code: func responseDefinition() (*design.ResponseDefinition, bool) {
  	r, ok := dslengine.CurrentDefinition().(*design.ResponseDefinition)
  	if !ok {
  		dslengine.IncompatibleDSL()
  	}
  	return r, ok
  }
docs: // responseDefinition returns true and current context if it is a ResponseDefinition,
  // nil and false otherwise.