It’s good to revisit several concepts in HTML for the purpose of optimally structuring it—for all kinds of usage and accessibility.
Every HTML element is a member of one or more content categories — these categories group elements that share common characteristics. This is a loose grouping (it doesn’t actually create a relationship among elements of these categories), but they help define and describe the categories’ shared behavior and their associated rules, especially when you come upon their intricate details. It’s also possible for elements to not be a member of any of these categories. Source
A sectioning root is an HTML element that can have its own outline, but the sections and headings inside it do not contribute to the outline of its ancestor. Besides <body> which is the logical sectioning root of a document, the following elements often introduce external content to the page: <blockquote>, <details>, <fieldset>, and <figure>. Source