Unicode存储为UTF-8格式编码

procedure TForm1.Button3Click(Sender: TObject);
var
  S: UTF8String;
  F: TextFile;
begin
  S := UTF8Encode(TntEdit1.Text);
  AssignFile(F, 'C:\test.txt');
  Rewrite(F);
  Write(F, #$EF + #$BB + #$BF); // UTF8??
  Write(F, S);
  CloseFile(F);
end;