The "category URL name" is a simple plain text field that will be part of your URL if you select URLs by category. I'm pretty sure if you have categories on your posts and they are linked then they will be linked using the "category URL name".

They need to be unique so that a category with a human name "sports" in 10 different blogs gets resolved to the correct category number. That's what you're seeing with "c12, c97, c1390041" - a unique value for that field.

I think you can't have spaces and I think I got cranked over it not letting me use dashes or underscores. Or something. It's almost like, to me, I might as well just use the stupid cNN format and forget about it but it wasn't my blog so I didn't worry too much on it.

Anyway there ya go!

I've got it now.

I never even noticed, but what did 1.10.x use for URLs when you selected a category?

Was it just a querystring parameter cat=id ?

Yes, even if you had the "extra path" box checked.

Thanks Ed.