Question about masking tokens in DataCollatorForPermutationLanguageModeling
According to the description from XLNet paper, the permutation LM does not need to corrupt the input in its data processing, and this is different from the Masked LM in BERT. But I found the below code in `DataCollatorForPermutationLanguageModeling` for XLNet replacing the specific tokens in the input data with the given mask_token. I'm confused about this operation. Could you please kindly make a simple explanation? Thank you very much in advance.

https://github.com/huggingface/transformers/blob/b29fd6971d9cd6ba2a824628effe243f543b8f61/src/transformers/data/data_collator.py#L1295