Question

Why would a HTML5 website adopt the following structure? I am specifically interested in the use of the outer <section> element.

I realise that this validates as HTML5, but I do not understand why a section would contain an article. I thought that a section was to be thought of like a “chapter” of an article. Why wouldn’t one just use <div id="main"> ... </div>? Is there a semantic advantage (perhaps for SEO) of using the outer section element?

Note: I have simplified the source by removing various container / inner wrapper DIV elements.

<div id="wrapper">
    <section id="main">
        <article id="home">
            <section class="block">
                <h1>Heading</h1>
                <p>Content...</p>
                <p>Content...</p>
            </section>
            <section class="block">
                <p>Content...</p>
                <p>Content...</p>
            </section>
        </article>
    </section>
</div>

I am unable to provide a link to the website in question because it contains content that some viewers may find offensive.

Answer 1

From the spec:

The section element represents a generic document or application
section…The section element is not a generic container element. When
an element is needed for styling purposes or as a convenience for
scripting, authors are encouraged to use the div element instead.

And:

Examples of sections would be chapters, the various tabbed pages in a
tabbed dialog box, or the numbered sections of a thesis. A Web site’s
home page could be split into sections for an introduction, news
items, and contact information.

So in my opinion, what you have demonstrated is not really a valid semantic use for the section element, and div would be better (or nothing at all, considering there is already the wrapper div). However, the two child section elements are probably used more as the spec intended.

I don’t believe any of the HTML5 elements (article, section etc.) have any real bearing on SEO at the moment, although they could in the future. And I may be wrong. I’m not an SEO expert.