significance of 'z'?

Question

hello,

i started out learning cocos2d and came across these lines of code:

-(id)init {
self=[super init];
if(self!=nil) {

 Sprite *bg = [Sprite spriteWithFile:@"menu.png"];

 [bg setPosition:ccp(240,160)];
 [self addChild:bg z:0];
 [self addChild:[MenuLayer node] z:1];
}
return self;

}

I ran the same lines of code with the following modification:

-(id)init {
self=[super init];
if(self!=nil) {

 Sprite *bg = [Sprite spriteWithFile:@"menu.png"];

 [bg setPosition:ccp(240,160)];
 [self addChild:bg];
 [self addChild:[MenuLayer node]];
}
return self;

}

Removing the 'z' parameter brought no change in the output, so what is its significance and what is it used for?

Thanks

Answer 1

It's the stacking order a bit like the CSS z-index z:1 will be on top of z:0