For example, if you upload a Rails 3 application that (as per the default) disables serving javascript and html files, CloudFoundry (and any PaaS that runs Rack

For example, if you upload a Rails 3 application that (as per the default) disables serving javascript and html files, CloudFoundry (and any PaaS that runs Rack basically) have to flip that switch for you. I believe that clause just makes sure such things are permitted. For Java apps, you have to generate XML files containing whatever the values turned out to be at runtime, etc.