Question about objc category

[forumer]

Hi,

I am reading the GNUstep source code and especially the parts that 
concern the loading of a Xib and I am currently looking at the following
code :

//https://github.com/gnustep/gnustep-gui/blob/master/Model/IBClasses.h

@interface NSCustomObject : NSObject
{
    NSString *className;
    id realObject;
    id extension;
}
@end


//https://github.com/gnustep/gnustep-gui/blob/master/Model/IBClasses.m

@implementation NSCustomObject (NibToGModel)
- (id)awakeAfterUsingCoder:(NSCoder*)aDecoder
{
#ifdef DEBUG
  NSLog (@"%x awakeAfterUsingCoder NSCustomObject: className = %@, 
realObject = %@, "
         @"extension = %@", self, className, realObject, extension);
#endif
  [objects addObject:self];
  return self;
}


What I don't understand is the line [objects addObject:self]; where 
does the ivar objects comes from ?
Is it the objects variable from the GSXibKeyedUnarchiver ? In this case 
does it mean when you use a category
you have access to the caller's context ?

Thanks