docs: def serialize_to_transport(self, encoding='utf-8', xslt_url=None):
          """Serialize to XML ``bytes`` with prolog.
  
          Args:
            encoding: str
              Encoding to use for XML doc bytes
            xslt_url: str
              If specified, add a processing instruction to the XML doc that specifies the
              download location for an XSLT stylesheet.
  
          Returns:
            bytes: XML holding a DataONEError based type.
  
          """
          assert encoding in ('utf-8', 'UTF-8')
          dataone_exception_pyxb = self.get_pyxb()
          return d1_common.xml.serialize_for_transport(
              dataone_exception_pyxb, xslt_url=xslt_url
          )