# Frontmatter

Each page may begin with a YAML **frontmatter** block, fenced by `---`, that sets the
page's metadata. Every field is optional — a page of pure Markdown is a valid page.

```md
---
id: writing-pages
title: Writing pages
keywords: [Markdown, frontmatter, authoring]
categories: [authoring]
related: [table-of-contents, other-book:overview]
toc: true
---

# Writing pages

Body content…
```

The block is stripped before rendering — it never appears in the page body. A block
that doesn't parse (or isn't terminated by a closing `---`) fails the
[compile](compiling.md).

## Fields

| Field | Sets | Details |
|-------|------|---------|
| `id` | the page's stable id (defaults to the file name) | [id](frontmatter-id.md) |
| `title` | the display title in the TOC, tabs and search | [title](frontmatter-title.md) |
| `keywords` | the page's entries in the keyword index | [keywords](frontmatter-keywords.md) |
| `categories` | facet tags for the category filter | [categories](frontmatter-categories.md) |
| `related` | the **See also** footer | [related](frontmatter-related.md) |
| `toc` | forces the "On this page" box on or off | [toc](frontmatter-toc.md) |