I want to talk about a thing and there's not much groundwork yet, so forgive me some false starts and some gropings in the dark.
Apocalypse World has 4 layers of rules. Like an onion or some other layered thing — wait, no. Like light bulb hanging over a table in a room.
1. The core of the game is barely visible. It's like the filament in the light bulb. It's these things:
— Vivid color
— A few stats and a simple die roll
— On a 10+, the best happens. On a 7-9, it's good but complicated. On a miss, it's never nothing, it's always something worse.
— The MC's agenda, principles, and what to always say.
That's a complete, playable game. Details of the dice aside, it's most of Over the Edge, for instance.
2. Built around that, the light bulb, is what I'd call fundamental Apocalypse World:
— The basic moves
— How harm works
— How experience works
— The MC's moves
— The structure of fronts and threats, but not their details.
That's also a complete, playable game, even though it's not the entirety of Apocalypse World. (Over the Edge has a light bulb around its filament too, but it's smaller than Apocalypse World's.)
3. The table we're playing at! This is all of Apocalypse World by the book:
— The character playbooks, character moves and special moves and all
— The details of fronts and threats
— Some of the peripheral moves
— All the crap, like holdings, angel kits, weapons, vehicles, gangs and all
— Character improvement, including the ungiven future.
This is the Apocalypse World we all play most of the time.
4. The room we're playing in. This is all the potential Apocalypse World that we can bring in if we want. Much of it isn't even in the book!
— The optional battle moves
— All kinds of custom moves
— MC love letters
— New playbooks
— New threat types
— New kinds of crap like monsters, hoards, caravans, space stations.
Most of us who play Apocalypse World bring some of these things in sometimes, but nobody has to, and obviously nobody can play by ALL the possible potential rules. Potential Apocalypse World is bigger than us.
Okay! Here's a cool thing about Apocalypse World's design in particular, if I may say it myself: Apocalypse World is designed to collapse gracefully downward.
— Forget the peripheral harm moves? That's cool. You're missing out, but the rules for harm have got you covered.
— Forget the rules for harm? that's cool. You're missing out, but the basic moves have got you covered. Just describe the splattering blood and let them handle the rest.
— Forget the basic moves? That's cool. You're missing out, but just remember that 10+ = hooray, 7-9 = mixed, and 6- = something worse happens.
— Don't want to make custom moves and countdowns for your threats all the time? That's cool. You're missing out, but the threat types, impulses, and threat moves have got you covered.
— Don't want to even write up your fronts and threats? That's cool. You're missing out, but your MC moves have got you covered.
— Forget your MC moves? That's cool. You're missing out, but as long as you remember your agenda and most of your principles and what to always say, you'll be okay.
The whole game is built so that if you mess up a rule in play, you mostly just naturally fall back on the level below it, and you're missing out a little but it works fine.