text: 
  
  TITLE
  Allow `do_lower_case=True` for any tokenizer
  
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  # 🚀 Feature request
  
  Extract the `do_lower_case` option to make it available for any tokenizer. Not just those that initially supported this, like the `BERT` tokenizers.
  
  ## Motivation
  
  Sometimes we want to specify `do_lower_case=True` in the `tokenizer_config.json` of a custom tokenizer to activate the lowercasing. The problem is that this obviously works only for tokenizers based on one that originally used this option.
  
  I think we should extract this feature to make it a shared one, that could be used with any tokenizer.
  
  Example of a model that would need this described here: https://github.com/huggingface/transformers/issues/9518
  
  ## Special care points
  
  - Make sure the `convert_slow_tokenizer` script also handles this, to activate the option in the resulting fast tokenizer.
  - Maybe some other options could have the same treatment?
  
  cc @LysandreJik @sgugger