<PackageReference Include="NETStandard.Library" Version="2.0.1" />

System.Text.EncoderFallbackBuffer

public abstract class EncoderFallbackBuffer
namespace System.Text { public abstract class EncoderFallbackBuffer { public abstract int Remaining { get; } protected EncoderFallbackBuffer(); public abstract bool Fallback(char charUnknownHigh, char charUnknownLow, int index); public abstract bool Fallback(char charUnknown, int index); public abstract char GetNextChar(); public abstract bool MovePrevious(); public virtual void Reset(); } }