code: def tag_builder(parser, token, cls, flow_type):
      
      tokens = token.split_contents()
      tokens_num = len(tokens)
  
      if tokens_num == 1 or (tokens_num == 3 and tokens[1] == 'for'):
          flow_name = None
          if tokens_num == 3:
              flow_name = tokens[2]
          return cls(flow_name)
      else:
          raise template.TemplateSyntaxError(
              '"sitegate_%(type)s_form" tag requires zero or two arguments. '
              'E.g. {%% sitegate_%(type)s_form %%} or '
              '{%% sitegate_%(type)s_form for ClassicSignup %%}.' % {'type': flow_type})
docs: Helper function handling flow form tags.