It's cool that they have that link. Most frame sites didn't. JS actually isn't necessary to make that work, they could have just interpolated the requested page server-side. But it only correctly points to one frame. It's the most important frame, to be fair, but it doesn't do anything for the other two frames.

I don't understand how pre-HTML5, non-AJAX reference docs qualify as an "SPA". This is just an ordinary web site.