These values can be used: msg Error messages that would otherwise be omitted will be given anyway. throw Error messages that would otherwise be omitted will be given anyway and also throw an exception and set v:errmsg. beep A message will be given when otherwise only a beep would be produced. The values can be combined, separated by a comma. "msg" and "throw" are useful for debugging 'foldexpr', 'formatexpr' or 'indentexpr'.

(default "")