Symfony\Component\Routing\RouteCollection::addPrefix PHP Method

    public function addPrefix($prefix, $defaults = array(), $requirements = array(), $options = array())
    {
        // a prefix must not end with a slash
        $prefix = rtrim($prefix, '/');

        if ('' === $prefix && empty($defaults) && empty($requirements) && empty($options)) {
            return;
        }

        // a prefix must start with a slash
        if ('' !== $prefix && '/' !== $prefix[0]) {
            $prefix = '/'.$prefix;
        }

        $this->prefix = $prefix.$this->prefix;

        foreach ($this->routes as $route) {
            if ($route instanceof RouteCollection) {
                $route->addPrefix($prefix, $defaults, $requirements, $options);
            } else {
                $route->setPattern($prefix.$route->getPattern());
                $route->addDefaults($defaults);
                $route->addRequirements($requirements);
                $route->addOptions($options);
            }
        }
    }

 /**
  * Adds a route collection to the current set of routes (at the end of the current set).
  *
  * @param RouteCollection $collection A RouteCollection instance
  * @param string          $prefix     An optional prefix to add before each pattern of the route collection
  */
 public function addCollection(RouteCollection $collection, $prefix = '')
 {
     $collection->addPrefix($prefix);
     foreach ($collection->getResources() as $resource) {
         $this->addResource($resource);
     }
     $this->routes = array_merge($this->routes, $collection->all());
 }