Pop over rules settings

Hi,

For my Pop over, I'd like to set "Visit via specific referrer."

When I drag and drop this option, there is an entry window that
has the word "Array" in it.

What goes here?

- WP conditional tags?
- URL?

Thanks!

P.S.
As a suggestion, when entering a post like this - and using the "Pick a plugin or theme" drop down, it is often hard to find the right plug-in.

For example, when looking for Pop over, it doesn't seem logical to me to search for "The" Pop Over. I invariably end up wasting time when trying to "pick a theme or plug-in."