Markdown metadata format
The older and simpler MultiMarkdown Metadata is actually incorporated into a few Markdown parsers. While it has more recently been updated to optionally support YAML deliminators, traditionally, the metadata ends and the Markdown document begins upon the first blank line (if the first line was blank, then no metadata). And while the syntax looks very similar to YAML, only key-value pairs are supported with no implied types. Here is an example from the MultiMarkdown docs:
Title: A Sample MultiMarkdown Document Author: Fletcher T. Penney Date: February 9, 2011 Comment: This is a comment intended to demonstrate metadata that spans multiple lines, yet is treated as a single value. CSS: http://example.com/standard.css
The MultiMarkdown parser includes a bunch of additional options which are unique to that parser, but the key-value metadata is used across multiple parsers. Unfortunately, I have never seen any two which behaved exactly the same. Without the Markdown rules defining such a format everyone has done their own slightly different interpretation resulting in a lot of variety.
The one thing that is more common is the support for YAML deliminators and basic key-value definitions.
Most Markdown renderers seem to support this YAML format for metadata at the top of the file:
--- layout: post published-on: 1 January 2000 title: Blogging Like a Boss --- Content goes here.