... subsections, which by their turn must also be placed into directories. Each Section is required to have content.md file, containing the Frontmatter for that section, and optional sidenotes.md file, that will be rendered to the right of the section. The Frontmatter must contain at least a Title property, and an optional ID property containing a unique slug for that section. Each Group must contain a single meta.md file, containing a Frontmatter like a Section, and an optional content.