code: func (f *ScriptField) Source() (interface{}, error) {
  	if f.script == nil {
  		return nil, errors.New("ScriptField expects script")
  	}
  	source := make(map[string]interface{})
  	src, err := f.script.Source()
  	if err != nil {
  		return nil, err
  	}
  	source["script"] = src
  	return source, nil
  }
docs: // Source returns the serializable JSON for the ScriptField.