code: func (c Config) String() string {
  	// sort 'provider' to the front and keep the keys stable.
  	var keys []string
  	for k := range c {
  		if k != "provider" {
  			keys = append(keys, k)
  		}
  	}
  	sort.Strings(keys)
  	keys = append([]string{"provider"}, keys...)
  
  	quote := func(s string) string {
  		if strings.ContainsAny(s, ` "\`) {
  			return strconv.Quote(s)
  		}
  		return s
  	}
  
  	var vals []string
  	for _, k := range keys {
  		v := c[k]
  		if v == "" {
  			continue
  		}
  		vals = append(vals, quote(k)+"="+quote(v))
  	}
  	return strings.Join(vals, " ")
  }
docs: // String formats a config map into the "key=val key=val ..."
  // understood by Parse. The order of the keys is stable.