iOS 7 represents the biggest change to Apple's design principles since the original iPhone, the company said — and that means lots of work for the developers who want their apps to look native on the platform. To that end, Apple published a user interface transition guide for iOS developers today, TechCrunch reports.

The guide, which is available only to members of Apple's developer program, walks designers through iOS 7 changes including edge-to-edge layouts, translucent menu and status bars, and buttons without borders. It also describes the three core themes of iOS 7. Those themes, as quoted by TechCrunch:

Deference. The UI helps users understand and interact with the content, but never competes with it.

Clarity. Text is legible at every size, icons are precise and lucid, adornments are subtle and appropriate, and a sharpened focus on functionality motivates the design.

Depth. Visual layers and realistic motion heighten users' delight and understanding.

Apple will continue to support iOS 6 for the time being. The latest version of Xcode will allow developers to manage multiple versions of an app and compare the way they will look on iOS 6 and 7.

No matter how developers feel about iOS 7 — and not everybody loves it — adjusting their apps to take advantage of it will require some work. Apple's transition guide gives them a solid, high-level overview of the design principles that went into the new look and feel.

The full guide can be found here.