docs: def validate(self, table: pd.DataFrame, failed_only=False) -> pd.DataFrame:
          """Return a dataframe of validation results for the appropriate series vs the vector of validators.
  
          Args:
              table (pd.DataFrame): A dataframe on which to apply validation logic.
              failed_only (bool): If ``True``: return only the indexes that failed to validate.
          """
          raise NotImplementedError("This method must be defined for each subclass.")