Supported formats reference

docmeta reads metadata from a document using a per-format extractor. The extractor is chosen from the file extension, or forced with --as <format>. Every extractor below is implemented and counts toward directory and glob walks.

Formats

Format (`--as` name)	Extensions	Metadata source
`markdown`	`.md`, `.markdown`	Leading YAML frontmatter (`--- … ---`).
`mdx`	`.mdx`	Leading YAML frontmatter (`--- … ---`).
`asciidoc`	`.adoc`, `.asciidoc`	YAML frontmatter, or the native header: `= Title` plus `:key: value` attributes.
`rst`	`.rst`	YAML frontmatter, or the native section title plus `:key: value` docinfo fields.
`xml`	`.xml`	Attributes of the root element.
`html`	`.html`, `.htm`	`<title>` plus `<meta name="…" content="…">` tags.

The --as name is the extractor name in the first column. The extension match is case-insensitive.

How each format is read

Markdown and MDX

Both read a leading YAML frontmatter block delimited by --- on its own line, closed by a matching --- or .... The block is parsed as YAML, so values keep their YAML types (strings, numbers, booleans, lists, maps). MDX uses the same frontmatter logic as Markdown; export const meta = {…} is not read.

---
type: guide
title: Getting started
tags: [setup, onboarding]
---

Malformed YAML in the block is reported as a per-file parse error rather than stopping the run. A file with no frontmatter block reports its metadata as not present.

AsciiDoc

AsciiDoc accepts two metadata styles. If the file opens with a complete YAML frontmatter block, that block is used. Otherwise docmeta reads the native document header — the lines from the top of the file down to the first blank line:

A leading = Title line becomes title.
Each :name: value line becomes a name key. A :name: with no value is true; an unset attribute (:!name: or :name!:) is false.
Other header lines (such as author or revision lines) are ignored.

= Getting started
:type: guide
:draft: false

reStructuredText

reStructuredText also accepts two styles. A complete leading YAML frontmatter block is used when present (as some MyST setups produce it). Otherwise docmeta reads the native page metadata:

A leading section title (a line underlined — and optionally overlined — with punctuation) becomes title.
The docinfo field list that follows — a run of :name: value fields — becomes the remaining keys. A :name: with no value is true. An explicit :title: field takes precedence over the heading.

Getting started
===============

:type: guide
:tags: [setup, onboarding]

XML

XML metadata comes from the attributes of the root element. Namespace declarations (xmlns and xmlns:*) are dropped as transport noise.

<document type="concept" version="2" />

This yields type: "concept" and version: 2. Malformed XML is reported as a per-file parse error.

HTML

HTML metadata comes from the document head:

<title>…</title> becomes title (the first <title> wins; its text is kept verbatim).
<meta name="X" content="Y"> becomes X: Y. property="X" is accepted in place of name for OpenGraph-style tags.
<meta> tags with neither name nor property (such as charset or http-equiv) carry no metadata and are skipped. For duplicate keys, the last tag wins.

<title>Getting started</title>
<meta name="type" content="guide">
<meta name="draft" content="false">

HTML parsing recovers from malformed markup, so extraction does not throw a parse error.

Type coercion

For every format except Markdown and MDX, individual values are parsed as YAML scalars, matching frontmatter typing. This means string-looking inputs are coerced to their natural types:

Raw value	Becomes	Type
`2`	`2`	number
`true`	`true`	boolean
`[a, b]`	`["a", "b"]`	array

An explicitly empty value (title="" in XML, content="" in HTML) stays the empty string rather than becoming null. Markdown and MDX get their types from parsing the whole frontmatter block as YAML, so the same coercions apply there through normal YAML rules.