keras/src/layers/reshaping/flatten.py/Flatten/__init__
class Flatten:    def __init__(self, data_format=None, **kwargs):
        super().__init__(**kwargs)
        self.data_format = backend.standardize_data_format(data_format)
        self.input_spec = InputSpec(min_ndim=1)
        self._channels_first = self.data_format == "channels_first"