sub variable {
    my $c = shift;
    my $oldvarref = $c->{'-variable'};
    my $oldval = $$oldvarref if $oldvarref;
    if(@_) {
	my $varref = shift;
        if ($oldvarref)
         {
	  $c->traceVdelete($oldvarref);
         }
	$c->{'-variable'} = $varref;
	$c->traceVariable($varref, 'w', sub { $c->value($_[1]) });
	$$varref = $oldval;
	_layoutRequest($c,2);
    }
    $oldval;
}