code: func (f *AccessLogFields) KeepHeader(header string) string {
  	defaultValue := AccessLogKeep
  	if f != nil && f.Headers != nil {
  		defaultValue = checkFieldHeaderValue(f.Headers.DefaultMode, defaultValue)
  
  		if v, ok := f.Headers.Names[header]; ok {
  			return checkFieldHeaderValue(v, defaultValue)
  		}
  	}
  	return defaultValue
  }
docs: // KeepHeader checks if the headers need to be kept, dropped or redacted and returns the status