public override void WriteSurrogateCharEntity( char lowChar, char highChar ) {
int surrogateChar = ( (int)lowChar - SurLowStart ) | ( ( (int)highChar - SurHighStart ) << 10 ) + 0x10000;
bufBytes[bufPos++] = (byte)'&';
bufBytes[bufPos++] = (byte)'#';
bufBytes[bufPos++] = (byte)'x';
RawText( surrogateChar.ToString( "X", NumberFormatInfo.InvariantInfo ) );
bufBytes[bufPos++] = (byte)';';
textPos = bufPos;
}