di_xml_example.php

use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\Config\FileLocator;
use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;

$container = new ContainerBuilder();
$loader = new XmlFileLoader($container, new FileLocator(__DIR__));
$loader->load('services.xml');

services.xml

<!-- src/Acme/HelloBundle/Resources/config/services.xml -->
<parameters>
    <!-- ... -->
    <parameter key="mailer.transport">sendmail</parameter>
</parameters>

<services>
    <service id="mailer" class="Mailer">
        <argument>%mailer.transport%</argument>
    </service>

    <service id="newsletter_manager" class="NewsletterManager">
        <call method="setMailer">
             <argument type="service" id="mailer" />
        </call>
    </service>
</services>