rails/rails — pull request #16153 by cirosantilli (2014-07-13 13:13:23+00:00)
Title: url_for options can be other types besides Hash. [ci skip]

I don't have enough knowledge to explain exactly how other types are treated, but a quick look at the source immediately enlightens the String and Array cases.

Also less confusing for users who are searching for non-Hash cases.