code: def _formatExternalIdentifiers(self, element, element_type):
          
          elementClause = None
          elements = []
          if not issubclass(element.__class__, dict):
              element = protocol.toJsonDict(element)
          if element['externalIdentifiers']:
              for _id in element['externalIdentifiers']:
                  elements.append(self._formatExternalIdentifier(
                      _id, element_type))
              elementClause = "({})".format(" || ".join(elements))
          return elementClause
docs: Formats several external identifiers for query