Similar to its early look at the Health app that later shipped in iOS 8, 9to5Mac today posted a comprehensive overview of the "Companion" app that iPhone owners will use to control and manage settings on the Apple Watch. The leak — complete with numerous screenshots — covers everything from customizing notifications to the method by which users will rearrange apps on the Watch's home screen.

The iPhone app will play a pivotal role in interacting with and setting up the Apple Watch. With it, you'll choose which contacts appear on the Watch's "Friends" screen, which allows for quicker messaging, and take granular control over the device's fitness features. Users will be able to decide whether to receive a reminder to stand up if they've been sitting for the majority of any hour, for example, or choose how often to be updated on their fitness goal progress throughout the day. Apple will also give users the option of getting a weekly summary on their efforts to get in better shape.

The Apple Watch Companion app's fitness and friends settings. (9to5Mac)

Since Apple Watch doesn't feature any kind of virtual keyboard, you'll have the choice of setting audio recordings or voice dictation as your preferred way of responding to incoming text messages. (Users can opt to choose every time rather than set a universal default for this setting.) The Companion app is also where you'll type out your short, canned replies to messages for when you're too busy to pull out your phone. Your Messages preferences can be set to mirror those of your iPhone or customized specifically for Apple Watch; for example, you can set the watch to display only texts from your contacts rather than all incoming messages

Customizing the Apple Watch's home screen with the Companion app. (9to5Mac)

Elsewhere, the screenshots confirm that Apple Watch will ship with usable storage space for music, personal photos, and watch apps. Apple will carry over its deep accessibility preferences to the wrist-worn device, and you'll be able to lock things down with a four-digit passcode — just like on iPhone and iPad. While wearing the watch, you can also set it to unlock automatically whenever your iPhone is nearby. The Apple Watch Companion app is expected to be released alongside the upcoming iOS 8.2 software update "early" this year. For the full summary and more details, head over to 9to5Mac.