# {
        #    "value": "B",
        #    "comment": "Both responses accurately state"
        #       " that the chemical formula for water is H2O."
        #       " However, Response B provides additional information"
        # .     " by explaining what the formula means.\\n[[B]]"
        # }
    """
    output_key: str = "results"  #: :meta private:
    output_parser: BaseOutputParser = Field(
        default_factory=PairwiseStringResultOutputParser
    )
    class Config:
        """Configuration for the PairwiseStringEvalChain."""
        extra = Extra.ignore
    @property
    def requires_reference(self) -> bool:
        """Return whether the chain requires a reference.
        Returns:
            bool: True if the chain requires a reference, False otherwise.
        """
        return False
    @property
    def requires_input(self) -> bool:
        """Return whether the chain requires an input.
        Returns:
            bool: True if the chain requires an input, False otherwise.
        """
        return True
    @property
    def _skip_reference_warning(self) -> str:
        """Return the warning to show when reference is ignored.
        Returns:
            str: The warning to show when reference is ignored.
        """
        return (
            f"Ignoring reference in {self.__class__.__name__}, as it is not expected."
            "\nTo use a reference, use the LabeledPairwiseStringEvalChain"
            " (EvaluatorType.LABELED_PAIRWISE_STRING) instead."
        )
[docs]    @classmethod
    def from_llm(
        cls,
        llm: BaseLanguageModel,
        *,