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Asides

Asides are represented by the aside element. When used inside an article, they are
meant to represent content that is related to the surrounding article but not part of it. For
example, an aside may contain a list of links for further reading, or a glossary list of
terms used in the article, or a sidebar. You can also place advertisements within an aside
element. The aside tag can also be used outside an article to contain content on the page
that is not directly relevant to the main content on the page. However, be sure that you’re
not using an aside tag when you should be using header, footer, or nav.

The aside tag can be used for any content that belongs in a section but isn’t considered
part of the main page flow. That means you can also use it for things like advertisements
that you want to display but wouldn’t want to treat as part of the page’s content.

Here’s an example of an aside for an article:

The Page Outline

In discussing the various sectioning tags in HTML5, I talked about the page outline
quite a bit. You already know that HTML is structured in a hierarchical fashion—tags
are nested and make up a tree-like structure. That’s one outline, but it’s not the one I’m
talking about. The browser also creates a semantic outline of the page that represents the
structure of the document in terms of the content.