code: func (l *logger) Verboseln(vals ...interface{}) {
  	s := fmt.Sprintln(vals...)
  	l.mut.Lock()
  	defer l.mut.Unlock()
  	l.logger.Output(2, "VERBOSE: "+s)
  	l.callHandlers(LevelVerbose, s)
  }
docs: // Infoln logs a line with a VERBOSE prefix.