UIKit User Interface Catalog: About Controls
https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/UIKitUICatalog/UIControl.html …#//apple_ref/doc/uid/TP40012857-UIControl-SW1
https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/UIKitUICatalog/UIControl.html …#//apple_ref/doc/uid/TP40012857-UIControl-SW1