static void ReplaceHandlerInternal( IBrush factory, Player player, CommandReader cmd ) {
CuboidDrawOperation op = new CuboidDrawOperation( player );
IBrushInstance brush = factory.MakeInstance( player, cmd, op );
if( brush == null ) return;
op.Brush = brush;
player.SelectionStart( 2, DrawOperationCallback, op, Permission.Draw );
player.MessageNow( "{0}: Click or &H/Mark&S 2 blocks.",
op.Brush.InstanceDescription );
}