I'm doing a website using the php framework symfony and twig. I want to display a custom page for errors like 404 or 500. I saw [here](http://symfony.com/doc/current/cookbook/controller/error_pages.html) how to do the custom page, I have the error.html.twig in `app/Resources/TwigBundle/views/Exception/error.html.twig` but it does not seem to be called, I'm also using the

```
_errors:
    resource: "@TwigBundle/Resources/config/routing/errors.xml"
    prefix:   /_error

```

in `routing_dev.yaml` and neither in the dev nor on the live site you can see the custom or the default error page.

I've looked everywhere to find how does this page gets called but I cannot find anything so if you know how to do it, or where can I find documents about this I would be really grateful.

--I know this question mmay be seen as too broad, but I really can't find anything on google about this, any help will be good--