Parameters are an important parts of routes in symfony, and in any other routing framework for that matter, and everyone knows how to add mandatory or optional parameters to a route. But did you know you can also silently pass arbitrary parameters to a route from the routing definitions ? This may not be a very clear description, so let's take an example. Say you have a tabbed navigation system, and you want to know in your template which tab is the current one. In a perfect world, you could assume one tab corresponds to a module and check this module, but let's say that one tab can contain multiples modules. How are you doing now ? Quite simply actually, by passing a tab parameter to your route.

foo_route:
  url:       /foo
  param: { tab: foobar }

bar_route:
  url:       /bar
  param: { tab: foobar }

Now you can access the tab parameter in your layout:

<?php $currentTab = $sf_params->get('tab'); ?>

Easy heh ? Of course this kind of parameters is not limited to tell which tab we're currently in, you can, for example, bypass the limitation of a system that requires a particular file to be in a particular location (not that using mod_rewrite would not be more efficient, I just wanted one more example):

foobar_xml:
  url:       /a/stupid/url/that/you/cant/change/foobar.xml
  param: { module: default, action: static, file: "/assets/foobar.xml", mimetype: "text/xml" }

Here we simply pass the file and mimetype parameters to an action that'll take care to serve the right file.

Handy ! But please note that you can't pass such parameters in sfPropelRouteCollection for now (yup, this a bug, and there's a ticket already).