The erload:System.Text.Encoding.GetBytes and erload:System.Text.Encoder.Convert methods call erload:System.Text.EncoderReplacementFallbackBuffer.Fallback if they encounter an unknown surrogate pair or character in their input. If the return value of erload:System.Text.EncoderReplacementFallbackBuffer.Fallback is true, the calling method can invoke EncoderReplacementFallbackBuffer.GetNextChar to obtain each character in the replacement fallback buffer.