src/transformers/models/xlnet/modeling_xlnet.py/XLNetLayer/__init__
class XLNetLayer:    def __init__(self, config):
        super().__init__()
        self.rel_attn = XLNetRelativeAttention(config)
        self.ff = XLNetFeedForward(config)
        self.dropout = nn.Dropout(config.dropout)
        self.chunk_size_feed_forward = config.chunk_size_feed_forward
        self.seq_len_dim = 1