使用PHP Simple HTML DOM Parser从html中提取dom元素

Question

I'm trying to extract links to the articles including the text, from this site using PHP Simple HTML DOM PARSER.

I want to extract all h2 tags for articles in the main page and I'm trying to do it this way:

    $html = file_get_html('http://www.winbeta.org');
    $articles = $html->getElementsByTagName('article');
    $a = null;

    foreach ($articles->find('h2') as $header) {
                $a[] = $header;
    }

    print_r($a);

according to the manual it should first get all the content inside article tags then for each article extract the h2 and save in array. but instead it gives me :

EDIT