utline -->
<!-- It produces an outline summary of an HTML document based on its markup -->

<!-- The following elements have their own self-contained outline -->
<!--
- Article
- Aside
- Nav
- Section
-->

<!-- For example: -->
<h1>Title
<section>
    <h2>Sub Title</h2>
</section>
</h1>
<!--
 Will produce the following output:
 1. Title
    1.1 Subtitle
 -->

<!-- Header -->
<!-- A group of introductory or navigational aids -->
<!--
 - There can be many different headers on a page
 - Generally, it appears a