symfony中的“动态”参数如何解决？

I was looking through the symfony source files.and I saw this in Symfony\Bundle\SecurityBundle\Resources\config\Security.xml:

<service id='security.role_hierarchy' ... >
    <argument>%security.role_hierarchy.roles%</arguments>

my question is about the %security.role_hierarchy.roles% paramater.this is the parameter provided by the user in the app/config/security.*ml under the role_hierarchy key. however I don't understand how that will resolve to 'security.role_hierarchy.roles'.

checkout the SecurityExtension and the createRoleHierarchy function. you'll see it takes the configuration of security.yml and translates it into the parameter you see.