Why do many (not all) transformer classes have their docstring starting with r###
grep -r -A 2 'class ' src/transformers 

here is just a sample of both:
src/transformers/modeling_tf_xlnet.py:# class TFXLNetForQuestionAnswering(TFXLNetPreTrainedModel):
src/transformers/modeling_tf_xlnet.py-#     r"""
src/transformers/tokenization_distilbert.py:class DistilBertTokenizer(BertTokenizer):
src/transformers/tokenization_distilbert.py-    r"""
src/transformers/tokenization_gpt2.py:class GPT2TokenizerFast(PreTrainedTokenizerFast):
src/transformers/tokenization_gpt2.py-    """
src/transformers/tokenization_auto.py:class AutoTokenizer:
src/transformers/tokenization_auto.py-    r""":class:`~transformers.AutoTokenizer` is a generic tokenizer class

Is there a special purpose for using a regex string? There doesn’t seem to be any pattern - it appears in some, but not the others classes’ docstring.
Thank you.