Ian's 12 sets/workout

I’ve seen several postings stating Ian King recommends limiting an entire workout to 12 sets. I don’t have my hands on his book, but I hope warm-up sets don’t count. e.g. If I’m doing squats and want to do 3 working sets of 6 reps each, I’ll do 5 or 6 warm-up sets before starting. Adding another bodypart really limits the number of sets or exercises one can do. Could someone who understands Ian’s methods please elaborate?