Document file names and front matter in the hello-world post

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

content/2026-10-24-hello-world.md

@@ -1,16 +1,74 @@
 ---
 title: Hello, world
-summary: The first post, and a quick tour of what a post can contain.
+summary: The first post, and a guide to writing one — file names, the header block, and what Markdown works.
 ---
 
 This site is a folder of Markdown files. Each file in `content/` becomes a
-post, and the newest one is listed first.
+post, and the newest one is listed first. This post explains how to write one.
 
-## What works
+## The file name
+
+Name each post `YYYY-MM-DD-slug.md`, for example `2026-10-24-hello-world.md`.
+
+- The **slug** is the part after the date. It becomes the post's address:
+  this file is served at `/posts/hello-world`.
+- Use lowercase letters, digits and hyphens only. A file with any other name
+  is skipped.
+- The date in the name is the post's date unless the header says otherwise.
+
+## The header block
+
+A post can start with an optional header block (often called *front matter*)
+between two `---` lines. This post's header is:
+
+```markdown
+---
+title: Hello, world
+summary: The first post, and a guide to writing one — file names, the header block, and what Markdown works.
+---
+```
+
+Each line is `key: value`. Four keys are recognised:
+
+| Key | What it does | If left out |
+|---|---|---|
+| `title` | The post's title, shown on the index page, at the top of the post and in the RSS feed | The first line of the post if it is a `# Heading` (that heading is then not repeated in the body); otherwise the slug |
+| `date` | The post's date, as `YYYY-MM-DD`. Posts are listed newest first | The date in the file name |
+| `summary` | One line shown under the title on the index page and used as the RSS description | Nothing is shown |
+| `draft` | Set to `true` to hide the post everywhere: index, post page and feed | `false` |
+
+Some details:
+
+- The block must be the very first thing in the file, and it must be closed
+  with a second `---` line.
+- Values can be wrapped in quotes, which are removed: `title: "Hello, world"`.
+- Lines starting with `#` inside the block are comments.
+- Keys other than the four above are ignored.
+- A post with a broken header, such as an unknown date format or a missing
+  closing `---`, is skipped and the problem is logged. The rest of the site is
+  unaffected.
+
+The header is optional. This is a complete post:
+
+```markdown
+# A short note
+
+Just a paragraph.
+```
+
+Its title is "A short note" and its date comes from the file name.
+
+## Publishing
+
+Posts are reviewed like code: add the file on a branch, open a pull request,
+and the post goes live once it is merged and deployed. To hold a post back
+after merging, set `draft: true`.
+
+## What Markdown works
 
 - **Bold**, *italic*, ~~strikethrough~~ and `inline code`
 - Links like https://posts.monoaf.com are linked automatically
-- Tables, task lists and fenced code blocks
+- Headings, lists, quotes, images, tables, task lists and fenced code blocks
 
 | Feature | Supported |
 |---|---|