use XML::Filter::Dispatcher qw( :all );

    my $f = XML::Filter::Dispatcher->new(
        Rules => [
            'foo'               => \&handle_foo_start_tag,
            '@bar'              => \&handle_bar_attr,

            ## Send any <foo> elts and their contents to $handler
            'snarf//self::node()'  => $handler,

            ## Print the text of all <description> elements
            'description' 
                    => [ 'string()' => sub { push @out, xvalue } ],
        ],

        Vars => {
            "id" => [ string => "12a" ],
        },
    );