20.13 Summary
SwiftUI user interfaces are declared in SwiftUI View files and are composed of components that conform to the View protocol. To conform with the View protocol a structure must contain a property named body which is itself a View.
SwiftUI provides a library of built-in components for use when designing user interface layouts. The appearance and behavior of a view can be configured by applying modifiers, and views can be modified and grouped together to create custom views and subviews. Similarly, custom container views can be created using the ViewBuilder closure property.
When a modifier is applied to a view, a new modified view is returned and subsequent modifiers are then applied to this modified view. This can have significant implications for the order in which modifiers are applied to a view.
