In 1994, The Unix-Haters Handbook was published containing a long list of missives about the software—everything from overly-cryptic command names that were optimized for Teletype machines, to irreversible file deletion, to unintuitive programs with far too many options. Over twenty years later, an overwhelming majority of these complaints are still valid even across the dozens of modern derivatives. Unix had become so widely used that changing its behavior would have challenging implications. For better

My only concern with this approach is that if someone calls #valid? on the form object afterwards, it would under the hood currently delete the existing errors on the form object and revalidate. The could have unexpected side effects where the errors added by the models passed in or the service called will be lost.

My concern with this approach is still that it's somewhat brittle with the current implementation of valid? because whilst valid? appears to be a predicate and should have no side effects, this is not the case and could remove the errors applied by one of the steps above.

I really can't see how we can trust browsers accept headers. :'( More about the situation than about your statement.

Safari sends following order application/xml (q is 1) application/xhtml+xml (q is 1) image/png (q is 1) text/html (q is 0.9) text/plain (q is 0.8) \*/\* (q is 0.5) So you visit www.myappp.com in safari and if the app supports .xml then Rails should render .xml file. This is not what user wants to see. User wants to see .html page not .xml page.

In the Set class we already called this - and difference, which it is ok but not really accurate because of the previous explanation, but probably not worthwhile to change it.

Basically, the standard said something, interpreters ignored it because the standard seemed illogical, but now interpreters like Bash have really confusing semantics, and no-one wants to fix it.