docs: def cnxml_to_html(cnxml_source):
      """Transform the CNXML source to HTML"""
      source = _string2io(cnxml_source)
      xml = etree.parse(source)
      # Run the CNXML to HTML transform
      xml = _transform('cnxml-to-html5.xsl', xml,
                       version='"{}"'.format(version))
      xml = XHTML_MODULE_BODY_XPATH(xml)
      return etree.tostring(xml[0])