It's possible to declare protocol name without methods:
use it your code (class definition, etc):
@interface World : NSObject @property (strong, nonatomic) NSArray<id<some>> *employees; @end
and later define protocol's method somewhere in your code:
@protocol Person - (NSString *)gender; - (NSString *)name; @end
It's useful when you don't need to know protocols details until you import that file with protocol definition. So, your class header file stays clear and contains details of the class only.