code: def _init_composite_fields(self):
          
          # The base_composite_fields class attribute is the *class-wide*
          # definition of fields. Because a particular *instance* of the class
          # might want to alter self.composite_fields, we create
          # self.composite_fields here by copying base_composite_fields.
          # Instances should always modify self.composite_fields; they should not
          # modify base_composite_fields.
          self.composite_fields = copy.deepcopy(self.base_composite_fields)
          self.forms = OrderedDict()
          self.formsets = OrderedDict()
          for name, field in self.composite_fields.items():
              self._init_composite_field(name, field)
docs: Setup the forms and formsets.