Markus is GitHub Flavored Markdown plus colon-fenced directives. These rules apply to every directive on every other page.

Front matter

A document may start with YAML front matter. Markus renders title, description, authors, and date as the document header and carries every other key through unchanged for the publishing system to use.

---
title: The future of local inference
description: A short summary.
authors:
  - Ada
  - Grace
date: 2026-09-04
---

The body starts here.

authors entries may also be mappings. Markus passes them through as data; it never turns them into HTML.

---
authors:
  - name: Ada Lovelace
    url: /authors/ada
---

Container directives

A container opens with three or more colons and a name, holds Markdown (including other directives), and closes with a line of colons.

:::callout{kind="tip"}
A container holds **Markdown**, lists, code, and other directives.
:::

Leaf directives

A leaf is two colons and a name on one line. It has attributes and no body. metric, video, and the diagram link are leaves.

::metric{value="12" unit="ms" label="p95 latency" delta="-8%"}

Attributes

Quoting and bare values

Values may use double quotes, single quotes, or no quotes. A bare name with no value is true; true, false, and numbers are coerced to their types.

:::card-grid{columns=2 label='Single quotes work'}
:::card{title="Double quotes" span=1}
Bare numbers are integers.
:::
:::

:::details{summary="Flags" open}
A bare name with no value is `true`.
:::

Multi-line attribute blocks

Long attribute blocks may span several lines. The opening { stays on the directive line; the block ends at the first } outside quotes. Inside a quoted value, a backslash escapes the next character.

::metric{
  value="12"
  unit="ms"
  label="Two quote kinds: ' and \""
}

:::callout{
  kind="note"
  title="Spread over lines"
}
Same meaning, easier to read.
:::

Trailing attribute lists

A kramdown-style {: key=value } line inside a container sets attributes after the content, which reads naturally for quotations.

:::pull-quote
> Measure what matters.
{: attribution="Editorial principle" }
:::

Element id

Every directive accepts id, which becomes the HTML id, so links can point at it.

:::callout{kind="note" id="anchor-demo" title="Linkable"}
[This link](#anchor-demo) points at the callout it sits in.
:::

Nesting

Containers nest freely except where a parent restricts its children, such as column inside two-up or tab inside tabs. Give the outer directive a longer colon fence when that makes the structure easier to read.

::::callout{kind="note" title="Outer"}
Outer body.

:::details{summary="Inner"}
An inner directive.
:::
::::

Directives in code fences are not scanned

Colon fences inside a code block are shown, not rendered, so documentation can quote Markus.

```md
:::callout{kind="note"}
This is shown, not rendered.
:::
```

:::callout{kind="note"}
This is shown, not rendered.
:::

Validation

Markus parses, validates, then renders. An unknown directive, an unknown attribute, a value outside its allowed set, or a child in the wrong parent stops the build with the line number. Attributes describe meaning, so there is no margin, color, or columns-template to reach for.

:::callout{kind="loud"}
Fails: kind must be note, tip, warning, or caution.
:::

:::callout{color="red"}
Fails: unknown attribute 'color'. Attributes describe meaning, not presentation.
:::

Check a file without rendering it:

markus validate page.md