generating URL from a named route

I am working with an example from Phalcon docs but have some problems.

The URL component should build /manual/en/translate.adapter.html but instead the following URL is being build: /manual/en/translate.adapter\.html (slash before .html).

My router is a copy from the docs:

// matches "/manual/en/translate.adapter.html"
$router->add(
    "/manual/([a-z]{2})/([a-z\.]+)\.html",
    array(
        "controller" => "manual",
        "action"     => "show",
        "language"   => 1,
        "file"       => 2
    )
)->setName("theexample"); // I have only added this line

The above code is from https://docs.phalcon.io/en/latest/reference/routing.html#usage-examples

Then, when I want to generate an URL like here:

$url = $this->url->get(array(
  "for" => "theexample",
  "language" => "en",
  "file" => "translate.adapter",
));

var_dum($url);

I receive this:

string '/manual/en/translate.adapter\.html' (length=34)

The same problem is with $this->response->redirect().

What is wrong? I have copied the example from the docs and only named a route. How to fix this slash before a dot?

TIA