Following http://symfony.com/doc/master/components/routing/hostname_pattern.html

Adding a Host Regex to Imported Routes¶
You can set a host regex on imported routes:

# app/config/routing.yml
acme_hello:
    resource: "@AcmeHelloBundle/Resources/config/routing.yml"
    host:     "hello.example.com"

The host hello.example.com will be set on each route loaded from the new routing resource.

Trying this with:

acme_hello:
    resource: "@AcmeHelloBundle/Resources/config/routing.yml"
    host: "/.domain.com|domain.com/"

Fails to match www.domain.com and domain.com, and any other combination.

Debug:

preg_match('/.domain.com |domain.com /', 'www.domain.com', $result);
var_dump($result)
array (size=1)
  0 => string '.domain.com'

Does symfony use something else than preg_match internally or am i missing something ?