About YAML frontmatter
YAML frontmatter is an authoring convention popularized by Jekyll that provides a way to add metadata to pages. It is a block of key-value content that lives at the top of every Markdown file within GitHub Docs. For more information, see the YAML frontmatter documentation.
YAML frontmatter values
The following frontmatter values have special meanings and requirements for GitHub Docs.
There's also a schema that's used by the test suite to validate every page's frontmatter.
For more information, see lib/frontmatter.js.