Entry UrI Format and ternary operators I tried setting up a URL format that takes the hierarchy of a structure into account, but deals with the magic __home__ slug transparently. 

So I did this:

{parent.uri == '__home__' ? '' : parent.uri}/{slug} 

Which works, but I wanted to tighten it up using the twig ternary ?:, like this: 

{parent.uri != '__home__' ?: ''}/{slug}

But that doesn't work at all, seems to choke on the ?: part. Is that a bug, or just a short-coming of the URL format system (not being actual twig)?
I don't think the ternary operator does what you want it to do. According to this page, the first part of your URL format would return 1 (true) if the parent uri is not __home__, or an empty string if it is.

You could try:

{ parent.uri != '__home__' ? parent.uri }/{slug}