It's possible to encode arbitrary metadata in AsciiDoc in the form of "roles" (https://docs.asciidoctor.org/asciidoc/latest/text/text-span-... ) or "blocks" (https://docs.asciidoctor.org/asciidoc/latest/blocks/delimite...).

The oddball reStructuredText also has a similar system of "roles" and "directives", but its syntax is kind of painful to use and IMO AsciiDoc is easier to read and write.