The aside tag
The aside tag defines a side part of the page in HTML (sidebar). It is used in the main structure of the page:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<body>
<div id="wrapper">
<header>
...
</header>
<main>
...
</main>
<aside>
...
</aside>
<footer>
...
</footer>
</div>
</body>
</html>
