extension route attempt in zend framework - this fails as every parameter is checked for each route :(

route_extension.php

<?php
$def = new Zend_Controller_Router_Route(
    ':module/:controller/:action/*',
    array(
        'module' => 'public',
        'controller' => 'index',
        'action'     => 'index'
    )
);

$ext = new Zend_Controller_Router_Route(
    ':ext',
    array(
        'ext' => 'html'
    )
);
        
$route = $def->chain($ext, '.');

echo $route->assemble(array('ext' => 'json')); // public/index/index/ext/json.json
?>