    def convert_tokens_to_string(self, tokens):
        """Converts a sequence of tokens (strings for sub-words) in a single string."""
        out_string = "".join(tokens).replace(SPIECE_UNDERLINE, " ").strip()
        return out_string
Converts a sequence of tokens (strings for sub-words) in a single string.
ptstructure/vqa/pytorchnlp/transformers/layoutxlm/tokenizer.py