code: def add_schema(self, schema):
          
  
          # serialize instances of SchemaNode before parsing
          if isinstance(schema, SchemaNode):
              schema = schema.to_schema()
  
          for subschema in self._get_subschemas(schema):
              # delegate to SchemaType object
              schema_generator = self._get_generator_for_schema(subschema)
              schema_generator.add_schema(subschema)
  
          # return self for easy method chaining
          return self
docs: Merges in an existing schema.
  
          arguments:
          * `schema` (required - `dict` or `SchemaNode`):
            an existing JSON Schema to merge.