langchain/chains/combine_documents/map_rerank.py/MapRerankDocumentsChain/combine_docs
class MapRerankDocumentsChain:    def combine_docs(
        self, docs: List[Document], callbacks: Callbacks = None, **kwargs: Any
    ) -> Tuple[str, dict]:
        """Combine documents in a map rerank manner.

        Combine by mapping first chain over all documents, then reranking the results.
        """
        results = self.llm_chain.apply_and_parse(
            # FYI - this is parallelized and so it is fast.
            [{**{self.document_variable_name: d.page_content}, **kwargs} for d in docs],
            callbacks=callbacks,
        )
        return self._process_results(docs, results)