docs: def colocate(self, others, why):
          """
          Colocate this operator with another.
          """
          if isinstance(self, Marker):
              return
          colocate_tag = '__spl_' + why + '$' + str(self.index)
          self._colocate_tag(colocate_tag)
          for op in others:
              op._colocate_tag(colocate_tag)