def convert_graphic_elements(self):
          
          for graphic in self.main.getroot().findall('.//graphic'):
              graphic.tag = 'img'
              graphic.attrib['alt'] = 'unowned-graphic'
              ns_xlink_href = ns_format(graphic, 'xlink:href')
              if ns_xlink_href in graphic.attrib:
                  xlink_href = graphic.attrib[ns_xlink_href]
                  file_name = xlink_href.split('.')[-1] + '.png'
                  img_dir = 'images-' + self.doi_suffix()
                  img_path = '/'.join([img_dir, file_name])
                  graphic.attrib['src'] = img_path
              remove_all_attributes(graphic, exclude=['id', 'class', 'alt', 'src'])
docs: This is a method for the odd special cases where <graphic> elements are
          standalone, or rather, not a part of a standard graphical element such
          as a figure or a table. This method should always be employed after the
          standard cases have already been handled.