docs: def p_bound_terminal(self, p):
          """bound_terminal : unbound_terminal"""
          if p[1][0].literal in ['*', '**']:
              p[0] = [_Segment(_BINDING, '$%d' % self.binding_var_count),
                      p[1][0],
                      _Segment(_END_BINDING, '')]
              self.binding_var_count += 1
          else:
              p[0] = p[1]