# config file:

engines:
   template_toolkit:
     PLUGIN_BASE: 'Template::Plugin'


# The filter code:

package Template::Plugin::FilterFence;

use Template::Plugin::Filter;
use base qw( Template::Plugin::Filter );

sub filter {
     my ($self, $text) = @_;
     return join ' ' # etc
}

1;

# The template that uses the filter:

<% USE FilterFence %>
<div id="main">
     <table>
       <% FOREACH row IN rows %>
       <tr><td><% row.0 %><td><% row.1 | $FilterFence %>
       <% END %>
     </table>
</div>

##</code><code>##

use Test::More;
use Template::Plugin::FilterFence;

my $t = 'Template::Plugin::FilterFence'->new;
is($t->filter(0), q(), 'zero');
is($t->filter(1), '|', 'one');
# etc.

##</code><code>##

sub init {
    my $self = shift;
    $self->install_filter('fence');
    return $self
}

##</code><code>##

<% row.1 | fence %>

##</code><code>##

Can't call method "define_filter" on an undefined value at .../Template/Plugin/Filter.pm line 117.

##</code><code>##

my $t = bless {}, 'Template::Plugin::FilterFence';

##</code><code>##

undef *Template::Plugin::FilterFence::init;