Q: How do I change the size of the first 5 bytes on line 12 of a rich edit?

A:

procedure TForm1.Button1Click(Sender: TObject);
begin
  with RichEdit1 do begin
    SelStart := perform(em_LineIndex, spinedit1.value, 0);
    SelLength := 5;
    SetFocus;
    SelAttributes.size := 16;
  end;
end;