https://learn.microsoft.com/pl-pl/dotnet/api/system.text.decoderreplacementfallbackbuffer?view=netframework-4.8.1&viewFallbackFrom=net-9.0
DecoderReplacementFallbackBuffer Class (System.Text) | Microsoft Learn
Represents a substitute output string that is emitted when the original input byte sequence cannot be decoded. This class cannot be inherited.
class systemtextmicrosoftlearn