src/transformers/models/markuplm/tokenization_markuplm.py/MarkupLMTokenizer/build_xpath_subs_with_special_tokens
class MarkupLMTokenizer:    def build_xpath_subs_with_special_tokens(
        self, xpath_subs_0: List[int], xpath_subs_1: Optional[List[int]] = None
    ) -> List[int]:
        pad = [self.pad_xpath_subs_seq]
        if len(xpath_subs_1) == 0:
            return pad + xpath_subs_0 + pad
        return pad + xpath_subs_0 + pad + xpath_subs_1 + pad