ARC: __bridge versus __bridge_retained using contextInfo test case

Consider this ARC code:

- (void)main {
    NSString *s = [[NSString alloc] initWithString:@"s"];
    [NSApp beginSheet:sheet 
           modalForWindow:window 
           modalDelegate:self 
           didEndSelector:@selector(sheetDidEnd:returnCode:context:) 
           contextInfo:(__bridge void *)s
    ];
}

- (void)sheetDidEnd:(NSWindow *)sheet returnCode:(NSInteger)returnCode context:(void *)context {
    NSString *s = (__bridge_transfer NSString *)context;
}

Question: on line 7, should __bridge be used, or __bridge_retained, or does it not matter, or does the choice depend on the string's retain count (that is, whether the string is explicitly alloced vs being autoreleased through a class initializer like +[NSString stringWithString:]?