OAS 3.1 uses all of JSON Schema draft 2020-12 including unevaluatedProperties. You won't find direct references to unevealuatedProperties in the OAS spec because it links to the JSON Schema spec instead of duplicating it's contents.

This object is a superset of the JSON Schema Specification Draft 2020-12.

for parsing and converting a superset of Markdown

We overload the meaning of "GFM" to mean "GitLab Flavored Markdown", which is a superset of GitHub's version. However it can cause confusion as they are not the same thing.

MDX is a superset of Markdown. It allows you to write JSX inside markdown. This includes importing and rendering React components!