docs: def seq_site_length(self):
          """Calculate length of a single sequence site based upon relative positions specified in peak descriptions.
  
          :return: Length of sequence site.
          :rtype: :py:class:`int`
          """
          relative_positions_set = set()
          for peak_descr in self:
              relative_positions_set.update(peak_descr.relative_positions)
          return len(relative_positions_set)