What does the UIViewController class do in viewDidLoad?

As in the title, I was wondering what a “standard” implementation is viewDidLoadin UIViewController? Does it really do something? It also matters if UIViewController'sI write in my subclass

-(void)viewDidLoad{
  [super viewDidLoad];
  /*custom code here*/
}

or

-(void)viewDidLoad{
  /*custom code here*/
  [super viewDidLoad];
}

?

PS This is not a duplicate, in other questions people ask when they should call [super viewDidLoad], while my main problem is what the implementation of UIViewController does with it.