<assets>
<?php
foreach (assetic_stylesheets(array(
'foo.css',
'bar.css',
), array(
'?foo',
'bar',
), array(
'name' => 'test123',
'output' => 'css/packed.css',
'debug' => true,
)) as $url) {
?>
<asset url="<?php
echo $url;
?>" />
<?php
}
?>
</assets>