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