  using only a sub-set of the output tokens as target which are selected with the target_mapping input.
To use XLNet for sequential decoding (i.e. not in fully bi-directional setting), use the perm_mask and
  target_mapping inputs to control the attention span and outputs (see examples in
  examples/pytorch/text-generation/run_generation.py)
XLNet is one of the few models that has no sequence length limit.
This model was contributed by thomwolf. The original code can be found here.
XLNetConfig
[[autodoc]] XLNetConfig
XLNetTokenizer
[[autodoc]] XLNetTokenizer
    - build_inputs_with_special_tokens
    - get_special_tokens_mask
    - create_token_type_ids_from_sequences
    - save_vocabulary
XLNetTokenizerFast
[[autodoc]] XLNetTokenizerFast
XLNet specific outputs
[[autodoc]] models.xlnet.modeling_xlnet.XLNetModelOutput
