respondTo example in Slim

respondto_slim.php

<?php

require 'Slim/Slim.php';

// Prepare app
$app = new Slim(array(
    'negotiation.enabled' => true
));

$app->get('/books/:id:format', function ($id) use ($app) {
    $format = $app->respondTo('html', 'xml', 'json');
    $data = do_something_to_get_data($id);
    switch($format) {
        case 'html':
            return $app->render('myTemplate.php', $data);
        case 'xml':
            $xml = do_something_to_make_xml($data);
            return $app->response()->write($xml);
        case 'json':
            $json = json_encode($data);
            return $app->response()->write($json);
    }        
});

// Run app
$app->run();

Got this working in my branch here:
https://github.com/njh/Slim/tree/negotiation

I would prefer:
$app->get('/books/:id/:format', function ($id, $format) use ($app) {
$format = $app->respondTo(ltrim($format, '.'), array('html', 'xml', 'json'));
...
});

or better:
$app->get('/books/:id.:format', function ($id, $format) use ($app) {
$format = $app->request->negotiateFormat($format, array('html', 'xml', 'json'));
...
});

and:

$app = new Slim();
$app->get('/books/:id\.:format', function ($id) use ($app) {
  $app->request->setContentType('html');
  echo "...";
})->conditions(array('format' => 'html'));