[myObj addObserver:self forKeyPath:@"theArray" options:0 context:NULL];

[myObj.theArray addObject:NSString.string];

[[myObj mutableArrayValueForKey:@"theArray"] addObject:NSString.string];

[myObject insertObject:newObject inTheArrayAtIndex:[myObject countOfTheArray]];

- (void) addTheArrayObject:(NSObject *) newObject {
    [self insertObject:newObject inTheArrayAtIndex:[self countOfTheArray]];
}

[myObj addObserver:self forKeyPath:@"theArray.@count" options:0 context:NULL];

- (NSMutableArray*) theMutableArray {
    return [self mutableArrayValueForKey:@"theArray"];
}

// Interface
@property (nonatomic, strong, readonly) NSMutableArray *items;

// Implementation
@synthesize items = _items;

- (NSMutableArray *)items
{
    return [self mutableArrayValueForKey:@"items"];
}

// Somewhere else
[myObject.items insertObject:@"test"]; // Will result in KVO notifications for key "items"

- (void)addSomeObject:(id)object {
    self.myArray = [self.myArray arrayByAddingObject:object];
}

- (void)removeSomeObject:(id)object {
    NSMutableArray * ma = [self.myArray mutableCopy];
    [ma removeObject:object];
    self.myArray = ma;
}