code: def add(self, opt, val=None):
          
  
          ov = opt.split('=', 1)
          o = ov[0]
          v = len(ov) > 1 and ov[1] or None
  
          if (v):
              if val != None:
                  raise AttributeError("ambiguous option value")
              val = v
  
          if val == False:
              return
  
          if val in (None, True):
              self.optlist.add(o)
          else:
              self.optdict[o] = val
docs: Add a suboption.