code: func (l *Logger) GetLogger(category string, formatter ...Formatter) *Logger {
  	if len(formatter) > 0 {
  		return &Logger{l.coreLogger, category, formatter[0]}
  	}
  	return &Logger{l.coreLogger, category, l.Formatter}
  }
docs: // GetLogger creates a logger with the specified category and log formatter.
  // Messages logged through this logger will carry the same category name.
  // The formatter, if not specified, will inherit from the calling logger.
  // It will be used to format all messages logged through this logger.