docs: def pseudoify(self):
          """
          Derive a pseudo-feature parent from the given multi-feature.
  
          The provided multi-feature does not need to be the representative. The
          newly created pseudo-feature has the same seqid as the provided multi-
          feature, and spans its entire range. Otherwise, the pseudo-feature is
          empty. It is used only for convenience in sorting.
          """
          assert self.is_toplevel
          assert self.is_multi
          assert len(self.multi_rep.siblings) > 0
          rep = self.multi_rep
  
          start = min([s.start for s in rep.siblings + [rep]])
          end = max([s.end for s in rep.siblings + [rep]])
  
          parent = Feature(None)
          parent._pseudo = True
          parent._seqid = self._seqid
          parent.set_coord(start, end)
          parent._strand = self._strand
          for sibling in rep.siblings + [rep]:
              parent.add_child(sibling, rangecheck=True)
          parent.children = sorted(parent.children)
          rep.siblings = sorted(rep.siblings)
  
          return parent