src/transformers/models/xlnet/modeling_tf_xlnet.py/TFXLNetMainLayer/build
class TFXLNetMainLayer:    def build(self, input_shape):
        initializer = get_initializer(self.initializer_range)
        self.mask_emb = self.add_weight(
            shape=(1, 1, self.d_model), initializer=initializer, trainable=True, name="mask_emb"
        )