We've been combing through all of Apple's publicly-released documentation and watching the WatchKit introduction video. This is everything we've learned about Apple Watch and how it works.

As of today, developers can now make apps for Apple Watch . Well, they're not separate apps so much as they are extensions of pre-existing iPhone apps, and there isn't a lot of flexibility in the WatchKit toolset — but it looks like that'll change next year.

An iPhone is required — at (almost) all times. In Apple’s own words, Watch apps extend iOS apps. "You begin your Watch app development with your existing iOS app, which must support iPhone." That’s in part because Watch apps’ processing power is all coming from the iPhone. Apple says that "as the wearer interacts with the Watch App, Apple Watch and iPhone pass information back and forth. Taps and other messages from Apple Watch cause code in your WatchKit Extension [e.g. iPhone] to execute." Another key phrase from Apple’s documentation: "A Watch app complements your iOS app; it does not replace it. If you measure interactions with your iOS app in minutes, you can expect interactions with your Watch app to be measured in seconds." The lone exceptions right now are dates, times, and timers, which do not need to call back to your iPhone. On the bright side, that means the watches won’t necessarily need constant upgrading — all you have to do is upgrade your iPhone. Or maybe not… Native apps are coming next year. Important footnote from the press release: "Starting later next year, developers will be able to create fully native apps for Apple Watch." We have no clue if those apps will have similar restrictions or if it’s an entirely different story. But seriously, can we at least get Snake?

The resolution for Apple Watch’s two "Retina displays." The UI documentation revealed that the smaller, 38mm device will be 272 x 340 pixels and the larger, 42mm one will be 312 x 390 pixels. That comes out to the same aspect ratio (4:5). There could be more Watch sizes later. "Unlike iOS, where you place views at a coordinate on the screen," Apple says, "with WatchKit, objects automatically flow downward from the top left corner of the screen, filling the available space." There’s a lot of flexibility with how you group and nest elements in a Watch app, but fundamentally this means apps flow like a responsive website and can fit whatever resolution is available now and in the future. That’ll make things a lot easier for developers and a lot nicer for watch owners should Apple decide to make a change.

There are two types of Apple Watch notifications. The "Short Look" is only seen briefly when you raise your wrist — it’s an app icon, an app name, and some brief information. If the wearer keeps their wrist raised long enough — "after a moment," according to Apple — the screen changes to a "Long Look" notification, which provides more information and is more customizable. For Long Looks, the app icon and name move to the top of the screen, and wearers can scroll down through the interface to use custom actions (such as "comment" or "favorite") or dismiss the notification. Glances. We already knew some of this, but now it's well documented. In addition to the app itself and the notification, developers can make "Glances" for quick view of information (e.g. time, weather, tasks left). All the information must fit on a single screen and is read-only, but you’ll be able to tap it to enter the corresponding app. No custom gestures. The interface is more or less locked to what Apple wants: vertical swipes scrolls through the screen, horizontal swipes go between pages, taps indicate selection, "force touch" opens up a context menu, and that digital crown scrolls through pages way faster. Additionally an edge swipe left goes back or up a page ("back to the parent interface controller," if we’re being technical), and an edge swipe up opens the "Glance" view. … About that "force touch" option. Hard-pressing can open up a simple menu with between one and four possible actions. It looks like AirPlay is supported (which makes sense since the iPhone supports AirPlay and is doing all the work anyway).