def word_to_chars(
        self, batch_or_word_index: int, word_index: Optional[int] = None, sequence_index: int = 0
    ) -> CharSpan:
        """
        Get the character span in the original string corresponding to given word in a sequence of the batch.

        Character spans are returned as a CharSpan NamedTuple with:

        - start: index of the first character in the original string
        - end: index of the character following the last character in the original string

        Can be called as:

        - `self.word_to_chars(word_index)` if batch size is 1
        - `self.word_to_chars(batch_index, word_index)` if batch size is greater or equal to 1

        Args:
            batch_or_word_index (`int`):
                Index of the sequence in the batch. If the batch only comprise one sequence, this can be the index of
                the word in the sequence
            word_index (`int`, *optional*):
                If a batch index is provided in *batch_or_token_index*, this can be the index of the word in the
                sequence.
            sequence_index (`int`, *optional*, defaults to 0):
                If pair of sequences are encoded in the batch this can be used to specify which sequence in the pair (0
                or 1) the provided word index belongs to.

        Returns:
            `CharSpan` or `List[CharSpan]`: Span(s) of the associated character or characters in the string. CharSpan
            are NamedTuple with:

                - start: index of the first character associated to the token in the original string
                - end: index of the character following the last character associated to the token in the original
                  string
        """

        if not self._encodings:
            raise ValueError("word_to_chars() is not available when using Python based tokenizers")
        if word_index is not None:
            batch_index = batch_or_word_index
        else:
            batch_index = 0
            word_index = batch_or_word_index
        return CharSpan(*(self._encodings[batch_index].word_to_chars(word_index, sequence_index)))

        Get the character span in the original string corresponding to given word in a sequence of the batch.

        Character spans are returned as a CharSpan NamedTuple with:

        - start: index of the first character in the original string
        - end: index of the character following the last character in the original string

        Can be called as:

        - `self.word_to_chars(word_index)` if batch size is 1
        - `self.word_to_chars(batch_index, word_index)` if batch size is greater or equal to 1

        Args:
            batch_or_word_index (`int`):
                Index of the sequence in the batch. If the batch only comprise one sequence, this can be the index of
                the word in the sequence
            word_index (`int`, *optional*):
                If a batch index is provided in *batch_or_token_index*, this can be the index of the word in the
                sequence.
            sequence_index (`int`, *optional*, defaults to 0):
                If pair of sequences are encoded in the batch this can be used to specify which sequence in the pair (0
                or 1) the provided word index belongs to.

        Returns:
            `CharSpan` or `List[CharSpan]`: Span(s) of the associated character or characters in the string. CharSpan
            are NamedTuple with:

                - start: index of the first character associated to the token in the original string
                - end: index of the character following the last character associated to the token in the original
                  string
        
dpkd/transformers/src/transformers/tokenization_utils_base.py