pkg/flags/urls.go
func (us *URLsValue) Set(s string) error {
	ss, err := types.NewURLs(strings.Split(s, ","))
	if err != nil {
		return err
	}
	*us = URLsValue(ss)
	return nil
}
func (us *URLsValue) Set(s string) error {
	ss, err := types.NewURLs(strings.Split(s, ","))
	if err != nil {
		return err
	}
	*us = URLsValue(ss)
	return nil
}
// Set parses a command line set of URLs formatted like:
// http://127.0.0.1:2380,http://10.1.1.2:80
// Implements "flag.Value" interface.