元素有两个作用，具体具有哪种作用取决于其是否位于<article>元素中。
<html>
<head>
<title>TODO supply a title</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<div>TODO write content</div>
<aside>
<section class="popular-recipes">
<h2>popular Recipes</h2>
<a href="">Yakitori (grilled chicken)</a>
<a href="">Tsukune (minced chicken patties)</a>
<a href="">Okonomiyaki (savory pancakes)</a>
<a href="">Mizutaki (chicken stew)</a>
</section>
<section class="contact-details">
<h2>Contact</h2>
<p>Yoko's kitchen<br/>
27 Redchurch Street<br/>
Shoreditch<br/>
London E2 7DP</p>
</section>
</aside>
</body>
</html>