AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.responseSerializer = [AFOnoResponseSerializer XMLResponseSerializer];
[manager GET:@"http://example.com/foo.xml" parameters:nil success:^(AFHTTPRequestOperation *operation, ONOXMLDocument *responseDocument) {
    for (ONOXMLElement *element in [responseDocument XPath:@"//item"]) {
        NSLog(@"%@", element);
    }
} failure:nil];

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.responseSerializer = [AFOnoResponseSerializer HTMLResponseSerializer];
[manager GET:@"http://example.com/bar.html" parameters:nil success:^(AFHTTPRequestOperation *operation, ONOXMLDocument *responseDocument) {
    for (ONOXMLElement *element in [responseDocument CSS:@"body ul li"]) {
        NSLog(@"%@", element);
    }
} failure:nil];