code: func _Set(filename, key, value string) error {
  	// Check if the key is already used.
  	conf, err := shconf.ParseFile(filename)
  	if err != nil {
  		if err != os.ErrNotExist {
  			return err
  		}
  		println("ErrNotExist") //TODO: remove
  	} else {
  		if _, err = conf.Get(key); err != shconf.ErrKey {
  			panic("OPS")
  		}
  	}
  
  	return file.AppendString(filename, key+string(conf.Separator())+value)
  }
docs: // == Set variables
  //
  // _Set sets the value named by the key in the given filename.