langchain/chains/combine_documents/refine.py/RefineDocumentsChain/_construct_initial_inputs
class RefineDocumentsChain:    def _construct_initial_inputs(
        self, docs: List[Document], **kwargs: Any
    ) -> Dict[str, Any]:
        base_info = {"page_content": docs[0].page_content}
        base_info.update(docs[0].metadata)
        document_info = {k: base_info[k] for k in self.document_prompt.input_variables}
        base_inputs: dict = {
            self.document_variable_name: self.document_prompt.format(**document_info)
        }
        inputs = {**base_inputs, **kwargs}
        return inputs