Split the given identifier at the first underscore into (rendered)
        name and subscript. Both `name` and `subscript` are rendered as
        strings

def _split_identifier(self, identifier):
        """Split the given identifier at the first underscore into (rendered)
        name and subscript. Both `name` and `subscript` are rendered as
        strings"""
        try:
            name, subscript = identifier.split("_", 1)
        except (TypeError, ValueError, AttributeError):
            name = identifier
            subscript = ''
        return self._render_str(name), self._render_str(subscript)