I've been trying to learn Core Data, and browsing through questions on Stack Overflow lead me to a recommendation that I try the tutorial on Core Data over at Cocoa Dev Central (Link).
Everything is making sense so far in the tutorial, but when I got to step 16, it wouldn't let me connect the + button to the Posts array controller. I've gone back and double, triple-checked each step along the way and can't see where anything is off, but it still won't let me connect. I'm using the latest versions of Xcode and Interface Builder (just re-downloaded them last week); could this be a version compatibility issue?
Addendum
Seems that the problem was in that I had to change the name by changing the class in the inspector, and that removed the default actions for the array controller. Changing the class back to NSArrayController restores functionality, but now it appears as "Array Controller" wherever it appears, which seems like it'd become problematic with 3 controllers in play once I fix the Authors and Topics controllers.
Got it. Under the inspector, use "Name" to change the name of the object, not "Class". Newbie error.