I guess I mean the phrase a little differently here. Rails does have a particular envelope that they support, but it is also pretty open to extensions. More importantly, if you do something slightly different, you do not end up having to debug reams of dubious, poorly tested code just to figure out how to get your nominally reasonable change to work. I spent a huge amount of time trying to figure out whether the change I really needed to make was in some XML file, some class annotation, or some custom code.