public void mark (TextPosition Start, TextPosition End)
	{
		if (Start == null || End == null) return;
		TextPosition P1, P2;
		if (Start.before(End))
		{
			P1 = Start;
			P2 = End;
		}
		else if (End.before(Start))
		{
			P1 = End;
			P2 = Start;
		}
		else return;
		ListElement e = P1.L;
		((Line)e.content()).block(P1.LPos, Line.START);
		if (e != P2.L) e = e.next();
		while (e != null && e != P2.L)
		{
			((Line)e.content()).block(0, Line.FULL);
			e = e.next();
		}
		if (e != null) ((Line)e.content()).block(P2.LPos, Line.END);
		repaint();
		requestFocus();
	}