code: def translate_index_to_position(self, index):
          
          # Find start of this line.
          row, row_index = self._find_line_start_index(index)
          col = index - row_index
  
          return row, col
docs: Given an index for the text, return the corresponding (row, col) tuple.
          (0-based. Returns (0, 0) for index=0.)