src/transformers/models/longformer/configuration_longformer.py/LongformerConfig/__init__
class LongformerConfig:    def __init__(self, attention_window: Union[List[int], int] = 512, sep_token_id: int = 2, **kwargs):
        super().__init__(sep_token_id=sep_token_id, **kwargs)
        self.attention_window = attention_window