Описание тега visual-format-language
Cocoa's language for specifying the layout of control objects on a visual canvas
You use the Cocoa Auto Layout system to define layout constraints for user interface elements. Constraints represent relationships between user interface elements such as “these views line up head to tail,” or “this button should move with this split view subview.” When laying out the user interface, a constraint satisfaction system arranges the elements in a way that most closely meets the constraints.