def METHOD_NAME(self, documents: List[Document]) -> Tuple[Dict, str]:  # type: ignore
    if self.split_by == "content_type":
        split_documents = self._split_by_content_type(documents)
    elif self.metadata_values:
        split_documents = self._split_by_metadata_values(self.metadata_values, documents)
    else:
        raise ValueError(
            "If split_by is set to the name of a metadata field, provide metadata_values if you want to split "
            "a list of Documents by a metadata field."
        )
    return split_documents, "split"