langchain/chains/conversational_retrieval/base.py/ConversationalRetrievalChain/_aget_docs
class ConversationalRetrievalChain:    async def _aget_docs(self, question: str, inputs: Dict[str, Any]) -> List[Document]:
        docs = await self.retriever.aget_relevant_documents(question)
        return self._reduce_tokens_below_limit(docs)