code: def _char_to_word_index(self, ci):
          
          i = None
          for i, co in enumerate(self.sentence.char_offsets):
              if ci == co:
                  return i
              elif ci < co:
                  return i - 1
          return i
docs: Return the index of the **word this char is in**.
  
          :param ci: The character-level index of the char.
          :type ci: int
          :return: The word-level index the char was in.
          :rtype: int