Compliance is one of those big underlying skills. Being able to follow directions from authority figures, such as parents, teachers, police. It also encompasses being aware of other people's rights, feelings and reactions, so that we can all function as a civil society. That way, you don't need specific instructions for every situation: don't break that kid's toy, don't hit that person.
Compliance is not Alex's strong suit.
He's willing to follow instructions. Sometimes. If the person giving the instructions is someone he has a strong relationship with. However, we, as a society, expect him to follow instructions even when he's never met the person in question. Such as the clerk at the store who tells him to wait in line if he wants to make a purchase.
His mindset is very functional. He will take whatever steps necessary to get his goal and unfortunately, he's discovered aggression is a very functional tool. It can always be escalated to a point where it can't be ignored and then the focus has to switch from whatever demand has been put on him to dealing with the aggression. He's not malicious, to him, it's a tool on an equal par with asking for things, only more reliable.
If he was compliant, we wouldn't have to worry (as much) about him turning around and thwacking someone because he doesn't like what's being asked. We wouldn't have to worry as much about him simply taking off because he doesn't want to stay and watch me pick out sweat pants in the store. We could go places as a family without a go-bag of distractions and having to eat or talk in shifts so that one person is watching over Alex. We would be able to be more effective dealing with problem behaviours and teaching skills, like using the toilet or eating.
This is one of the main reasons we're going to Disney with just one child at a time. Because the Happiest Place on Earth should not become a site of daily meltdowns, attacks and having to choose between staying with one child or chasing after the other. Alex would not be tolerate of Nathan wanting to see something other than what he wants to see. (He won't tolerate us wanting to see something different either, but we can handle our disappointment a little better.)
When the primary consideration for any given day is dealing with how to manage Alex since he will not accept being on anyone else's agenda, then he's not compliant.