Restoring an optional, secondary document window

gistfile1.m

- (void)restoreDocumentWindowWithIdentifier:(NSString *)identifier state:(NSCoder *)state completionHandler:(void (^)(NSWindow *, NSError *))completionHandler;
{
    if ([identifier isEqualToString:@"Secondary"])
    {
        // Rely on main controller to create secondary window
        if (![[self windowControllers] count]) [self makeWindowControllers];
        MyWindowController *mainController = [[self windowControllers] objectAtIndex:0];
        completionHandler([[mainController secondaryWindowController] window], nil);
    }
    else
    {
        [super restoreDocumentWindowWithIdentifier:identifier state:state completionHandler:completionHandler];
    }
}