code: def zoom_in_frag(self, curr_frag):
          
          level = curr_frag[1]
          frag = curr_frag[0]
          output = []
          if level > 0:
              str_level = str(level)
              sub_low = self.spec_level[str_level]["fragments_dict"][frag][
                  "sub_low_index"
              ]
              sub_high = self.spec_level[str_level]["fragments_dict"][frag][
                  "sub_high_index"
              ]
              new_level = level - 1
              for i in range(sub_low, sub_high + 1):
                  output.append((i, new_level))
          else:
              output.append(curr_frag)
          return output
docs: :param curr_frag: