code: def model_node(**kwargs):
      
      kwargs.setdefault('default', {})
  
      def decorator(model):
          return types.ModelType(model, **kwargs)
  
      return decorator
docs: Decorates a ``schematics.Model`` class to add it as a field
      of type ``schematic.types.ModelType``.
  
      Keyword arguments are passed to ``schematic.types.ModelType``.
  
      Example:
  
      .. code-block:: python
          :emphasize-lines: 8,13
  
          from schematics import Model, types
          from rafter.contrib.schematics.helpers import model_node
  
  
          class MyModel(Model):
              name = types.StringType()
  
              @model_node()
              class options(Model):
                  status = types.IntType()
  
              # With arguments and another name
              @model_node(serialized_name='extra', required=True)
              class _extra(Model):
                  test = types.StringType()