File: vendor/symfony/symfony/src/Symfony/Bundle/TwigBundle/Resources/config/routing/errors.xml

<?xml version="1.0" encoding="UTF-8" ?>

<routes xmlns="http://symfony.com/schema/routing"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/routing http://symfony.com/schema/routing/routing-1.0.xsd">

    <route id="_twig_error_test" path="/{code}.{_format}">
        <default key="_controller">twig.controller.preview_error:previewErrorPageAction</default>
        <default key="_format">html</default>
        <requirement key="code">\d+</requirement>
    </route>
</routes>