This section is used as the start of a chapter, it has a thin line above and an optional side heading
Chapters with only a thin line do not have a heading (the heading is set in the title section — usually level h2), a nominal h6 level (h6 headings do not display) is also given to satisfy HTML validation requirements (sections must contain a heading element).
If a side heading is used, this will have an h2 heading level
This is a typical section, it will be numbered X.Y.
Sections have an h2 heading level.
This is a typical subsection, it will be numbered X.Y.Z.
Subsections have an h3 heading level.
This is an inline section, it has no number but does appy emphasis to a distinct section of text
Inline sections have an h4 heading level.
This is an additional section row it follows any section and allows additional sidebars to be used and aligned with the top of the row text.
additional section rows are constructed with <div> elements (rather than <section> elements and consequently do not require a heading).
As many additional section rows can be added as are needed.