Why can't I access the right UserDefaults?

I'm making a Safari App Extension and I want to store some user data with UserDefaults. Using the defaults command line utility, I've set up a com.willwhite.AppName-Extension domain with an underlying plist file with some test values.


In my SafariExtensionHandler code, I have this line:


let userDefaults = UserDefaults(suiteName: "com.willwhite.AppName-Extension")


What I get as the value of userDefaults is, I believe, the standard defaults object (it's the same object as what I get when I pass nil as the suiteName). I'm expecting it to be the defaults that I've set up for my extension using the defaults command line utility. Please could you tell me what is going wrong?