docs: def _to_viewitem(self, prog_var):
          """
          Convert a ProgramVariable instance to a DDGViewItem object.
  
          :param ProgramVariable prog_var: The ProgramVariable object to convert.
          :return:                         The converted DDGViewItem object.
          :rtype:                          DDGViewItem
          """
  
          return DDGViewItem(self._ddg, prog_var, simplified=self._simplified)