Answer 1

Extracted from w3schools (http://www.w3schools.com/html/html5_semantic_elements.asp):

Nesting <article> in <section> or Vice Versa?

The <article> element specifies independent, self-contained content.

The <section> element defines section in a document.

Can we use the definitions to decide how to nest those elements? No, we cannot!

So, on the Internet, you will find HTML pages with <section> elements containing <article> elements, and <article> elements containing <sections> elements.

You will also find pages with <section> elements containing <section> elements, and <article> elements containing <article> elements.

Example for a newspaper: The sport articles in the sport section, may have a technical section in each article.